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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-13 14:07:11 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-13 14:07:11 +0000
commit63847496f14c813a5d80efd5b7de0f1294ffe1e3 (patch)
tree01c7571c7c762ceee70638549a99834fdd7c411b /src/wal.c
parentInitial commit. (diff)
downloadsqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.tar.xz
sqlite3-63847496f14c813a5d80efd5b7de0f1294ffe1e3.zip
Adding upstream version 3.45.1.upstream/3.45.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+/*
+** 2010 February 1
+**
+** The author disclaims copyright to this source code. In place of
+** a legal notice, here is a blessing:
+**
+** May you do good and not evil.
+** May you find forgiveness for yourself and forgive others.
+** May you share freely, never taking more than you give.
+**
+*************************************************************************
+**
+** This file contains the implementation of a write-ahead log (WAL) used in
+** "journal_mode=WAL" mode.
+**
+** WRITE-AHEAD LOG (WAL) FILE FORMAT
+**
+** A WAL file consists of a header followed by zero or more "frames".
+** Each frame records the revised content of a single page from the
+** database file. All changes to the database are recorded by writing
+** frames into the WAL. Transactions commit when a frame is written that
+** contains a commit marker. A single WAL can and usually does record
+** multiple transactions. Periodically, the content of the WAL is
+** transferred back into the database file in an operation called a
+** "checkpoint".
+**
+** A single WAL file can be used multiple times. In other words, the
+** WAL can fill up with frames and then be checkpointed and then new
+** frames can overwrite the old ones. A WAL always grows from beginning
+** toward the end. Checksums and counters attached to each frame are
+** used to determine which frames within the WAL are valid and which
+** are leftovers from prior checkpoints.
+**
+** The WAL header is 32 bytes in size and consists of the following eight
+** big-endian 32-bit unsigned integer values:
+**
+** 0: Magic number. 0x377f0682 or 0x377f0683
+** 4: File format version. Currently 3007000
+** 8: Database page size. Example: 1024
+** 12: Checkpoint sequence number
+** 16: Salt-1, random integer incremented with each checkpoint
+** 20: Salt-2, a different random integer changing with each ckpt
+** 24: Checksum-1 (first part of checksum for first 24 bytes of header).
+** 28: Checksum-2 (second part of checksum for first 24 bytes of header).
+**
+** Immediately following the wal-header are zero or more frames. Each
+** frame consists of a 24-byte frame-header followed by a <page-size> bytes
+** of page data. The frame-header is six big-endian 32-bit unsigned
+** integer values, as follows:
+**
+** 0: Page number.
+** 4: For commit records, the size of the database image in pages
+** after the commit. For all other records, zero.
+** 8: Salt-1 (copied from the header)
+** 12: Salt-2 (copied from the header)
+** 16: Checksum-1.
+** 20: Checksum-2.
+**
+** A frame is considered valid if and only if the following conditions are
+** true:
+**
+** (1) The salt-1 and salt-2 values in the frame-header match
+** salt values in the wal-header
+**
+** (2) The checksum values in the final 8 bytes of the frame-header
+** exactly match the checksum computed consecutively on the
+** WAL header and the first 8 bytes and the content of all frames
+** up to and including the current frame.
+**
+** The checksum is computed using 32-bit big-endian integers if the
+** magic number in the first 4 bytes of the WAL is 0x377f0683 and it
+** is computed using little-endian if the magic number is 0x377f0682.
+** The checksum values are always stored in the frame header in a
+** big-endian format regardless of which byte order is used to compute
+** the checksum. The checksum is computed by interpreting the input as
+** an even number of unsigned 32-bit integers: x[0] through x[N]. The
+** algorithm used for the checksum is as follows:
+**
+** for i from 0 to n-1 step 2:
+** s0 += x[i] + s1;
+** s1 += x[i+1] + s0;
+** endfor
+**
+** Note that s0 and s1 are both weighted checksums using fibonacci weights
+** in reverse order (the largest fibonacci weight occurs on the first element
+** of the sequence being summed.) The s1 value spans all 32-bit
+** terms of the sequence whereas s0 omits the final term.
+**
+** On a checkpoint, the WAL is first VFS.xSync-ed, then valid content of the
+** WAL is transferred into the database, then the database is VFS.xSync-ed.
+** The VFS.xSync operations serve as write barriers - all writes launched
+** before the xSync must complete before any write that launches after the
+** xSync begins.
+**
+** After each checkpoint, the salt-1 value is incremented and the salt-2
+** value is randomized. This prevents old and new frames in the WAL from
+** being considered valid at the same time and being checkpointing together
+** following a crash.
+**
+** READER ALGORITHM
+**
+** To read a page from the database (call it page number P), a reader
+** first checks the WAL to see if it contains page P. If so, then the
+** last valid instance of page P that is a followed by a commit frame
+** or is a commit frame itself becomes the value read. If the WAL
+** contains no copies of page P that are valid and which are a commit
+** frame or are followed by a commit frame, then page P is read from
+** the database file.
+**
+** To start a read transaction, the reader records the index of the last
+** valid frame in the WAL. The reader uses this recorded "mxFrame" value
+** for all subsequent read operations. New transactions can be appended
+** to the WAL, but as long as the reader uses its original mxFrame value
+** and ignores the newly appended content, it will see a consistent snapshot
+** of the database from a single point in time. This technique allows
+** multiple concurrent readers to view different versions of the database
+** content simultaneously.
+**
+** The reader algorithm in the previous paragraphs works correctly, but
+** because frames for page P can appear anywhere within the WAL, the
+** reader has to scan the entire WAL looking for page P frames. If the
+** WAL is large (multiple megabytes is typical) that scan can be slow,
+** and read performance suffers. To overcome this problem, a separate
+** data structure called the wal-index is maintained to expedite the
+** search for frames of a particular page.
+**
+** WAL-INDEX FORMAT
+**
+** Conceptually, the wal-index is shared memory, though VFS implementations
+** might choose to implement the wal-index using a mmapped file. Because
+** the wal-index is shared memory, SQLite does not support journal_mode=WAL
+** on a network filesystem. All users of the database must be able to
+** share memory.
+**
+** In the default unix and windows implementation, the wal-index is a mmapped
+** file whose name is the database name with a "-shm" suffix added. For that
+** reason, the wal-index is sometimes called the "shm" file.
+**
+** The wal-index is transient. After a crash, the wal-index can (and should
+** be) reconstructed from the original WAL file. In fact, the VFS is required
+** to either truncate or zero the header of the wal-index when the last
+** connection to it closes. Because the wal-index is transient, it can
+** use an architecture-specific format; it does not have to be cross-platform.
+** Hence, unlike the database and WAL file formats which store all values
+** as big endian, the wal-index can store multi-byte values in the native
+** byte order of the host computer.
+**
+** The purpose of the wal-index is to answer this question quickly: Given
+** a page number P and a maximum frame index M, return the index of the
+** last frame in the wal before frame M for page P in the WAL, or return
+** NULL if there are no frames for page P in the WAL prior to M.
+**
+** The wal-index consists of a header region, followed by an one or
+** more index blocks.
+**
+** The wal-index header contains the total number of frames within the WAL
+** in the mxFrame field.
+**
+** Each index block except for the first contains information on
+** HASHTABLE_NPAGE frames. The first index block contains information on
+** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and
+** HASHTABLE_NPAGE are selected so that together the wal-index header and
+** first index block are the same size as all other index blocks in the
+** wal-index. The values are:
+**
+** HASHTABLE_NPAGE 4096
+** HASHTABLE_NPAGE_ONE 4062
+**
+** Each index block contains two sections, a page-mapping that contains the
+** database page number associated with each wal frame, and a hash-table
+** that allows readers to query an index block for a specific page number.
+** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE
+** for the first index block) 32-bit page numbers. The first entry in the
+** first index-block contains the database page number corresponding to the
+** first frame in the WAL file. The first entry in the second index block
+** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in
+** the log, and so on.
+**
+** The last index block in a wal-index usually contains less than the full
+** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers,
+** depending on the contents of the WAL file. This does not change the
+** allocated size of the page-mapping array - the page-mapping array merely
+** contains unused entries.
+**
+** Even without using the hash table, the last frame for page P
+** can be found by scanning the page-mapping sections of each index block
+** starting with the last index block and moving toward the first, and
+** within each index block, starting at the end and moving toward the
+** beginning. The first entry that equals P corresponds to the frame
+** holding the content for that page.
+**
+** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers.
+** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the
+** hash table for each page number in the mapping section, so the hash
+** table is never more than half full. The expected number of collisions
+** prior to finding a match is 1. Each entry of the hash table is an
+** 1-based index of an entry in the mapping section of the same
+** index block. Let K be the 1-based index of the largest entry in
+** the mapping section. (For index blocks other than the last, K will
+** always be exactly HASHTABLE_NPAGE (4096) and for the last index block
+** K will be (mxFrame%HASHTABLE_NPAGE).) Unused slots of the hash table
+** contain a value of 0.
+**
+** To look for page P in the hash table, first compute a hash iKey on
+** P as follows:
+**
+** iKey = (P * 383) % HASHTABLE_NSLOT
+**
+** Then start scanning entries of the hash table, starting with iKey
+** (wrapping around to the beginning when the end of the hash table is
+** reached) until an unused hash slot is found. Let the first unused slot
+** be at index iUnused. (iUnused might be less than iKey if there was
+** wrap-around.) Because the hash table is never more than half full,
+** the search is guaranteed to eventually hit an unused entry. Let
+** iMax be the value between iKey and iUnused, closest to iUnused,
+** where aHash[iMax]==P. If there is no iMax entry (if there exists
+** no hash slot such that aHash[i]==p) then page P is not in the
+** current index block. Otherwise the iMax-th mapping entry of the
+** current index block corresponds to the last entry that references
+** page P.
+**
+** A hash search begins with the last index block and moves toward the
+** first index block, looking for entries corresponding to page P. On
+** average, only two or three slots in each index block need to be
+** examined in order to either find the last entry for page P, or to
+** establish that no such entry exists in the block. Each index block
+** holds over 4000 entries. So two or three index blocks are sufficient
+** to cover a typical 10 megabyte WAL file, assuming 1K pages. 8 or 10
+** comparisons (on average) suffice to either locate a frame in the
+** WAL or to establish that the frame does not exist in the WAL. This
+** is much faster than scanning the entire 10MB WAL.
+**
+** Note that entries are added in order of increasing K. Hence, one
+** reader might be using some value K0 and a second reader that started
+** at a later time (after additional transactions were added to the WAL
+** and to the wal-index) might be using a different value K1, where K1>K0.
+** Both readers can use the same hash table and mapping section to get
+** the correct result. There may be entries in the hash table with
+** K>K0 but to the first reader, those entries will appear to be unused
+** slots in the hash table and so the first reader will get an answer as
+** if no values greater than K0 had ever been inserted into the hash table
+** in the first place - which is what reader one wants. Meanwhile, the
+** second reader using K1 will see additional values that were inserted
+** later, which is exactly what reader two wants.
+**
+** When a rollback occurs, the value of K is decreased. Hash table entries
+** that correspond to frames greater than the new K value are removed
+** from the hash table at this point.
+*/
+#ifndef SQLITE_OMIT_WAL
+
+#include "wal.h"
+
+/*
+** Trace output macros
+*/
+#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
+int sqlite3WalTrace = 0;
+# define WALTRACE(X) if(sqlite3WalTrace) sqlite3DebugPrintf X
+#else
+# define WALTRACE(X)
+#endif
+
+/*
+** The maximum (and only) versions of the wal and wal-index formats
+** that may be interpreted by this version of SQLite.
+**
+** If a client begins recovering a WAL file and finds that (a) the checksum
+** values in the wal-header are correct and (b) the version field is not
+** WAL_MAX_VERSION, recovery fails and SQLite returns SQLITE_CANTOPEN.
+**
+** Similarly, if a client successfully reads a wal-index header (i.e. the
+** checksum test is successful) and finds that the version field is not
+** WALINDEX_MAX_VERSION, then no read-transaction is opened and SQLite
+** returns SQLITE_CANTOPEN.
+*/
+#define WAL_MAX_VERSION 3007000
+#define WALINDEX_MAX_VERSION 3007000
+
+/*
+** Index numbers for various locking bytes. WAL_NREADER is the number
+** of available reader locks and should be at least 3. The default
+** is SQLITE_SHM_NLOCK==8 and WAL_NREADER==5.
+**
+** Technically, the various VFSes are free to implement these locks however
+** they see fit. However, compatibility is encouraged so that VFSes can
+** interoperate. The standard implementation used on both unix and windows
+** is for the index number to indicate a byte offset into the
+** WalCkptInfo.aLock[] array in the wal-index header. In other words, all
+** locks are on the shm file. The WALINDEX_LOCK_OFFSET constant (which
+** should be 120) is the location in the shm file for the first locking
+** byte.
+*/
+#define WAL_WRITE_LOCK 0
+#define WAL_ALL_BUT_WRITE 1
+#define WAL_CKPT_LOCK 1
+#define WAL_RECOVER_LOCK 2
+#define WAL_READ_LOCK(I) (3+(I))
+#define WAL_NREADER (SQLITE_SHM_NLOCK-3)
+
+
+/* Object declarations */
+typedef struct WalIndexHdr WalIndexHdr;
+typedef struct WalIterator WalIterator;
+typedef struct WalCkptInfo WalCkptInfo;
+
+
+/*
+** The following object holds a copy of the wal-index header content.
+**
+** The actual header in the wal-index consists of two copies of this
+** object followed by one instance of the WalCkptInfo object.
+** For all versions of SQLite through 3.10.0 and probably beyond,
+** the locking bytes (WalCkptInfo.aLock) start at offset 120 and
+** the total header size is 136 bytes.
+**
+** The szPage value can be any power of 2 between 512 and 32768, inclusive.
+** Or it can be 1 to represent a 65536-byte page. The latter case was
+** added in 3.7.1 when support for 64K pages was added.
+*/
+struct WalIndexHdr {
+ u32 iVersion; /* Wal-index version */
+ u32 unused; /* Unused (padding) field */
+ u32 iChange; /* Counter incremented each transaction */
+ u8 isInit; /* 1 when initialized */
+ u8 bigEndCksum; /* True if checksums in WAL are big-endian */
+ u16 szPage; /* Database page size in bytes. 1==64K */
+ u32 mxFrame; /* Index of last valid frame in the WAL */
+ u32 nPage; /* Size of database in pages */
+ u32 aFrameCksum[2]; /* Checksum of last frame in log */
+ u32 aSalt[2]; /* Two salt values copied from WAL header */
+ u32 aCksum[2]; /* Checksum over all prior fields */
+};
+
+/*
+** A copy of the following object occurs in the wal-index immediately
+** following the second copy of the WalIndexHdr. This object stores
+** information used by checkpoint.
+**
+** nBackfill is the number of frames in the WAL that have been written
+** back into the database. (We call the act of moving content from WAL to
+** database "backfilling".) The nBackfill number is never greater than
+** WalIndexHdr.mxFrame. nBackfill can only be increased by threads
+** holding the WAL_CKPT_LOCK lock (which includes a recovery thread).
+** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from
+** mxFrame back to zero when the WAL is reset.
+**
+** nBackfillAttempted is the largest value of nBackfill that a checkpoint
+** has attempted to achieve. Normally nBackfill==nBackfillAtempted, however
+** the nBackfillAttempted is set before any backfilling is done and the
+** nBackfill is only set after all backfilling completes. So if a checkpoint
+** crashes, nBackfillAttempted might be larger than nBackfill. The
+** WalIndexHdr.mxFrame must never be less than nBackfillAttempted.
+**
+** The aLock[] field is a set of bytes used for locking. These bytes should
+** never be read or written.
+**
+** There is one entry in aReadMark[] for each reader lock. If a reader
+** holds read-lock K, then the value in aReadMark[K] is no greater than
+** the mxFrame for that reader. The value READMARK_NOT_USED (0xffffffff)
+** for any aReadMark[] means that entry is unused. aReadMark[0] is
+** a special case; its value is never used and it exists as a place-holder
+** to avoid having to offset aReadMark[] indexes by one. Readers holding
+** WAL_READ_LOCK(0) always ignore the entire WAL and read all content
+** directly from the database.
+**
+** The value of aReadMark[K] may only be changed by a thread that
+** is holding an exclusive lock on WAL_READ_LOCK(K). Thus, the value of
+** aReadMark[K] cannot changed while there is a reader is using that mark
+** since the reader will be holding a shared lock on WAL_READ_LOCK(K).
+**
+** The checkpointer may only transfer frames from WAL to database where
+** the frame numbers are less than or equal to every aReadMark[] that is
+** in use (that is, every aReadMark[j] for which there is a corresponding
+** WAL_READ_LOCK(j)). New readers (usually) pick the aReadMark[] with the
+** largest value and will increase an unused aReadMark[] to mxFrame if there
+** is not already an aReadMark[] equal to mxFrame. The exception to the
+** previous sentence is when nBackfill equals mxFrame (meaning that everything
+** in the WAL has been backfilled into the database) then new readers
+** will choose aReadMark[0] which has value 0 and hence such reader will
+** get all their all content directly from the database file and ignore
+** the WAL.
+**
+** Writers normally append new frames to the end of the WAL. However,
+** if nBackfill equals mxFrame (meaning that all WAL content has been
+** written back into the database) and if no readers are using the WAL
+** (in other words, if there are no WAL_READ_LOCK(i) where i>0) then
+** the writer will first "reset" the WAL back to the beginning and start
+** writing new content beginning at frame 1.
+**
+** We assume that 32-bit loads are atomic and so no locks are needed in
+** order to read from any aReadMark[] entries.
+*/
+struct WalCkptInfo {
+ u32 nBackfill; /* Number of WAL frames backfilled into DB */
+ u32 aReadMark[WAL_NREADER]; /* Reader marks */
+ u8 aLock[SQLITE_SHM_NLOCK]; /* Reserved space for locks */
+ u32 nBackfillAttempted; /* WAL frames perhaps written, or maybe not */
+ u32 notUsed0; /* Available for future enhancements */
+};
+#define READMARK_NOT_USED 0xffffffff
+
+/*
+** This is a schematic view of the complete 136-byte header of the
+** wal-index file (also known as the -shm file):
+**
+** +-----------------------------+
+** 0: | iVersion | \
+** +-----------------------------+ |
+** 4: | (unused padding) | |
+** +-----------------------------+ |
+** 8: | iChange | |
+** +-------+-------+-------------+ |
+** 12: | bInit | bBig | szPage | |
+** +-------+-------+-------------+ |
+** 16: | mxFrame | | First copy of the
+** +-----------------------------+ | WalIndexHdr object
+** 20: | nPage | |
+** +-----------------------------+ |
+** 24: | aFrameCksum | |
+** | | |
+** +-----------------------------+ |
+** 32: | aSalt | |
+** | | |
+** +-----------------------------+ |
+** 40: | aCksum | |
+** | | /
+** +-----------------------------+
+** 48: | iVersion | \
+** +-----------------------------+ |
+** 52: | (unused padding) | |
+** +-----------------------------+ |
+** 56: | iChange | |
+** +-------+-------+-------------+ |
+** 60: | bInit | bBig | szPage | |
+** +-------+-------+-------------+ | Second copy of the
+** 64: | mxFrame | | WalIndexHdr
+** +-----------------------------+ |
+** 68: | nPage | |
+** +-----------------------------+ |
+** 72: | aFrameCksum | |
+** | | |
+** +-----------------------------+ |
+** 80: | aSalt | |
+** | | |
+** +-----------------------------+ |
+** 88: | aCksum | |
+** | | /
+** +-----------------------------+
+** 96: | nBackfill |
+** +-----------------------------+
+** 100: | 5 read marks |
+** | |
+** | |
+** | |
+** | |
+** +-------+-------+------+------+
+** 120: | Write | Ckpt | Rcvr | Rd0 | \
+** +-------+-------+------+------+ ) 8 lock bytes
+** | Read1 | Read2 | Rd3 | Rd4 | /
+** +-------+-------+------+------+
+** 128: | nBackfillAttempted |
+** +-----------------------------+
+** 132: | (unused padding) |
+** +-----------------------------+
+*/
+
+/* A block of WALINDEX_LOCK_RESERVED bytes beginning at
+** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems
+** only support mandatory file-locks, we do not read or write data
+** from the region of the file on which locks are applied.
+*/
+#define WALINDEX_LOCK_OFFSET (sizeof(WalIndexHdr)*2+offsetof(WalCkptInfo,aLock))
+#define WALINDEX_HDR_SIZE (sizeof(WalIndexHdr)*2+sizeof(WalCkptInfo))
+
+/* Size of header before each frame in wal */
+#define WAL_FRAME_HDRSIZE 24
+
+/* Size of write ahead log header, including checksum. */
+#define WAL_HDRSIZE 32
+
+/* WAL magic value. Either this value, or the same value with the least
+** significant bit also set (WAL_MAGIC | 0x00000001) is stored in 32-bit
+** big-endian format in the first 4 bytes of a WAL file.
+**
+** If the LSB is set, then the checksums for each frame within the WAL
+** file are calculated by treating all data as an array of 32-bit
+** big-endian words. Otherwise, they are calculated by interpreting
+** all data as 32-bit little-endian words.
+*/
+#define WAL_MAGIC 0x377f0682
+
+/*
+** Return the offset of frame iFrame in the write-ahead log file,
+** assuming a database page size of szPage bytes. The offset returned
+** is to the start of the write-ahead log frame-header.
+*/
+#define walFrameOffset(iFrame, szPage) ( \
+ WAL_HDRSIZE + ((iFrame)-1)*(i64)((szPage)+WAL_FRAME_HDRSIZE) \
+)
+
+/*
+** An open write-ahead log file is represented by an instance of the
+** following object.
+*/
+struct Wal {
+ sqlite3_vfs *pVfs; /* The VFS used to create pDbFd */
+ sqlite3_file *pDbFd; /* File handle for the database file */
+ sqlite3_file *pWalFd; /* File handle for WAL file */
+ u32 iCallback; /* Value to pass to log callback (or 0) */
+ i64 mxWalSize; /* Truncate WAL to this size upon reset */
+ int nWiData; /* Size of array apWiData */
+ int szFirstBlock; /* Size of first block written to WAL file */
+ volatile u32 **apWiData; /* Pointer to wal-index content in memory */
+ u32 szPage; /* Database page size */
+ i16 readLock; /* Which read lock is being held. -1 for none */
+ u8 syncFlags; /* Flags to use to sync header writes */
+ u8 exclusiveMode; /* Non-zero if connection is in exclusive mode */
+ u8 writeLock; /* True if in a write transaction */
+ u8 ckptLock; /* True if holding a checkpoint lock */
+ u8 readOnly; /* WAL_RDWR, WAL_RDONLY, or WAL_SHM_RDONLY */
+ u8 truncateOnCommit; /* True to truncate WAL file on commit */
+ u8 syncHeader; /* Fsync the WAL header if true */
+ u8 padToSectorBoundary; /* Pad transactions out to the next sector */
+ u8 bShmUnreliable; /* SHM content is read-only and unreliable */
+ WalIndexHdr hdr; /* Wal-index header for current transaction */
+ u32 minFrame; /* Ignore wal frames before this one */
+ u32 iReCksum; /* On commit, recalculate checksums from here */
+ const char *zWalName; /* Name of WAL file */
+ u32 nCkpt; /* Checkpoint sequence counter in the wal-header */
+#ifdef SQLITE_USE_SEH
+ u32 lockMask; /* Mask of locks held */
+ void *pFree; /* Pointer to sqlite3_free() if exception thrown */
+ u32 *pWiValue; /* Value to write into apWiData[iWiPg] */
+ int iWiPg; /* Write pWiValue into apWiData[iWiPg] */
+ int iSysErrno; /* System error code following exception */
+#endif
+#ifdef SQLITE_DEBUG
+ int nSehTry; /* Number of nested SEH_TRY{} blocks */
+ u8 lockError; /* True if a locking error has occurred */
+#endif
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */
+#endif
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ sqlite3 *db;
+#endif
+};
+
+/*
+** Candidate values for Wal.exclusiveMode.
+*/
+#define WAL_NORMAL_MODE 0
+#define WAL_EXCLUSIVE_MODE 1
+#define WAL_HEAPMEMORY_MODE 2
+
+/*
+** Possible values for WAL.readOnly
+*/
+#define WAL_RDWR 0 /* Normal read/write connection */
+#define WAL_RDONLY 1 /* The WAL file is readonly */
+#define WAL_SHM_RDONLY 2 /* The SHM file is readonly */
+
+/*
+** Each page of the wal-index mapping contains a hash-table made up of
+** an array of HASHTABLE_NSLOT elements of the following type.
+*/
+typedef u16 ht_slot;
+
+/*
+** This structure is used to implement an iterator that loops through
+** all frames in the WAL in database page order. Where two or more frames
+** correspond to the same database page, the iterator visits only the
+** frame most recently written to the WAL (in other words, the frame with
+** the largest index).
+**
+** The internals of this structure are only accessed by:
+**
+** walIteratorInit() - Create a new iterator,
+** walIteratorNext() - Step an iterator,
+** walIteratorFree() - Free an iterator.
+**
+** This functionality is used by the checkpoint code (see walCheckpoint()).
+*/
+struct WalIterator {
+ u32 iPrior; /* Last result returned from the iterator */
+ int nSegment; /* Number of entries in aSegment[] */
+ struct WalSegment {
+ int iNext; /* Next slot in aIndex[] not yet returned */
+ ht_slot *aIndex; /* i0, i1, i2... such that aPgno[iN] ascend */
+ u32 *aPgno; /* Array of page numbers. */
+ int nEntry; /* Nr. of entries in aPgno[] and aIndex[] */
+ int iZero; /* Frame number associated with aPgno[0] */
+ } aSegment[1]; /* One for every 32KB page in the wal-index */
+};
+
+/*
+** Define the parameters of the hash tables in the wal-index file. There
+** is a hash-table following every HASHTABLE_NPAGE page numbers in the
+** wal-index.
+**
+** Changing any of these constants will alter the wal-index format and
+** create incompatibilities.
+*/
+#define HASHTABLE_NPAGE 4096 /* Must be power of 2 */
+#define HASHTABLE_HASH_1 383 /* Should be prime */
+#define HASHTABLE_NSLOT (HASHTABLE_NPAGE*2) /* Must be a power of 2 */
+
+/*
+** The block of page numbers associated with the first hash-table in a
+** wal-index is smaller than usual. This is so that there is a complete
+** hash-table on each aligned 32KB page of the wal-index.
+*/
+#define HASHTABLE_NPAGE_ONE (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32)))
+
+/* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */
+#define WALINDEX_PGSZ ( \
+ sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \
+)
+
+/*
+** Structured Exception Handling (SEH) is a Windows-specific technique
+** for catching exceptions raised while accessing memory-mapped files.
+**
+** The -DSQLITE_USE_SEH compile-time option means to use SEH to catch and
+** deal with system-level errors that arise during WAL -shm file processing.
+** Without this compile-time option, any system-level faults that appear
+** while accessing the memory-mapped -shm file will cause a process-wide
+** signal to be deliver, which will more than likely cause the entire
+** process to exit.
+*/
+#ifdef SQLITE_USE_SEH
+#include <Windows.h>
+
+/* Beginning of a block of code in which an exception might occur */
+# define SEH_TRY __try { \
+ assert( walAssertLockmask(pWal) && pWal->nSehTry==0 ); \
+ VVA_ONLY(pWal->nSehTry++);
+
+/* The end of a block of code in which an exception might occur */
+# define SEH_EXCEPT(X) \
+ VVA_ONLY(pWal->nSehTry--); \
+ assert( pWal->nSehTry==0 ); \
+ } __except( sehExceptionFilter(pWal, GetExceptionCode(), GetExceptionInformation() ) ){ X }
+
+/* Simulate a memory-mapping fault in the -shm file for testing purposes */
+# define SEH_INJECT_FAULT sehInjectFault(pWal)
+
+/*
+** The second argument is the return value of GetExceptionCode() for the
+** current exception. Return EXCEPTION_EXECUTE_HANDLER if the exception code
+** indicates that the exception may have been caused by accessing the *-shm
+** file mapping. Or EXCEPTION_CONTINUE_SEARCH otherwise.
+*/
+static int sehExceptionFilter(Wal *pWal, int eCode, EXCEPTION_POINTERS *p){
+ VVA_ONLY(pWal->nSehTry--);
+ if( eCode==EXCEPTION_IN_PAGE_ERROR ){
+ if( p && p->ExceptionRecord && p->ExceptionRecord->NumberParameters>=3 ){
+ /* From MSDN: For this type of exception, the first element of the
+ ** ExceptionInformation[] array is a read-write flag - 0 if the exception
+ ** was thrown while reading, 1 if while writing. The second element is
+ ** the virtual address being accessed. The "third array element specifies
+ ** the underlying NTSTATUS code that resulted in the exception". */
+ pWal->iSysErrno = (int)p->ExceptionRecord->ExceptionInformation[2];
+ }
+ return EXCEPTION_EXECUTE_HANDLER;
+ }
+ return EXCEPTION_CONTINUE_SEARCH;
+}
+
+/*
+** If one is configured, invoke the xTestCallback callback with 650 as
+** the argument. If it returns true, throw the same exception that is
+** thrown by the system if the *-shm file mapping is accessed after it
+** has been invalidated.
+*/
+static void sehInjectFault(Wal *pWal){
+ int res;
+ assert( pWal->nSehTry>0 );
+
+ res = sqlite3FaultSim(650);
+ if( res!=0 ){
+ ULONG_PTR aArg[3];
+ aArg[0] = 0;
+ aArg[1] = 0;
+ aArg[2] = (ULONG_PTR)res;
+ RaiseException(EXCEPTION_IN_PAGE_ERROR, 0, 3, (const ULONG_PTR*)aArg);
+ }
+}
+
+/*
+** There are two ways to use this macro. To set a pointer to be freed
+** if an exception is thrown:
+**
+** SEH_FREE_ON_ERROR(0, pPtr);
+**
+** and to cancel the same:
+**
+** SEH_FREE_ON_ERROR(pPtr, 0);
+**
+** In the first case, there must not already be a pointer registered to
+** be freed. In the second case, pPtr must be the registered pointer.
+*/
+#define SEH_FREE_ON_ERROR(X,Y) \
+ assert( (X==0 || Y==0) && pWal->pFree==X ); pWal->pFree = Y
+
+/*
+** There are two ways to use this macro. To arrange for pWal->apWiData[iPg]
+** to be set to pValue if an exception is thrown:
+**
+** SEH_SET_ON_ERROR(iPg, pValue);
+**
+** and to cancel the same:
+**
+** SEH_SET_ON_ERROR(0, 0);
+*/
+#define SEH_SET_ON_ERROR(X,Y) pWal->iWiPg = X; pWal->pWiValue = Y
+
+#else
+# define SEH_TRY VVA_ONLY(pWal->nSehTry++);
+# define SEH_EXCEPT(X) VVA_ONLY(pWal->nSehTry--); assert( pWal->nSehTry==0 );
+# define SEH_INJECT_FAULT assert( pWal->nSehTry>0 );
+# define SEH_FREE_ON_ERROR(X,Y)
+# define SEH_SET_ON_ERROR(X,Y)
+#endif /* ifdef SQLITE_USE_SEH */
+
+
+/*
+** Obtain a pointer to the iPage'th page of the wal-index. The wal-index
+** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are
+** numbered from zero.
+**
+** If the wal-index is currently smaller the iPage pages then the size
+** of the wal-index might be increased, but only if it is safe to do
+** so. It is safe to enlarge the wal-index if pWal->writeLock is true
+** or pWal->exclusiveMode==WAL_HEAPMEMORY_MODE.
+**
+** Three possible result scenarios:
+**
+** (1) rc==SQLITE_OK and *ppPage==Requested-Wal-Index-Page
+** (2) rc>=SQLITE_ERROR and *ppPage==NULL
+** (3) rc==SQLITE_OK and *ppPage==NULL // only if iPage==0
+**
+** Scenario (3) can only occur when pWal->writeLock is false and iPage==0
+*/
+static SQLITE_NOINLINE int walIndexPageRealloc(
+ Wal *pWal, /* The WAL context */
+ int iPage, /* The page we seek */
+ volatile u32 **ppPage /* Write the page pointer here */
+){
+ int rc = SQLITE_OK;
+
+ /* Enlarge the pWal->apWiData[] array if required */
+ if( pWal->nWiData<=iPage ){
+ sqlite3_int64 nByte = sizeof(u32*)*(iPage+1);
+ volatile u32 **apNew;
+ apNew = (volatile u32 **)sqlite3Realloc((void *)pWal->apWiData, nByte);
+ if( !apNew ){
+ *ppPage = 0;
+ return SQLITE_NOMEM_BKPT;
+ }
+ memset((void*)&apNew[pWal->nWiData], 0,
+ sizeof(u32*)*(iPage+1-pWal->nWiData));
+ pWal->apWiData = apNew;
+ pWal->nWiData = iPage+1;
+ }
+
+ /* Request a pointer to the required page from the VFS */
+ assert( pWal->apWiData[iPage]==0 );
+ if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){
+ pWal->apWiData[iPage] = (u32 volatile *)sqlite3MallocZero(WALINDEX_PGSZ);
+ if( !pWal->apWiData[iPage] ) rc = SQLITE_NOMEM_BKPT;
+ }else{
+ rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ,
+ pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
+ );
+ assert( pWal->apWiData[iPage]!=0
+ || rc!=SQLITE_OK
+ || (pWal->writeLock==0 && iPage==0) );
+ testcase( pWal->apWiData[iPage]==0 && rc==SQLITE_OK );
+ if( rc==SQLITE_OK ){
+ if( iPage>0 && sqlite3FaultSim(600) ) rc = SQLITE_NOMEM;
+ }else if( (rc&0xff)==SQLITE_READONLY ){
+ pWal->readOnly |= WAL_SHM_RDONLY;
+ if( rc==SQLITE_READONLY ){
+ rc = SQLITE_OK;
+ }
+ }
+ }
+
+ *ppPage = pWal->apWiData[iPage];
+ assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
+ return rc;
+}
+static int walIndexPage(
+ Wal *pWal, /* The WAL context */
+ int iPage, /* The page we seek */
+ volatile u32 **ppPage /* Write the page pointer here */
+){
+ SEH_INJECT_FAULT;
+ if( pWal->nWiData<=iPage || (*ppPage = pWal->apWiData[iPage])==0 ){
+ return walIndexPageRealloc(pWal, iPage, ppPage);
+ }
+ return SQLITE_OK;
+}
+
+/*
+** Return a pointer to the WalCkptInfo structure in the wal-index.
+*/
+static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
+ assert( pWal->nWiData>0 && pWal->apWiData[0] );
+ SEH_INJECT_FAULT;
+ return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]);
+}
+
+/*
+** Return a pointer to the WalIndexHdr structure in the wal-index.
+*/
+static volatile WalIndexHdr *walIndexHdr(Wal *pWal){
+ assert( pWal->nWiData>0 && pWal->apWiData[0] );
+ SEH_INJECT_FAULT;
+ return (volatile WalIndexHdr*)pWal->apWiData[0];
+}
+
+/*
+** The argument to this macro must be of type u32. On a little-endian
+** architecture, it returns the u32 value that results from interpreting
+** the 4 bytes as a big-endian value. On a big-endian architecture, it
+** returns the value that would be produced by interpreting the 4 bytes
+** of the input value as a little-endian integer.
+*/
+#define BYTESWAP32(x) ( \
+ (((x)&0x000000FF)<<24) + (((x)&0x0000FF00)<<8) \
+ + (((x)&0x00FF0000)>>8) + (((x)&0xFF000000)>>24) \
+)
+
+/*
+** Generate or extend an 8 byte checksum based on the data in
+** array aByte[] and the initial values of aIn[0] and aIn[1] (or
+** initial values of 0 and 0 if aIn==NULL).
+**
+** The checksum is written back into aOut[] before returning.
+**
+** nByte must be a positive multiple of 8.
+*/
+static void walChecksumBytes(
+ int nativeCksum, /* True for native byte-order, false for non-native */
+ u8 *a, /* Content to be checksummed */
+ int nByte, /* Bytes of content in a[]. Must be a multiple of 8. */
+ const u32 *aIn, /* Initial checksum value input */
+ u32 *aOut /* OUT: Final checksum value output */
+){
+ u32 s1, s2;
+ u32 *aData = (u32 *)a;
+ u32 *aEnd = (u32 *)&a[nByte];
+
+ if( aIn ){
+ s1 = aIn[0];
+ s2 = aIn[1];
+ }else{
+ s1 = s2 = 0;
+ }
+
+ assert( nByte>=8 );
+ assert( (nByte&0x00000007)==0 );
+ assert( nByte<=65536 );
+ assert( nByte%4==0 );
+
+ if( !nativeCksum ){
+ do {
+ s1 += BYTESWAP32(aData[0]) + s2;
+ s2 += BYTESWAP32(aData[1]) + s1;
+ aData += 2;
+ }while( aData<aEnd );
+ }else if( nByte%64==0 ){
+ do {
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ }while( aData<aEnd );
+ }else{
+ do {
+ s1 += *aData++ + s2;
+ s2 += *aData++ + s1;
+ }while( aData<aEnd );
+ }
+ assert( aData==aEnd );
+
+ aOut[0] = s1;
+ aOut[1] = s2;
+}
+
+/*
+** If there is the possibility of concurrent access to the SHM file
+** from multiple threads and/or processes, then do a memory barrier.
+*/
+static void walShmBarrier(Wal *pWal){
+ if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
+ sqlite3OsShmBarrier(pWal->pDbFd);
+ }
+}
+
+/*
+** Add the SQLITE_NO_TSAN as part of the return-type of a function
+** definition as a hint that the function contains constructs that
+** might give false-positive TSAN warnings.
+**
+** See tag-20200519-1.
+*/
+#if defined(__clang__) && !defined(SQLITE_NO_TSAN)
+# define SQLITE_NO_TSAN __attribute__((no_sanitize_thread))
+#else
+# define SQLITE_NO_TSAN
+#endif
+
+/*
+** Write the header information in pWal->hdr into the wal-index.
+**
+** The checksum on pWal->hdr is updated before it is written.
+*/
+static SQLITE_NO_TSAN void walIndexWriteHdr(Wal *pWal){
+ volatile WalIndexHdr *aHdr = walIndexHdr(pWal);
+ const int nCksum = offsetof(WalIndexHdr, aCksum);
+
+ assert( pWal->writeLock );
+ pWal->hdr.isInit = 1;
+ pWal->hdr.iVersion = WALINDEX_MAX_VERSION;
+ walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);
+ /* Possible TSAN false-positive. See tag-20200519-1 */
+ memcpy((void*)&aHdr[1], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
+ walShmBarrier(pWal);
+ memcpy((void*)&aHdr[0], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
+}
+
+/*
+** This function encodes a single frame header and writes it to a buffer
+** supplied by the caller. A frame-header is made up of a series of
+** 4-byte big-endian integers, as follows:
+**
+** 0: Page number.
+** 4: For commit records, the size of the database image in pages
+** after the commit. For all other records, zero.
+** 8: Salt-1 (copied from the wal-header)
+** 12: Salt-2 (copied from the wal-header)
+** 16: Checksum-1.
+** 20: Checksum-2.
+*/
+static void walEncodeFrame(
+ Wal *pWal, /* The write-ahead log */
+ u32 iPage, /* Database page number for frame */
+ u32 nTruncate, /* New db size (or 0 for non-commit frames) */
+ u8 *aData, /* Pointer to page data */
+ u8 *aFrame /* OUT: Write encoded frame here */
+){
+ int nativeCksum; /* True for native byte-order checksums */
+ u32 *aCksum = pWal->hdr.aFrameCksum;
+ assert( WAL_FRAME_HDRSIZE==24 );
+ sqlite3Put4byte(&aFrame[0], iPage);
+ sqlite3Put4byte(&aFrame[4], nTruncate);
+ if( pWal->iReCksum==0 ){
+ memcpy(&aFrame[8], pWal->hdr.aSalt, 8);
+
+ nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
+ walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
+ walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
+
+ sqlite3Put4byte(&aFrame[16], aCksum[0]);
+ sqlite3Put4byte(&aFrame[20], aCksum[1]);
+ }else{
+ memset(&aFrame[8], 0, 16);
+ }
+}
+
+/*
+** Check to see if the frame with header in aFrame[] and content
+** in aData[] is valid. If it is a valid frame, fill *piPage and
+** *pnTruncate and return true. Return if the frame is not valid.
+*/
+static int walDecodeFrame(
+ Wal *pWal, /* The write-ahead log */
+ u32 *piPage, /* OUT: Database page number for frame */
+ u32 *pnTruncate, /* OUT: New db size (or 0 if not commit) */
+ u8 *aData, /* Pointer to page data (for checksum) */
+ u8 *aFrame /* Frame data */
+){
+ int nativeCksum; /* True for native byte-order checksums */
+ u32 *aCksum = pWal->hdr.aFrameCksum;
+ u32 pgno; /* Page number of the frame */
+ assert( WAL_FRAME_HDRSIZE==24 );
+
+ /* A frame is only valid if the salt values in the frame-header
+ ** match the salt values in the wal-header.
+ */
+ if( memcmp(&pWal->hdr.aSalt, &aFrame[8], 8)!=0 ){
+ return 0;
+ }
+
+ /* A frame is only valid if the page number is greater than zero.
+ */
+ pgno = sqlite3Get4byte(&aFrame[0]);
+ if( pgno==0 ){
+ return 0;
+ }
+
+ /* A frame is only valid if a checksum of the WAL header,
+ ** all prior frames, the first 16 bytes of this frame-header,
+ ** and the frame-data matches the checksum in the last 8
+ ** bytes of this frame-header.
+ */
+ nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
+ walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
+ walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
+ if( aCksum[0]!=sqlite3Get4byte(&aFrame[16])
+ || aCksum[1]!=sqlite3Get4byte(&aFrame[20])
+ ){
+ /* Checksum failed. */
+ return 0;
+ }
+
+ /* If we reach this point, the frame is valid. Return the page number
+ ** and the new database size.
+ */
+ *piPage = pgno;
+ *pnTruncate = sqlite3Get4byte(&aFrame[4]);
+ return 1;
+}
+
+
+#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
+/*
+** Names of locks. This routine is used to provide debugging output and is not
+** a part of an ordinary build.
+*/
+static const char *walLockName(int lockIdx){
+ if( lockIdx==WAL_WRITE_LOCK ){
+ return "WRITE-LOCK";
+ }else if( lockIdx==WAL_CKPT_LOCK ){
+ return "CKPT-LOCK";
+ }else if( lockIdx==WAL_RECOVER_LOCK ){
+ return "RECOVER-LOCK";
+ }else{
+ static char zName[15];
+ sqlite3_snprintf(sizeof(zName), zName, "READ-LOCK[%d]",
+ lockIdx-WAL_READ_LOCK(0));
+ return zName;
+ }
+}
+#endif /*defined(SQLITE_TEST) || defined(SQLITE_DEBUG) */
+
+
+/*
+** Set or release locks on the WAL. Locks are either shared or exclusive.
+** A lock cannot be moved directly between shared and exclusive - it must go
+** through the unlocked state first.
+**
+** In locking_mode=EXCLUSIVE, all of these routines become no-ops.
+*/
+static int walLockShared(Wal *pWal, int lockIdx){
+ int rc;
+ if( pWal->exclusiveMode ) return SQLITE_OK;
+ rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
+ SQLITE_SHM_LOCK | SQLITE_SHM_SHARED);
+ WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal,
+ walLockName(lockIdx), rc ? "failed" : "ok"));
+ VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); )
+#ifdef SQLITE_USE_SEH
+ if( rc==SQLITE_OK ) pWal->lockMask |= (1 << lockIdx);
+#endif
+ return rc;
+}
+static void walUnlockShared(Wal *pWal, int lockIdx){
+ if( pWal->exclusiveMode ) return;
+ (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
+ SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED);
+#ifdef SQLITE_USE_SEH
+ pWal->lockMask &= ~(1 << lockIdx);
+#endif
+ WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx)));
+}
+static int walLockExclusive(Wal *pWal, int lockIdx, int n){
+ int rc;
+ if( pWal->exclusiveMode ) return SQLITE_OK;
+ rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
+ SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE);
+ WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal,
+ walLockName(lockIdx), n, rc ? "failed" : "ok"));
+ VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); )
+#ifdef SQLITE_USE_SEH
+ if( rc==SQLITE_OK ){
+ pWal->lockMask |= (((1<<n)-1) << (SQLITE_SHM_NLOCK+lockIdx));
+ }
+#endif
+ return rc;
+}
+static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){
+ if( pWal->exclusiveMode ) return;
+ (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
+ SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE);
+#ifdef SQLITE_USE_SEH
+ pWal->lockMask &= ~(((1<<n)-1) << (SQLITE_SHM_NLOCK+lockIdx));
+#endif
+ WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal,
+ walLockName(lockIdx), n));
+}
+
+/*
+** Compute a hash on a page number. The resulting hash value must land
+** between 0 and (HASHTABLE_NSLOT-1). The walHashNext() function advances
+** the hash to the next value in the event of a collision.
+*/
+static int walHash(u32 iPage){
+ assert( iPage>0 );
+ assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 );
+ return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1);
+}
+static int walNextHash(int iPriorHash){
+ return (iPriorHash+1)&(HASHTABLE_NSLOT-1);
+}
+
+/*
+** An instance of the WalHashLoc object is used to describe the location
+** of a page hash table in the wal-index. This becomes the return value
+** from walHashGet().
+*/
+typedef struct WalHashLoc WalHashLoc;
+struct WalHashLoc {
+ volatile ht_slot *aHash; /* Start of the wal-index hash table */
+ volatile u32 *aPgno; /* aPgno[1] is the page of first frame indexed */
+ u32 iZero; /* One less than the frame number of first indexed*/
+};
+
+/*
+** Return pointers to the hash table and page number array stored on
+** page iHash of the wal-index. The wal-index is broken into 32KB pages
+** numbered starting from 0.
+**
+** Set output variable pLoc->aHash to point to the start of the hash table
+** in the wal-index file. Set pLoc->iZero to one less than the frame
+** number of the first frame indexed by this hash table. If a
+** slot in the hash table is set to N, it refers to frame number
+** (pLoc->iZero+N) in the log.
+**
+** Finally, set pLoc->aPgno so that pLoc->aPgno[0] is the page number of the
+** first frame indexed by the hash table, frame (pLoc->iZero).
+*/
+static int walHashGet(
+ Wal *pWal, /* WAL handle */
+ int iHash, /* Find the iHash'th table */
+ WalHashLoc *pLoc /* OUT: Hash table location */
+){
+ int rc; /* Return code */
+
+ rc = walIndexPage(pWal, iHash, &pLoc->aPgno);
+ assert( rc==SQLITE_OK || iHash>0 );
+
+ if( pLoc->aPgno ){
+ pLoc->aHash = (volatile ht_slot *)&pLoc->aPgno[HASHTABLE_NPAGE];
+ if( iHash==0 ){
+ pLoc->aPgno = &pLoc->aPgno[WALINDEX_HDR_SIZE/sizeof(u32)];
+ pLoc->iZero = 0;
+ }else{
+ pLoc->iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE;
+ }
+ }else if( NEVER(rc==SQLITE_OK) ){
+ rc = SQLITE_ERROR;
+ }
+ return rc;
+}
+
+/*
+** Return the number of the wal-index page that contains the hash-table
+** and page-number array that contain entries corresponding to WAL frame
+** iFrame. The wal-index is broken up into 32KB pages. Wal-index pages
+** are numbered starting from 0.
+*/
+static int walFramePage(u32 iFrame){
+ int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE;
+ assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE)
+ && (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE)
+ && (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE))
+ && (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)
+ && (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE))
+ );
+ assert( iHash>=0 );
+ return iHash;
+}
+
+/*
+** Return the page number associated with frame iFrame in this WAL.
+*/
+static u32 walFramePgno(Wal *pWal, u32 iFrame){
+ int iHash = walFramePage(iFrame);
+ SEH_INJECT_FAULT;
+ if( iHash==0 ){
+ return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1];
+ }
+ return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE];
+}
+
+/*
+** Remove entries from the hash table that point to WAL slots greater
+** than pWal->hdr.mxFrame.
+**
+** This function is called whenever pWal->hdr.mxFrame is decreased due
+** to a rollback or savepoint.
+**
+** At most only the hash table containing pWal->hdr.mxFrame needs to be
+** updated. Any later hash tables will be automatically cleared when
+** pWal->hdr.mxFrame advances to the point where those hash tables are
+** actually needed.
+*/
+static void walCleanupHash(Wal *pWal){
+ WalHashLoc sLoc; /* Hash table location */
+ int iLimit = 0; /* Zero values greater than this */
+ int nByte; /* Number of bytes to zero in aPgno[] */
+ int i; /* Used to iterate through aHash[] */
+
+ assert( pWal->writeLock );
+ testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE-1 );
+ testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE );
+ testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE+1 );
+
+ if( pWal->hdr.mxFrame==0 ) return;
+
+ /* Obtain pointers to the hash-table and page-number array containing
+ ** the entry that corresponds to frame pWal->hdr.mxFrame. It is guaranteed
+ ** that the page said hash-table and array reside on is already mapped.(1)
+ */
+ assert( pWal->nWiData>walFramePage(pWal->hdr.mxFrame) );
+ assert( pWal->apWiData[walFramePage(pWal->hdr.mxFrame)] );
+ i = walHashGet(pWal, walFramePage(pWal->hdr.mxFrame), &sLoc);
+ if( NEVER(i) ) return; /* Defense-in-depth, in case (1) above is wrong */
+
+ /* Zero all hash-table entries that correspond to frame numbers greater
+ ** than pWal->hdr.mxFrame.
+ */
+ iLimit = pWal->hdr.mxFrame - sLoc.iZero;
+ assert( iLimit>0 );
+ for(i=0; i<HASHTABLE_NSLOT; i++){
+ if( sLoc.aHash[i]>iLimit ){
+ sLoc.aHash[i] = 0;
+ }
+ }
+
+ /* Zero the entries in the aPgno array that correspond to frames with
+ ** frame numbers greater than pWal->hdr.mxFrame.
+ */
+ nByte = (int)((char *)sLoc.aHash - (char *)&sLoc.aPgno[iLimit]);
+ assert( nByte>=0 );
+ memset((void *)&sLoc.aPgno[iLimit], 0, nByte);
+
+#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
+ /* Verify that the every entry in the mapping region is still reachable
+ ** via the hash table even after the cleanup.
+ */
+ if( iLimit ){
+ int j; /* Loop counter */
+ int iKey; /* Hash key */
+ for(j=0; j<iLimit; j++){
+ for(iKey=walHash(sLoc.aPgno[j]);sLoc.aHash[iKey];iKey=walNextHash(iKey)){
+ if( sLoc.aHash[iKey]==j+1 ) break;
+ }
+ assert( sLoc.aHash[iKey]==j+1 );
+ }
+ }
+#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
+}
+
+
+/*
+** Set an entry in the wal-index that will map database page number
+** pPage into WAL frame iFrame.
+*/
+static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
+ int rc; /* Return code */
+ WalHashLoc sLoc; /* Wal-index hash table location */
+
+ rc = walHashGet(pWal, walFramePage(iFrame), &sLoc);
+
+ /* Assuming the wal-index file was successfully mapped, populate the
+ ** page number array and hash table entry.
+ */
+ if( rc==SQLITE_OK ){
+ int iKey; /* Hash table key */
+ int idx; /* Value to write to hash-table slot */
+ int nCollide; /* Number of hash collisions */
+
+ idx = iFrame - sLoc.iZero;
+ assert( idx <= HASHTABLE_NSLOT/2 + 1 );
+
+ /* If this is the first entry to be added to this hash-table, zero the
+ ** entire hash table and aPgno[] array before proceeding.
+ */
+ if( idx==1 ){
+ int nByte = (int)((u8*)&sLoc.aHash[HASHTABLE_NSLOT] - (u8*)sLoc.aPgno);
+ assert( nByte>=0 );
+ memset((void*)sLoc.aPgno, 0, nByte);
+ }
+
+ /* If the entry in aPgno[] is already set, then the previous writer
+ ** must have exited unexpectedly in the middle of a transaction (after
+ ** writing one or more dirty pages to the WAL to free up memory).
+ ** Remove the remnants of that writers uncommitted transaction from
+ ** the hash-table before writing any new entries.
+ */
+ if( sLoc.aPgno[idx-1] ){
+ walCleanupHash(pWal);
+ assert( !sLoc.aPgno[idx-1] );
+ }
+
+ /* Write the aPgno[] array entry and the hash-table slot. */
+ nCollide = idx;
+ for(iKey=walHash(iPage); sLoc.aHash[iKey]; iKey=walNextHash(iKey)){
+ if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT;
+ }
+ sLoc.aPgno[idx-1] = iPage;
+ AtomicStore(&sLoc.aHash[iKey], (ht_slot)idx);
+
+#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
+ /* Verify that the number of entries in the hash table exactly equals
+ ** the number of entries in the mapping region.
+ */
+ {
+ int i; /* Loop counter */
+ int nEntry = 0; /* Number of entries in the hash table */
+ for(i=0; i<HASHTABLE_NSLOT; i++){ if( sLoc.aHash[i] ) nEntry++; }
+ assert( nEntry==idx );
+ }
+
+ /* Verify that the every entry in the mapping region is reachable
+ ** via the hash table. This turns out to be a really, really expensive
+ ** thing to check, so only do this occasionally - not on every
+ ** iteration.
+ */
+ if( (idx&0x3ff)==0 ){
+ int i; /* Loop counter */
+ for(i=0; i<idx; i++){
+ for(iKey=walHash(sLoc.aPgno[i]);
+ sLoc.aHash[iKey];
+ iKey=walNextHash(iKey)){
+ if( sLoc.aHash[iKey]==i+1 ) break;
+ }
+ assert( sLoc.aHash[iKey]==i+1 );
+ }
+ }
+#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
+ }
+
+ return rc;
+}
+
+
+/*
+** Recover the wal-index by reading the write-ahead log file.
+**
+** This routine first tries to establish an exclusive lock on the
+** wal-index to prevent other threads/processes from doing anything
+** with the WAL or wal-index while recovery is running. The
+** WAL_RECOVER_LOCK is also held so that other threads will know
+** that this thread is running recovery. If unable to establish
+** the necessary locks, this routine returns SQLITE_BUSY.
+*/
+static int walIndexRecover(Wal *pWal){
+ int rc; /* Return Code */
+ i64 nSize; /* Size of log file */
+ u32 aFrameCksum[2] = {0, 0};
+ int iLock; /* Lock offset to lock for checkpoint */
+
+ /* Obtain an exclusive lock on all byte in the locking range not already
+ ** locked by the caller. The caller is guaranteed to have locked the
+ ** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte.
+ ** If successful, the same bytes that are locked here are unlocked before
+ ** this function returns.
+ */
+ assert( pWal->ckptLock==1 || pWal->ckptLock==0 );
+ assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 );
+ assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE );
+ assert( pWal->writeLock );
+ iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;
+ rc = walLockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
+ if( rc ){
+ return rc;
+ }
+
+ WALTRACE(("WAL%p: recovery begin...\n", pWal));
+
+ memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
+
+ rc = sqlite3OsFileSize(pWal->pWalFd, &nSize);
+ if( rc!=SQLITE_OK ){
+ goto recovery_error;
+ }
+
+ if( nSize>WAL_HDRSIZE ){
+ u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */
+ u32 *aPrivate = 0; /* Heap copy of *-shm hash being populated */
+ u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */
+ int szFrame; /* Number of bytes in buffer aFrame[] */
+ u8 *aData; /* Pointer to data part of aFrame buffer */
+ int szPage; /* Page size according to the log */
+ u32 magic; /* Magic value read from WAL header */
+ u32 version; /* Magic value read from WAL header */
+ int isValid; /* True if this frame is valid */
+ u32 iPg; /* Current 32KB wal-index page */
+ u32 iLastFrame; /* Last frame in wal, based on nSize alone */
+
+ /* Read in the WAL header. */
+ rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
+ if( rc!=SQLITE_OK ){
+ goto recovery_error;
+ }
+
+ /* If the database page size is not a power of two, or is greater than
+ ** SQLITE_MAX_PAGE_SIZE, conclude that the WAL file contains no valid
+ ** data. Similarly, if the 'magic' value is invalid, ignore the whole
+ ** WAL file.
+ */
+ magic = sqlite3Get4byte(&aBuf[0]);
+ szPage = sqlite3Get4byte(&aBuf[8]);
+ if( (magic&0xFFFFFFFE)!=WAL_MAGIC
+ || szPage&(szPage-1)
+ || szPage>SQLITE_MAX_PAGE_SIZE
+ || szPage<512
+ ){
+ goto finished;
+ }
+ pWal->hdr.bigEndCksum = (u8)(magic&0x00000001);
+ pWal->szPage = szPage;
+ pWal->nCkpt = sqlite3Get4byte(&aBuf[12]);
+ memcpy(&pWal->hdr.aSalt, &aBuf[16], 8);
+
+ /* Verify that the WAL header checksum is correct */
+ walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN,
+ aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum
+ );
+ if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24])
+ || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28])
+ ){
+ goto finished;
+ }
+
+ /* Verify that the version number on the WAL format is one that
+ ** are able to understand */
+ version = sqlite3Get4byte(&aBuf[4]);
+ if( version!=WAL_MAX_VERSION ){
+ rc = SQLITE_CANTOPEN_BKPT;
+ goto finished;
+ }
+
+ /* Malloc a buffer to read frames into. */
+ szFrame = szPage + WAL_FRAME_HDRSIZE;
+ aFrame = (u8 *)sqlite3_malloc64(szFrame + WALINDEX_PGSZ);
+ SEH_FREE_ON_ERROR(0, aFrame);
+ if( !aFrame ){
+ rc = SQLITE_NOMEM_BKPT;
+ goto recovery_error;
+ }
+ aData = &aFrame[WAL_FRAME_HDRSIZE];
+ aPrivate = (u32*)&aData[szPage];
+
+ /* Read all frames from the log file. */
+ iLastFrame = (nSize - WAL_HDRSIZE) / szFrame;
+ for(iPg=0; iPg<=(u32)walFramePage(iLastFrame); iPg++){
+ u32 *aShare;
+ u32 iFrame; /* Index of last frame read */
+ u32 iLast = MIN(iLastFrame, HASHTABLE_NPAGE_ONE+iPg*HASHTABLE_NPAGE);
+ u32 iFirst = 1 + (iPg==0?0:HASHTABLE_NPAGE_ONE+(iPg-1)*HASHTABLE_NPAGE);
+ u32 nHdr, nHdr32;
+ rc = walIndexPage(pWal, iPg, (volatile u32**)&aShare);
+ assert( aShare!=0 || rc!=SQLITE_OK );
+ if( aShare==0 ) break;
+ SEH_SET_ON_ERROR(iPg, aShare);
+ pWal->apWiData[iPg] = aPrivate;
+
+ for(iFrame=iFirst; iFrame<=iLast; iFrame++){
+ i64 iOffset = walFrameOffset(iFrame, szPage);
+ u32 pgno; /* Database page number for frame */
+ u32 nTruncate; /* dbsize field from frame header */
+
+ /* Read and decode the next log frame. */
+ rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
+ if( rc!=SQLITE_OK ) break;
+ isValid = walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame);
+ if( !isValid ) break;
+ rc = walIndexAppend(pWal, iFrame, pgno);
+ if( NEVER(rc!=SQLITE_OK) ) break;
+
+ /* If nTruncate is non-zero, this is a commit record. */
+ if( nTruncate ){
+ pWal->hdr.mxFrame = iFrame;
+ pWal->hdr.nPage = nTruncate;
+ pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16));
+ testcase( szPage<=32768 );
+ testcase( szPage>=65536 );
+ aFrameCksum[0] = pWal->hdr.aFrameCksum[0];
+ aFrameCksum[1] = pWal->hdr.aFrameCksum[1];
+ }
+ }
+ pWal->apWiData[iPg] = aShare;
+ SEH_SET_ON_ERROR(0,0);
+ nHdr = (iPg==0 ? WALINDEX_HDR_SIZE : 0);
+ nHdr32 = nHdr / sizeof(u32);
+#ifndef SQLITE_SAFER_WALINDEX_RECOVERY
+ /* Memcpy() should work fine here, on all reasonable implementations.
+ ** Technically, memcpy() might change the destination to some
+ ** intermediate value before setting to the final value, and that might
+ ** cause a concurrent reader to malfunction. Memcpy() is allowed to
+ ** do that, according to the spec, but no memcpy() implementation that
+ ** we know of actually does that, which is why we say that memcpy()
+ ** is safe for this. Memcpy() is certainly a lot faster.
+ */
+ memcpy(&aShare[nHdr32], &aPrivate[nHdr32], WALINDEX_PGSZ-nHdr);
+#else
+ /* In the event that some platform is found for which memcpy()
+ ** changes the destination to some intermediate value before
+ ** setting the final value, this alternative copy routine is
+ ** provided.
+ */
+ {
+ int i;
+ for(i=nHdr32; i<WALINDEX_PGSZ/sizeof(u32); i++){
+ if( aShare[i]!=aPrivate[i] ){
+ /* Atomic memory operations are not required here because if
+ ** the value needs to be changed, that means it is not being
+ ** accessed concurrently. */
+ aShare[i] = aPrivate[i];
+ }
+ }
+ }
+#endif
+ SEH_INJECT_FAULT;
+ if( iFrame<=iLast ) break;
+ }
+
+ SEH_FREE_ON_ERROR(aFrame, 0);
+ sqlite3_free(aFrame);
+ }
+
+finished:
+ if( rc==SQLITE_OK ){
+ volatile WalCkptInfo *pInfo;
+ int i;
+ pWal->hdr.aFrameCksum[0] = aFrameCksum[0];
+ pWal->hdr.aFrameCksum[1] = aFrameCksum[1];
+ walIndexWriteHdr(pWal);
+
+ /* Reset the checkpoint-header. This is safe because this thread is
+ ** currently holding locks that exclude all other writers and
+ ** checkpointers. Then set the values of read-mark slots 1 through N.
+ */
+ pInfo = walCkptInfo(pWal);
+ pInfo->nBackfill = 0;
+ pInfo->nBackfillAttempted = pWal->hdr.mxFrame;
+ pInfo->aReadMark[0] = 0;
+ for(i=1; i<WAL_NREADER; i++){
+ rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ if( rc==SQLITE_OK ){
+ if( i==1 && pWal->hdr.mxFrame ){
+ pInfo->aReadMark[i] = pWal->hdr.mxFrame;
+ }else{
+ pInfo->aReadMark[i] = READMARK_NOT_USED;
+ }
+ SEH_INJECT_FAULT;
+ walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ }else if( rc!=SQLITE_BUSY ){
+ goto recovery_error;
+ }
+ }
+
+ /* If more than one frame was recovered from the log file, report an
+ ** event via sqlite3_log(). This is to help with identifying performance
+ ** problems caused by applications routinely shutting down without
+ ** checkpointing the log file.
+ */
+ if( pWal->hdr.nPage ){
+ sqlite3_log(SQLITE_NOTICE_RECOVER_WAL,
+ "recovered %d frames from WAL file %s",
+ pWal->hdr.mxFrame, pWal->zWalName
+ );
+ }
+ }
+
+recovery_error:
+ WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
+ walUnlockExclusive(pWal, iLock, WAL_READ_LOCK(0)-iLock);
+ return rc;
+}
+
+/*
+** Close an open wal-index.
+*/
+static void walIndexClose(Wal *pWal, int isDelete){
+ if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE || pWal->bShmUnreliable ){
+ int i;
+ for(i=0; i<pWal->nWiData; i++){
+ sqlite3_free((void *)pWal->apWiData[i]);
+ pWal->apWiData[i] = 0;
+ }
+ }
+ if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
+ sqlite3OsShmUnmap(pWal->pDbFd, isDelete);
+ }
+}
+
+/*
+** Open a connection to the WAL file zWalName. The database file must
+** already be opened on connection pDbFd. The buffer that zWalName points
+** to must remain valid for the lifetime of the returned Wal* handle.
+**
+** A SHARED lock should be held on the database file when this function
+** is called. The purpose of this SHARED lock is to prevent any other
+** client from unlinking the WAL or wal-index file. If another process
+** were to do this just after this client opened one of these files, the
+** system would be badly broken.
+**
+** If the log file is successfully opened, SQLITE_OK is returned and
+** *ppWal is set to point to a new WAL handle. If an error occurs,
+** an SQLite error code is returned and *ppWal is left unmodified.
+*/
+int sqlite3WalOpen(
+ sqlite3_vfs *pVfs, /* vfs module to open wal and wal-index */
+ sqlite3_file *pDbFd, /* The open database file */
+ const char *zWalName, /* Name of the WAL file */
+ int bNoShm, /* True to run in heap-memory mode */
+ i64 mxWalSize, /* Truncate WAL to this size on reset */
+ Wal **ppWal /* OUT: Allocated Wal handle */
+){
+ int rc; /* Return Code */
+ Wal *pRet; /* Object to allocate and return */
+ int flags; /* Flags passed to OsOpen() */
+
+ assert( zWalName && zWalName[0] );
+ assert( pDbFd );
+
+ /* Verify the values of various constants. Any changes to the values
+ ** of these constants would result in an incompatible on-disk format
+ ** for the -shm file. Any change that causes one of these asserts to
+ ** fail is a backward compatibility problem, even if the change otherwise
+ ** works.
+ **
+ ** This table also serves as a helpful cross-reference when trying to
+ ** interpret hex dumps of the -shm file.
+ */
+ assert( 48 == sizeof(WalIndexHdr) );
+ assert( 40 == sizeof(WalCkptInfo) );
+ assert( 120 == WALINDEX_LOCK_OFFSET );
+ assert( 136 == WALINDEX_HDR_SIZE );
+ assert( 4096 == HASHTABLE_NPAGE );
+ assert( 4062 == HASHTABLE_NPAGE_ONE );
+ assert( 8192 == HASHTABLE_NSLOT );
+ assert( 383 == HASHTABLE_HASH_1 );
+ assert( 32768 == WALINDEX_PGSZ );
+ assert( 8 == SQLITE_SHM_NLOCK );
+ assert( 5 == WAL_NREADER );
+ assert( 24 == WAL_FRAME_HDRSIZE );
+ assert( 32 == WAL_HDRSIZE );
+ assert( 120 == WALINDEX_LOCK_OFFSET + WAL_WRITE_LOCK );
+ assert( 121 == WALINDEX_LOCK_OFFSET + WAL_CKPT_LOCK );
+ assert( 122 == WALINDEX_LOCK_OFFSET + WAL_RECOVER_LOCK );
+ assert( 123 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(0) );
+ assert( 124 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(1) );
+ assert( 125 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(2) );
+ assert( 126 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(3) );
+ assert( 127 == WALINDEX_LOCK_OFFSET + WAL_READ_LOCK(4) );
+
+ /* In the amalgamation, the os_unix.c and os_win.c source files come before
+ ** this source file. Verify that the #defines of the locking byte offsets
+ ** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value.
+ ** For that matter, if the lock offset ever changes from its initial design
+ ** value of 120, we need to know that so there is an assert() to check it.
+ */
+#ifdef WIN_SHM_BASE
+ assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET );
+#endif
+#ifdef UNIX_SHM_BASE
+ assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET );
+#endif
+
+
+ /* Allocate an instance of struct Wal to return. */
+ *ppWal = 0;
+ pRet = (Wal*)sqlite3MallocZero(sizeof(Wal) + pVfs->szOsFile);
+ if( !pRet ){
+ return SQLITE_NOMEM_BKPT;
+ }
+
+ pRet->pVfs = pVfs;
+ pRet->pWalFd = (sqlite3_file *)&pRet[1];
+ pRet->pDbFd = pDbFd;
+ pRet->readLock = -1;
+ pRet->mxWalSize = mxWalSize;
+ pRet->zWalName = zWalName;
+ pRet->syncHeader = 1;
+ pRet->padToSectorBoundary = 1;
+ pRet->exclusiveMode = (bNoShm ? WAL_HEAPMEMORY_MODE: WAL_NORMAL_MODE);
+
+ /* Open file handle on the write-ahead log file. */
+ flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
+ rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
+ if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
+ pRet->readOnly = WAL_RDONLY;
+ }
+
+ if( rc!=SQLITE_OK ){
+ walIndexClose(pRet, 0);
+ sqlite3OsClose(pRet->pWalFd);
+ sqlite3_free(pRet);
+ }else{
+ int iDC = sqlite3OsDeviceCharacteristics(pDbFd);
+ if( iDC & SQLITE_IOCAP_SEQUENTIAL ){ pRet->syncHeader = 0; }
+ if( iDC & SQLITE_IOCAP_POWERSAFE_OVERWRITE ){
+ pRet->padToSectorBoundary = 0;
+ }
+ *ppWal = pRet;
+ WALTRACE(("WAL%d: opened\n", pRet));
+ }
+ return rc;
+}
+
+/*
+** Change the size to which the WAL file is truncated on each reset.
+*/
+void sqlite3WalLimit(Wal *pWal, i64 iLimit){
+ if( pWal ) pWal->mxWalSize = iLimit;
+}
+
+/*
+** Find the smallest page number out of all pages held in the WAL that
+** has not been returned by any prior invocation of this method on the
+** same WalIterator object. Write into *piFrame the frame index where
+** that page was last written into the WAL. Write into *piPage the page
+** number.
+**
+** Return 0 on success. If there are no pages in the WAL with a page
+** number larger than *piPage, then return 1.
+*/
+static int walIteratorNext(
+ WalIterator *p, /* Iterator */
+ u32 *piPage, /* OUT: The page number of the next page */
+ u32 *piFrame /* OUT: Wal frame index of next page */
+){
+ u32 iMin; /* Result pgno must be greater than iMin */
+ u32 iRet = 0xFFFFFFFF; /* 0xffffffff is never a valid page number */
+ int i; /* For looping through segments */
+
+ iMin = p->iPrior;
+ assert( iMin<0xffffffff );
+ for(i=p->nSegment-1; i>=0; i--){
+ struct WalSegment *pSegment = &p->aSegment[i];
+ while( pSegment->iNext<pSegment->nEntry ){
+ u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]];
+ if( iPg>iMin ){
+ if( iPg<iRet ){
+ iRet = iPg;
+ *piFrame = pSegment->iZero + pSegment->aIndex[pSegment->iNext];
+ }
+ break;
+ }
+ pSegment->iNext++;
+ }
+ }
+
+ *piPage = p->iPrior = iRet;
+ return (iRet==0xFFFFFFFF);
+}
+
+/*
+** This function merges two sorted lists into a single sorted list.
+**
+** aLeft[] and aRight[] are arrays of indices. The sort key is
+** aContent[aLeft[]] and aContent[aRight[]]. Upon entry, the following
+** is guaranteed for all J<K:
+**
+** aContent[aLeft[J]] < aContent[aLeft[K]]
+** aContent[aRight[J]] < aContent[aRight[K]]
+**
+** This routine overwrites aRight[] with a new (probably longer) sequence
+** of indices such that the aRight[] contains every index that appears in
+** either aLeft[] or the old aRight[] and such that the second condition
+** above is still met.
+**
+** The aContent[aLeft[X]] values will be unique for all X. And the
+** aContent[aRight[X]] values will be unique too. But there might be
+** one or more combinations of X and Y such that
+**
+** aLeft[X]!=aRight[Y] && aContent[aLeft[X]] == aContent[aRight[Y]]
+**
+** When that happens, omit the aLeft[X] and use the aRight[Y] index.
+*/
+static void walMerge(
+ const u32 *aContent, /* Pages in wal - keys for the sort */
+ ht_slot *aLeft, /* IN: Left hand input list */
+ int nLeft, /* IN: Elements in array *paLeft */
+ ht_slot **paRight, /* IN/OUT: Right hand input list */
+ int *pnRight, /* IN/OUT: Elements in *paRight */
+ ht_slot *aTmp /* Temporary buffer */
+){
+ int iLeft = 0; /* Current index in aLeft */
+ int iRight = 0; /* Current index in aRight */
+ int iOut = 0; /* Current index in output buffer */
+ int nRight = *pnRight;
+ ht_slot *aRight = *paRight;
+
+ assert( nLeft>0 && nRight>0 );
+ while( iRight<nRight || iLeft<nLeft ){
+ ht_slot logpage;
+ Pgno dbpage;
+
+ if( (iLeft<nLeft)
+ && (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]])
+ ){
+ logpage = aLeft[iLeft++];
+ }else{
+ logpage = aRight[iRight++];
+ }
+ dbpage = aContent[logpage];
+
+ aTmp[iOut++] = logpage;
+ if( iLeft<nLeft && aContent[aLeft[iLeft]]==dbpage ) iLeft++;
+
+ assert( iLeft>=nLeft || aContent[aLeft[iLeft]]>dbpage );
+ assert( iRight>=nRight || aContent[aRight[iRight]]>dbpage );
+ }
+
+ *paRight = aLeft;
+ *pnRight = iOut;
+ memcpy(aLeft, aTmp, sizeof(aTmp[0])*iOut);
+}
+
+/*
+** Sort the elements in list aList using aContent[] as the sort key.
+** Remove elements with duplicate keys, preferring to keep the
+** larger aList[] values.
+**
+** The aList[] entries are indices into aContent[]. The values in
+** aList[] are to be sorted so that for all J<K:
+**
+** aContent[aList[J]] < aContent[aList[K]]
+**
+** For any X and Y such that
+**
+** aContent[aList[X]] == aContent[aList[Y]]
+**
+** Keep the larger of the two values aList[X] and aList[Y] and discard
+** the smaller.
+*/
+static void walMergesort(
+ const u32 *aContent, /* Pages in wal */
+ ht_slot *aBuffer, /* Buffer of at least *pnList items to use */
+ ht_slot *aList, /* IN/OUT: List to sort */
+ int *pnList /* IN/OUT: Number of elements in aList[] */
+){
+ struct Sublist {
+ int nList; /* Number of elements in aList */
+ ht_slot *aList; /* Pointer to sub-list content */
+ };
+
+ const int nList = *pnList; /* Size of input list */
+ int nMerge = 0; /* Number of elements in list aMerge */
+ ht_slot *aMerge = 0; /* List to be merged */
+ int iList; /* Index into input list */
+ u32 iSub = 0; /* Index into aSub array */
+ struct Sublist aSub[13]; /* Array of sub-lists */
+
+ memset(aSub, 0, sizeof(aSub));
+ assert( nList<=HASHTABLE_NPAGE && nList>0 );
+ assert( HASHTABLE_NPAGE==(1<<(ArraySize(aSub)-1)) );
+
+ for(iList=0; iList<nList; iList++){
+ nMerge = 1;
+ aMerge = &aList[iList];
+ for(iSub=0; iList & (1<<iSub); iSub++){
+ struct Sublist *p;
+ assert( iSub<ArraySize(aSub) );
+ p = &aSub[iSub];
+ assert( p->aList && p->nList<=(1<<iSub) );
+ assert( p->aList==&aList[iList&~((2<<iSub)-1)] );
+ walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
+ }
+ aSub[iSub].aList = aMerge;
+ aSub[iSub].nList = nMerge;
+ }
+
+ for(iSub++; iSub<ArraySize(aSub); iSub++){
+ if( nList & (1<<iSub) ){
+ struct Sublist *p;
+ assert( iSub<ArraySize(aSub) );
+ p = &aSub[iSub];
+ assert( p->nList<=(1<<iSub) );
+ assert( p->aList==&aList[nList&~((2<<iSub)-1)] );
+ walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
+ }
+ }
+ assert( aMerge==aList );
+ *pnList = nMerge;
+
+#ifdef SQLITE_DEBUG
+ {
+ int i;
+ for(i=1; i<*pnList; i++){
+ assert( aContent[aList[i]] > aContent[aList[i-1]] );
+ }
+ }
+#endif
+}
+
+/*
+** Free an iterator allocated by walIteratorInit().
+*/
+static void walIteratorFree(WalIterator *p){
+ sqlite3_free(p);
+}
+
+/*
+** Construct a WalInterator object that can be used to loop over all
+** pages in the WAL following frame nBackfill in ascending order. Frames
+** nBackfill or earlier may be included - excluding them is an optimization
+** only. The caller must hold the checkpoint lock.
+**
+** On success, make *pp point to the newly allocated WalInterator object
+** return SQLITE_OK. Otherwise, return an error code. If this routine
+** returns an error, the value of *pp is undefined.
+**
+** The calling routine should invoke walIteratorFree() to destroy the
+** WalIterator object when it has finished with it.
+*/
+static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){
+ WalIterator *p; /* Return value */
+ int nSegment; /* Number of segments to merge */
+ u32 iLast; /* Last frame in log */
+ sqlite3_int64 nByte; /* Number of bytes to allocate */
+ int i; /* Iterator variable */
+ ht_slot *aTmp; /* Temp space used by merge-sort */
+ int rc = SQLITE_OK; /* Return Code */
+
+ /* This routine only runs while holding the checkpoint lock. And
+ ** it only runs if there is actually content in the log (mxFrame>0).
+ */
+ assert( pWal->ckptLock && pWal->hdr.mxFrame>0 );
+ iLast = pWal->hdr.mxFrame;
+
+ /* Allocate space for the WalIterator object. */
+ nSegment = walFramePage(iLast) + 1;
+ nByte = sizeof(WalIterator)
+ + (nSegment-1)*sizeof(struct WalSegment)
+ + iLast*sizeof(ht_slot);
+ p = (WalIterator *)sqlite3_malloc64(nByte
+ + sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)
+ );
+ if( !p ){
+ return SQLITE_NOMEM_BKPT;
+ }
+ memset(p, 0, nByte);
+ p->nSegment = nSegment;
+ aTmp = (ht_slot*)&(((u8*)p)[nByte]);
+ SEH_FREE_ON_ERROR(0, p);
+ for(i=walFramePage(nBackfill+1); rc==SQLITE_OK && i<nSegment; i++){
+ WalHashLoc sLoc;
+
+ rc = walHashGet(pWal, i, &sLoc);
+ if( rc==SQLITE_OK ){
+ int j; /* Counter variable */
+ int nEntry; /* Number of entries in this segment */
+ ht_slot *aIndex; /* Sorted index for this segment */
+
+ if( (i+1)==nSegment ){
+ nEntry = (int)(iLast - sLoc.iZero);
+ }else{
+ nEntry = (int)((u32*)sLoc.aHash - (u32*)sLoc.aPgno);
+ }
+ aIndex = &((ht_slot *)&p->aSegment[p->nSegment])[sLoc.iZero];
+ sLoc.iZero++;
+
+ for(j=0; j<nEntry; j++){
+ aIndex[j] = (ht_slot)j;
+ }
+ walMergesort((u32 *)sLoc.aPgno, aTmp, aIndex, &nEntry);
+ p->aSegment[i].iZero = sLoc.iZero;
+ p->aSegment[i].nEntry = nEntry;
+ p->aSegment[i].aIndex = aIndex;
+ p->aSegment[i].aPgno = (u32 *)sLoc.aPgno;
+ }
+ }
+ if( rc!=SQLITE_OK ){
+ SEH_FREE_ON_ERROR(p, 0);
+ walIteratorFree(p);
+ p = 0;
+ }
+ *pp = p;
+ return rc;
+}
+
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+
+
+/*
+** Attempt to enable blocking locks that block for nMs ms. Return 1 if
+** blocking locks are successfully enabled, or 0 otherwise.
+*/
+static int walEnableBlockingMs(Wal *pWal, int nMs){
+ int rc = sqlite3OsFileControl(
+ pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&nMs
+ );
+ return (rc==SQLITE_OK);
+}
+
+/*
+** Attempt to enable blocking locks. Blocking locks are enabled only if (a)
+** they are supported by the VFS, and (b) the database handle is configured
+** with a busy-timeout. Return 1 if blocking locks are successfully enabled,
+** or 0 otherwise.
+*/
+static int walEnableBlocking(Wal *pWal){
+ int res = 0;
+ if( pWal->db ){
+ int tmout = pWal->db->busyTimeout;
+ if( tmout ){
+ res = walEnableBlockingMs(pWal, tmout);
+ }
+ }
+ return res;
+}
+
+/*
+** Disable blocking locks.
+*/
+static void walDisableBlocking(Wal *pWal){
+ int tmout = 0;
+ sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout);
+}
+
+/*
+** If parameter bLock is true, attempt to enable blocking locks, take
+** the WRITER lock, and then disable blocking locks. If blocking locks
+** cannot be enabled, no attempt to obtain the WRITER lock is made. Return
+** an SQLite error code if an error occurs, or SQLITE_OK otherwise. It is not
+** an error if blocking locks can not be enabled.
+**
+** If the bLock parameter is false and the WRITER lock is held, release it.
+*/
+int sqlite3WalWriteLock(Wal *pWal, int bLock){
+ int rc = SQLITE_OK;
+ assert( pWal->readLock<0 || bLock==0 );
+ if( bLock ){
+ assert( pWal->db );
+ if( walEnableBlocking(pWal) ){
+ rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ if( rc==SQLITE_OK ){
+ pWal->writeLock = 1;
+ }
+ walDisableBlocking(pWal);
+ }
+ }else if( pWal->writeLock ){
+ walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ pWal->writeLock = 0;
+ }
+ return rc;
+}
+
+/*
+** Set the database handle used to determine if blocking locks are required.
+*/
+void sqlite3WalDb(Wal *pWal, sqlite3 *db){
+ pWal->db = db;
+}
+
+#else
+# define walEnableBlocking(x) 0
+# define walDisableBlocking(x)
+# define walEnableBlockingMs(pWal, ms) 0
+# define sqlite3WalDb(pWal, db)
+#endif /* ifdef SQLITE_ENABLE_SETLK_TIMEOUT */
+
+
+/*
+** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and
+** n. If the attempt fails and parameter xBusy is not NULL, then it is a
+** busy-handler function. Invoke it and retry the lock until either the
+** lock is successfully obtained or the busy-handler returns 0.
+*/
+static int walBusyLock(
+ Wal *pWal, /* WAL connection */
+ int (*xBusy)(void*), /* Function to call when busy */
+ void *pBusyArg, /* Context argument for xBusyHandler */
+ int lockIdx, /* Offset of first byte to lock */
+ int n /* Number of bytes to lock */
+){
+ int rc;
+ do {
+ rc = walLockExclusive(pWal, lockIdx, n);
+ }while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) );
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ if( rc==SQLITE_BUSY_TIMEOUT ){
+ walDisableBlocking(pWal);
+ rc = SQLITE_BUSY;
+ }
+#endif
+ return rc;
+}
+
+/*
+** The cache of the wal-index header must be valid to call this function.
+** Return the page-size in bytes used by the database.
+*/
+static int walPagesize(Wal *pWal){
+ return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
+}
+
+/*
+** The following is guaranteed when this function is called:
+**
+** a) the WRITER lock is held,
+** b) the entire log file has been checkpointed, and
+** c) any existing readers are reading exclusively from the database
+** file - there are no readers that may attempt to read a frame from
+** the log file.
+**
+** This function updates the shared-memory structures so that the next
+** client to write to the database (which may be this one) does so by
+** writing frames into the start of the log file.
+**
+** The value of parameter salt1 is used as the aSalt[1] value in the
+** new wal-index header. It should be passed a pseudo-random value (i.e.
+** one obtained from sqlite3_randomness()).
+*/
+static void walRestartHdr(Wal *pWal, u32 salt1){
+ volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+ int i; /* Loop counter */
+ u32 *aSalt = pWal->hdr.aSalt; /* Big-endian salt values */
+ pWal->nCkpt++;
+ pWal->hdr.mxFrame = 0;
+ sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
+ memcpy(&pWal->hdr.aSalt[1], &salt1, 4);
+ walIndexWriteHdr(pWal);
+ AtomicStore(&pInfo->nBackfill, 0);
+ pInfo->nBackfillAttempted = 0;
+ pInfo->aReadMark[1] = 0;
+ for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
+ assert( pInfo->aReadMark[0]==0 );
+}
+
+/*
+** Copy as much content as we can from the WAL back into the database file
+** in response to an sqlite3_wal_checkpoint() request or the equivalent.
+**
+** The amount of information copies from WAL to database might be limited
+** by active readers. This routine will never overwrite a database page
+** that a concurrent reader might be using.
+**
+** All I/O barrier operations (a.k.a fsyncs) occur in this routine when
+** SQLite is in WAL-mode in synchronous=NORMAL. That means that if
+** checkpoints are always run by a background thread or background
+** process, foreground threads will never block on a lengthy fsync call.
+**
+** Fsync is called on the WAL before writing content out of the WAL and
+** into the database. This ensures that if the new content is persistent
+** in the WAL and can be recovered following a power-loss or hard reset.
+**
+** Fsync is also called on the database file if (and only if) the entire
+** WAL content is copied into the database file. This second fsync makes
+** it safe to delete the WAL since the new content will persist in the
+** database file.
+**
+** This routine uses and updates the nBackfill field of the wal-index header.
+** This is the only routine that will increase the value of nBackfill.
+** (A WAL reset or recovery will revert nBackfill to zero, but not increase
+** its value.)
+**
+** The caller must be holding sufficient locks to ensure that no other
+** checkpoint is running (in any other thread or process) at the same
+** time.
+*/
+static int walCheckpoint(
+ Wal *pWal, /* Wal connection */
+ sqlite3 *db, /* Check for interrupts on this handle */
+ int eMode, /* One of PASSIVE, FULL or RESTART */
+ int (*xBusy)(void*), /* Function to call when busy */
+ void *pBusyArg, /* Context argument for xBusyHandler */
+ int sync_flags, /* Flags for OsSync() (or 0) */
+ u8 *zBuf /* Temporary buffer to use */
+){
+ int rc = SQLITE_OK; /* Return code */
+ int szPage; /* Database page-size */
+ WalIterator *pIter = 0; /* Wal iterator context */
+ u32 iDbpage = 0; /* Next database page to write */
+ u32 iFrame = 0; /* Wal frame containing data for iDbpage */
+ u32 mxSafeFrame; /* Max frame that can be backfilled */
+ u32 mxPage; /* Max database page to write */
+ int i; /* Loop counter */
+ volatile WalCkptInfo *pInfo; /* The checkpoint status information */
+
+ szPage = walPagesize(pWal);
+ testcase( szPage<=32768 );
+ testcase( szPage>=65536 );
+ pInfo = walCkptInfo(pWal);
+ if( pInfo->nBackfill<pWal->hdr.mxFrame ){
+
+ /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
+ ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
+ assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );
+
+ /* Compute in mxSafeFrame the index of the last frame of the WAL that is
+ ** safe to write into the database. Frames beyond mxSafeFrame might
+ ** overwrite database pages that are in use by active readers and thus
+ ** cannot be backfilled from the WAL.
+ */
+ mxSafeFrame = pWal->hdr.mxFrame;
+ mxPage = pWal->hdr.nPage;
+ for(i=1; i<WAL_NREADER; i++){
+ u32 y = AtomicLoad(pInfo->aReadMark+i); SEH_INJECT_FAULT;
+ if( mxSafeFrame>y ){
+ assert( y<=pWal->hdr.mxFrame );
+ rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
+ if( rc==SQLITE_OK ){
+ u32 iMark = (i==1 ? mxSafeFrame : READMARK_NOT_USED);
+ AtomicStore(pInfo->aReadMark+i, iMark); SEH_INJECT_FAULT;
+ walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ }else if( rc==SQLITE_BUSY ){
+ mxSafeFrame = y;
+ xBusy = 0;
+ }else{
+ goto walcheckpoint_out;
+ }
+ }
+ }
+
+ /* Allocate the iterator */
+ if( pInfo->nBackfill<mxSafeFrame ){
+ rc = walIteratorInit(pWal, pInfo->nBackfill, &pIter);
+ assert( rc==SQLITE_OK || pIter==0 );
+ }
+
+ if( pIter
+ && (rc = walBusyLock(pWal,xBusy,pBusyArg,WAL_READ_LOCK(0),1))==SQLITE_OK
+ ){
+ u32 nBackfill = pInfo->nBackfill;
+ pInfo->nBackfillAttempted = mxSafeFrame; SEH_INJECT_FAULT;
+
+ /* Sync the WAL to disk */
+ rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags));
+
+ /* If the database may grow as a result of this checkpoint, hint
+ ** about the eventual size of the db file to the VFS layer.
+ */
+ if( rc==SQLITE_OK ){
+ i64 nReq = ((i64)mxPage * szPage);
+ i64 nSize; /* Current size of database file */
+ sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_CKPT_START, 0);
+ rc = sqlite3OsFileSize(pWal->pDbFd, &nSize);
+ if( rc==SQLITE_OK && nSize<nReq ){
+ if( (nSize+65536+(i64)pWal->hdr.mxFrame*szPage)<nReq ){
+ /* If the size of the final database is larger than the current
+ ** database plus the amount of data in the wal file, plus the
+ ** maximum size of the pending-byte page (65536 bytes), then
+ ** must be corruption somewhere. */
+ rc = SQLITE_CORRUPT_BKPT;
+ }else{
+ sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT,&nReq);
+ }
+ }
+
+ }
+
+ /* Iterate through the contents of the WAL, copying data to the db file */
+ while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
+ i64 iOffset;
+ assert( walFramePgno(pWal, iFrame)==iDbpage );
+ SEH_INJECT_FAULT;
+ if( AtomicLoad(&db->u1.isInterrupted) ){
+ rc = db->mallocFailed ? SQLITE_NOMEM_BKPT : SQLITE_INTERRUPT;
+ break;
+ }
+ if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ){
+ continue;
+ }
+ iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE;
+ /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
+ rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset);
+ if( rc!=SQLITE_OK ) break;
+ iOffset = (iDbpage-1)*(i64)szPage;
+ testcase( IS_BIG_INT(iOffset) );
+ rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset);
+ if( rc!=SQLITE_OK ) break;
+ }
+ sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_CKPT_DONE, 0);
+
+ /* If work was actually accomplished... */
+ if( rc==SQLITE_OK ){
+ if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
+ i64 szDb = pWal->hdr.nPage*(i64)szPage;
+ testcase( IS_BIG_INT(szDb) );
+ rc = sqlite3OsTruncate(pWal->pDbFd, szDb);
+ if( rc==SQLITE_OK ){
+ rc = sqlite3OsSync(pWal->pDbFd, CKPT_SYNC_FLAGS(sync_flags));
+ }
+ }
+ if( rc==SQLITE_OK ){
+ AtomicStore(&pInfo->nBackfill, mxSafeFrame); SEH_INJECT_FAULT;
+ }
+ }
+
+ /* Release the reader lock held while backfilling */
+ walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1);
+ }
+
+ if( rc==SQLITE_BUSY ){
+ /* Reset the return code so as not to report a checkpoint failure
+ ** just because there are active readers. */
+ rc = SQLITE_OK;
+ }
+ }
+
+ /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the
+ ** entire wal file has been copied into the database file, then block
+ ** until all readers have finished using the wal file. This ensures that
+ ** the next process to write to the database restarts the wal file.
+ */
+ if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
+ assert( pWal->writeLock );
+ SEH_INJECT_FAULT;
+ if( pInfo->nBackfill<pWal->hdr.mxFrame ){
+ rc = SQLITE_BUSY;
+ }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
+ u32 salt1;
+ sqlite3_randomness(4, &salt1);
+ assert( pInfo->nBackfill==pWal->hdr.mxFrame );
+ rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1);
+ if( rc==SQLITE_OK ){
+ if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){
+ /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as
+ ** SQLITE_CHECKPOINT_RESTART with the addition that it also
+ ** truncates the log file to zero bytes just prior to a
+ ** successful return.
+ **
+ ** In theory, it might be safe to do this without updating the
+ ** wal-index header in shared memory, as all subsequent reader or
+ ** writer clients should see that the entire log file has been
+ ** checkpointed and behave accordingly. This seems unsafe though,
+ ** as it would leave the system in a state where the contents of
+ ** the wal-index header do not match the contents of the
+ ** file-system. To avoid this, update the wal-index header to
+ ** indicate that the log file contains zero valid frames. */
+ walRestartHdr(pWal, salt1);
+ rc = sqlite3OsTruncate(pWal->pWalFd, 0);
+ }
+ walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
+ }
+ }
+ }
+
+ walcheckpoint_out:
+ SEH_FREE_ON_ERROR(pIter, 0);
+ walIteratorFree(pIter);
+ return rc;
+}
+
+/*
+** If the WAL file is currently larger than nMax bytes in size, truncate
+** it to exactly nMax bytes. If an error occurs while doing so, ignore it.
+*/
+static void walLimitSize(Wal *pWal, i64 nMax){
+ i64 sz;
+ int rx;
+ sqlite3BeginBenignMalloc();
+ rx = sqlite3OsFileSize(pWal->pWalFd, &sz);
+ if( rx==SQLITE_OK && (sz > nMax ) ){
+ rx = sqlite3OsTruncate(pWal->pWalFd, nMax);
+ }
+ sqlite3EndBenignMalloc();
+ if( rx ){
+ sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName);
+ }
+}
+
+#ifdef SQLITE_USE_SEH
+/*
+** This is the "standard" exception handler used in a few places to handle
+** an exception thrown by reading from the *-shm mapping after it has become
+** invalid in SQLITE_USE_SEH builds. It is used as follows:
+**
+** SEH_TRY { ... }
+** SEH_EXCEPT( rc = walHandleException(pWal); )
+**
+** This function does three things:
+**
+** 1) Determines the locks that should be held, based on the contents of
+** the Wal.readLock, Wal.writeLock and Wal.ckptLock variables. All other
+** held locks are assumed to be transient locks that would have been
+** released had the exception not been thrown and are dropped.
+**
+** 2) Frees the pointer at Wal.pFree, if any, using sqlite3_free().
+**
+** 3) Set pWal->apWiData[pWal->iWiPg] to pWal->pWiValue if not NULL
+**
+** 4) Returns SQLITE_IOERR.
+*/
+static int walHandleException(Wal *pWal){
+ if( pWal->exclusiveMode==0 ){
+ static const int S = 1;
+ static const int E = (1<<SQLITE_SHM_NLOCK);
+ int ii;
+ u32 mUnlock = pWal->lockMask & ~(
+ (pWal->readLock<0 ? 0 : (S << WAL_READ_LOCK(pWal->readLock)))
+ | (pWal->writeLock ? (E << WAL_WRITE_LOCK) : 0)
+ | (pWal->ckptLock ? (E << WAL_CKPT_LOCK) : 0)
+ );
+ for(ii=0; ii<SQLITE_SHM_NLOCK; ii++){
+ if( (S<<ii) & mUnlock ) walUnlockShared(pWal, ii);
+ if( (E<<ii) & mUnlock ) walUnlockExclusive(pWal, ii, 1);
+ }
+ }
+ sqlite3_free(pWal->pFree);
+ pWal->pFree = 0;
+ if( pWal->pWiValue ){
+ pWal->apWiData[pWal->iWiPg] = pWal->pWiValue;
+ pWal->pWiValue = 0;
+ }
+ return SQLITE_IOERR_IN_PAGE;
+}
+
+/*
+** Assert that the Wal.lockMask mask, which indicates the locks held
+** by the connenction, is consistent with the Wal.readLock, Wal.writeLock
+** and Wal.ckptLock variables. To be used as:
+**
+** assert( walAssertLockmask(pWal) );
+*/
+static int walAssertLockmask(Wal *pWal){
+ if( pWal->exclusiveMode==0 ){
+ static const int S = 1;
+ static const int E = (1<<SQLITE_SHM_NLOCK);
+ u32 mExpect = (
+ (pWal->readLock<0 ? 0 : (S << WAL_READ_LOCK(pWal->readLock)))
+ | (pWal->writeLock ? (E << WAL_WRITE_LOCK) : 0)
+ | (pWal->ckptLock ? (E << WAL_CKPT_LOCK) : 0)
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ | (pWal->pSnapshot ? (pWal->lockMask & (1 << WAL_CKPT_LOCK)) : 0)
+#endif
+ );
+ assert( mExpect==pWal->lockMask );
+ }
+ return 1;
+}
+
+/*
+** Return and zero the "system error" field set when an
+** EXCEPTION_IN_PAGE_ERROR exception is caught.
+*/
+int sqlite3WalSystemErrno(Wal *pWal){
+ int iRet = 0;
+ if( pWal ){
+ iRet = pWal->iSysErrno;
+ pWal->iSysErrno = 0;
+ }
+ return iRet;
+}
+
+#else
+# define walAssertLockmask(x) 1
+#endif /* ifdef SQLITE_USE_SEH */
+
+/*
+** Close a connection to a log file.
+*/
+int sqlite3WalClose(
+ Wal *pWal, /* Wal to close */
+ sqlite3 *db, /* For interrupt flag */
+ int sync_flags, /* Flags to pass to OsSync() (or 0) */
+ int nBuf,
+ u8 *zBuf /* Buffer of at least nBuf bytes */
+){
+ int rc = SQLITE_OK;
+ if( pWal ){
+ int isDelete = 0; /* True to unlink wal and wal-index files */
+
+ assert( walAssertLockmask(pWal) );
+
+ /* If an EXCLUSIVE lock can be obtained on the database file (using the
+ ** ordinary, rollback-mode locking methods, this guarantees that the
+ ** connection associated with this log file is the only connection to
+ ** the database. In this case checkpoint the database and unlink both
+ ** the wal and wal-index files.
+ **
+ ** The EXCLUSIVE lock is not released before returning.
+ */
+ if( zBuf!=0
+ && SQLITE_OK==(rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE))
+ ){
+ if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
+ pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
+ }
+ rc = sqlite3WalCheckpoint(pWal, db,
+ SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
+ );
+ if( rc==SQLITE_OK ){
+ int bPersist = -1;
+ sqlite3OsFileControlHint(
+ pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist
+ );
+ if( bPersist!=1 ){
+ /* Try to delete the WAL file if the checkpoint completed and
+ ** fsynced (rc==SQLITE_OK) and if we are not in persistent-wal
+ ** mode (!bPersist) */
+ isDelete = 1;
+ }else if( pWal->mxWalSize>=0 ){
+ /* Try to truncate the WAL file to zero bytes if the checkpoint
+ ** completed and fsynced (rc==SQLITE_OK) and we are in persistent
+ ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
+ ** non-negative value (pWal->mxWalSize>=0). Note that we truncate
+ ** to zero bytes as truncating to the journal_size_limit might
+ ** leave a corrupt WAL file on disk. */
+ walLimitSize(pWal, 0);
+ }
+ }
+ }
+
+ walIndexClose(pWal, isDelete);
+ sqlite3OsClose(pWal->pWalFd);
+ if( isDelete ){
+ sqlite3BeginBenignMalloc();
+ sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);
+ sqlite3EndBenignMalloc();
+ }
+ WALTRACE(("WAL%p: closed\n", pWal));
+ sqlite3_free((void *)pWal->apWiData);
+ sqlite3_free(pWal);
+ }
+ return rc;
+}
+
+/*
+** Try to read the wal-index header. Return 0 on success and 1 if
+** there is a problem.
+**
+** The wal-index is in shared memory. Another thread or process might
+** be writing the header at the same time this procedure is trying to
+** read it, which might result in inconsistency. A dirty read is detected
+** by verifying that both copies of the header are the same and also by
+** a checksum on the header.
+**
+** If and only if the read is consistent and the header is different from
+** pWal->hdr, then pWal->hdr is updated to the content of the new header
+** and *pChanged is set to 1.
+**
+** If the checksum cannot be verified return non-zero. If the header
+** is read successfully and the checksum verified, return zero.
+*/
+static SQLITE_NO_TSAN int walIndexTryHdr(Wal *pWal, int *pChanged){
+ u32 aCksum[2]; /* Checksum on the header content */
+ WalIndexHdr h1, h2; /* Two copies of the header content */
+ WalIndexHdr volatile *aHdr; /* Header in shared memory */
+
+ /* The first page of the wal-index must be mapped at this point. */
+ assert( pWal->nWiData>0 && pWal->apWiData[0] );
+
+ /* Read the header. This might happen concurrently with a write to the
+ ** same area of shared memory on a different CPU in a SMP,
+ ** meaning it is possible that an inconsistent snapshot is read
+ ** from the file. If this happens, return non-zero.
+ **
+ ** tag-20200519-1:
+ ** There are two copies of the header at the beginning of the wal-index.
+ ** When reading, read [0] first then [1]. Writes are in the reverse order.
+ ** Memory barriers are used to prevent the compiler or the hardware from
+ ** reordering the reads and writes. TSAN and similar tools can sometimes
+ ** give false-positive warnings about these accesses because the tools do not
+ ** account for the double-read and the memory barrier. The use of mutexes
+ ** here would be problematic as the memory being accessed is potentially
+ ** shared among multiple processes and not all mutex implementations work
+ ** reliably in that environment.
+ */
+ aHdr = walIndexHdr(pWal);
+ memcpy(&h1, (void *)&aHdr[0], sizeof(h1)); /* Possible TSAN false-positive */
+ walShmBarrier(pWal);
+ memcpy(&h2, (void *)&aHdr[1], sizeof(h2));
+
+ if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
+ return 1; /* Dirty read */
+ }
+ if( h1.isInit==0 ){
+ return 1; /* Malformed header - probably all zeros */
+ }
+ walChecksumBytes(1, (u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum);
+ if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){
+ return 1; /* Checksum does not match */
+ }
+
+ if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){
+ *pChanged = 1;
+ memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr));
+ pWal->szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
+ testcase( pWal->szPage<=32768 );
+ testcase( pWal->szPage>=65536 );
+ }
+
+ /* The header was successfully read. Return zero. */
+ return 0;
+}
+
+/*
+** This is the value that walTryBeginRead returns when it needs to
+** be retried.
+*/
+#define WAL_RETRY (-1)
+
+/*
+** Read the wal-index header from the wal-index and into pWal->hdr.
+** If the wal-header appears to be corrupt, try to reconstruct the
+** wal-index from the WAL before returning.
+**
+** Set *pChanged to 1 if the wal-index header value in pWal->hdr is
+** changed by this operation. If pWal->hdr is unchanged, set *pChanged
+** to 0.
+**
+** If the wal-index header is successfully read, return SQLITE_OK.
+** Otherwise an SQLite error code.
+*/
+static int walIndexReadHdr(Wal *pWal, int *pChanged){
+ int rc; /* Return code */
+ int badHdr; /* True if a header read failed */
+ volatile u32 *page0; /* Chunk of wal-index containing header */
+
+ /* Ensure that page 0 of the wal-index (the page that contains the
+ ** wal-index header) is mapped. Return early if an error occurs here.
+ */
+ assert( pChanged );
+ rc = walIndexPage(pWal, 0, &page0);
+ if( rc!=SQLITE_OK ){
+ assert( rc!=SQLITE_READONLY ); /* READONLY changed to OK in walIndexPage */
+ if( rc==SQLITE_READONLY_CANTINIT ){
+ /* The SQLITE_READONLY_CANTINIT return means that the shared-memory
+ ** was openable but is not writable, and this thread is unable to
+ ** confirm that another write-capable connection has the shared-memory
+ ** open, and hence the content of the shared-memory is unreliable,
+ ** since the shared-memory might be inconsistent with the WAL file
+ ** and there is no writer on hand to fix it. */
+ assert( page0==0 );
+ assert( pWal->writeLock==0 );
+ assert( pWal->readOnly & WAL_SHM_RDONLY );
+ pWal->bShmUnreliable = 1;
+ pWal->exclusiveMode = WAL_HEAPMEMORY_MODE;
+ *pChanged = 1;
+ }else{
+ return rc; /* Any other non-OK return is just an error */
+ }
+ }else{
+ /* page0 can be NULL if the SHM is zero bytes in size and pWal->writeLock
+ ** is zero, which prevents the SHM from growing */
+ testcase( page0!=0 );
+ }
+ assert( page0!=0 || pWal->writeLock==0 );
+
+ /* If the first page of the wal-index has been mapped, try to read the
+ ** wal-index header immediately, without holding any lock. This usually
+ ** works, but may fail if the wal-index header is corrupt or currently
+ ** being modified by another thread or process.
+ */
+ badHdr = (page0 ? walIndexTryHdr(pWal, pChanged) : 1);
+
+ /* If the first attempt failed, it might have been due to a race
+ ** with a writer. So get a WRITE lock and try again.
+ */
+ if( badHdr ){
+ if( pWal->bShmUnreliable==0 && (pWal->readOnly & WAL_SHM_RDONLY) ){
+ if( SQLITE_OK==(rc = walLockShared(pWal, WAL_WRITE_LOCK)) ){
+ walUnlockShared(pWal, WAL_WRITE_LOCK);
+ rc = SQLITE_READONLY_RECOVERY;
+ }
+ }else{
+ int bWriteLock = pWal->writeLock;
+ if( bWriteLock
+ || SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1))
+ ){
+ pWal->writeLock = 1;
+ if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
+ badHdr = walIndexTryHdr(pWal, pChanged);
+ if( badHdr ){
+ /* If the wal-index header is still malformed even while holding
+ ** a WRITE lock, it can only mean that the header is corrupted and
+ ** needs to be reconstructed. So run recovery to do exactly that.
+ ** Disable blocking locks first. */
+ walDisableBlocking(pWal);
+ rc = walIndexRecover(pWal);
+ *pChanged = 1;
+ }
+ }
+ if( bWriteLock==0 ){
+ pWal->writeLock = 0;
+ walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ }
+ }
+ }
+ }
+
+ /* If the header is read successfully, check the version number to make
+ ** sure the wal-index was not constructed with some future format that
+ ** this version of SQLite cannot understand.
+ */
+ if( badHdr==0 && pWal->hdr.iVersion!=WALINDEX_MAX_VERSION ){
+ rc = SQLITE_CANTOPEN_BKPT;
+ }
+ if( pWal->bShmUnreliable ){
+ if( rc!=SQLITE_OK ){
+ walIndexClose(pWal, 0);
+ pWal->bShmUnreliable = 0;
+ assert( pWal->nWiData>0 && pWal->apWiData[0]==0 );
+ /* walIndexRecover() might have returned SHORT_READ if a concurrent
+ ** writer truncated the WAL out from under it. If that happens, it
+ ** indicates that a writer has fixed the SHM file for us, so retry */
+ if( rc==SQLITE_IOERR_SHORT_READ ) rc = WAL_RETRY;
+ }
+ pWal->exclusiveMode = WAL_NORMAL_MODE;
+ }
+
+ return rc;
+}
+
+/*
+** Open a transaction in a connection where the shared-memory is read-only
+** and where we cannot verify that there is a separate write-capable connection
+** on hand to keep the shared-memory up-to-date with the WAL file.
+**
+** This can happen, for example, when the shared-memory is implemented by
+** memory-mapping a *-shm file, where a prior writer has shut down and
+** left the *-shm file on disk, and now the present connection is trying
+** to use that database but lacks write permission on the *-shm file.
+** Other scenarios are also possible, depending on the VFS implementation.
+**
+** Precondition:
+**
+** The *-wal file has been read and an appropriate wal-index has been
+** constructed in pWal->apWiData[] using heap memory instead of shared
+** memory.
+**
+** If this function returns SQLITE_OK, then the read transaction has
+** been successfully opened. In this case output variable (*pChanged)
+** is set to true before returning if the caller should discard the
+** contents of the page cache before proceeding. Or, if it returns
+** WAL_RETRY, then the heap memory wal-index has been discarded and
+** the caller should retry opening the read transaction from the
+** beginning (including attempting to map the *-shm file).
+**
+** If an error occurs, an SQLite error code is returned.
+*/
+static int walBeginShmUnreliable(Wal *pWal, int *pChanged){
+ i64 szWal; /* Size of wal file on disk in bytes */
+ i64 iOffset; /* Current offset when reading wal file */
+ u8 aBuf[WAL_HDRSIZE]; /* Buffer to load WAL header into */
+ u8 *aFrame = 0; /* Malloc'd buffer to load entire frame */
+ int szFrame; /* Number of bytes in buffer aFrame[] */
+ u8 *aData; /* Pointer to data part of aFrame buffer */
+ volatile void *pDummy; /* Dummy argument for xShmMap */
+ int rc; /* Return code */
+ u32 aSaveCksum[2]; /* Saved copy of pWal->hdr.aFrameCksum */
+
+ assert( pWal->bShmUnreliable );
+ assert( pWal->readOnly & WAL_SHM_RDONLY );
+ assert( pWal->nWiData>0 && pWal->apWiData[0] );
+
+ /* Take WAL_READ_LOCK(0). This has the effect of preventing any
+ ** writers from running a checkpoint, but does not stop them
+ ** from running recovery. */
+ rc = walLockShared(pWal, WAL_READ_LOCK(0));
+ if( rc!=SQLITE_OK ){
+ if( rc==SQLITE_BUSY ) rc = WAL_RETRY;
+ goto begin_unreliable_shm_out;
+ }
+ pWal->readLock = 0;
+
+ /* Check to see if a separate writer has attached to the shared-memory area,
+ ** thus making the shared-memory "reliable" again. Do this by invoking
+ ** the xShmMap() routine of the VFS and looking to see if the return
+ ** is SQLITE_READONLY instead of SQLITE_READONLY_CANTINIT.
+ **
+ ** If the shared-memory is now "reliable" return WAL_RETRY, which will
+ ** cause the heap-memory WAL-index to be discarded and the actual
+ ** shared memory to be used in its place.
+ **
+ ** This step is important because, even though this connection is holding
+ ** the WAL_READ_LOCK(0) which prevents a checkpoint, a writer might
+ ** have already checkpointed the WAL file and, while the current
+ ** is active, wrap the WAL and start overwriting frames that this
+ ** process wants to use.
+ **
+ ** Once sqlite3OsShmMap() has been called for an sqlite3_file and has
+ ** returned any SQLITE_READONLY value, it must return only SQLITE_READONLY
+ ** or SQLITE_READONLY_CANTINIT or some error for all subsequent invocations,
+ ** even if some external agent does a "chmod" to make the shared-memory
+ ** writable by us, until sqlite3OsShmUnmap() has been called.
+ ** This is a requirement on the VFS implementation.
+ */
+ rc = sqlite3OsShmMap(pWal->pDbFd, 0, WALINDEX_PGSZ, 0, &pDummy);
+ assert( rc!=SQLITE_OK ); /* SQLITE_OK not possible for read-only connection */
+ if( rc!=SQLITE_READONLY_CANTINIT ){
+ rc = (rc==SQLITE_READONLY ? WAL_RETRY : rc);
+ goto begin_unreliable_shm_out;
+ }
+
+ /* We reach this point only if the real shared-memory is still unreliable.
+ ** Assume the in-memory WAL-index substitute is correct and load it
+ ** into pWal->hdr.
+ */
+ memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr));
+
+ /* Make sure some writer hasn't come in and changed the WAL file out
+ ** from under us, then disconnected, while we were not looking.
+ */
+ rc = sqlite3OsFileSize(pWal->pWalFd, &szWal);
+ if( rc!=SQLITE_OK ){
+ goto begin_unreliable_shm_out;
+ }
+ if( szWal<WAL_HDRSIZE ){
+ /* If the wal file is too small to contain a wal-header and the
+ ** wal-index header has mxFrame==0, then it must be safe to proceed
+ ** reading the database file only. However, the page cache cannot
+ ** be trusted, as a read/write connection may have connected, written
+ ** the db, run a checkpoint, truncated the wal file and disconnected
+ ** since this client's last read transaction. */
+ *pChanged = 1;
+ rc = (pWal->hdr.mxFrame==0 ? SQLITE_OK : WAL_RETRY);
+ goto begin_unreliable_shm_out;
+ }
+
+ /* Check the salt keys at the start of the wal file still match. */
+ rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
+ if( rc!=SQLITE_OK ){
+ goto begin_unreliable_shm_out;
+ }
+ if( memcmp(&pWal->hdr.aSalt, &aBuf[16], 8) ){
+ /* Some writer has wrapped the WAL file while we were not looking.
+ ** Return WAL_RETRY which will cause the in-memory WAL-index to be
+ ** rebuilt. */
+ rc = WAL_RETRY;
+ goto begin_unreliable_shm_out;
+ }
+
+ /* Allocate a buffer to read frames into */
+ assert( (pWal->szPage & (pWal->szPage-1))==0 );
+ assert( pWal->szPage>=512 && pWal->szPage<=65536 );
+ szFrame = pWal->szPage + WAL_FRAME_HDRSIZE;
+ aFrame = (u8 *)sqlite3_malloc64(szFrame);
+ if( aFrame==0 ){
+ rc = SQLITE_NOMEM_BKPT;
+ goto begin_unreliable_shm_out;
+ }
+ aData = &aFrame[WAL_FRAME_HDRSIZE];
+
+ /* Check to see if a complete transaction has been appended to the
+ ** wal file since the heap-memory wal-index was created. If so, the
+ ** heap-memory wal-index is discarded and WAL_RETRY returned to
+ ** the caller. */
+ aSaveCksum[0] = pWal->hdr.aFrameCksum[0];
+ aSaveCksum[1] = pWal->hdr.aFrameCksum[1];
+ for(iOffset=walFrameOffset(pWal->hdr.mxFrame+1, pWal->szPage);
+ iOffset+szFrame<=szWal;
+ iOffset+=szFrame
+ ){
+ u32 pgno; /* Database page number for frame */
+ u32 nTruncate; /* dbsize field from frame header */
+
+ /* Read and decode the next log frame. */
+ rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
+ if( rc!=SQLITE_OK ) break;
+ if( !walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame) ) break;
+
+ /* If nTruncate is non-zero, then a complete transaction has been
+ ** appended to this wal file. Set rc to WAL_RETRY and break out of
+ ** the loop. */
+ if( nTruncate ){
+ rc = WAL_RETRY;
+ break;
+ }
+ }
+ pWal->hdr.aFrameCksum[0] = aSaveCksum[0];
+ pWal->hdr.aFrameCksum[1] = aSaveCksum[1];
+
+ begin_unreliable_shm_out:
+ sqlite3_free(aFrame);
+ if( rc!=SQLITE_OK ){
+ int i;
+ for(i=0; i<pWal->nWiData; i++){
+ sqlite3_free((void*)pWal->apWiData[i]);
+ pWal->apWiData[i] = 0;
+ }
+ pWal->bShmUnreliable = 0;
+ sqlite3WalEndReadTransaction(pWal);
+ *pChanged = 1;
+ }
+ return rc;
+}
+
+/*
+** The final argument passed to walTryBeginRead() is of type (int*). The
+** caller should invoke walTryBeginRead as follows:
+**
+** int cnt = 0;
+** do {
+** rc = walTryBeginRead(..., &cnt);
+** }while( rc==WAL_RETRY );
+**
+** The final value of "cnt" is of no use to the caller. It is used by
+** the implementation of walTryBeginRead() as follows:
+**
+** + Each time walTryBeginRead() is called, it is incremented. Once
+** it reaches WAL_RETRY_PROTOCOL_LIMIT - indicating that walTryBeginRead()
+** has many times been invoked and failed with WAL_RETRY - walTryBeginRead()
+** returns SQLITE_PROTOCOL.
+**
+** + If SQLITE_ENABLE_SETLK_TIMEOUT is defined and walTryBeginRead() failed
+** because a blocking lock timed out (SQLITE_BUSY_TIMEOUT from the OS
+** layer), the WAL_RETRY_BLOCKED_MASK bit is set in "cnt". In this case
+** the next invocation of walTryBeginRead() may omit an expected call to
+** sqlite3OsSleep(). There has already been a delay when the previous call
+** waited on a lock.
+*/
+#define WAL_RETRY_PROTOCOL_LIMIT 100
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+# define WAL_RETRY_BLOCKED_MASK 0x10000000
+#else
+# define WAL_RETRY_BLOCKED_MASK 0
+#endif
+
+/*
+** Attempt to start a read transaction. This might fail due to a race or
+** other transient condition. When that happens, it returns WAL_RETRY to
+** indicate to the caller that it is safe to retry immediately.
+**
+** On success return SQLITE_OK. On a permanent failure (such an
+** I/O error or an SQLITE_BUSY because another process is running
+** recovery) return a positive error code.
+**
+** The useWal parameter is true to force the use of the WAL and disable
+** the case where the WAL is bypassed because it has been completely
+** checkpointed. If useWal==0 then this routine calls walIndexReadHdr()
+** to make a copy of the wal-index header into pWal->hdr. If the
+** wal-index header has changed, *pChanged is set to 1 (as an indication
+** to the caller that the local page cache is obsolete and needs to be
+** flushed.) When useWal==1, the wal-index header is assumed to already
+** be loaded and the pChanged parameter is unused.
+**
+** The caller must set the cnt parameter to the number of prior calls to
+** this routine during the current read attempt that returned WAL_RETRY.
+** This routine will start taking more aggressive measures to clear the
+** race conditions after multiple WAL_RETRY returns, and after an excessive
+** number of errors will ultimately return SQLITE_PROTOCOL. The
+** SQLITE_PROTOCOL return indicates that some other process has gone rogue
+** and is not honoring the locking protocol. There is a vanishingly small
+** chance that SQLITE_PROTOCOL could be returned because of a run of really
+** bad luck when there is lots of contention for the wal-index, but that
+** possibility is so small that it can be safely neglected, we believe.
+**
+** On success, this routine obtains a read lock on
+** WAL_READ_LOCK(pWal->readLock). The pWal->readLock integer is
+** in the range 0 <= pWal->readLock < WAL_NREADER. If pWal->readLock==(-1)
+** that means the Wal does not hold any read lock. The reader must not
+** access any database page that is modified by a WAL frame up to and
+** including frame number aReadMark[pWal->readLock]. The reader will
+** use WAL frames up to and including pWal->hdr.mxFrame if pWal->readLock>0
+** Or if pWal->readLock==0, then the reader will ignore the WAL
+** completely and get all content directly from the database file.
+** If the useWal parameter is 1 then the WAL will never be ignored and
+** this routine will always set pWal->readLock>0 on success.
+** When the read transaction is completed, the caller must release the
+** lock on WAL_READ_LOCK(pWal->readLock) and set pWal->readLock to -1.
+**
+** This routine uses the nBackfill and aReadMark[] fields of the header
+** to select a particular WAL_READ_LOCK() that strives to let the
+** checkpoint process do as much work as possible. This routine might
+** update values of the aReadMark[] array in the header, but if it does
+** so it takes care to hold an exclusive lock on the corresponding
+** WAL_READ_LOCK() while changing values.
+*/
+static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
+ volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */
+ u32 mxReadMark; /* Largest aReadMark[] value */
+ int mxI; /* Index of largest aReadMark[] value */
+ int i; /* Loop counter */
+ int rc = SQLITE_OK; /* Return code */
+ u32 mxFrame; /* Wal frame to lock to */
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ int nBlockTmout = 0;
+#endif
+
+ assert( pWal->readLock<0 ); /* Not currently locked */
+
+ /* useWal may only be set for read/write connections */
+ assert( (pWal->readOnly & WAL_SHM_RDONLY)==0 || useWal==0 );
+
+ /* Take steps to avoid spinning forever if there is a protocol error.
+ **
+ ** Circumstances that cause a RETRY should only last for the briefest
+ ** instances of time. No I/O or other system calls are done while the
+ ** locks are held, so the locks should not be held for very long. But
+ ** if we are unlucky, another process that is holding a lock might get
+ ** paged out or take a page-fault that is time-consuming to resolve,
+ ** during the few nanoseconds that it is holding the lock. In that case,
+ ** it might take longer than normal for the lock to free.
+ **
+ ** After 5 RETRYs, we begin calling sqlite3OsSleep(). The first few
+ ** calls to sqlite3OsSleep() have a delay of 1 microsecond. Really this
+ ** is more of a scheduler yield than an actual delay. But on the 10th
+ ** an subsequent retries, the delays start becoming longer and longer,
+ ** so that on the 100th (and last) RETRY we delay for 323 milliseconds.
+ ** The total delay time before giving up is less than 10 seconds.
+ */
+ (*pCnt)++;
+ if( *pCnt>5 ){
+ int nDelay = 1; /* Pause time in microseconds */
+ int cnt = (*pCnt & ~WAL_RETRY_BLOCKED_MASK);
+ if( cnt>WAL_RETRY_PROTOCOL_LIMIT ){
+ VVA_ONLY( pWal->lockError = 1; )
+ return SQLITE_PROTOCOL;
+ }
+ if( *pCnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39;
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ /* In SQLITE_ENABLE_SETLK_TIMEOUT builds, configure the file-descriptor
+ ** to block for locks for approximately nDelay us. This affects three
+ ** locks: (a) the shared lock taken on the DMS slot in os_unix.c (if
+ ** using os_unix.c), (b) the WRITER lock taken in walIndexReadHdr() if the
+ ** first attempted read fails, and (c) the shared lock taken on the
+ ** read-mark.
+ **
+ ** If the previous call failed due to an SQLITE_BUSY_TIMEOUT error,
+ ** then sleep for the minimum of 1us. The previous call already provided
+ ** an extra delay while it was blocking on the lock.
+ */
+ nBlockTmout = (nDelay+998) / 1000;
+ if( !useWal && walEnableBlockingMs(pWal, nBlockTmout) ){
+ if( *pCnt & WAL_RETRY_BLOCKED_MASK ) nDelay = 1;
+ }
+#endif
+ sqlite3OsSleep(pWal->pVfs, nDelay);
+ *pCnt &= ~WAL_RETRY_BLOCKED_MASK;
+ }
+
+ if( !useWal ){
+ assert( rc==SQLITE_OK );
+ if( pWal->bShmUnreliable==0 ){
+ rc = walIndexReadHdr(pWal, pChanged);
+ }
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ walDisableBlocking(pWal);
+ if( rc==SQLITE_BUSY_TIMEOUT ){
+ rc = SQLITE_BUSY;
+ *pCnt |= WAL_RETRY_BLOCKED_MASK;
+ }
+#endif
+ if( rc==SQLITE_BUSY ){
+ /* If there is not a recovery running in another thread or process
+ ** then convert BUSY errors to WAL_RETRY. If recovery is known to
+ ** be running, convert BUSY to BUSY_RECOVERY. There is a race here
+ ** which might cause WAL_RETRY to be returned even if BUSY_RECOVERY
+ ** would be technically correct. But the race is benign since with
+ ** WAL_RETRY this routine will be called again and will probably be
+ ** right on the second iteration.
+ */
+ if( pWal->apWiData[0]==0 ){
+ /* This branch is taken when the xShmMap() method returns SQLITE_BUSY.
+ ** We assume this is a transient condition, so return WAL_RETRY. The
+ ** xShmMap() implementation used by the default unix and win32 VFS
+ ** modules may return SQLITE_BUSY due to a race condition in the
+ ** code that determines whether or not the shared-memory region
+ ** must be zeroed before the requested page is returned.
+ */
+ rc = WAL_RETRY;
+ }else if( SQLITE_OK==(rc = walLockShared(pWal, WAL_RECOVER_LOCK)) ){
+ walUnlockShared(pWal, WAL_RECOVER_LOCK);
+ rc = WAL_RETRY;
+ }else if( rc==SQLITE_BUSY ){
+ rc = SQLITE_BUSY_RECOVERY;
+ }
+ }
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+ else if( pWal->bShmUnreliable ){
+ return walBeginShmUnreliable(pWal, pChanged);
+ }
+ }
+
+ assert( pWal->nWiData>0 );
+ assert( pWal->apWiData[0]!=0 );
+ pInfo = walCkptInfo(pWal);
+ SEH_INJECT_FAULT;
+ if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0)
+#endif
+ ){
+ /* The WAL has been completely backfilled (or it is empty).
+ ** and can be safely ignored.
+ */
+ rc = walLockShared(pWal, WAL_READ_LOCK(0));
+ walShmBarrier(pWal);
+ if( rc==SQLITE_OK ){
+ if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
+ /* It is not safe to allow the reader to continue here if frames
+ ** may have been appended to the log before READ_LOCK(0) was obtained.
+ ** When holding READ_LOCK(0), the reader ignores the entire log file,
+ ** which implies that the database file contains a trustworthy
+ ** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from
+ ** happening, this is usually correct.
+ **
+ ** However, if frames have been appended to the log (or if the log
+ ** is wrapped and written for that matter) before the READ_LOCK(0)
+ ** is obtained, that is not necessarily true. A checkpointer may
+ ** have started to backfill the appended frames but crashed before
+ ** it finished. Leaving a corrupt image in the database file.
+ */
+ walUnlockShared(pWal, WAL_READ_LOCK(0));
+ return WAL_RETRY;
+ }
+ pWal->readLock = 0;
+ return SQLITE_OK;
+ }else if( rc!=SQLITE_BUSY ){
+ return rc;
+ }
+ }
+
+ /* If we get this far, it means that the reader will want to use
+ ** the WAL to get at content from recent commits. The job now is
+ ** to select one of the aReadMark[] entries that is closest to
+ ** but not exceeding pWal->hdr.mxFrame and lock that entry.
+ */
+ mxReadMark = 0;
+ mxI = 0;
+ mxFrame = pWal->hdr.mxFrame;
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ if( pWal->pSnapshot && pWal->pSnapshot->mxFrame<mxFrame ){
+ mxFrame = pWal->pSnapshot->mxFrame;
+ }
+#endif
+ for(i=1; i<WAL_NREADER; i++){
+ u32 thisMark = AtomicLoad(pInfo->aReadMark+i); SEH_INJECT_FAULT;
+ if( mxReadMark<=thisMark && thisMark<=mxFrame ){
+ assert( thisMark!=READMARK_NOT_USED );
+ mxReadMark = thisMark;
+ mxI = i;
+ }
+ }
+ if( (pWal->readOnly & WAL_SHM_RDONLY)==0
+ && (mxReadMark<mxFrame || mxI==0)
+ ){
+ for(i=1; i<WAL_NREADER; i++){
+ rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ if( rc==SQLITE_OK ){
+ AtomicStore(pInfo->aReadMark+i,mxFrame);
+ mxReadMark = mxFrame;
+ mxI = i;
+ walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ break;
+ }else if( rc!=SQLITE_BUSY ){
+ return rc;
+ }
+ }
+ }
+ if( mxI==0 ){
+ assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
+ return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTINIT;
+ }
+
+ (void)walEnableBlockingMs(pWal, nBlockTmout);
+ rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
+ walDisableBlocking(pWal);
+ if( rc ){
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ if( rc==SQLITE_BUSY_TIMEOUT ){
+ *pCnt |= WAL_RETRY_BLOCKED_MASK;
+ }
+#else
+ assert( rc!=SQLITE_BUSY_TIMEOUT );
+#endif
+ assert( (rc&0xFF)!=SQLITE_BUSY||rc==SQLITE_BUSY||rc==SQLITE_BUSY_TIMEOUT );
+ return (rc&0xFF)==SQLITE_BUSY ? WAL_RETRY : rc;
+ }
+ /* Now that the read-lock has been obtained, check that neither the
+ ** value in the aReadMark[] array or the contents of the wal-index
+ ** header have changed.
+ **
+ ** It is necessary to check that the wal-index header did not change
+ ** between the time it was read and when the shared-lock was obtained
+ ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
+ ** that the log file may have been wrapped by a writer, or that frames
+ ** that occur later in the log than pWal->hdr.mxFrame may have been
+ ** copied into the database by a checkpointer. If either of these things
+ ** happened, then reading the database with the current value of
+ ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
+ ** instead.
+ **
+ ** Before checking that the live wal-index header has not changed
+ ** since it was read, set Wal.minFrame to the first frame in the wal
+ ** file that has not yet been checkpointed. This client will not need
+ ** to read any frames earlier than minFrame from the wal file - they
+ ** can be safely read directly from the database file.
+ **
+ ** Because a ShmBarrier() call is made between taking the copy of
+ ** nBackfill and checking that the wal-header in shared-memory still
+ ** matches the one cached in pWal->hdr, it is guaranteed that the
+ ** checkpointer that set nBackfill was not working with a wal-index
+ ** header newer than that cached in pWal->hdr. If it were, that could
+ ** cause a problem. The checkpointer could omit to checkpoint
+ ** a version of page X that lies before pWal->minFrame (call that version
+ ** A) on the basis that there is a newer version (version B) of the same
+ ** page later in the wal file. But if version B happens to like past
+ ** frame pWal->hdr.mxFrame - then the client would incorrectly assume
+ ** that it can read version A from the database file. However, since
+ ** we can guarantee that the checkpointer that set nBackfill could not
+ ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
+ */
+ pWal->minFrame = AtomicLoad(&pInfo->nBackfill)+1; SEH_INJECT_FAULT;
+ walShmBarrier(pWal);
+ if( AtomicLoad(pInfo->aReadMark+mxI)!=mxReadMark
+ || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
+ ){
+ walUnlockShared(pWal, WAL_READ_LOCK(mxI));
+ return WAL_RETRY;
+ }else{
+ assert( mxReadMark<=pWal->hdr.mxFrame );
+ pWal->readLock = (i16)mxI;
+ }
+ return rc;
+}
+
+#ifdef SQLITE_ENABLE_SNAPSHOT
+/*
+** This function does the work of sqlite3WalSnapshotRecover().
+*/
+static int walSnapshotRecover(
+ Wal *pWal, /* WAL handle */
+ void *pBuf1, /* Temp buffer pWal->szPage bytes in size */
+ void *pBuf2 /* Temp buffer pWal->szPage bytes in size */
+){
+ int szPage = (int)pWal->szPage;
+ int rc;
+ i64 szDb; /* Size of db file in bytes */
+
+ rc = sqlite3OsFileSize(pWal->pDbFd, &szDb);
+ if( rc==SQLITE_OK ){
+ volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+ u32 i = pInfo->nBackfillAttempted;
+ for(i=pInfo->nBackfillAttempted; i>AtomicLoad(&pInfo->nBackfill); i--){
+ WalHashLoc sLoc; /* Hash table location */
+ u32 pgno; /* Page number in db file */
+ i64 iDbOff; /* Offset of db file entry */
+ i64 iWalOff; /* Offset of wal file entry */
+
+ rc = walHashGet(pWal, walFramePage(i), &sLoc);
+ if( rc!=SQLITE_OK ) break;
+ assert( i - sLoc.iZero - 1 >=0 );
+ pgno = sLoc.aPgno[i-sLoc.iZero-1];
+ iDbOff = (i64)(pgno-1) * szPage;
+
+ if( iDbOff+szPage<=szDb ){
+ iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
+ rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
+
+ if( rc==SQLITE_OK ){
+ rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
+ }
+
+ if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
+ break;
+ }
+ }
+
+ pInfo->nBackfillAttempted = i-1;
+ }
+ }
+
+ return rc;
+}
+
+/*
+** Attempt to reduce the value of the WalCkptInfo.nBackfillAttempted
+** variable so that older snapshots can be accessed. To do this, loop
+** through all wal frames from nBackfillAttempted to (nBackfill+1),
+** comparing their content to the corresponding page with the database
+** file, if any. Set nBackfillAttempted to the frame number of the
+** first frame for which the wal file content matches the db file.
+**
+** This is only really safe if the file-system is such that any page
+** writes made by earlier checkpointers were atomic operations, which
+** is not always true. It is also possible that nBackfillAttempted
+** may be left set to a value larger than expected, if a wal frame
+** contains content that duplicate of an earlier version of the same
+** page.
+**
+** SQLITE_OK is returned if successful, or an SQLite error code if an
+** error occurs. It is not an error if nBackfillAttempted cannot be
+** decreased at all.
+*/
+int sqlite3WalSnapshotRecover(Wal *pWal){
+ int rc;
+
+ assert( pWal->readLock>=0 );
+ rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
+ if( rc==SQLITE_OK ){
+ void *pBuf1 = sqlite3_malloc(pWal->szPage);
+ void *pBuf2 = sqlite3_malloc(pWal->szPage);
+ if( pBuf1==0 || pBuf2==0 ){
+ rc = SQLITE_NOMEM;
+ }else{
+ pWal->ckptLock = 1;
+ SEH_TRY {
+ rc = walSnapshotRecover(pWal, pBuf1, pBuf2);
+ }
+ SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+ pWal->ckptLock = 0;
+ }
+
+ sqlite3_free(pBuf1);
+ sqlite3_free(pBuf2);
+ walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
+ }
+
+ return rc;
+}
+#endif /* SQLITE_ENABLE_SNAPSHOT */
+
+/*
+** This function does the work of sqlite3WalBeginReadTransaction() (see
+** below). That function simply calls this one inside an SEH_TRY{...} block.
+*/
+static int walBeginReadTransaction(Wal *pWal, int *pChanged){
+ int rc; /* Return code */
+ int cnt = 0; /* Number of TryBeginRead attempts */
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ int ckptLock = 0;
+ int bChanged = 0;
+ WalIndexHdr *pSnapshot = pWal->pSnapshot;
+#endif
+
+ assert( pWal->ckptLock==0 );
+ assert( pWal->nSehTry>0 );
+
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ if( pSnapshot ){
+ if( memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){
+ bChanged = 1;
+ }
+
+ /* It is possible that there is a checkpointer thread running
+ ** concurrent with this code. If this is the case, it may be that the
+ ** checkpointer has already determined that it will checkpoint
+ ** snapshot X, where X is later in the wal file than pSnapshot, but
+ ** has not yet set the pInfo->nBackfillAttempted variable to indicate
+ ** its intent. To avoid the race condition this leads to, ensure that
+ ** there is no checkpointer process by taking a shared CKPT lock
+ ** before checking pInfo->nBackfillAttempted. */
+ (void)walEnableBlocking(pWal);
+ rc = walLockShared(pWal, WAL_CKPT_LOCK);
+ walDisableBlocking(pWal);
+
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+ ckptLock = 1;
+ }
+#endif
+
+ do{
+ rc = walTryBeginRead(pWal, pChanged, 0, &cnt);
+ }while( rc==WAL_RETRY );
+ testcase( (rc&0xff)==SQLITE_BUSY );
+ testcase( (rc&0xff)==SQLITE_IOERR );
+ testcase( rc==SQLITE_PROTOCOL );
+ testcase( rc==SQLITE_OK );
+
+#ifdef SQLITE_ENABLE_SNAPSHOT
+ if( rc==SQLITE_OK ){
+ if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){
+ /* At this point the client has a lock on an aReadMark[] slot holding
+ ** a value equal to or smaller than pSnapshot->mxFrame, but pWal->hdr
+ ** is populated with the wal-index header corresponding to the head
+ ** of the wal file. Verify that pSnapshot is still valid before
+ ** continuing. Reasons why pSnapshot might no longer be valid:
+ **
+ ** (1) The WAL file has been reset since the snapshot was taken.
+ ** In this case, the salt will have changed.
+ **
+ ** (2) A checkpoint as been attempted that wrote frames past
+ ** pSnapshot->mxFrame into the database file. Note that the
+ ** checkpoint need not have completed for this to cause problems.
+ */
+ volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+
+ assert( pWal->readLock>0 || pWal->hdr.mxFrame==0 );
+ assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame );
+
+ /* Check that the wal file has not been wrapped. Assuming that it has
+ ** not, also check that no checkpointer has attempted to checkpoint any
+ ** frames beyond pSnapshot->mxFrame. If either of these conditions are
+ ** true, return SQLITE_ERROR_SNAPSHOT. Otherwise, overwrite pWal->hdr
+ ** with *pSnapshot and set *pChanged as appropriate for opening the
+ ** snapshot. */
+ if( !memcmp(pSnapshot->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
+ && pSnapshot->mxFrame>=pInfo->nBackfillAttempted
+ ){
+ assert( pWal->readLock>0 );
+ memcpy(&pWal->hdr, pSnapshot, sizeof(WalIndexHdr));
+ *pChanged = bChanged;
+ }else{
+ rc = SQLITE_ERROR_SNAPSHOT;
+ }
+
+ /* A client using a non-current snapshot may not ignore any frames
+ ** from the start of the wal file. This is because, for a system
+ ** where (minFrame < iSnapshot < maxFrame), a checkpointer may
+ ** have omitted to checkpoint a frame earlier than minFrame in
+ ** the file because there exists a frame after iSnapshot that
+ ** is the same database page. */
+ pWal->minFrame = 1;
+
+ if( rc!=SQLITE_OK ){
+ sqlite3WalEndReadTransaction(pWal);
+ }
+ }
+ }
+
+ /* Release the shared CKPT lock obtained above. */
+ if( ckptLock ){
+ assert( pSnapshot );
+ walUnlockShared(pWal, WAL_CKPT_LOCK);
+ }
+#endif
+ return rc;
+}
+
+/*
+** Begin a read transaction on the database.
+**
+** This routine used to be called sqlite3OpenSnapshot() and with good reason:
+** it takes a snapshot of the state of the WAL and wal-index for the current
+** instant in time. The current thread will continue to use this snapshot.
+** Other threads might append new content to the WAL and wal-index but
+** that extra content is ignored by the current thread.
+**
+** If the database contents have changes since the previous read
+** transaction, then *pChanged is set to 1 before returning. The
+** Pager layer will use this to know that its cache is stale and
+** needs to be flushed.
+*/
+int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
+ int rc;
+ SEH_TRY {
+ rc = walBeginReadTransaction(pWal, pChanged);
+ }
+ SEH_EXCEPT( rc = walHandleException(pWal); )
+ return rc;
+}
+
+/*
+** Finish with a read transaction. All this does is release the
+** read-lock.
+*/
+void sqlite3WalEndReadTransaction(Wal *pWal){
+ sqlite3WalEndWriteTransaction(pWal);
+ if( pWal->readLock>=0 ){
+ walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
+ pWal->readLock = -1;
+ }
+}
+
+/*
+** Search the wal file for page pgno. If found, set *piRead to the frame that
+** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
+** to zero.
+**
+** Return SQLITE_OK if successful, or an error code if an error occurs. If an
+** error does occur, the final value of *piRead is undefined.
+*/
+static int walFindFrame(
+ Wal *pWal, /* WAL handle */
+ Pgno pgno, /* Database page number to read data for */
+ u32 *piRead /* OUT: Frame number (or zero) */
+){
+ u32 iRead = 0; /* If !=0, WAL frame to return data from */
+ u32 iLast = pWal->hdr.mxFrame; /* Last page in WAL for this reader */
+ int iHash; /* Used to loop through N hash tables */
+ int iMinHash;
+
+ /* This routine is only be called from within a read transaction. */
+ assert( pWal->readLock>=0 || pWal->lockError );
+
+ /* If the "last page" field of the wal-index header snapshot is 0, then
+ ** no data will be read from the wal under any circumstances. Return early
+ ** in this case as an optimization. Likewise, if pWal->readLock==0,
+ ** then the WAL is ignored by the reader so return early, as if the
+ ** WAL were empty.
+ */
+ if( iLast==0 || (pWal->readLock==0 && pWal->bShmUnreliable==0) ){
+ *piRead = 0;
+ return SQLITE_OK;
+ }
+
+ /* Search the hash table or tables for an entry matching page number
+ ** pgno. Each iteration of the following for() loop searches one
+ ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
+ **
+ ** This code might run concurrently to the code in walIndexAppend()
+ ** that adds entries to the wal-index (and possibly to this hash
+ ** table). This means the value just read from the hash
+ ** slot (aHash[iKey]) may have been added before or after the
+ ** current read transaction was opened. Values added after the
+ ** read transaction was opened may have been written incorrectly -
+ ** i.e. these slots may contain garbage data. However, we assume
+ ** that any slots written before the current read transaction was
+ ** opened remain unmodified.
+ **
+ ** For the reasons above, the if(...) condition featured in the inner
+ ** loop of the following block is more stringent that would be required
+ ** if we had exclusive access to the hash-table:
+ **
+ ** (aPgno[iFrame]==pgno):
+ ** This condition filters out normal hash-table collisions.
+ **
+ ** (iFrame<=iLast):
+ ** This condition filters out entries that were added to the hash
+ ** table after the current read-transaction had started.
+ */
+ iMinHash = walFramePage(pWal->minFrame);
+ for(iHash=walFramePage(iLast); iHash>=iMinHash; iHash--){
+ WalHashLoc sLoc; /* Hash table location */
+ int iKey; /* Hash slot index */
+ int nCollide; /* Number of hash collisions remaining */
+ int rc; /* Error code */
+ u32 iH;
+
+ rc = walHashGet(pWal, iHash, &sLoc);
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+ nCollide = HASHTABLE_NSLOT;
+ iKey = walHash(pgno);
+ SEH_INJECT_FAULT;
+ while( (iH = AtomicLoad(&sLoc.aHash[iKey]))!=0 ){
+ u32 iFrame = iH + sLoc.iZero;
+ if( iFrame<=iLast && iFrame>=pWal->minFrame && sLoc.aPgno[iH-1]==pgno ){
+ assert( iFrame>iRead || CORRUPT_DB );
+ iRead = iFrame;
+ }
+ if( (nCollide--)==0 ){
+ *piRead = 0;
+ return SQLITE_CORRUPT_BKPT;
+ }
+ iKey = walNextHash(iKey);
+ }
+ if( iRead ) break;
+ }
+
+#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
+ /* If expensive assert() statements are available, do a linear search
+ ** of the wal-index file content. Make sure the results agree with the
+ ** result obtained using the hash indexes above. */
+ {
+ u32 iRead2 = 0;
+ u32 iTest;
+ assert( pWal->bShmUnreliable || pWal->minFrame>0 );
+ for(iTest=iLast; iTest>=pWal->minFrame && iTest>0; iTest--){
+ if( walFramePgno(pWal, iTest)==pgno ){
+ iRead2 = iTest;
+ break;
+ }
+ }
+ assert( iRead==iRead2 );
+ }
+#endif
+
+ *piRead = iRead;
+ return SQLITE_OK;
+}
+
+/*
+** Search the wal file for page pgno. If found, set *piRead to the frame that
+** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
+** to zero.
+**
+** Return SQLITE_OK if successful, or an error code if an error occurs. If an
+** error does occur, the final value of *piRead is undefined.
+**
+** The difference between this function and walFindFrame() is that this
+** function wraps walFindFrame() in an SEH_TRY{...} block.
+*/
+int sqlite3WalFindFrame(
+ Wal *pWal, /* WAL handle */
+ Pgno pgno, /* Database page number to read data for */
+ u32 *piRead /* OUT: Frame number (or zero) */
+){
+ int rc;
+ SEH_TRY {
+ rc = walFindFrame(pWal, pgno, piRead);
+ }
+ SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+ return rc;
+}
+
+/*
+** Read the contents of frame iRead from the wal file into buffer pOut
+** (which is nOut bytes in size). Return SQLITE_OK if successful, or an
+** error code otherwise.
+*/
+int sqlite3WalReadFrame(
+ Wal *pWal, /* WAL handle */
+ u32 iRead, /* Frame to read */
+ int nOut, /* Size of buffer pOut in bytes */
+ u8 *pOut /* Buffer to write page data to */
+){
+ int sz;
+ i64 iOffset;
+ sz = pWal->hdr.szPage;
+ sz = (sz&0xfe00) + ((sz&0x0001)<<16);
+ testcase( sz<=32768 );
+ testcase( sz>=65536 );
+ iOffset = walFrameOffset(iRead, sz) + WAL_FRAME_HDRSIZE;
+ /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */
+ return sqlite3OsRead(pWal->pWalFd, pOut, (nOut>sz ? sz : nOut), iOffset);
+}
+
+/*
+** Return the size of the database in pages (or zero, if unknown).
+*/
+Pgno sqlite3WalDbsize(Wal *pWal){
+ if( pWal && ALWAYS(pWal->readLock>=0) ){
+ return pWal->hdr.nPage;
+ }
+ return 0;
+}
+
+
+/*
+** This function starts a write transaction on the WAL.
+**
+** A read transaction must have already been started by a prior call
+** to sqlite3WalBeginReadTransaction().
+**
+** If another thread or process has written into the database since
+** the read transaction was started, then it is not possible for this
+** thread to write as doing so would cause a fork. So this routine
+** returns SQLITE_BUSY in that case and no write transaction is started.
+**
+** There can only be a single writer active at a time.
+*/
+int sqlite3WalBeginWriteTransaction(Wal *pWal){
+ int rc;
+
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ /* If the write-lock is already held, then it was obtained before the
+ ** read-transaction was even opened, making this call a no-op.
+ ** Return early. */
+ if( pWal->writeLock ){
+ assert( !memcmp(&pWal->hdr,(void *)walIndexHdr(pWal),sizeof(WalIndexHdr)) );
+ return SQLITE_OK;
+ }
+#endif
+
+ /* Cannot start a write transaction without first holding a read
+ ** transaction. */
+ assert( pWal->readLock>=0 );
+ assert( pWal->writeLock==0 && pWal->iReCksum==0 );
+
+ if( pWal->readOnly ){
+ return SQLITE_READONLY;
+ }
+
+ /* Only one writer allowed at a time. Get the write lock. Return
+ ** SQLITE_BUSY if unable.
+ */
+ rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ if( rc ){
+ return rc;
+ }
+ pWal->writeLock = 1;
+
+ /* If another connection has written to the database file since the
+ ** time the read transaction on this connection was started, then
+ ** the write is disallowed.
+ */
+ SEH_TRY {
+ if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){
+ rc = SQLITE_BUSY_SNAPSHOT;
+ }
+ }
+ SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+
+ if( rc!=SQLITE_OK ){
+ walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ pWal->writeLock = 0;
+ }
+ return rc;
+}
+
+/*
+** End a write transaction. The commit has already been done. This
+** routine merely releases the lock.
+*/
+int sqlite3WalEndWriteTransaction(Wal *pWal){
+ if( pWal->writeLock ){
+ walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
+ pWal->writeLock = 0;
+ pWal->iReCksum = 0;
+ pWal->truncateOnCommit = 0;
+ }
+ return SQLITE_OK;
+}
+
+/*
+** If any data has been written (but not committed) to the log file, this
+** function moves the write-pointer back to the start of the transaction.
+**
+** Additionally, the callback function is invoked for each frame written
+** to the WAL since the start of the transaction. If the callback returns
+** other than SQLITE_OK, it is not invoked again and the error code is
+** returned to the caller.
+**
+** Otherwise, if the callback function does not return an error, this
+** function returns SQLITE_OK.
+*/
+int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
+ int rc = SQLITE_OK;
+ if( ALWAYS(pWal->writeLock) ){
+ Pgno iMax = pWal->hdr.mxFrame;
+ Pgno iFrame;
+
+ SEH_TRY {
+ /* Restore the clients cache of the wal-index header to the state it
+ ** was in before the client began writing to the database.
+ */
+ memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));
+
+ for(iFrame=pWal->hdr.mxFrame+1;
+ ALWAYS(rc==SQLITE_OK) && iFrame<=iMax;
+ iFrame++
+ ){
+ /* This call cannot fail. Unless the page for which the page number
+ ** is passed as the second argument is (a) in the cache and
+ ** (b) has an outstanding reference, then xUndo is either a no-op
+ ** (if (a) is false) or simply expels the page from the cache (if (b)
+ ** is false).
+ **
+ ** If the upper layer is doing a rollback, it is guaranteed that there
+ ** are no outstanding references to any page other than page 1. And
+ ** page 1 is never written to the log until the transaction is
+ ** committed. As a result, the call to xUndo may not fail.
+ */
+ assert( walFramePgno(pWal, iFrame)!=1 );
+ rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
+ }
+ if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal);
+ }
+ SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+ }
+ return rc;
+}
+
+/*
+** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32
+** values. This function populates the array with values required to
+** "rollback" the write position of the WAL handle back to the current
+** point in the event of a savepoint rollback (via WalSavepointUndo()).
+*/
+void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData){
+ assert( pWal->writeLock );
+ aWalData[0] = pWal->hdr.mxFrame;
+ aWalData[1] = pWal->hdr.aFrameCksum[0];
+ aWalData[2] = pWal->hdr.aFrameCksum[1];
+ aWalData[3] = pWal->nCkpt;
+}
+
+/*
+** Move the write position of the WAL back to the point identified by
+** the values in the aWalData[] array. aWalData must point to an array
+** of WAL_SAVEPOINT_NDATA u32 values that has been previously populated
+** by a call to WalSavepoint().
+*/
+int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
+ int rc = SQLITE_OK;
+
+ assert( pWal->writeLock );
+ assert( aWalData[3]!=pWal->nCkpt || aWalData[0]<=pWal->hdr.mxFrame );
+
+ if( aWalData[3]!=pWal->nCkpt ){
+ /* This savepoint was opened immediately after the write-transaction
+ ** was started. Right after that, the writer decided to wrap around
+ ** to the start of the log. Update the savepoint values to match.
+ */
+ aWalData[0] = 0;
+ aWalData[3] = pWal->nCkpt;
+ }
+
+ if( aWalData[0]<pWal->hdr.mxFrame ){
+ pWal->hdr.mxFrame = aWalData[0];
+ pWal->hdr.aFrameCksum[0] = aWalData[1];
+ pWal->hdr.aFrameCksum[1] = aWalData[2];
+ SEH_TRY {
+ walCleanupHash(pWal);
+ }
+ SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+ }
+
+ return rc;
+}
+
+/*
+** This function is called just before writing a set of frames to the log
+** file (see sqlite3WalFrames()). It checks to see if, instead of appending
+** to the current log file, it is possible to overwrite the start of the
+** existing log file with the new frames (i.e. "reset" the log). If so,
+** it sets pWal->hdr.mxFrame to 0. Otherwise, pWal->hdr.mxFrame is left
+** unchanged.
+**
+** SQLITE_OK is returned if no error is encountered (regardless of whether
+** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned
+** if an error occurs.
+*/
+static int walRestartLog(Wal *pWal){
+ int rc = SQLITE_OK;
+ int cnt;
+
+ if( pWal->readLock==0 ){
+ volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+ assert( pInfo->nBackfill==pWal->hdr.mxFrame );
+ if( pInfo->nBackfill>0 ){
+ u32 salt1;
+ sqlite3_randomness(4, &salt1);
+ rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
+ if( rc==SQLITE_OK ){
+ /* If all readers are using WAL_READ_LOCK(0) (in other words if no
+ ** readers are currently using the WAL), then the transactions
+ ** frames will overwrite the start of the existing log. Update the
+ ** wal-index header to reflect this.
+ **
+ ** In theory it would be Ok to update the cache of the header only
+ ** at this point. But updating the actual wal-index header is also
+ ** safe and means there is no special case for sqlite3WalUndo()
+ ** to handle if this transaction is rolled back. */
+ walRestartHdr(pWal, salt1);
+ walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
+ }else if( rc!=SQLITE_BUSY ){
+ return rc;
+ }
+ }
+ walUnlockShared(pWal, WAL_READ_LOCK(0));
+ pWal->readLock = -1;
+ cnt = 0;
+ do{
+ int notUsed;
+ rc = walTryBeginRead(pWal, &notUsed, 1, &cnt);
+ }while( rc==WAL_RETRY );
+ assert( (rc&0xff)!=SQLITE_BUSY ); /* BUSY not possible when useWal==1 */
+ testcase( (rc&0xff)==SQLITE_IOERR );
+ testcase( rc==SQLITE_PROTOCOL );
+ testcase( rc==SQLITE_OK );
+ }
+ return rc;
+}
+
+/*
+** Information about the current state of the WAL file and where
+** the next fsync should occur - passed from sqlite3WalFrames() into
+** walWriteToLog().
+*/
+typedef struct WalWriter {
+ Wal *pWal; /* The complete WAL information */
+ sqlite3_file *pFd; /* The WAL file to which we write */
+ sqlite3_int64 iSyncPoint; /* Fsync at this offset */
+ int syncFlags; /* Flags for the fsync */
+ int szPage; /* Size of one page */
+} WalWriter;
+
+/*
+** Write iAmt bytes of content into the WAL file beginning at iOffset.
+** Do a sync when crossing the p->iSyncPoint boundary.
+**
+** In other words, if iSyncPoint is in between iOffset and iOffset+iAmt,
+** first write the part before iSyncPoint, then sync, then write the
+** rest.
+*/
+static int walWriteToLog(
+ WalWriter *p, /* WAL to write to */
+ void *pContent, /* Content to be written */
+ int iAmt, /* Number of bytes to write */
+ sqlite3_int64 iOffset /* Start writing at this offset */
+){
+ int rc;
+ if( iOffset<p->iSyncPoint && iOffset+iAmt>=p->iSyncPoint ){
+ int iFirstAmt = (int)(p->iSyncPoint - iOffset);
+ rc = sqlite3OsWrite(p->pFd, pContent, iFirstAmt, iOffset);
+ if( rc ) return rc;
+ iOffset += iFirstAmt;
+ iAmt -= iFirstAmt;
+ pContent = (void*)(iFirstAmt + (char*)pContent);
+ assert( WAL_SYNC_FLAGS(p->syncFlags)!=0 );
+ rc = sqlite3OsSync(p->pFd, WAL_SYNC_FLAGS(p->syncFlags));
+ if( iAmt==0 || rc ) return rc;
+ }
+ rc = sqlite3OsWrite(p->pFd, pContent, iAmt, iOffset);
+ return rc;
+}
+
+/*
+** Write out a single frame of the WAL
+*/
+static int walWriteOneFrame(
+ WalWriter *p, /* Where to write the frame */
+ PgHdr *pPage, /* The page of the frame to be written */
+ int nTruncate, /* The commit flag. Usually 0. >0 for commit */
+ sqlite3_int64 iOffset /* Byte offset at which to write */
+){
+ int rc; /* Result code from subfunctions */
+ void *pData; /* Data actually written */
+ u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-header in */
+ pData = pPage->pData;
+ walEncodeFrame(p->pWal, pPage->pgno, nTruncate, pData, aFrame);
+ rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset);
+ if( rc ) return rc;
+ /* Write the page data */
+ rc = walWriteToLog(p, pData, p->szPage, iOffset+sizeof(aFrame));
+ return rc;
+}
+
+/*
+** This function is called as part of committing a transaction within which
+** one or more frames have been overwritten. It updates the checksums for
+** all frames written to the wal file by the current transaction starting
+** with the earliest to have been overwritten.
+**
+** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
+*/
+static int walRewriteChecksums(Wal *pWal, u32 iLast){
+ const int szPage = pWal->szPage;/* Database page size */
+ int rc = SQLITE_OK; /* Return code */
+ u8 *aBuf; /* Buffer to load data from wal file into */
+ u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-headers in */
+ u32 iRead; /* Next frame to read from wal file */
+ i64 iCksumOff;
+
+ aBuf = sqlite3_malloc(szPage + WAL_FRAME_HDRSIZE);
+ if( aBuf==0 ) return SQLITE_NOMEM_BKPT;
+
+ /* Find the checksum values to use as input for the recalculating the
+ ** first checksum. If the first frame is frame 1 (implying that the current
+ ** transaction restarted the wal file), these values must be read from the
+ ** wal-file header. Otherwise, read them from the frame header of the
+ ** previous frame. */
+ assert( pWal->iReCksum>0 );
+ if( pWal->iReCksum==1 ){
+ iCksumOff = 24;
+ }else{
+ iCksumOff = walFrameOffset(pWal->iReCksum-1, szPage) + 16;
+ }
+ rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, iCksumOff);
+ pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf);
+ pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]);
+
+ iRead = pWal->iReCksum;
+ pWal->iReCksum = 0;
+ for(; rc==SQLITE_OK && iRead<=iLast; iRead++){
+ i64 iOff = walFrameOffset(iRead, szPage);
+ rc = sqlite3OsRead(pWal->pWalFd, aBuf, szPage+WAL_FRAME_HDRSIZE, iOff);
+ if( rc==SQLITE_OK ){
+ u32 iPgno, nDbSize;
+ iPgno = sqlite3Get4byte(aBuf);
+ nDbSize = sqlite3Get4byte(&aBuf[4]);
+
+ walEncodeFrame(pWal, iPgno, nDbSize, &aBuf[WAL_FRAME_HDRSIZE], aFrame);
+ rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOff);
+ }
+ }
+
+ sqlite3_free(aBuf);
+ return rc;
+}
+
+/*
+** Write a set of frames to the log. The caller must hold the write-lock
+** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
+*/
+static int walFrames(
+ Wal *pWal, /* Wal handle to write to */
+ int szPage, /* Database page-size in bytes */
+ PgHdr *pList, /* List of dirty pages to write */
+ Pgno nTruncate, /* Database size after this commit */
+ int isCommit, /* True if this is a commit */
+ int sync_flags /* Flags to pass to OsSync() (or 0) */
+){
+ int rc; /* Used to catch return codes */
+ u32 iFrame; /* Next frame address */
+ PgHdr *p; /* Iterator to run through pList with. */
+ PgHdr *pLast = 0; /* Last frame in list */
+ int nExtra = 0; /* Number of extra copies of last page */
+ int szFrame; /* The size of a single frame */
+ i64 iOffset; /* Next byte to write in WAL file */
+ WalWriter w; /* The writer */
+ u32 iFirst = 0; /* First frame that may be overwritten */
+ WalIndexHdr *pLive; /* Pointer to shared header */
+
+ assert( pList );
+ assert( pWal->writeLock );
+
+ /* If this frame set completes a transaction, then nTruncate>0. If
+ ** nTruncate==0 then this frame set does not complete the transaction. */
+ assert( (isCommit!=0)==(nTruncate!=0) );
+
+#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
+ { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){}
+ WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n",
+ pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill"));
+ }
+#endif
+
+ pLive = (WalIndexHdr*)walIndexHdr(pWal);
+ if( memcmp(&pWal->hdr, (void *)pLive, sizeof(WalIndexHdr))!=0 ){
+ iFirst = pLive->mxFrame+1;
+ }
+
+ /* See if it is possible to write these frames into the start of the
+ ** log file, instead of appending to it at pWal->hdr.mxFrame.
+ */
+ if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){
+ return rc;
+ }
+
+ /* If this is the first frame written into the log, write the WAL
+ ** header to the start of the WAL file. See comments at the top of
+ ** this source file for a description of the WAL header format.
+ */
+ iFrame = pWal->hdr.mxFrame;
+ if( iFrame==0 ){
+ u8 aWalHdr[WAL_HDRSIZE]; /* Buffer to assemble wal-header in */
+ u32 aCksum[2]; /* Checksum for wal-header */
+
+ sqlite3Put4byte(&aWalHdr[0], (WAL_MAGIC | SQLITE_BIGENDIAN));
+ sqlite3Put4byte(&aWalHdr[4], WAL_MAX_VERSION);
+ sqlite3Put4byte(&aWalHdr[8], szPage);
+ sqlite3Put4byte(&aWalHdr[12], pWal->nCkpt);
+ if( pWal->nCkpt==0 ) sqlite3_randomness(8, pWal->hdr.aSalt);
+ memcpy(&aWalHdr[16], pWal->hdr.aSalt, 8);
+ walChecksumBytes(1, aWalHdr, WAL_HDRSIZE-2*4, 0, aCksum);
+ sqlite3Put4byte(&aWalHdr[24], aCksum[0]);
+ sqlite3Put4byte(&aWalHdr[28], aCksum[1]);
+
+ pWal->szPage = szPage;
+ pWal->hdr.bigEndCksum = SQLITE_BIGENDIAN;
+ pWal->hdr.aFrameCksum[0] = aCksum[0];
+ pWal->hdr.aFrameCksum[1] = aCksum[1];
+ pWal->truncateOnCommit = 1;
+
+ rc = sqlite3OsWrite(pWal->pWalFd, aWalHdr, sizeof(aWalHdr), 0);
+ WALTRACE(("WAL%p: wal-header write %s\n", pWal, rc ? "failed" : "ok"));
+ if( rc!=SQLITE_OK ){
+ return rc;
+ }
+
+ /* Sync the header (unless SQLITE_IOCAP_SEQUENTIAL is true or unless
+ ** all syncing is turned off by PRAGMA synchronous=OFF). Otherwise
+ ** an out-of-order write following a WAL restart could result in
+ ** database corruption. See the ticket:
+ **
+ ** https://sqlite.org/src/info/ff5be73dee
+ */
+ if( pWal->syncHeader ){
+ rc = sqlite3OsSync(pWal->pWalFd, CKPT_SYNC_FLAGS(sync_flags));
+ if( rc ) return rc;
+ }
+ }
+ if( (int)pWal->szPage!=szPage ){
+ return SQLITE_CORRUPT_BKPT; /* TH3 test case: cov1/corrupt155.test */
+ }
+
+ /* Setup information needed to write frames into the WAL */
+ w.pWal = pWal;
+ w.pFd = pWal->pWalFd;
+ w.iSyncPoint = 0;
+ w.syncFlags = sync_flags;
+ w.szPage = szPage;
+ iOffset = walFrameOffset(iFrame+1, szPage);
+ szFrame = szPage + WAL_FRAME_HDRSIZE;
+
+ /* Write all frames into the log file exactly once */
+ for(p=pList; p; p=p->pDirty){
+ int nDbSize; /* 0 normally. Positive == commit flag */
+
+ /* Check if this page has already been written into the wal file by
+ ** the current transaction. If so, overwrite the existing frame and
+ ** set Wal.writeLock to WAL_WRITELOCK_RECKSUM - indicating that
+ ** checksums must be recomputed when the transaction is committed. */
+ if( iFirst && (p->pDirty || isCommit==0) ){
+ u32 iWrite = 0;
+ VVA_ONLY(rc =) walFindFrame(pWal, p->pgno, &iWrite);
+ assert( rc==SQLITE_OK || iWrite==0 );
+ if( iWrite>=iFirst ){
+ i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE;
+ void *pData;
+ if( pWal->iReCksum==0 || iWrite<pWal->iReCksum ){
+ pWal->iReCksum = iWrite;
+ }
+ pData = p->pData;
+ rc = sqlite3OsWrite(pWal->pWalFd, pData, szPage, iOff);
+ if( rc ) return rc;
+ p->flags &= ~PGHDR_WAL_APPEND;
+ continue;
+ }
+ }
+
+ iFrame++;
+ assert( iOffset==walFrameOffset(iFrame, szPage) );
+ nDbSize = (isCommit && p->pDirty==0) ? nTruncate : 0;
+ rc = walWriteOneFrame(&w, p, nDbSize, iOffset);
+ if( rc ) return rc;
+ pLast = p;
+ iOffset += szFrame;
+ p->flags |= PGHDR_WAL_APPEND;
+ }
+
+ /* Recalculate checksums within the wal file if required. */
+ if( isCommit && pWal->iReCksum ){
+ rc = walRewriteChecksums(pWal, iFrame);
+ if( rc ) return rc;
+ }
+
+ /* If this is the end of a transaction, then we might need to pad
+ ** the transaction and/or sync the WAL file.
+ **
+ ** Padding and syncing only occur if this set of frames complete a
+ ** transaction and if PRAGMA synchronous=FULL. If synchronous==NORMAL
+ ** or synchronous==OFF, then no padding or syncing are needed.
+ **
+ ** If SQLITE_IOCAP_POWERSAFE_OVERWRITE is defined, then padding is not
+ ** needed and only the sync is done. If padding is needed, then the
+ ** final frame is repeated (with its commit mark) until the next sector
+ ** boundary is crossed. Only the part of the WAL prior to the last
+ ** sector boundary is synced; the part of the last frame that extends
+ ** past the sector boundary is written after the sync.
+ */
+ if( isCommit && WAL_SYNC_FLAGS(sync_flags)!=0 ){
+ int bSync = 1;
+ if( pWal->padToSectorBoundary ){
+ int sectorSize = sqlite3SectorSize(pWal->pWalFd);
+ w.iSyncPoint = ((iOffset+sectorSize-1)/sectorSize)*sectorSize;
+ bSync = (w.iSyncPoint==iOffset);
+ testcase( bSync );
+ while( iOffset<w.iSyncPoint ){
+ rc = walWriteOneFrame(&w, pLast, nTruncate, iOffset);
+ if( rc ) return rc;
+ iOffset += szFrame;
+ nExtra++;
+ assert( pLast!=0 );
+ }
+ }
+ if( bSync ){
+ assert( rc==SQLITE_OK );
+ rc = sqlite3OsSync(w.pFd, WAL_SYNC_FLAGS(sync_flags));
+ }
+ }
+
+ /* If this frame set completes the first transaction in the WAL and
+ ** if PRAGMA journal_size_limit is set, then truncate the WAL to the
+ ** journal size limit, if possible.
+ */
+ if( isCommit && pWal->truncateOnCommit && pWal->mxWalSize>=0 ){
+ i64 sz = pWal->mxWalSize;
+ if( walFrameOffset(iFrame+nExtra+1, szPage)>pWal->mxWalSize ){
+ sz = walFrameOffset(iFrame+nExtra+1, szPage);
+ }
+ walLimitSize(pWal, sz);
+ pWal->truncateOnCommit = 0;
+ }
+
+ /* Append data to the wal-index. It is not necessary to lock the
+ ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index
+ ** guarantees that there are no other writers, and no data that may
+ ** be in use by existing readers is being overwritten.
+ */
+ iFrame = pWal->hdr.mxFrame;
+ for(p=pList; p && rc==SQLITE_OK; p=p->pDirty){
+ if( (p->flags & PGHDR_WAL_APPEND)==0 ) continue;
+ iFrame++;
+ rc = walIndexAppend(pWal, iFrame, p->pgno);
+ }
+ assert( pLast!=0 || nExtra==0 );
+ while( rc==SQLITE_OK && nExtra>0 ){
+ iFrame++;
+ nExtra--;
+ rc = walIndexAppend(pWal, iFrame, pLast->pgno);
+ }
+
+ if( rc==SQLITE_OK ){
+ /* Update the private copy of the header. */
+ pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16));
+ testcase( szPage<=32768 );
+ testcase( szPage>=65536 );
+ pWal->hdr.mxFrame = iFrame;
+ if( isCommit ){
+ pWal->hdr.iChange++;
+ pWal->hdr.nPage = nTruncate;
+ }
+ /* If this is a commit, update the wal-index header too. */
+ if( isCommit ){
+ walIndexWriteHdr(pWal);
+ pWal->iCallback = iFrame;
+ }
+ }
+
+ WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok"));
+ return rc;
+}
+
+/*
+** Write a set of frames to the log. The caller must hold the write-lock
+** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
+**
+** The difference between this function and walFrames() is that this
+** function wraps walFrames() in an SEH_TRY{...} block.
+*/
+int sqlite3WalFrames(
+ Wal *pWal, /* Wal handle to write to */
+ int szPage, /* Database page-size in bytes */
+ PgHdr *pList, /* List of dirty pages to write */
+ Pgno nTruncate, /* Database size after this commit */
+ int isCommit, /* True if this is a commit */
+ int sync_flags /* Flags to pass to OsSync() (or 0) */
+){
+ int rc;
+ SEH_TRY {
+ rc = walFrames(pWal, szPage, pList, nTruncate, isCommit, sync_flags);
+ }
+ SEH_EXCEPT( rc = walHandleException(pWal); )
+ return rc;
+}
+
+/*
+** This routine is called to implement sqlite3_wal_checkpoint() and
+** related interfaces.
+**
+** Obtain a CHECKPOINT lock and then backfill as much information as
+** we can from WAL into the database.
+**
+** If parameter xBusy is not NULL, it is a pointer to a busy-handler
+** callback. In this case this function runs a blocking checkpoint.
+*/
+int sqlite3WalCheckpoint(
+ Wal *pWal, /* Wal connection */
+ sqlite3 *db, /* Check this handle's interrupt flag */
+ int eMode, /* PASSIVE, FULL, RESTART, or TRUNCATE */
+ int (*xBusy)(void*), /* Function to call when busy */
+ void *pBusyArg, /* Context argument for xBusyHandler */
+ int sync_flags, /* Flags to sync db file with (or 0) */
+ int nBuf, /* Size of temporary buffer */
+ u8 *zBuf, /* Temporary buffer to use */
+ int *pnLog, /* OUT: Number of frames in WAL */
+ int *pnCkpt /* OUT: Number of backfilled frames in WAL */
+){
+ int rc; /* Return code */
+ int isChanged = 0; /* True if a new wal-index header is loaded */
+ int eMode2 = eMode; /* Mode to pass to walCheckpoint() */
+ int (*xBusy2)(void*) = xBusy; /* Busy handler for eMode2 */
+
+ assert( pWal->ckptLock==0 );
+ assert( pWal->writeLock==0 );
+
+ /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
+ ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
+ assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );
+
+ if( pWal->readOnly ) return SQLITE_READONLY;
+ WALTRACE(("WAL%p: checkpoint begins\n", pWal));
+
+ /* Enable blocking locks, if possible. */
+ sqlite3WalDb(pWal, db);
+ if( xBusy2 ) (void)walEnableBlocking(pWal);
+
+ /* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive
+ ** "checkpoint" lock on the database file.
+ ** EVIDENCE-OF: R-10421-19736 If any other process is running a
+ ** checkpoint operation at the same time, the lock cannot be obtained and
+ ** SQLITE_BUSY is returned.
+ ** EVIDENCE-OF: R-53820-33897 Even if there is a busy-handler configured,
+ ** it will not be invoked in this case.
+ */
+ rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
+ testcase( rc==SQLITE_BUSY );
+ testcase( rc!=SQLITE_OK && xBusy2!=0 );
+ if( rc==SQLITE_OK ){
+ pWal->ckptLock = 1;
+
+ /* IMPLEMENTATION-OF: R-59782-36818 The SQLITE_CHECKPOINT_FULL, RESTART and
+ ** TRUNCATE modes also obtain the exclusive "writer" lock on the database
+ ** file.
+ **
+ ** EVIDENCE-OF: R-60642-04082 If the writer lock cannot be obtained
+ ** immediately, and a busy-handler is configured, it is invoked and the
+ ** writer lock retried until either the busy-handler returns 0 or the
+ ** lock is successfully obtained.
+ */
+ if( eMode!=SQLITE_CHECKPOINT_PASSIVE ){
+ rc = walBusyLock(pWal, xBusy2, pBusyArg, WAL_WRITE_LOCK, 1);
+ if( rc==SQLITE_OK ){
+ pWal->writeLock = 1;
+ }else if( rc==SQLITE_BUSY ){
+ eMode2 = SQLITE_CHECKPOINT_PASSIVE;
+ xBusy2 = 0;
+ rc = SQLITE_OK;
+ }
+ }
+ }
+
+
+ /* Read the wal-index header. */
+ SEH_TRY {
+ if( rc==SQLITE_OK ){
+ /* For a passive checkpoint, do not re-enable blocking locks after
+ ** reading the wal-index header. A passive checkpoint should not block
+ ** or invoke the busy handler. The only lock such a checkpoint may
+ ** attempt to obtain is a lock on a read-slot, and it should give up
+ ** immediately and do a partial checkpoint if it cannot obtain it. */
+ walDisableBlocking(pWal);
+ rc = walIndexReadHdr(pWal, &isChanged);
+ if( eMode2!=SQLITE_CHECKPOINT_PASSIVE ) (void)walEnableBlocking(pWal);
+ if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
+ sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
+ }
+ }
+
+ /* Copy data from the log to the database file. */
+ if( rc==SQLITE_OK ){
+ if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
+ rc = SQLITE_CORRUPT_BKPT;
+ }else{
+ rc = walCheckpoint(pWal, db, eMode2, xBusy2, pBusyArg, sync_flags,zBuf);
+ }
+
+ /* If no error occurred, set the output variables. */
+ if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
+ if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
+ SEH_INJECT_FAULT;
+ if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
+ }
+ }
+ }
+ SEH_EXCEPT( rc = walHandleException(pWal); )
+
+ if( isChanged ){
+ /* If a new wal-index header was loaded before the checkpoint was
+ ** performed, then the pager-cache associated with pWal is now
+ ** out of date. So zero the cached wal-index header to ensure that
+ ** next time the pager opens a snapshot on this database it knows that
+ ** the cache needs to be reset.
+ */
+ memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
+ }
+
+ walDisableBlocking(pWal);
+ sqlite3WalDb(pWal, 0);
+
+ /* Release the locks. */
+ sqlite3WalEndWriteTransaction(pWal);
+ if( pWal->ckptLock ){
+ walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
+ pWal->ckptLock = 0;
+ }
+ WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ if( rc==SQLITE_BUSY_TIMEOUT ) rc = SQLITE_BUSY;
+#endif
+ return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc);
+}
+
+/* Return the value to pass to a sqlite3_wal_hook callback, the
+** number of frames in the WAL at the point of the last commit since
+** sqlite3WalCallback() was called. If no commits have occurred since
+** the last call, then return 0.
+*/
+int sqlite3WalCallback(Wal *pWal){
+ u32 ret = 0;
+ if( pWal ){
+ ret = pWal->iCallback;
+ pWal->iCallback = 0;
+ }
+ return (int)ret;
+}
+
+/*
+** This function is called to change the WAL subsystem into or out
+** of locking_mode=EXCLUSIVE.
+**
+** If op is zero, then attempt to change from locking_mode=EXCLUSIVE
+** into locking_mode=NORMAL. This means that we must acquire a lock
+** on the pWal->readLock byte. If the WAL is already in locking_mode=NORMAL
+** or if the acquisition of the lock fails, then return 0. If the
+** transition out of exclusive-mode is successful, return 1. This
+** operation must occur while the pager is still holding the exclusive
+** lock on the main database file.
+**
+** If op is one, then change from locking_mode=NORMAL into
+** locking_mode=EXCLUSIVE. This means that the pWal->readLock must
+** be released. Return 1 if the transition is made and 0 if the
+** WAL is already in exclusive-locking mode - meaning that this
+** routine is a no-op. The pager must already hold the exclusive lock
+** on the main database file before invoking this operation.
+**
+** If op is negative, then do a dry-run of the op==1 case but do
+** not actually change anything. The pager uses this to see if it
+** should acquire the database exclusive lock prior to invoking
+** the op==1 case.
+*/
+int sqlite3WalExclusiveMode(Wal *pWal, int op){
+ int rc;
+ assert( pWal->writeLock==0 );
+ assert( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE || op==-1 );
+
+ /* pWal->readLock is usually set, but might be -1 if there was a
+ ** prior error while attempting to acquire are read-lock. This cannot
+ ** happen if the connection is actually in exclusive mode (as no xShmLock
+ ** locks are taken in this case). Nor should the pager attempt to
+ ** upgrade to exclusive-mode following such an error.
+ */
+#ifndef SQLITE_USE_SEH
+ assert( pWal->readLock>=0 || pWal->lockError );
+#endif
+ assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) );
+
+ if( op==0 ){
+ if( pWal->exclusiveMode!=WAL_NORMAL_MODE ){
+ pWal->exclusiveMode = WAL_NORMAL_MODE;
+ if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){
+ pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
+ }
+ rc = pWal->exclusiveMode==WAL_NORMAL_MODE;
+ }else{
+ /* Already in locking_mode=NORMAL */
+ rc = 0;
+ }
+ }else if( op>0 ){
+ assert( pWal->exclusiveMode==WAL_NORMAL_MODE );
+ assert( pWal->readLock>=0 );
+ walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
+ pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
+ rc = 1;
+ }else{
+ rc = pWal->exclusiveMode==WAL_NORMAL_MODE;
+ }
+ return rc;
+}
+
+/*
+** Return true if the argument is non-NULL and the WAL module is using
+** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
+** WAL module is using shared-memory, return false.
+*/
+int sqlite3WalHeapMemory(Wal *pWal){
+ return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
+}
+
+#ifdef SQLITE_ENABLE_SNAPSHOT
+/* Create a snapshot object. The content of a snapshot is opaque to
+** every other subsystem, so the WAL module can put whatever it needs
+** in the object.
+*/
+int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){
+ int rc = SQLITE_OK;
+ WalIndexHdr *pRet;
+ static const u32 aZero[4] = { 0, 0, 0, 0 };
+
+ assert( pWal->readLock>=0 && pWal->writeLock==0 );
+
+ if( memcmp(&pWal->hdr.aFrameCksum[0],aZero,16)==0 ){
+ *ppSnapshot = 0;
+ return SQLITE_ERROR;
+ }
+ pRet = (WalIndexHdr*)sqlite3_malloc(sizeof(WalIndexHdr));
+ if( pRet==0 ){
+ rc = SQLITE_NOMEM_BKPT;
+ }else{
+ memcpy(pRet, &pWal->hdr, sizeof(WalIndexHdr));
+ *ppSnapshot = (sqlite3_snapshot*)pRet;
+ }
+
+ return rc;
+}
+
+/* Try to open on pSnapshot when the next read-transaction starts
+*/
+void sqlite3WalSnapshotOpen(
+ Wal *pWal,
+ sqlite3_snapshot *pSnapshot
+){
+ pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
+}
+
+/*
+** Return a +ve value if snapshot p1 is newer than p2. A -ve value if
+** p1 is older than p2 and zero if p1 and p2 are the same snapshot.
+*/
+int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){
+ WalIndexHdr *pHdr1 = (WalIndexHdr*)p1;
+ WalIndexHdr *pHdr2 = (WalIndexHdr*)p2;
+
+ /* aSalt[0] is a copy of the value stored in the wal file header. It
+ ** is incremented each time the wal file is restarted. */
+ if( pHdr1->aSalt[0]<pHdr2->aSalt[0] ) return -1;
+ if( pHdr1->aSalt[0]>pHdr2->aSalt[0] ) return +1;
+ if( pHdr1->mxFrame<pHdr2->mxFrame ) return -1;
+ if( pHdr1->mxFrame>pHdr2->mxFrame ) return +1;
+ return 0;
+}
+
+/*
+** The caller currently has a read transaction open on the database.
+** This function takes a SHARED lock on the CHECKPOINTER slot and then
+** checks if the snapshot passed as the second argument is still
+** available. If so, SQLITE_OK is returned.
+**
+** If the snapshot is not available, SQLITE_ERROR is returned. Or, if
+** the CHECKPOINTER lock cannot be obtained, SQLITE_BUSY. If any error
+** occurs (any value other than SQLITE_OK is returned), the CHECKPOINTER
+** lock is released before returning.
+*/
+int sqlite3WalSnapshotCheck(Wal *pWal, sqlite3_snapshot *pSnapshot){
+ int rc;
+ SEH_TRY {
+ rc = walLockShared(pWal, WAL_CKPT_LOCK);
+ if( rc==SQLITE_OK ){
+ WalIndexHdr *pNew = (WalIndexHdr*)pSnapshot;
+ if( memcmp(pNew->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
+ || pNew->mxFrame<walCkptInfo(pWal)->nBackfillAttempted
+ ){
+ rc = SQLITE_ERROR_SNAPSHOT;
+ walUnlockShared(pWal, WAL_CKPT_LOCK);
+ }
+ }
+ }
+ SEH_EXCEPT( rc = walHandleException(pWal); )
+ return rc;
+}
+
+/*
+** Release a lock obtained by an earlier successful call to
+** sqlite3WalSnapshotCheck().
+*/
+void sqlite3WalSnapshotUnlock(Wal *pWal){
+ assert( pWal );
+ walUnlockShared(pWal, WAL_CKPT_LOCK);
+}
+
+
+#endif /* SQLITE_ENABLE_SNAPSHOT */
+
+#ifdef SQLITE_ENABLE_ZIPVFS
+/*
+** If the argument is not NULL, it points to a Wal object that holds a
+** read-lock. This function returns the database page-size if it is known,
+** or zero if it is not (or if pWal is NULL).
+*/
+int sqlite3WalFramesize(Wal *pWal){
+ assert( pWal==0 || pWal->readLock>=0 );
+ return (pWal ? pWal->szPage : 0);
+}
+#endif
+
+/* Return the sqlite3_file object for the WAL file
+*/
+sqlite3_file *sqlite3WalFile(Wal *pWal){
+ return pWal->pWalFd;
+}
+
+#endif /* #ifndef SQLITE_OMIT_WAL */
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-25 20:51:46 +0000