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+/*
+** 2008 October 7
+**
+** 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 code use to implement an in-memory rollback journal.
+** The in-memory rollback journal is used to journal transactions for
+** ":memory:" databases and when the journal_mode=MEMORY pragma is used.
+**
+** Update: The in-memory journal is also used to temporarily cache
+** smaller journals that are not critical for power-loss recovery.
+** For example, statement journals that are not too big will be held
+** entirely in memory, thus reducing the number of file I/O calls, and
+** more importantly, reducing temporary file creation events. If these
+** journals become too large for memory, they are spilled to disk. But
+** in the common case, they are usually small and no file I/O needs to
+** occur.
+*/
+#include "sqliteInt.h"
+
+/* Forward references to internal structures */
+typedef struct MemJournal MemJournal;
+typedef struct FilePoint FilePoint;
+typedef struct FileChunk FileChunk;
+
+/*
+** The rollback journal is composed of a linked list of these structures.
+**
+** The zChunk array is always at least 8 bytes in size - usually much more.
+** Its actual size is stored in the MemJournal.nChunkSize variable.
+*/
+struct FileChunk {
+ FileChunk *pNext; /* Next chunk in the journal */
+ u8 zChunk[8]; /* Content of this chunk */
+};
+
+/*
+** By default, allocate this many bytes of memory for each FileChunk object.
+*/
+#define MEMJOURNAL_DFLT_FILECHUNKSIZE 1024
+
+/*
+** For chunk size nChunkSize, return the number of bytes that should
+** be allocated for each FileChunk structure.
+*/
+#define fileChunkSize(nChunkSize) (sizeof(FileChunk) + ((nChunkSize)-8))
+
+/*
+** An instance of this object serves as a cursor into the rollback journal.
+** The cursor can be either for reading or writing.
+*/
+struct FilePoint {
+ sqlite3_int64 iOffset; /* Offset from the beginning of the file */
+ FileChunk *pChunk; /* Specific chunk into which cursor points */
+};
+
+/*
+** This structure is a subclass of sqlite3_file. Each open memory-journal
+** is an instance of this class.
+*/
+struct MemJournal {
+ const sqlite3_io_methods *pMethod; /* Parent class. MUST BE FIRST */
+ int nChunkSize; /* In-memory chunk-size */
+
+ int nSpill; /* Bytes of data before flushing */
+ FileChunk *pFirst; /* Head of in-memory chunk-list */
+ FilePoint endpoint; /* Pointer to the end of the file */
+ FilePoint readpoint; /* Pointer to the end of the last xRead() */
+
+ int flags; /* xOpen flags */
+ sqlite3_vfs *pVfs; /* The "real" underlying VFS */
+ const char *zJournal; /* Name of the journal file */
+};
+
+/*
+** Read data from the in-memory journal file. This is the implementation
+** of the sqlite3_vfs.xRead method.
+*/
+static int memjrnlRead(
+ sqlite3_file *pJfd, /* The journal file from which to read */
+ void *zBuf, /* Put the results here */
+ int iAmt, /* Number of bytes to read */
+ sqlite_int64 iOfst /* Begin reading at this offset */
+){
+ MemJournal *p = (MemJournal *)pJfd;
+ u8 *zOut = zBuf;
+ int nRead = iAmt;
+ int iChunkOffset;
+ FileChunk *pChunk;
+
+ if( (iAmt+iOfst)>p->endpoint.iOffset ){
+ return SQLITE_IOERR_SHORT_READ;
+ }
+ assert( p->readpoint.iOffset==0 || p->readpoint.pChunk!=0 );
+ if( p->readpoint.iOffset!=iOfst || iOfst==0 ){
+ sqlite3_int64 iOff = 0;
+ for(pChunk=p->pFirst;
+ ALWAYS(pChunk) && (iOff+p->nChunkSize)<=iOfst;
+ pChunk=pChunk->pNext
+ ){
+ iOff += p->nChunkSize;
+ }
+ }else{
+ pChunk = p->readpoint.pChunk;
+ assert( pChunk!=0 );
+ }
+
+ iChunkOffset = (int)(iOfst%p->nChunkSize);
+ do {
+ int iSpace = p->nChunkSize - iChunkOffset;
+ int nCopy = MIN(nRead, (p->nChunkSize - iChunkOffset));
+ memcpy(zOut, (u8*)pChunk->zChunk + iChunkOffset, nCopy);
+ zOut += nCopy;
+ nRead -= iSpace;
+ iChunkOffset = 0;
+ } while( nRead>=0 && (pChunk=pChunk->pNext)!=0 && nRead>0 );
+ p->readpoint.iOffset = pChunk ? iOfst+iAmt : 0;
+ p->readpoint.pChunk = pChunk;
+
+ return SQLITE_OK;
+}
+
+/*
+** Free the list of FileChunk structures headed at MemJournal.pFirst.
+*/
+static void memjrnlFreeChunks(FileChunk *pFirst){
+ FileChunk *pIter;
+ FileChunk *pNext;
+ for(pIter=pFirst; pIter; pIter=pNext){
+ pNext = pIter->pNext;
+ sqlite3_free(pIter);
+ }
+}
+
+/*
+** Flush the contents of memory to a real file on disk.
+*/
+static int memjrnlCreateFile(MemJournal *p){
+ int rc;
+ sqlite3_file *pReal = (sqlite3_file*)p;
+ MemJournal copy = *p;
+
+ memset(p, 0, sizeof(MemJournal));
+ rc = sqlite3OsOpen(copy.pVfs, copy.zJournal, pReal, copy.flags, 0);
+ if( rc==SQLITE_OK ){
+ int nChunk = copy.nChunkSize;
+ i64 iOff = 0;
+ FileChunk *pIter;
+ for(pIter=copy.pFirst; pIter; pIter=pIter->pNext){
+ if( iOff + nChunk > copy.endpoint.iOffset ){
+ nChunk = copy.endpoint.iOffset - iOff;
+ }
+ rc = sqlite3OsWrite(pReal, (u8*)pIter->zChunk, nChunk, iOff);
+ if( rc ) break;
+ iOff += nChunk;
+ }
+ if( rc==SQLITE_OK ){
+ /* No error has occurred. Free the in-memory buffers. */
+ memjrnlFreeChunks(copy.pFirst);
+ }
+ }
+ if( rc!=SQLITE_OK ){
+ /* If an error occurred while creating or writing to the file, restore
+ ** the original before returning. This way, SQLite uses the in-memory
+ ** journal data to roll back changes made to the internal page-cache
+ ** before this function was called. */
+ sqlite3OsClose(pReal);
+ *p = copy;
+ }
+ return rc;
+}
+
+
+/* Forward reference */
+static int memjrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size);
+
+/*
+** Write data to the file.
+*/
+static int memjrnlWrite(
+ sqlite3_file *pJfd, /* The journal file into which to write */
+ const void *zBuf, /* Take data to be written from here */
+ int iAmt, /* Number of bytes to write */
+ sqlite_int64 iOfst /* Begin writing at this offset into the file */
+){
+ MemJournal *p = (MemJournal *)pJfd;
+ int nWrite = iAmt;
+ u8 *zWrite = (u8 *)zBuf;
+
+ /* If the file should be created now, create it and write the new data
+ ** into the file on disk. */
+ if( p->nSpill>0 && (iAmt+iOfst)>p->nSpill ){
+ int rc = memjrnlCreateFile(p);
+ if( rc==SQLITE_OK ){
+ rc = sqlite3OsWrite(pJfd, zBuf, iAmt, iOfst);
+ }
+ return rc;
+ }
+
+ /* If the contents of this write should be stored in memory */
+ else{
+ /* An in-memory journal file should only ever be appended to. Random
+ ** access writes are not required. The only exception to this is when
+ ** the in-memory journal is being used by a connection using the
+ ** atomic-write optimization. In this case the first 28 bytes of the
+ ** journal file may be written as part of committing the transaction. */
+ assert( iOfst<=p->endpoint.iOffset );
+ if( iOfst>0 && iOfst!=p->endpoint.iOffset ){
+ memjrnlTruncate(pJfd, iOfst);
+ }
+ if( iOfst==0 && p->pFirst ){
+ assert( p->nChunkSize>iAmt );
+ memcpy((u8*)p->pFirst->zChunk, zBuf, iAmt);
+ }else{
+ while( nWrite>0 ){
+ FileChunk *pChunk = p->endpoint.pChunk;
+ int iChunkOffset = (int)(p->endpoint.iOffset%p->nChunkSize);
+ int iSpace = MIN(nWrite, p->nChunkSize - iChunkOffset);
+
+ assert( pChunk!=0 || iChunkOffset==0 );
+ if( iChunkOffset==0 ){
+ /* New chunk is required to extend the file. */
+ FileChunk *pNew = sqlite3_malloc(fileChunkSize(p->nChunkSize));
+ if( !pNew ){
+ return SQLITE_IOERR_NOMEM_BKPT;
+ }
+ pNew->pNext = 0;
+ if( pChunk ){
+ assert( p->pFirst );
+ pChunk->pNext = pNew;
+ }else{
+ assert( !p->pFirst );
+ p->pFirst = pNew;
+ }
+ pChunk = p->endpoint.pChunk = pNew;
+ }
+
+ assert( pChunk!=0 );
+ memcpy((u8*)pChunk->zChunk + iChunkOffset, zWrite, iSpace);
+ zWrite += iSpace;
+ nWrite -= iSpace;
+ p->endpoint.iOffset += iSpace;
+ }
+ }
+ }
+
+ return SQLITE_OK;
+}
+
+/*
+** Truncate the in-memory file.
+*/
+static int memjrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
+ MemJournal *p = (MemJournal *)pJfd;
+ assert( p->endpoint.pChunk==0 || p->endpoint.pChunk->pNext==0 );
+ if( size<p->endpoint.iOffset ){
+ FileChunk *pIter = 0;
+ if( size==0 ){
+ memjrnlFreeChunks(p->pFirst);
+ p->pFirst = 0;
+ }else{
+ i64 iOff = p->nChunkSize;
+ for(pIter=p->pFirst; ALWAYS(pIter) && iOff<size; pIter=pIter->pNext){
+ iOff += p->nChunkSize;
+ }
+ if( ALWAYS(pIter) ){
+ memjrnlFreeChunks(pIter->pNext);
+ pIter->pNext = 0;
+ }
+ }
+
+ p->endpoint.pChunk = pIter;
+ p->endpoint.iOffset = size;
+ p->readpoint.pChunk = 0;
+ p->readpoint.iOffset = 0;
+ }
+ return SQLITE_OK;
+}
+
+/*
+** Close the file.
+*/
+static int memjrnlClose(sqlite3_file *pJfd){
+ MemJournal *p = (MemJournal *)pJfd;
+ memjrnlFreeChunks(p->pFirst);
+ return SQLITE_OK;
+}
+
+/*
+** Sync the file.
+**
+** If the real file has been created, call its xSync method. Otherwise,
+** syncing an in-memory journal is a no-op.
+*/
+static int memjrnlSync(sqlite3_file *pJfd, int flags){
+ UNUSED_PARAMETER2(pJfd, flags);
+ return SQLITE_OK;
+}
+
+/*
+** Query the size of the file in bytes.
+*/
+static int memjrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
+ MemJournal *p = (MemJournal *)pJfd;
+ *pSize = (sqlite_int64) p->endpoint.iOffset;
+ return SQLITE_OK;
+}
+
+/*
+** Table of methods for MemJournal sqlite3_file object.
+*/
+static const struct sqlite3_io_methods MemJournalMethods = {
+ 1, /* iVersion */
+ memjrnlClose, /* xClose */
+ memjrnlRead, /* xRead */
+ memjrnlWrite, /* xWrite */
+ memjrnlTruncate, /* xTruncate */
+ memjrnlSync, /* xSync */
+ memjrnlFileSize, /* xFileSize */
+ 0, /* xLock */
+ 0, /* xUnlock */
+ 0, /* xCheckReservedLock */
+ 0, /* xFileControl */
+ 0, /* xSectorSize */
+ 0, /* xDeviceCharacteristics */
+ 0, /* xShmMap */
+ 0, /* xShmLock */
+ 0, /* xShmBarrier */
+ 0, /* xShmUnmap */
+ 0, /* xFetch */
+ 0 /* xUnfetch */
+};
+
+/*
+** Open a journal file.
+**
+** The behaviour of the journal file depends on the value of parameter
+** nSpill. If nSpill is 0, then the journal file is always create and
+** accessed using the underlying VFS. If nSpill is less than zero, then
+** all content is always stored in main-memory. Finally, if nSpill is a
+** positive value, then the journal file is initially created in-memory
+** but may be flushed to disk later on. In this case the journal file is
+** flushed to disk either when it grows larger than nSpill bytes in size,
+** or when sqlite3JournalCreate() is called.
+*/
+int sqlite3JournalOpen(
+ sqlite3_vfs *pVfs, /* The VFS to use for actual file I/O */
+ const char *zName, /* Name of the journal file */
+ sqlite3_file *pJfd, /* Preallocated, blank file handle */
+ int flags, /* Opening flags */
+ int nSpill /* Bytes buffered before opening the file */
+){
+ MemJournal *p = (MemJournal*)pJfd;
+
+ assert( zName || nSpill<0 || (flags & SQLITE_OPEN_EXCLUSIVE) );
+
+ /* Zero the file-handle object. If nSpill was passed zero, initialize
+ ** it using the sqlite3OsOpen() function of the underlying VFS. In this
+ ** case none of the code in this module is executed as a result of calls
+ ** made on the journal file-handle. */
+ memset(p, 0, sizeof(MemJournal));
+ if( nSpill==0 ){
+ return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);
+ }
+
+ if( nSpill>0 ){
+ p->nChunkSize = nSpill;
+ }else{
+ p->nChunkSize = 8 + MEMJOURNAL_DFLT_FILECHUNKSIZE - sizeof(FileChunk);
+ assert( MEMJOURNAL_DFLT_FILECHUNKSIZE==fileChunkSize(p->nChunkSize) );
+ }
+
+ pJfd->pMethods = (const sqlite3_io_methods*)&MemJournalMethods;
+ p->nSpill = nSpill;
+ p->flags = flags;
+ p->zJournal = zName;
+ p->pVfs = pVfs;
+ return SQLITE_OK;
+}
+
+/*
+** Open an in-memory journal file.
+*/
+void sqlite3MemJournalOpen(sqlite3_file *pJfd){
+ sqlite3JournalOpen(0, 0, pJfd, 0, -1);
+}
+
+#if defined(SQLITE_ENABLE_ATOMIC_WRITE) \
+ || defined(SQLITE_ENABLE_BATCH_ATOMIC_WRITE)
+/*
+** If the argument p points to a MemJournal structure that is not an
+** in-memory-only journal file (i.e. is one that was opened with a +ve
+** nSpill parameter or as SQLITE_OPEN_MAIN_JOURNAL), and the underlying
+** file has not yet been created, create it now.
+*/
+int sqlite3JournalCreate(sqlite3_file *pJfd){
+ int rc = SQLITE_OK;
+ MemJournal *p = (MemJournal*)pJfd;
+ if( pJfd->pMethods==&MemJournalMethods && (
+#ifdef SQLITE_ENABLE_ATOMIC_WRITE
+ p->nSpill>0
+#else
+ /* While this appears to not be possible without ATOMIC_WRITE, the
+ ** paths are complex, so it seems prudent to leave the test in as
+ ** a NEVER(), in case our analysis is subtly flawed. */
+ NEVER(p->nSpill>0)
+#endif
+#ifdef SQLITE_ENABLE_BATCH_ATOMIC_WRITE
+ || (p->flags & SQLITE_OPEN_MAIN_JOURNAL)
+#endif
+ )){
+ rc = memjrnlCreateFile(p);
+ }
+ return rc;
+}
+#endif
+
+/*
+** The file-handle passed as the only argument is open on a journal file.
+** Return true if this "journal file" is currently stored in heap memory,
+** or false otherwise.
+*/
+int sqlite3JournalIsInMemory(sqlite3_file *p){
+ return p->pMethods==&MemJournalMethods;
+}
+
+/*
+** Return the number of bytes required to store a JournalFile that uses vfs
+** pVfs to create the underlying on-disk files.
+*/
+int sqlite3JournalSize(sqlite3_vfs *pVfs){
+ return MAX(pVfs->szOsFile, (int)sizeof(MemJournal));
+}