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Diffstat (limited to 'src/notify.c')
| -rw-r--r-- | src/notify.c | 332 |
1 files changed, 332 insertions, 0 deletions
diff --git a/src/notify.c b/src/notify.c new file mode 100644 index 0000000..4960ab7 --- /dev/null +++ b/src/notify.c @@ -0,0 +1,332 @@ +/* +** 2009 March 3 +** +** 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 the sqlite3_unlock_notify() +** API method and its associated functionality. +*/ +#include "sqliteInt.h" +#include "btreeInt.h" + +/* Omit this entire file if SQLITE_ENABLE_UNLOCK_NOTIFY is not defined. */ +#ifdef SQLITE_ENABLE_UNLOCK_NOTIFY + +/* +** Public interfaces: +** +** sqlite3ConnectionBlocked() +** sqlite3ConnectionUnlocked() +** sqlite3ConnectionClosed() +** sqlite3_unlock_notify() +*/ + +#define assertMutexHeld() \ + assert( sqlite3_mutex_held(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MAIN)) ) + +/* +** Head of a linked list of all sqlite3 objects created by this process +** for which either sqlite3.pBlockingConnection or sqlite3.pUnlockConnection +** is not NULL. This variable may only accessed while the STATIC_MAIN +** mutex is held. +*/ +static sqlite3 *SQLITE_WSD sqlite3BlockedList = 0; + +#ifndef NDEBUG +/* +** This function is a complex assert() that verifies the following +** properties of the blocked connections list: +** +** 1) Each entry in the list has a non-NULL value for either +** pUnlockConnection or pBlockingConnection, or both. +** +** 2) All entries in the list that share a common value for +** xUnlockNotify are grouped together. +** +** 3) If the argument db is not NULL, then none of the entries in the +** blocked connections list have pUnlockConnection or pBlockingConnection +** set to db. This is used when closing connection db. +*/ +static void checkListProperties(sqlite3 *db){ + sqlite3 *p; + for(p=sqlite3BlockedList; p; p=p->pNextBlocked){ + int seen = 0; + sqlite3 *p2; + + /* Verify property (1) */ + assert( p->pUnlockConnection || p->pBlockingConnection ); + + /* Verify property (2) */ + for(p2=sqlite3BlockedList; p2!=p; p2=p2->pNextBlocked){ + if( p2->xUnlockNotify==p->xUnlockNotify ) seen = 1; + assert( p2->xUnlockNotify==p->xUnlockNotify || !seen ); + assert( db==0 || p->pUnlockConnection!=db ); + assert( db==0 || p->pBlockingConnection!=db ); + } + } +} +#else +# define checkListProperties(x) +#endif + +/* +** Remove connection db from the blocked connections list. If connection +** db is not currently a part of the list, this function is a no-op. +*/ +static void removeFromBlockedList(sqlite3 *db){ + sqlite3 **pp; + assertMutexHeld(); + for(pp=&sqlite3BlockedList; *pp; pp = &(*pp)->pNextBlocked){ + if( *pp==db ){ + *pp = (*pp)->pNextBlocked; + break; + } + } +} + +/* +** Add connection db to the blocked connections list. It is assumed +** that it is not already a part of the list. +*/ +static void addToBlockedList(sqlite3 *db){ + sqlite3 **pp; + assertMutexHeld(); + for( + pp=&sqlite3BlockedList; + *pp && (*pp)->xUnlockNotify!=db->xUnlockNotify; + pp=&(*pp)->pNextBlocked + ); + db->pNextBlocked = *pp; + *pp = db; +} + +/* +** Obtain the STATIC_MAIN mutex. +*/ +static void enterMutex(void){ + sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MAIN)); + checkListProperties(0); +} + +/* +** Release the STATIC_MAIN mutex. +*/ +static void leaveMutex(void){ + assertMutexHeld(); + checkListProperties(0); + sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MAIN)); +} + +/* +** Register an unlock-notify callback. +** +** This is called after connection "db" has attempted some operation +** but has received an SQLITE_LOCKED error because another connection +** (call it pOther) in the same process was busy using the same shared +** cache. pOther is found by looking at db->pBlockingConnection. +** +** If there is no blocking connection, the callback is invoked immediately, +** before this routine returns. +** +** If pOther is already blocked on db, then report SQLITE_LOCKED, to indicate +** a deadlock. +** +** Otherwise, make arrangements to invoke xNotify when pOther drops +** its locks. +** +** Each call to this routine overrides any prior callbacks registered +** on the same "db". If xNotify==0 then any prior callbacks are immediately +** cancelled. +*/ +int sqlite3_unlock_notify( + sqlite3 *db, + void (*xNotify)(void **, int), + void *pArg +){ + int rc = SQLITE_OK; + + sqlite3_mutex_enter(db->mutex); + enterMutex(); + + if( xNotify==0 ){ + removeFromBlockedList(db); + db->pBlockingConnection = 0; + db->pUnlockConnection = 0; + db->xUnlockNotify = 0; + db->pUnlockArg = 0; + }else if( 0==db->pBlockingConnection ){ + /* The blocking transaction has been concluded. Or there never was a + ** blocking transaction. In either case, invoke the notify callback + ** immediately. + */ + xNotify(&pArg, 1); + }else{ + sqlite3 *p; + + for(p=db->pBlockingConnection; p && p!=db; p=p->pUnlockConnection){} + if( p ){ + rc = SQLITE_LOCKED; /* Deadlock detected. */ + }else{ + db->pUnlockConnection = db->pBlockingConnection; + db->xUnlockNotify = xNotify; + db->pUnlockArg = pArg; + removeFromBlockedList(db); + addToBlockedList(db); + } + } + + leaveMutex(); + assert( !db->mallocFailed ); + sqlite3ErrorWithMsg(db, rc, (rc?"database is deadlocked":0)); + sqlite3_mutex_leave(db->mutex); + return rc; +} + +/* +** This function is called while stepping or preparing a statement +** associated with connection db. The operation will return SQLITE_LOCKED +** to the user because it requires a lock that will not be available +** until connection pBlocker concludes its current transaction. +*/ +void sqlite3ConnectionBlocked(sqlite3 *db, sqlite3 *pBlocker){ + enterMutex(); + if( db->pBlockingConnection==0 && db->pUnlockConnection==0 ){ + addToBlockedList(db); + } + db->pBlockingConnection = pBlocker; + leaveMutex(); +} + +/* +** This function is called when +** the transaction opened by database db has just finished. Locks held +** by database connection db have been released. +** +** This function loops through each entry in the blocked connections +** list and does the following: +** +** 1) If the sqlite3.pBlockingConnection member of a list entry is +** set to db, then set pBlockingConnection=0. +** +** 2) If the sqlite3.pUnlockConnection member of a list entry is +** set to db, then invoke the configured unlock-notify callback and +** set pUnlockConnection=0. +** +** 3) If the two steps above mean that pBlockingConnection==0 and +** pUnlockConnection==0, remove the entry from the blocked connections +** list. +*/ +void sqlite3ConnectionUnlocked(sqlite3 *db){ + void (*xUnlockNotify)(void **, int) = 0; /* Unlock-notify cb to invoke */ + int nArg = 0; /* Number of entries in aArg[] */ + sqlite3 **pp; /* Iterator variable */ + void **aArg; /* Arguments to the unlock callback */ + void **aDyn = 0; /* Dynamically allocated space for aArg[] */ + void *aStatic[16]; /* Starter space for aArg[]. No malloc required */ + + aArg = aStatic; + enterMutex(); /* Enter STATIC_MAIN mutex */ + + /* This loop runs once for each entry in the blocked-connections list. */ + for(pp=&sqlite3BlockedList; *pp; /* no-op */ ){ + sqlite3 *p = *pp; + + /* Step 1. */ + if( p->pBlockingConnection==db ){ + p->pBlockingConnection = 0; + } + + /* Step 2. */ + if( p->pUnlockConnection==db ){ + assert( p->xUnlockNotify ); + if( p->xUnlockNotify!=xUnlockNotify && nArg!=0 ){ + xUnlockNotify(aArg, nArg); + nArg = 0; + } + + sqlite3BeginBenignMalloc(); + assert( aArg==aDyn || (aDyn==0 && aArg==aStatic) ); + assert( nArg<=(int)ArraySize(aStatic) || aArg==aDyn ); + if( (!aDyn && nArg==(int)ArraySize(aStatic)) + || (aDyn && nArg==(int)(sqlite3MallocSize(aDyn)/sizeof(void*))) + ){ + /* The aArg[] array needs to grow. */ + void **pNew = (void **)sqlite3Malloc(nArg*sizeof(void *)*2); + if( pNew ){ + memcpy(pNew, aArg, nArg*sizeof(void *)); + sqlite3_free(aDyn); + aDyn = aArg = pNew; + }else{ + /* This occurs when the array of context pointers that need to + ** be passed to the unlock-notify callback is larger than the + ** aStatic[] array allocated on the stack and the attempt to + ** allocate a larger array from the heap has failed. + ** + ** This is a difficult situation to handle. Returning an error + ** code to the caller is insufficient, as even if an error code + ** is returned the transaction on connection db will still be + ** closed and the unlock-notify callbacks on blocked connections + ** will go unissued. This might cause the application to wait + ** indefinitely for an unlock-notify callback that will never + ** arrive. + ** + ** Instead, invoke the unlock-notify callback with the context + ** array already accumulated. We can then clear the array and + ** begin accumulating any further context pointers without + ** requiring any dynamic allocation. This is sub-optimal because + ** it means that instead of one callback with a large array of + ** context pointers the application will receive two or more + ** callbacks with smaller arrays of context pointers, which will + ** reduce the applications ability to prioritize multiple + ** connections. But it is the best that can be done under the + ** circumstances. + */ + xUnlockNotify(aArg, nArg); + nArg = 0; + } + } + sqlite3EndBenignMalloc(); + + aArg[nArg++] = p->pUnlockArg; + xUnlockNotify = p->xUnlockNotify; + p->pUnlockConnection = 0; + p->xUnlockNotify = 0; + p->pUnlockArg = 0; + } + + /* Step 3. */ + if( p->pBlockingConnection==0 && p->pUnlockConnection==0 ){ + /* Remove connection p from the blocked connections list. */ + *pp = p->pNextBlocked; + p->pNextBlocked = 0; + }else{ + pp = &p->pNextBlocked; + } + } + + if( nArg!=0 ){ + xUnlockNotify(aArg, nArg); + } + sqlite3_free(aDyn); + leaveMutex(); /* Leave STATIC_MAIN mutex */ +} + +/* +** This is called when the database connection passed as an argument is +** being closed. The connection is removed from the blocked list. +*/ +void sqlite3ConnectionClosed(sqlite3 *db){ + sqlite3ConnectionUnlocked(db); + enterMutex(); + removeFromBlockedList(db); + checkListProperties(db); + leaveMutex(); +} +#endif |