diff options
Diffstat (limited to 'src/wal.c')
| -rw-r--r-- | src/wal.c | 418 |
1 files changed, 270 insertions, 148 deletions
@@ -467,6 +467,9 @@ struct Wal { #ifdef SQLITE_ENABLE_SNAPSHOT WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */ #endif +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT + sqlite3 *db; +#endif }; /* @@ -565,7 +568,7 @@ static SQLITE_NOINLINE int walIndexPageRealloc( if( pWal->nWiData<=iPage ){ sqlite3_int64 nByte = sizeof(u32*)*(iPage+1); volatile u32 **apNew; - apNew = (volatile u32 **)sqlite3_realloc64((void *)pWal->apWiData, nByte); + apNew = (volatile u32 **)sqlite3Realloc((void *)pWal->apWiData, nByte); if( !apNew ){ *ppPage = 0; return SQLITE_NOMEM_BKPT; @@ -686,6 +689,10 @@ static void walChecksumBytes( 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); @@ -693,11 +700,24 @@ static void walShmBarrier(Wal *pWal){ } /* +** 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 void walIndexWriteHdr(Wal *pWal){ +static SQLITE_NO_TSAN void walIndexWriteHdr(Wal *pWal){ volatile WalIndexHdr *aHdr = walIndexHdr(pWal); const int nCksum = offsetof(WalIndexHdr, aCksum); @@ -705,6 +725,7 @@ static void walIndexWriteHdr(Wal *pWal){ 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)); @@ -840,7 +861,7 @@ static int walLockShared(Wal *pWal, int lockIdx){ 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!=SQLITE_BUSY); ) + VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); ) return rc; } static void walUnlockShared(Wal *pWal, int lockIdx){ @@ -856,7 +877,7 @@ static int walLockExclusive(Wal *pWal, int lockIdx, int 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!=SQLITE_BUSY); ) + VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && (rc&0xFF)!=SQLITE_BUSY); ) return rc; } static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){ @@ -1075,7 +1096,7 @@ static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){ if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT; } sLoc.aPgno[idx] = iPage; - sLoc.aHash[iKey] = (ht_slot)idx; + AtomicStore(&sLoc.aHash[iKey], (ht_slot)idx); #ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT /* Verify that the number of entries in the hash table exactly equals @@ -1128,11 +1149,6 @@ static int walIndexRecover(Wal *pWal){ u32 aFrameCksum[2] = {0, 0}; int iLock; /* Lock offset to lock for checkpoint */ -#ifdef SQLITE_ENABLE_SETLK_TIMEOUT - int tmout = 0; - sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout); -#endif - /* 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. @@ -1681,6 +1697,89 @@ static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){ return rc; } +#ifdef SQLITE_ENABLE_SETLK_TIMEOUT +/* +** 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 ){ + int rc; + rc = sqlite3OsFileControl( + pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout + ); + res = (rc==SQLITE_OK); + } + } + 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; +} + +/* +** Take an exclusive WRITE lock. Blocking if so configured. +*/ +static int walLockWriter(Wal *pWal){ + int rc; + walEnableBlocking(pWal); + rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1); + walDisableBlocking(pWal); + return rc; +} +#else +# define walEnableBlocking(x) 0 +# define walDisableBlocking(x) +# define walLockWriter(pWal) walLockExclusive((pWal), WAL_WRITE_LOCK, 1) +# 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 @@ -1698,6 +1797,12 @@ static int walBusyLock( 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; } @@ -1735,7 +1840,7 @@ static void walRestartHdr(Wal *pWal, u32 salt1){ sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0])); memcpy(&pWal->hdr.aSalt[1], &salt1, 4); walIndexWriteHdr(pWal); - pInfo->nBackfill = 0; + AtomicStore(&pInfo->nBackfill, 0); pInfo->nBackfillAttempted = 0; pInfo->aReadMark[1] = 0; for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED; @@ -1810,32 +1915,13 @@ static int walCheckpoint( mxSafeFrame = pWal->hdr.mxFrame; mxPage = pWal->hdr.nPage; for(i=1; i<WAL_NREADER; i++){ - /* Thread-sanitizer reports that the following is an unsafe read, - ** as some other thread may be in the process of updating the value - ** of the aReadMark[] slot. The assumption here is that if that is - ** happening, the other client may only be increasing the value, - ** not decreasing it. So assuming either that either the "old" or - ** "new" version of the value is read, and not some arbitrary value - ** that would never be written by a real client, things are still - ** safe. - ** - ** Astute readers have pointed out that the assumption stated in the - ** last sentence of the previous paragraph is not guaranteed to be - ** true for all conforming systems. However, the assumption is true - ** for all compilers and architectures in common use today (circa - ** 2019-11-27) and the alternatives are both slow and complex, and - ** so we will continue to go with the current design for now. If this - ** bothers you, or if you really are running on a system where aligned - ** 32-bit reads and writes are not atomic, then you can simply avoid - ** the use of WAL mode, or only use WAL mode together with - ** PRAGMA locking_mode=EXCLUSIVE and all will be well. - */ - u32 y = pInfo->aReadMark[i]; + u32 y = AtomicLoad(pInfo->aReadMark+i); if( mxSafeFrame>y ){ assert( y<=pWal->hdr.mxFrame ); rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1); if( rc==SQLITE_OK ){ - pInfo->aReadMark[i] = (i==1 ? mxSafeFrame : READMARK_NOT_USED); + u32 iMark = (i==1 ? mxSafeFrame : READMARK_NOT_USED); + AtomicStore(pInfo->aReadMark+i, iMark); walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); }else if( rc==SQLITE_BUSY ){ mxSafeFrame = y; @@ -1853,7 +1939,7 @@ static int walCheckpoint( } if( pIter - && (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0),1))==SQLITE_OK + && (rc = walBusyLock(pWal,xBusy,pBusyArg,WAL_READ_LOCK(0),1))==SQLITE_OK ){ u32 nBackfill = pInfo->nBackfill; @@ -1868,6 +1954,7 @@ static int walCheckpoint( 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 ){ sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq); @@ -1895,6 +1982,7 @@ static int walCheckpoint( 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 ){ @@ -1907,11 +1995,7 @@ static int walCheckpoint( } } if( rc==SQLITE_OK ){ - rc = sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_CKPT_DONE, 0); - if( rc==SQLITE_NOTFOUND ) rc = SQLITE_OK; - } - if( rc==SQLITE_OK ){ - pInfo->nBackfill = mxSafeFrame; + AtomicStore(&pInfo->nBackfill, mxSafeFrame); } } @@ -2070,7 +2154,7 @@ int sqlite3WalClose( ** If the checksum cannot be verified return non-zero. If the header ** is read successfully and the checksum verified, return zero. */ -static int walIndexTryHdr(Wal *pWal, int *pChanged){ +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 */ @@ -2083,13 +2167,19 @@ static int walIndexTryHdr(Wal *pWal, int *pChanged){ ** 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. + ** 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 implementions work + ** reliably in that environment. */ aHdr = walIndexHdr(pWal); - memcpy(&h1, (void *)&aHdr[0], sizeof(h1)); + memcpy(&h1, (void *)&aHdr[0], sizeof(h1)); /* Possible TSAN false-positive */ walShmBarrier(pWal); memcpy(&h2, (void *)&aHdr[1], sizeof(h2)); @@ -2179,28 +2269,32 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){ /* If the first attempt failed, it might have been due to a race ** with a writer. So get a WRITE lock and try again. */ - assert( badHdr==0 || pWal->writeLock==0 ); 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 if( 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. - */ - rc = walIndexRecover(pWal); - *pChanged = 1; + }else{ + int bWriteLock = pWal->writeLock; + if( bWriteLock || SQLITE_OK==(rc = walLockWriter(pWal)) ){ + 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. + */ + rc = walIndexRecover(pWal); + *pChanged = 1; + } + } + if( bWriteLock==0 ){ + pWal->writeLock = 0; + walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); } } - pWal->writeLock = 0; - walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1); } } @@ -2530,7 +2624,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){ assert( pWal->nWiData>0 ); assert( pWal->apWiData[0]!=0 ); pInfo = walCkptInfo(pWal); - if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame + if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame #ifdef SQLITE_ENABLE_SNAPSHOT && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0) #endif @@ -2697,7 +2791,7 @@ int sqlite3WalSnapshotRecover(Wal *pWal){ rc = SQLITE_NOMEM; }else{ u32 i = pInfo->nBackfillAttempted; - for(i=pInfo->nBackfillAttempted; i>pInfo->nBackfill; i--){ + 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 */ @@ -2752,22 +2846,36 @@ int sqlite3WalSnapshotRecover(Wal *pWal){ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){ int rc; /* Return code */ int cnt = 0; /* Number of TryBeginRead attempts */ -#ifdef SQLITE_ENABLE_SETLK_TIMEOUT - int tmout = 0; -#endif - #ifdef SQLITE_ENABLE_SNAPSHOT int bChanged = 0; WalIndexHdr *pSnapshot = pWal->pSnapshot; - if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){ - bChanged = 1; - } #endif -#ifdef SQLITE_ENABLE_SETLK_TIMEOUT - /* Disable blocking locks. They are not useful when trying to open a - ** read-transaction, and blocking may cause deadlock anyway. */ - sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout); + assert( pWal->ckptLock==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; + } + pWal->ckptLock = 1; + } #endif do{ @@ -2778,16 +2886,6 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){ testcase( rc==SQLITE_PROTOCOL ); testcase( rc==SQLITE_OK ); -#ifdef SQLITE_ENABLE_SETLK_TIMEOUT - /* If they were disabled earlier and the read-transaction has been - ** successfully opened, re-enable blocking locks. This is because the - ** connection may attempt to upgrade to a write-transaction, which does - ** benefit from using blocking locks. */ - if( rc==SQLITE_OK ){ - sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_LOCK_TIMEOUT, (void*)&tmout); - } -#endif - #ifdef SQLITE_ENABLE_SNAPSHOT if( rc==SQLITE_OK ){ if( pSnapshot && memcmp(pSnapshot, &pWal->hdr, sizeof(WalIndexHdr))!=0 ){ @@ -2809,48 +2907,42 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){ assert( pWal->readLock>0 || pWal->hdr.mxFrame==0 ); assert( pInfo->aReadMark[pWal->readLock]<=pSnapshot->mxFrame ); - /* 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. - ** - ** TODO: Does the aReadMark[] lock prevent a checkpointer from doing - ** this already? - */ - rc = walLockShared(pWal, WAL_CKPT_LOCK); - - if( rc==SQLITE_OK ){ - /* 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; - } - - /* Release the shared CKPT lock obtained above. */ - walUnlockShared(pWal, WAL_CKPT_LOCK); - pWal->minFrame = 1; + /* 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( pWal->ckptLock ){ + assert( pSnapshot ); + walUnlockShared(pWal, WAL_CKPT_LOCK); + pWal->ckptLock = 0; + } #endif return rc; } @@ -2930,14 +3022,15 @@ int sqlite3WalFindFrame( 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; - for(iKey=walHash(pgno); sLoc.aHash[iKey]; iKey=walNextHash(iKey)){ - u32 iH = sLoc.aHash[iKey]; + iKey = walHash(pgno); + while( (iH = AtomicLoad(&sLoc.aHash[iKey]))!=0 ){ u32 iFrame = iH + sLoc.iZero; if( iFrame<=iLast && iFrame>=pWal->minFrame && sLoc.aPgno[iH]==pgno ){ assert( iFrame>iRead || CORRUPT_DB ); @@ -2946,6 +3039,7 @@ int sqlite3WalFindFrame( if( (nCollide--)==0 ){ return SQLITE_CORRUPT_BKPT; } + iKey = walNextHash(iKey); } if( iRead ) break; } @@ -3021,6 +3115,16 @@ Pgno sqlite3WalDbsize(Wal *pWal){ 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 ); @@ -3597,45 +3701,52 @@ int sqlite3WalCheckpoint( if( pWal->readOnly ) return SQLITE_READONLY; WALTRACE(("WAL%p: checkpoint begins\n", pWal)); + /* Enable blocking locks, if possible. If blocking locks are successfully + ** enabled, set xBusy2=0 so that the busy-handler is never invoked. */ + sqlite3WalDb(pWal, db); + (void)walEnableBlocking(pWal); + /* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive - ** "checkpoint" lock on the database file. */ + ** "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); - if( rc ){ - /* 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. - */ - testcase( rc==SQLITE_BUSY ); - testcase( xBusy!=0 ); - return rc; - } - pWal->ckptLock = 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, xBusy, 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; + /* 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. */ if( rc==SQLITE_OK ){ + walDisableBlocking(pWal); rc = walIndexReadHdr(pWal, &isChanged); + (void)walEnableBlocking(pWal); if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){ sqlite3OsUnfetch(pWal->pDbFd, 0, 0); } @@ -3667,11 +3778,19 @@ int sqlite3WalCheckpoint( memset(&pWal->hdr, 0, sizeof(WalIndexHdr)); } + walDisableBlocking(pWal); + sqlite3WalDb(pWal, 0); + /* Release the locks. */ sqlite3WalEndWriteTransaction(pWal); - walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1); - pWal->ckptLock = 0; + 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); } @@ -3788,7 +3907,10 @@ int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot){ /* Try to open on pSnapshot when the next read-transaction starts */ -void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot){ +void sqlite3WalSnapshotOpen( + Wal *pWal, + sqlite3_snapshot *pSnapshot +){ pWal->pSnapshot = (WalIndexHdr*)pSnapshot; } |