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Add mutexes to fix a race condition in wal.c. This isn't a very good fix.

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FossilOrigin-Name: 3d159939cc2beb18c4ca0c8e9a99a75d4107e6e4
This commit is contained in:
dan
2010-04-26 10:40:52 +00:00
parent c438efd68a
commit cd11fb28c3
6 changed files with 49 additions and 31 deletions
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30
src/wal.c
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@@ -119,7 +119,12 @@ struct LogSummaryHdr {
** A 64 KB log-summary mapping corresponds to a log file containing over
** 13000 frames, so the mapping size does not need to be increased often.
*/
#define LOGSUMMARY_MMAP_INCREMENT (64*1024)
#ifdef SQLITE_TEST
int sqlite3_walsummary_mmap_incr = 128;
# define LOGSUMMARY_MMAP_INCREMENT sqlite3_walsummary_mmap_incr
#else
# define LOGSUMMARY_MMAP_INCREMENT (64*1024)
#endif
/*
** There is one instance of this structure for each log-summary object
@@ -611,9 +616,10 @@ static int logSummaryEntry(u32 iFrame){
static void logSummaryAppend(LogSummary *pSummary, u32 iFrame, u32 iPage){
u32 iSlot = logSummaryEntry(iFrame);
if( (iSlot+128)>=pSummary->nData ){
while( (iSlot+128)>=pSummary->nData ){
int nByte = pSummary->nData*4 + LOGSUMMARY_MMAP_INCREMENT;
/* Unmap and remap the log-summary file. */
sqlite3_mutex_enter(pSummary->mutex);
munmap(pSummary->aData, pSummary->nData*4);
pSummary->aData = 0;
@@ -1377,8 +1383,11 @@ int logSummaryTryHdr(Log *pLog, int *pChanged){
u32 aCksum[2] = {1, 1};
u32 aHdr[LOGSUMMARY_HDR_NFIELD+2];
/* First try to read the header without a lock. Verify the checksum
** before returning. This will almost always work.
/* Read the header. The caller may or may not have locked the log-summary
** file, meaning it is possible that an inconsistent snapshot is read
** from the file. If this happens, return SQLITE_ERROR. The caller will
** retry. Or, if the caller has already locked the file and the header
** still looks inconsistent, it will run recovery.
*/
memcpy(aHdr, pLog->pSummary->aData, sizeof(aHdr));
logChecksumBytes((u8*)aHdr, sizeof(u32)*LOGSUMMARY_HDR_NFIELD, aCksum);
@@ -1410,10 +1419,16 @@ int logSummaryReadHdr(Log *pLog, int *pChanged){
/* First try to read the header without a lock. Verify the checksum
** before returning. This will almost always work.
**
** TODO: Doing this causes a race-condition with the code that resizes
** the mapping. Unless Log.pSummary->mutex is held, it is possible that
** LogSummary.aData is invalid.
*/
#if 0
if( SQLITE_OK==logSummaryTryHdr(pLog, pChanged) ){
return SQLITE_OK;
}
#endif
/* If the first attempt to read the header failed, lock the log-summary
** file and try again. If the header checksum verification fails this
@@ -1502,11 +1517,14 @@ void sqlite3WalCloseSnapshot(Log *pLog){
*/
int sqlite3WalRead(Log *pLog, Pgno pgno, int *pInLog, u8 *pOut){
u32 iRead = 0;
u32 *aData = pLog->pSummary->aData;
u32 *aData;
int iFrame = (pLog->hdr.iLastPg & 0xFFFFFF00);
assert( pLog->isLocked );
sqlite3_mutex_enter(pLog->pSummary->mutex);
aData = pLog->pSummary->aData;
/* Do a linear search of the unindexed block of page-numbers (if any)
** at the end of the log-summary. An alternative to this would be to
** build an index in private memory each time a read transaction is
@@ -1549,6 +1567,8 @@ int sqlite3WalRead(Log *pLog, Pgno pgno, int *pInLog, u8 *pOut){
}
assert( iRead==0 || aData[logSummaryEntry(iRead)]==pgno );
sqlite3_mutex_leave(pLog->pSummary->mutex);
/* If iRead is non-zero, then it is the log frame number that contains the
** required page. Read and return data from the log file.
*/