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Add further test cases for the logic in sqlite3WalBeginReadTransaction().

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FossilOrigin-Name: a49713db39d0d6940b368206d4e669aa69aa1fe5
This commit is contained in:
dan
2010-06-05 19:18:59 +00:00
parent eb8cb3a851
commit 640aac48f3
4 changed files with 86 additions and 15 deletions
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10
src/wal.c
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@@ -1747,7 +1747,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
rc = walLockShared(pWal, WAL_READ_LOCK(0));
sqlite3OsShmBarrier(pWal->pDbFd);
if( rc==SQLITE_OK ){
if( memcmp(pHdr, &pWal->hdr, sizeof(WalIndexHdr)) ){
if( memcmp((void *)pHdr, &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,
@@ -1832,15 +1832,15 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
** instead.
**
** This does not guarantee that the copy wal-index header is up to
** date before proceeding. This would not be possible without somehow
** blocking writers. It only guarantees that a damaging checkpoint or
** This does not guarantee that the copy of the wal-index header is up to
** date before proceeding. That would not be possible without somehow
** blocking writers. It only guarantees that a dangerous checkpoint or
** log-wrap (either of which would require an exclusive lock on
** WAL_READ_LOCK(mxI)) has not occurred since the snapshot was valid.
*/
sqlite3OsShmBarrier(pWal->pDbFd);
if( pInfo->aReadMark[mxI]!=mxReadMark
|| memcmp(pHdr, &pWal->hdr, sizeof(WalIndexHdr))
|| memcmp((void *)pHdr, &pWal->hdr, sizeof(WalIndexHdr))
){
walUnlockShared(pWal, WAL_READ_LOCK(mxI));
return WAL_RETRY;