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Allow sqlite3_snapshot_open() to be called to change the snapshot after a

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read transaction is already open on database.

FossilOrigin-Name: 051ac0152048ef52723196c26ca5f2629dafb782aec1c66fc30531bf54335043
This commit is contained in:
dan
2018-08-06 17:12:36 +00:00
parent f018fd5284
commit fa3d4c19a9
11 changed files with 343 additions and 36 deletions
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37
src/wal.c
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@@ -3769,6 +3769,43 @@ int sqlite3_snapshot_cmp(sqlite3_snapshot *p1, sqlite3_snapshot *p2){
if( pHdr1->mxFrame>pHdr2->mxFrame ) return +1;
return 0;
}
/*
** The caller currently has a read transaction open on the database.
** This function takes a SHARED lock on the CHECKPOINTER slot and then
** checks if the snapshot passed as the second argument is still
** available. If so, SQLITE_OK is returned.
**
** If the snapshot is not available, SQLITE_ERROR is returned. Or, if
** the CHECKPOINTER lock cannot be obtained, SQLITE_BUSY. If any error
** occurs (any value other than SQLITE_OK is returned), the CHECKPOINTER
** lock is released before returning.
*/
int sqlite3WalSnapshotCheck(Wal *pWal, sqlite3_snapshot *pSnapshot){
int rc;
rc = walLockShared(pWal, WAL_CKPT_LOCK);
if( rc==SQLITE_OK ){
WalIndexHdr *pNew = (WalIndexHdr*)pSnapshot;
if( memcmp(pNew->aSalt, pWal->hdr.aSalt, sizeof(pWal->hdr.aSalt))
|| pNew->mxFrame<walCkptInfo(pWal)->nBackfillAttempted
){
rc = SQLITE_BUSY_SNAPSHOT;
walUnlockShared(pWal, WAL_CKPT_LOCK);
}
}
return rc;
}
/*
** Release a lock obtained by an earlier successful call to
** sqlite3WalSnapshotCheck().
*/
void sqlite3WalSnapshotUnlock(Wal *pWal){
assert( pWal );
walUnlockShared(pWal, WAL_CKPT_LOCK);
}
#endif /* SQLITE_ENABLE_SNAPSHOT */
#ifdef SQLITE_ENABLE_ZIPVFS