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Overview
| Comment: | Add a comment to wal.c to explain why a race condition is safe. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
bc33af866403c23d548dd47056753158 |
| User & Date: | dan 2015-04-13 17:43:43 |
Context
|
2015-04-13
| ||
| 19:14 | Remove the out2-prerelease VDBE opcode property and its associated code, for a 0.5% performance improvement. (check-in: e29c7f2c user: drh tags: trunk) | |
| 17:43 | Add a comment to wal.c to explain why a race condition is safe. (check-in: bc33af86 user: dan tags: trunk) | |
| 14:44 | Remove a faulty assert() from the btree balancing logic. (check-in: d06669d9 user: drh tags: trunk) | |
Changes
Changes to src/wal.c.
1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 |
** safe to write into the database. Frames beyond mxSafeFrame might
** overwrite database pages that are in use by active readers and thus
** cannot be backfilled from the WAL.
*/
mxSafeFrame = pWal->hdr.mxFrame;
mxPage = pWal->hdr.nPage;
for(i=1; i<WAL_NREADER; i++){
u32 y = 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);
walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
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> > > > > > > > |
1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 |
** safe to write into the database. Frames beyond mxSafeFrame might
** overwrite database pages that are in use by active readers and thus
** cannot be backfilled from the WAL.
*/
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. */
u32 y = 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);
walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
|