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Add a comment to wal.c to explain why a race condition is safe.

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FossilOrigin-Name: bc33af866403c23d548dd4705675315810d52d7f
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dan
2015-04-13 17:43:43 +00:00
parent c01501a386
commit 1fe0af200d
3 changed files with 16 additions and 8 deletions
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8
src/wal.c
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@@ -1730,6 +1730,14 @@ 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. */
u32 y = pInfo->aReadMark[i];
if( mxSafeFrame>y ){
assert( y<=pWal->hdr.mxFrame );