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Documentation improvement and minor code cleanups for the latch facility.

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Improve the documentation around weak-memory-ordering risks, and do a pass
of general editorialization on the comments in the latch code.  Make the
Windows latch code more like the Unix latch code where feasible; in
particular provide the same Assert checks in both implementations.
Fix poorly-placed WaitLatch call in syncrep.c.

This patch resolves, for the moment, concerns around weak-memory-ordering
bugs in latch-related code: we have documented the restrictions and checked
that existing calls meet them.  In 9.2 I hope that we will install suitable
memory barrier instructions in SetLatch/ResetLatch, so that their callers
don't need to be quite so careful.
This commit is contained in:
Tom Lane
2011-08-09 15:30:45 -04:00
parent cff60f2dfa
commit 4e15a4db5e
5 changed files with 185 additions and 124 deletions
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2
src/backend/storage/lmgr/proc.c
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@ -332,7 +332,7 @@ InitProcess(void)
MyProc->waitLSN.xrecoff = 0;
MyProc->syncRepState = SYNC_REP_NOT_WAITING;
SHMQueueElemInit(&(MyProc->syncRepLinks));
OwnLatch((Latch *) &MyProc->waitLatch);
OwnLatch(&MyProc->waitLatch);
/*
* We might be reusing a semaphore that belonged to a failed process. So