Thread: pgsql: Seems I was too optimistic in supposing that sinval's maxMsgNum

Log Message:
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Seems I was too optimistic in supposing that sinval's maxMsgNum could be
read and written without a lock.  The value itself is atomic, sure, but on
processors with weak memory ordering it's possible for a reader to see the
value change before it sees the associated message written into the buffer
array.  Fix by introducing a spinlock that's used just to read and write
maxMsgNum.  (We could do this with less overhead if we recognized a concept
of "memory access barrier"; is it worth introducing such a thing?  At the
moment probably not --- I can't measure any clear slowdown from adding the
spinlock, so this solution is probably fine.)  Per buildfarm results.

Modified Files:
--------------
    pgsql/src/backend/storage/ipc:
        sinvaladt.c (r1.71 -> r1.72)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/sinvaladt.c?r1=1.71&r2=1.72)