On 03/09/10 21:16, Tom Lane wrote:
Heikki Linnakangas<heikki.linnakan...@enterprisedb.com> writes:
WaitLatch had to set the pid on the Latch struct to allow other
processes to send the signal. Another process could call SetLatch and
read the pid field, while WaitLatch is just setting it. I think we'll
have to put a spinlock there, if we can't assume that assignment of
pid_t is atomic. It's not the end of the world..
Yes it is. Signal handlers can't take spinlocks (what if they interrupt
while the mainline is holding the lock?).
Ok, I see.
It's probably not too unreasonable to assume that pid_t assignment is
atomic. But I'm still thinking that we have bigger problems than that
if there are really cases where SetLatch can execute at approximately
the same time as a latch owner is coming or going.
I don't see how to avoid it. A walsender, or any process really, can
exit at any time. It can make the latch inaccessible to others before it
exits to minimize the window, but it's always going to be possible that
another process is just about to call SetLatch when you exit.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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