On 2020/11/05 5:36, Heikki Linnakangas wrote:
On 04/11/2020 15:17, Heikki Linnakangas wrote:
On 04/11/2020 14:03, Fujii Masao wrote:
Or ISTM that WakeupRecovery() should set the latch only when the latch
has not been reset to NULL yet.
Got to be careful with race conditions, if the latch is set to NULL at
the same time that WakeupRecovery() is called.
I don't think commit 113d3591b8 got this quite right:
void
WakeupRecovery(void)
{
if (XLogCtl->recoveryWakeupLatch)
SetLatch(XLogCtl->recoveryWakeupLatch);
}
If XLogCtl->recoveryWakeupLatch is set to NULL between the if and the SetLatch,
you'll still get a segfault. That's highly unlikely to happen in practice because
the compiler will optimize that into a single load instruction, but could happen
with -O0. I think you'd need to do the access only once, using a volatile pointer,
to make that safe. Maybe it's simpler to just not reset it to NULL, after all.
Yes, you're right. I agree it's simpler to remove the code resetting
the latch to NULL. Also as the comment for that code explains,
basically it's not necessary to reset it to NULL.
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
