At Sat, 18 Apr 2020 00:01:42 -0700, Noah Misch <n...@leadboat.com> wrote in > On Fri, Apr 17, 2020 at 05:06:29PM +0900, Kyotaro Horiguchi wrote: > > At Fri, 17 Apr 2020 17:00:15 +0900 (JST), Kyotaro Horiguchi > > <horikyota....@gmail.com> wrote in > > > By the way, if latch is consumed in WalSndLoop, succeeding call to > > > WalSndWaitForWal cannot be woke-up by the latch-set. Doesn't that > > > cause missing wakeups? (in other words, overlooking of wakeup latch). > > > > - Since the only source other than timeout of walsender wakeup is latch, > > - we should avoid wasteful consuming of latch. (It is the same issue > > - with [1]). > > > > + Since walsender is wokeup by LSN advancement via latch, we should > > + avoid wasteful consuming of latch. (It is the same issue with [1]). > > > > > > > If wakeup signal is not remembered on walsender (like > > > InterruptPending), WalSndPhysical cannot enter a sleep with > > > confidence. > > No; per latch.h, "What must be avoided is placing any checks for asynchronous > events after WaitLatch and before ResetLatch, as that creates a race > condition." In other words, the thing to avoid is calling ResetLatch() > without next examining all pending work that a latch would signal. Each > walsender.c WaitLatch call does follow the rules.
I didn't meant that, of course. I thought of more or less the same with moving the trigger from latch to signal then the handler sets a flag and SetLatch(). If we use bare latch, we should avoid false entering to sleep, which also makes thinks compolex. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
