On Thu, Nov 7, 2019 at 10:46 AM Pavel Stehule <pavel.stehule@gmail.com> wrote: > > čt 7. 11. 2019 v 3:42 odesílatel Amit Kapila <amit.kapila16@gmail.com> napsal: >> >> On Wed, Nov 6, 2019 at 11:46 PM Pavel Stehule <pavel.stehule@gmail.com> wrote: >> > >> > st 6. 11. 2019 v 14:59 odesílatel Tom Lane <tgl@sss.pgh.pa.us> napsal: >> >> >> >> Amit Kapila <amit.kapila16@gmail.com> writes: >> >> > I think there is still a window where the same problem can happen, say >> >> > the signal has been sent by SendProcSignal to the required process and >> >> > it releases the ProcArrayLock. Now, the target process exits and a >> >> > new process gets the same pid before the signal is received. >> >> >> >> In principle, no use of Unix signals is ever safe against this sort >> >> of race condition --- process A can never know that process B didn't >> >> exit immediately before A does kill(B, n). In practice, it's okay >> >> because the kernel is expected not to reassign a dead PID for some >> >> reasonable grace period [1]. I'd be inclined to lean more heavily >> >> on that expectation than anything internal to Postgres. That is, >> >> remembering the PID we want to kill for some small number of >> >> microseconds is probably a safer API than anything that depends on >> >> the contents of the ProcArray, because there indeed *isn't* any >> >> guarantee that a ProcArray entry won't be recycled immediately. >> >> >> >> Right, this makes sense. I think I was overly paranoid about this >> behavior even though that was used at a few other places as this patch >> might need to rely on many pids not being reused after the lock is >> released. >> >> > >> > >> > so we can return back to just simple killing. >> > >> >> I think so. I think we might want to add a comment about this race >> condition and add or reference to comments in pg_signal_backend which >> mentions the same race condition. > > > Please, can you do it. It's bad task for my with my bad English. >
Okay, no problem. I will pick the previous version and do this. I will post the patch in a day or so for your review.
