On Thu, Dec 15, 2016 at 4:17 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: > On Thu, Dec 15, 2016 at 10:04 AM, Andres Freund <and...@anarazel.de> wrote: >> Hi, >> >> On 2016-12-12 16:46:38 +0900, Michael Paquier wrote: >>> Ashutosh, could you try it and see if it improves things? >> >> So what's the theory of why this triggers pldebugger hangs, but >> apparently causes not many other problems? >> > > The theory is that with pldebugger latch event gets triggered before > FD_READ due to which it seems like the second event gets lost and > WaitForMultipleObjects() keeps on waiting indefinitely. The probable > reason is that we fail to reset the event due to which we are seeing > this behavior. That seems to be required as per msdn as well, as > pointed by Robert upthread. > > Find attached patch to implement the resetting of event only for the > required case. This fixes the reported problem.
After some study I don't think this is quite right yet. The client code is not obliged to call ModifyWaitEvent() before again calling WaitEventSetWait(). I think it should be the responsibility of WaitEventSetWaitBlock() to reset the event, if needed, before calling WaitForMultipleObjects(). BTW, I suggest this rewritten comment: /*------ * FD_READ events are edge-triggered on Windows per * https://msdn.microsoft.com/en-us/library/windows/desktop/ms741576(v=vs.85).aspx * but users of the latch facility are entitled to expect * level-triggered behavior. Indeed, this function itself * expects level-triggered behavior, since it doesn't guarantee * that a read event will be returned if the latch is set at the * same time. Even if it did, the caller might drop that event * expecting it to reoccur on next call. So, we must force * the event to be reset if this WaitEventSet is used again in * order to avoid an indefinite hang. *------ */ The dashes keep pgindent from inserting a line break into the link. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers