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Use a long lived WaitEventSet for WaitLatch().
Create LatchWaitSet at backend startup time, and use it to implement WaitLatch(). This avoids repeated epoll/kqueue setup and teardown system calls. Reorder SubPostmasterMain() slightly so that we restore the postmaster pipe and Windows signal emulation before we reach InitPostmasterChild(), to make this work in EXEC_BACKEND builds. Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> Discussion: https://postgr.es/m/CA%2BhUKGJAC4Oqao%3DqforhNey20J8CiG2R%3DoBPqvfR0vOJrFysGw%40mail.gmail.com
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@ -56,6 +56,7 @@
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#include "storage/latch.h"
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#include "storage/pmsignal.h"
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#include "storage/shmem.h"
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#include "utils/memutils.h"
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/*
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* Select the fd readiness primitive to use. Normally the "most modern"
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@ -129,6 +130,12 @@ struct WaitEventSet
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#endif
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};
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/* A common WaitEventSet used to implement WatchLatch() */
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static WaitEventSet *LatchWaitSet;
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/* The position of the latch in LatchWaitSet. */
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#define LatchWaitSetLatchPos 0
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#ifndef WIN32
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/* Are we currently in WaitLatch? The signal handler would like to know. */
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static volatile sig_atomic_t waiting = false;
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@ -242,6 +249,24 @@ InitializeLatchSupport(void)
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#endif
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}
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void
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InitializeLatchWaitSet(void)
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{
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int latch_pos PG_USED_FOR_ASSERTS_ONLY;
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Assert(LatchWaitSet == NULL);
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/* Set up the WaitEventSet used by WaitLatch(). */
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LatchWaitSet = CreateWaitEventSet(TopMemoryContext, 2);
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latch_pos = AddWaitEventToSet(LatchWaitSet, WL_LATCH_SET, PGINVALID_SOCKET,
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MyLatch, NULL);
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if (IsUnderPostmaster)
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AddWaitEventToSet(LatchWaitSet, WL_EXIT_ON_PM_DEATH,
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PGINVALID_SOCKET, NULL, NULL);
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Assert(latch_pos == LatchWaitSetLatchPos);
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}
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/*
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* Initialize a process-local latch.
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*/
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@ -365,8 +390,31 @@ int
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WaitLatch(Latch *latch, int wakeEvents, long timeout,
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uint32 wait_event_info)
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{
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return WaitLatchOrSocket(latch, wakeEvents, PGINVALID_SOCKET, timeout,
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wait_event_info);
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WaitEvent event;
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/* Postmaster-managed callers must handle postmaster death somehow. */
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Assert(!IsUnderPostmaster ||
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(wakeEvents & WL_EXIT_ON_PM_DEATH) ||
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(wakeEvents & WL_POSTMASTER_DEATH));
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/*
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* Some callers may have a latch other than MyLatch, or no latch at all,
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* or want to handle postmaster death differently. It's cheap to assign
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* those, so just do it every time.
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*/
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if (!(wakeEvents & WL_LATCH_SET))
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latch = NULL;
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ModifyWaitEvent(LatchWaitSet, LatchWaitSetLatchPos, WL_LATCH_SET, latch);
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LatchWaitSet->exit_on_postmaster_death =
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((wakeEvents & WL_EXIT_ON_PM_DEATH) != 0);
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if (WaitEventSetWait(LatchWaitSet,
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(wakeEvents & WL_TIMEOUT) ? timeout : -1,
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&event, 1,
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wait_event_info) == 0)
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return WL_TIMEOUT;
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else
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return event.events;
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}
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/*
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@ -830,7 +878,8 @@ AddWaitEventToSet(WaitEventSet *set, uint32 events, pgsocket fd, Latch *latch,
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/*
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* Change the event mask and, in the WL_LATCH_SET case, the latch associated
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* with the WaitEvent.
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* with the WaitEvent. The latch may be changed to NULL to disable the latch
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* temporarily, and then set back to a latch later.
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*
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* 'pos' is the id returned by AddWaitEventToSet.
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*/
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@ -862,7 +911,6 @@ ModifyWaitEvent(WaitEventSet *set, int pos, uint32 events, Latch *latch)
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if (event->events & WL_LATCH_SET &&
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events != event->events)
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{
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/* we could allow to disable latch events for a while */
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elog(ERROR, "cannot modify latch event");
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}
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