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Use WaitLatch() for condition variables.

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Previously, condition_variable.c created a long lived WaitEventSet to
avoid extra system calls.  WaitLatch() now uses something similar
internally, so there is no point in wasting an extra kernel descriptor.

Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGJAC4Oqao%3DqforhNey20J8CiG2R%3DoBPqvfR0vOJrFysGw%40mail.gmail.com
This commit is contained in:
Thomas Munro 2020-07-30 17:23:32 +12:00
parent 3347c982ba
commit e2d394df5d
1 changed files with 5 additions and 23 deletions
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28
src/backend/storage/lmgr/condition_variable.c
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@ -30,9 +30,6 @@
/* Initially, we are not prepared to sleep on any condition variable. */ /* Initially, we are not prepared to sleep on any condition variable. */
static ConditionVariable *cv_sleep_target = NULL; static ConditionVariable *cv_sleep_target = NULL;
/* Reusable WaitEventSet. */
static WaitEventSet *cv_wait_event_set = NULL;
/* /*
* Initialize a condition variable. * Initialize a condition variable.
*/ */
@ -62,23 +59,6 @@ ConditionVariablePrepareToSleep(ConditionVariable *cv)
{ {
int pgprocno = MyProc->pgprocno; int pgprocno = MyProc->pgprocno;
/*
* If first time through in this process, create a WaitEventSet, which
* we'll reuse for all condition variable sleeps.
*/
if (cv_wait_event_set == NULL)
{
WaitEventSet *new_event_set;
new_event_set = CreateWaitEventSet(TopMemoryContext, 2);
AddWaitEventToSet(new_event_set, WL_LATCH_SET, PGINVALID_SOCKET,
MyLatch, NULL);
AddWaitEventToSet(new_event_set, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
NULL, NULL);
/* Don't set cv_wait_event_set until we have a correct WES. */
cv_wait_event_set = new_event_set;
}
/* /*
* If some other sleep is already prepared, cancel it; this is necessary * If some other sleep is already prepared, cancel it; this is necessary
* because we have just one static variable tracking the prepared sleep, * because we have just one static variable tracking the prepared sleep,
@ -135,6 +115,7 @@ ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
long cur_timeout = -1; long cur_timeout = -1;
instr_time start_time; instr_time start_time;
instr_time cur_time; instr_time cur_time;
int wait_events;
/* /*
* If the caller didn't prepare to sleep explicitly, then do so now and * If the caller didn't prepare to sleep explicitly, then do so now and
@ -166,19 +147,20 @@ ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
INSTR_TIME_SET_CURRENT(start_time); INSTR_TIME_SET_CURRENT(start_time);
Assert(timeout >= 0 && timeout <= INT_MAX); Assert(timeout >= 0 && timeout <= INT_MAX);
cur_timeout = timeout; cur_timeout = timeout;
wait_events = WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH;
} }
else
wait_events = WL_LATCH_SET | WL_EXIT_ON_PM_DEATH;
while (true) while (true)
{ {
WaitEvent event;
bool done = false; bool done = false;
/* /*
* Wait for latch to be set. (If we're awakened for some other * Wait for latch to be set. (If we're awakened for some other
* reason, the code below will cope anyway.) * reason, the code below will cope anyway.)
*/ */
(void) WaitEventSetWait(cv_wait_event_set, cur_timeout, &event, 1, (void) WaitLatch(MyLatch, wait_events, cur_timeout, wait_event_info);
wait_event_info);
/* Reset latch before examining the state of the wait list. */ /* Reset latch before examining the state of the wait list. */
ResetLatch(MyLatch); ResetLatch(MyLatch);