Allow condition variables to be used in interrupt code.

macdice · macdice · commit f5a5773a9dc4 · 2021-03-01T17:24:47.000+13:00
Adjust the condition variable sleep loop to work correctly when code reached by its internal CHECK_FOR_INTERRUPTS() call interacts with another condition variable. There are no such cases currently, but a proposed patch would do this. Discussion: https://postgr.es/m/CA+hUKGLdemy2gBm80kz20GTe6hNVwoErE8KwcJk6-U56oStjtg@mail.gmail.com
diff --git a/src/backend/storage/lmgr/condition_variable.c b/src/backend/storage/lmgr/condition_variable.c
@@ -165,8 +165,6 @@ ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
 		/* Reset latch before examining the state of the wait list. */
 		ResetLatch(MyLatch);
 
-		CHECK_FOR_INTERRUPTS();
-
 		/*
 		 * If this process has been taken out of the wait list, then we know
 		 * that it has been signaled by ConditionVariableSignal (or
@@ -190,6 +188,15 @@ ConditionVariableTimedSleep(ConditionVariable *cv, long timeout,
 		}
 		SpinLockRelease(&cv->mutex);
 
+		/*
+		 * Check for interrupts, and return spuriously if that caused the
+		 * current sleep target to change (meaning that interrupt handler code
+		 * waited for a different condition variable).
+		 */
+		CHECK_FOR_INTERRUPTS();
+		if (cv != cv_sleep_target)
+			done = true;
+
 		/* We were signaled, so return */
 		if (done)
 			return false;
