Fix kqueue support under debugger on macOS.

macdice · macdice · commit 7bc84a1f304a · 2020-03-18T13:05:07.000+13:00
While running under a debugger, macOS's getppid() can return the debugger's PID. That could cause a backend to exit because it falsely believed that the postmaster had died, since commit 815c2f0. Continue to use getppid() as a fast postmaster check after adding the postmaster's PID to a kqueue, to close a PID-reuse race, but double check that it actually exited by trying to read the pipe. The new check isn't reached in the common case. Reported-by: Alexander Korotkov <a.korotkov@postgrespro.ru> Discussion: https://postgr.es/m/CA%2BhUKGKhAxJ8V8RVwCo6zJaeVrdOG1kFBHGZOOjf6DzW_omeMA%40mail.gmail.com
diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
@@ -1094,8 +1094,17 @@ WaitEventAdjustKqueue(WaitEventSet *set, WaitEvent *event, int old_events)
 					 errmsg("%s failed: %m",
 							"kevent()")));
 	}
-	else if (event->events == WL_POSTMASTER_DEATH && PostmasterPid != getppid())
+	else if (event->events == WL_POSTMASTER_DEATH &&
+			 PostmasterPid != getppid() &&
+			 !PostmasterIsAlive())
+	{
+		/*
+		 * The extra PostmasterIsAliveInternal() check prevents false alarms on
+		 * systems that give a different value for getppid() while being traced
+		 * by a debugger.
+		 */
 		set->report_postmaster_not_running = true;
+	}
 }
 
 #endif
