From bf740ce9e5d82612889d131f34c079215973ca00 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Thu, 19 Mar 2015 10:56:34 -0400 Subject: [PATCH] Fix status reporting for terminated bgworkers that were never started. Previously, GetBackgroundWorkerPid() would return BGWH_NOT_YET_STARTED if the slot used for the worker registration had not been reused by unrelated activity, and BGWH_STOPPED if it had. Either way, a process that had requested notification when the state of one of its background workers changed did not receive such notifications. Fix things so that GetBackgroundWorkerPid() always returns BGWH_STOPPED in this situation, so that we do not erroneously give waiters the impression that the worker will eventually be started; and send notifications just as we would if the process terminated after having been started, so that it's possible to wait for the postmaster to process a worker termination request without polling. Discovered by Amit Kapila during testing of parallel sequential scan. Analysis and fix by me. Back-patch to 9.4; there may not be anyone relying on this interface yet, but if anyone is, the new behavior is a clear improvement. --- src/backend/postmaster/bgworker.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c index 267b916327..cf7524f492 100644 --- a/src/backend/postmaster/bgworker.c +++ b/src/backend/postmaster/bgworker.c @@ -244,14 +244,37 @@ BackgroundWorkerStateChange(void) rw->rw_terminate = true; if (rw->rw_pid != 0) kill(rw->rw_pid, SIGTERM); + else + { + /* Report never-started, now-terminated worker as dead. */ + ReportBackgroundWorkerPID(rw); + } } continue; } - /* If it's already flagged as do not restart, just release the slot. */ + /* + * If the worker is marked for termination, we don't need to add it + * to the registered workers list; we can just free the slot. + * However, if bgw_notify_pid is set, the process that registered the + * worker may need to know that we've processed the terminate request, + * so be sure to signal it. + */ if (slot->terminate) { + int notify_pid; + + /* + * We need a memory barrier here to make sure that the load of + * bgw_notify_pid completes before the store to in_use. + */ + notify_pid = slot->worker.bgw_notify_pid; + pg_memory_barrier(); + slot->pid = 0; slot->in_use = false; + if (notify_pid != 0) + kill(notify_pid, SIGUSR1); + continue; } -- 2.40.0