3 files changed, 37 insertions, 3 deletions

diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c
index cd99b0b3927..42760b92bb1 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -430,6 +430,39 @@ ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
 }
 
 /*
+ * Report that the PID of a background worker is now zero because a
+ * previously-running background worker has exited.
+ *
+ * This function should only be called from the postmaster.
+ */
+void
+ReportBackgroundWorkerExit(slist_mutable_iter *cur)
+{
+	RegisteredBgWorker *rw;
+	BackgroundWorkerSlot *slot;
+
+	rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
+
+	Assert(rw->rw_shmem_slot < max_worker_processes);
+	slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
+	slot->pid = rw->rw_pid;
+
+	/*
+	 * If this worker is slated for deregistration, do that before notifying
+	 * the process which started it.  Otherwise, if that process tries to
+	 * reuse the slot immediately, it might not be available yet.  In theory
+	 * that could happen anyway if the process checks slot->pid at just the
+	 * wrong moment, but this makes the window narrower.
+	 */
+	if (rw->rw_terminate ||
+		rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
+		ForgetBackgroundWorker(cur);
+
+	if (rw->rw_worker.bgw_notify_pid != 0)
+		kill(rw->rw_worker.bgw_notify_pid, SIGUSR1);
+}
+
+/*
  * Cancel SIGUSR1 notifications for a PID belonging to an exiting backend.
  *
  * This function should only be called from the postmaster.
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 271c4920002..2cf17ac42e0 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -3050,9 +3050,9 @@ CleanupBackgroundWorker(int pid,
 						int exitstatus) /* child's exit status */
 {
 	char		namebuf[MAXPGPATH];
-	slist_iter	iter;
+	slist_mutable_iter	iter;
 
-	slist_foreach(iter, &BackgroundWorkerList)
+	slist_foreach_modify(iter, &BackgroundWorkerList)
 	{
 		RegisteredBgWorker *rw;
 
@@ -3126,7 +3126,7 @@ CleanupBackgroundWorker(int pid,
 		rw->rw_backend = NULL;
 		rw->rw_pid = 0;
 		rw->rw_child_slot = 0;
-		ReportBackgroundWorkerPID(rw);	/* report child death */
+		ReportBackgroundWorkerExit(&iter);	/* report child death */
 
 		LogChildExit(EXIT_STATUS_0(exitstatus) ? DEBUG1 : LOG,
 					 namebuf, pid, exitstatus);
diff --git a/src/include/postmaster/bgworker_internals.h b/src/include/postmaster/bgworker_internals.h
index 4c94b815b12..9a2de4f4d04 100644
--- a/src/include/postmaster/bgworker_internals.h
+++ b/src/include/postmaster/bgworker_internals.h
@@ -42,6 +42,7 @@ extern void BackgroundWorkerShmemInit(void);
 extern void BackgroundWorkerStateChange(void);
 extern void ForgetBackgroundWorker(slist_mutable_iter *cur);
 extern void ReportBackgroundWorkerPID(RegisteredBgWorker *);
+extern void ReportBackgroundWorkerExit(slist_mutable_iter *cur);
 extern void BackgroundWorkerStopNotifications(pid_t pid);
 extern void ResetBackgroundWorkerCrashTimes(void);