pg_cron issues when a postgres process crashes

When postmaster reinitializes postgres processes because of the crash of one of them, pg_cron is terminated and is not subsequently restarted. The reason is that it supplies the BGW_NEVER_RESTART flag to the RegisterBackgroundWorker. I wonder why?

The other issue is that pg_cron continues to run when postmaster dies (i.e. killed by -9). The docs actually deal with that:

> Backends which need to suspend execution only temporarily should use an interruptible sleep rather than exiting; this can be achieved by calling WaitLatch(). Make sure the WL_POSTMASTER_DEATH flag is set when calling that function, and verify the return code for a prompt exit in the emergency case that postgres itself has terminated.

That's quite easy to fix:
```
$ git diff
diff --git a/src/pg_cron.c b/src/pg_cron.c
index a7e42c5..8d4ab05 100644
--- a/src/pg_cron.c
+++ b/src/pg_cron.c
@@ -152,7 +152,7 @@ _PG_init(void)
/* set up common data for all our workers */
worker.bgw_flags = BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION;
worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
- worker.bgw_restart_time = BGW_NEVER_RESTART;
+ worker.bgw_restart_time = 1;
worker.bgw_main = PgCronWorkerMain;
worker.bgw_main_arg = Int32GetDatum(0);
worker.bgw_notify_pid = 0;
@@ -544,16 +544,23 @@ ShouldRunTask(entry *schedule, TimestampTz currentTime, bool doWild,
static void
WaitForCronTasks(List *taskList)
{
+ int rc;
int taskCount = list_length(taskList);

if (taskCount > 0)
{
PollForTasks(taskList);
}
- else
+
+ /* wait for new jobs */
+ rc = WaitLatch(MyLatch,
+ WL_LATCH_SET | WL_POSTMASTER_DEATH,
+ taskCount > 0 ? 0: MaxWait, PG_WAIT_EXTENSION);
+ ResetLatch(MyLatch);
+ if (rc & WL_POSTMASTER_DEATH)
{
- /* wait for new jobs */
- pg_usleep(MaxWait*1000L);
+ /* Postmaster died and we should bail out immediately */
+ proc_exit(1);
}
}
```

I think there should be a few additional changes, namely WaitLatch should go to the main loop and the signals should SetLatch as well. What do you think?