Setup SIGUSR1 procsignal_sigusr1_handler handler.

This is normally automatically done when a bgworker declares the
BGWORKER_BACKEND_DATABASE_CONNECTION flag, but our bgworker doesn't connect to
databases, even though it calls InitPostgres, which will still initialize a new
bacckend and thus participate to the ProcSignal infrastructure.

This wasn't a problem until recently, but now that DROP DATABASE relies on
PROCSIG_BARRIER to work on Windows (see commit
4eb2176318d0561846c1f9fb3c68bede799d640f) we need to respond to ProcSignal
notifications.

Author: rjuju

collector.c

@@ -339,8 +339,16 @@ collector_main(Datum main_arg)
 	 * any equivalent of the backend's command-read loop, where interrupts can
 	 * be processed immediately, so make sure ImmediateInterruptOK is turned
 	 * off.
+	 *
+	 * We also want to respond to the ProcSignal notifications.  This is done
+	 * in the upstream provided procsignal_sigusr1_handler, which is
+	 * automatically used if a bgworker connects to a database.  But since our
+	 * worker doesn't connect to any database even though it calls
+	 * InitPostgres, which will still initializze a new backend and thus
+	 * partitipate to the ProcSignal infrastructure.
 	 */
 	pqsignal(SIGTERM, handle_sigterm);
+	pqsignal(SIGUSR1, procsignal_sigusr1_handler);
 	BackgroundWorkerUnblockSignals();
 
 #if PG_VERSION_NUM >= 110000
@@ -379,6 +387,9 @@ collector_main(Datum main_arg)
 		bool			write_history,
 						write_profile;
 
+		/* We need an explicit call for at least ProcSignal notifications. */
+		CHECK_FOR_INTERRUPTS();
+
 		/* Wait calculate time to next sample for history or profile */
 		current_ts = GetCurrentTimestamp();