Comments for patch for CORE-2993

src/jrd/jrd.cpp

@@ -4104,6 +4104,11 @@ void JRD_print_procedure_info(thread_db* tdbb, const char* mesg)
 		dbb->dbb_ast_flags &= ~DBB_monitor_off;
 		LCK_lock(tdbb, dbb->dbb_monitor_lock, LCK_SR, LCK_WAIT);
 
+		// While waiting for return from LCK_lock call above the blocking AST (see 
+		// DatabaseSnapshot::blockingAst) was called and set DBB_monitor_off flag 
+		// again. But it not released lock as lck_id was unknown at that moment. 
+		// Do it now to not block another process waiting for a monitoring lock.
+
 		if (dbb->dbb_ast_flags & DBB_monitor_off)
 			LCK_release(tdbb, dbb->dbb_monitor_lock);
 	}
@@ -4207,7 +4212,8 @@ static void check_database(thread_db* tdbb)
 		status_exception::raise(Arg::Gds(isc_cancelled));
 	}
 
-	// Enable signal handler for the monitoring stuff
+	// Enable signal handler for the monitoring stuff.
+	// See also comments in JRD_reshedule.
 
 	if (dbb->dbb_ast_flags & DBB_monitor_off)
 	{