From 1c1140f4f327dfed482abcdceb0ed3cdb6c2fb7b Mon Sep 17 00:00:00 2001
From: Gregory Eremin <g@erem.in>
Date: Sun, 10 Jan 2016 14:52:32 +0300
Subject: [PATCH] Fix a rare crash when restarting a system task after shutdown
 was called

---
 satan.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/satan.go b/satan.go
index 50441c5..24b2c3c 100644
--- a/satan.go
+++ b/satan.go
@@ -143,6 +143,16 @@ func (s *Satan) processTask(t *task) {
 }
 
 func (s *Satan) processSystemTask(t *task) {
+	// Abort starting a system task if shutdown was already called. Otherwise
+	// incrementing a wait group counter will cause a panic. This should be an
+	// extremely rare scenario when a system task crashes and tries to restart
+	// after a shutdown call.
+	select {
+	case <-s.shutdownSystem:
+		return
+	default:
+	}
+
 	s.wgSystem.Add(1)
 	defer s.wgSystem.Done()
 	defer func() {