From c1b327c06abf6876dc4ba57d0e4ea7c5bfad0ebb Mon Sep 17 00:00:00 2001
From: Dave Collins <davec@conformal.com>
Date: Thu, 3 Oct 2013 09:28:18 -0500
Subject: [PATCH] Make the signal handling concurrent safe.

---
 signal.go | 39 ++++++++++++++++++++++++++++-----------
 1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/signal.go b/signal.go
index e4a42011..6f8340e7 100644
--- a/signal.go
+++ b/signal.go
@@ -12,9 +12,31 @@ import (
 // interruptChannel is used to receive SIGINT (Ctrl+C) signals.
 var interruptChannel chan os.Signal
 
-// interruptCallbacks is a list of callbacks to invoke when a SIGINT (Ctrl+C) is
-// received.
-var interruptCallbacks []func()
+// addHandlerChannel is used to add an interrupt handler to the list of handlers
+// to be invoked on SIGINT (Ctrl+C) signals.
+var addHandlerChannel = make(chan func())
+
+// mainInterruptHandler listens for SIGINT (Ctrl+C) signals on the
+// interruptChannel and invokes the registered interruptCallbacks accordingly.
+// It also listens for callback registration.  It must be run as a goroutine.
+func mainInterruptHandler() {
+	// interruptCallbacks is a list of callbacks to invoke when a
+	// SIGINT (Ctrl+C) is received.
+	var interruptCallbacks []func()
+
+	for {
+		select {
+		case <-interruptChannel:
+			for _, callback := range interruptCallbacks {
+				callback()
+			}
+			os.Exit(0)
+
+		case handler := <-addHandlerChannel:
+			interruptCallbacks = append(interruptCallbacks, handler)
+		}
+	}
+}
 
 // addInterruptHandler adds a handler to call when a SIGINT (Ctrl+C) is
 // received.
@@ -24,13 +46,8 @@ func addInterruptHandler(handler func()) {
 	if interruptChannel == nil {
 		interruptChannel = make(chan os.Signal, 1)
 		signal.Notify(interruptChannel, os.Interrupt)
-		go func() {
-			<-interruptChannel
-			for _, callback := range interruptCallbacks {
-				callback()
-			}
-			os.Exit(0)
-		}()
+		go mainInterruptHandler()
 	}
-	interruptCallbacks = append(interruptCallbacks, handler)
+
+	addHandlerChannel <- handler
 }