Make the signal handling concurrent safe.

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
+// addHandlerChannel is used to add an interrupt handler to the list of handlers
-// received.
+// to be invoked on SIGINT (Ctrl+C) signals.
-var interruptCallbacks []func()
+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() {
+		go mainInterruptHandler()
-			<-interruptChannel
-			for _, callback := range interruptCallbacks {
-				callback()
-			}
-			os.Exit(0)
-		}()
 	}
-	interruptCallbacks = append(interruptCallbacks, handler)
+
+	addHandlerChannel <- handler
 }