From d70a39254ccb8dfcb902b5d2b4c4b0bdbd82ee66 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Tue, 22 Mar 2016 18:42:01 -0700
Subject: [PATCH] create signal.go to handle SIGINT's

---
 signal.go | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 signal.go

diff --git a/signal.go b/signal.go
new file mode 100644
index 00000000..e7c5ef86
--- /dev/null
+++ b/signal.go
@@ -0,0 +1,80 @@
+package main
+
+// Heavily inspired by https://github.com/btcsuite/btcd/blob/master/signal.go
+
+import (
+	"os"
+	"os/signal"
+)
+
+// interruptChannel is used to receive SIGINT (Ctrl+C) signals.
+var interruptChannel chan os.Signal
+
+// 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()
+
+	// isShutdown is a flag which is used to indicate whether or not
+	// the shutdown signal has already been received and hence any future
+	// attempts to add a new interrupt handler should invoke them
+	// immediately.
+	var isShutdown bool
+
+	for {
+		select {
+		case <-interruptChannel:
+			// Ignore more than one shutdown signal.
+			if isShutdown {
+				ltndLog.Infof("Received SIGINT (Ctrl+C).  " +
+					"Already shutting down...")
+				continue
+			}
+
+			isShutdown = true
+			ltndLog.Infof("Received SIGINT (Ctrl+C).  Shutting down...")
+
+			// Run handlers in LIFO order.
+			for i := range interruptCallbacks {
+				idx := len(interruptCallbacks) - 1 - i
+				callback := interruptCallbacks[idx]
+				callback()
+			}
+
+			// Signal the main goroutine to shutdown.
+			go func() {
+				shutdownChannel <- struct{}{}
+			}()
+
+		case handler := <-addHandlerChannel:
+			// The shutdown signal has already been received, so
+			// just invoke and new handlers immediately.
+			if isShutdown {
+				handler()
+			}
+
+			interruptCallbacks = append(interruptCallbacks, handler)
+		}
+	}
+}
+
+// addInterruptHandler adds a handler to call when a SIGINT (Ctrl+C) is
+// received.
+func addInterruptHandler(handler func()) {
+	// Create the channel and start the main interrupt handler which invokes
+	// all other callbacks and exits if not already done.
+	if interruptChannel == nil {
+		interruptChannel = make(chan os.Signal, 1)
+		signal.Notify(interruptChannel, os.Interrupt)
+		go mainInterruptHandler()
+	}
+
+	addHandlerChannel <- handler
+}