Merge pull request #2311 from amrfaissal/fix-2310

Ability to register pre/post signal handlers

grace/grace.go

@@ -85,23 +85,31 @@ var (
 
 	isChild     bool
 	socketOrder string
-	once        sync.Once
+
+	hookableSignals []os.Signal
 )
 
-func onceInit() {
-	regLock = &sync.Mutex{}
+func init() {
 	flag.BoolVar(&isChild, "graceful", false, "listen on open fd (after forking)")
 	flag.StringVar(&socketOrder, "socketorder", "", "previous initialization order - used when more than one listener was started")
+
+	regLock = &sync.Mutex{}
 	runningServers = make(map[string]*Server)
 	runningServersOrder = []string{}
 	socketPtrOffsetMap = make(map[string]uint)
+
+	hookableSignals = []os.Signal{
+		syscall.SIGHUP,
+		syscall.SIGINT,
+		syscall.SIGTERM,
+	}
 }
 
 // NewServer returns a new graceServer.
 func NewServer(addr string, handler http.Handler) (srv *Server) {
-	once.Do(onceInit)
 	regLock.Lock()
 	defer regLock.Unlock()
+
 	if !flag.Parsed() {
 		flag.Parse()
 	}

grace/server.go

@@ -162,9 +162,7 @@ func (srv *Server) handleSignals() {
 
 	signal.Notify(
 		srv.sigChan,
-		syscall.SIGHUP,
-		syscall.SIGINT,
-		syscall.SIGTERM,
+		hookableSignals...,
 	)
 
 	pid := syscall.Getpid()
@@ -290,3 +288,19 @@ func (srv *Server) fork() (err error) {
 
 	return
 }
+
+// RegisterSignalHook registers a function to be run PreSignal or PostSignal for a given signal.
+func (srv *Server) RegisterSignalHook(ppFlag int, sig os.Signal, f func()) (err error) {
+	if ppFlag != PreSignal && ppFlag != PostSignal {
+		err = fmt.Errorf("Invalid ppFlag argument. Must be either grace.PreSignal or grace.PostSignal.")
+		return
+	}
+	for _, s := range hookableSignals {
+		if s == sig {
+			srv.SignalHooks[ppFlag][sig] = append(srv.SignalHooks[ppFlag][sig], f)
+			return
+		}
+	}
+	err = fmt.Errorf("Signal '%v' is not supported.", sig)
+	return
+}