fix: add lock to terminate handler

README.md

@@ -10,5 +10,6 @@ waiter.AddCloseHandler(func() {
 		nacl.FinalizeStan()
 	}, false)
 
+// blocking wait, if no need to block (with http server, for example), you can omit .Wait() call
 waiter.Wait()
 ```

close_handler.go

@@ -1,8 +1,11 @@
 package grawt
 
+import "sync"
+
 type CloseHandler struct {
+	sync.Mutex
 	waiter      *Waiter
-	Quit        chan bool
+	Quit        chan struct{}
 	active      bool
 	autoDone    bool
 	handlerFunc *func()

waiter.go

@@ -9,17 +9,18 @@ import (
 )
 
 type Waiter struct {
+	blockingMode  bool
 	waitGroup     sync.WaitGroup
 	closeHandlers []*CloseHandler
 }
 
 func (w *Waiter) addHandler(f *func(), autoDone bool) *CloseHandler {
 	ch := CloseHandler{
-		w,
+		waiter:      w,
-		make(chan bool, 1),
+		Quit:        make(chan struct{}, 1),
-		true,
+		active:      true,
-		autoDone,
+		autoDone:    autoDone,
-		f,
+		handlerFunc: f,
 	}
 	w.waitGroup.Add(1)
 	w.closeHandlers = append(w.closeHandlers, &ch)
@@ -31,11 +32,15 @@ func (w *Waiter) terminateHandler(h *CloseHandler, forceWaitGroupDone bool) {
 	if h.handlerFunc != nil && *h.handlerFunc != nil {
 		(*h.handlerFunc)()
 	}
-	h.Quit <- true
+	h.Lock()
+	if h.active {
+		close(h.Quit)
+	}
 	if h.autoDone || forceWaitGroupDone {
 		w.waitGroup.Done()
 	}
 	h.active = false
+	h.Unlock()
 }
 
 func (w *Waiter) AddCloseHandler(f func(), waitForChannel bool) *CloseHandler {
@@ -53,9 +58,17 @@ func (w *Waiter) Halt(err error) {
 	} else {
 		log.Info("Program was terminated gracefully.")
 	}
+	if !w.blockingMode {
+		if err != nil {
+			os.Exit(1)
+		} else {
+			os.Exit(0)
+		}
+	}
 }
 
 func (w *Waiter) Wait() {
+	w.blockingMode = true
 	log.Info("Waiting...")
 	w.waitGroup.Wait()
 }
@@ -67,6 +80,7 @@ func (w *Waiter) onSignal(sig os.Signal) {
 
 func NewWaiter() *Waiter {
 	w := Waiter{
+		false,
 		sync.WaitGroup{},
 		make([]*CloseHandler, 0),
 	}