event: panic for duplicate type

event/event.go

@@ -3,6 +3,7 @@ package event
 
 import (
 	"errors"
+	"fmt"
 	"reflect"
 	"sync"
 )
@@ -40,6 +41,7 @@ var ErrMuxClosed = errors.New("event: mux closed")
 func (mux *TypeMux) Subscribe(types ...interface{}) Subscription {
 	sub := newsub(mux)
 	mux.mutex.Lock()
+	defer mux.mutex.Unlock()
 	if mux.stopped {
 		close(sub.postC)
 	} else {
@@ -49,13 +51,15 @@ func (mux *TypeMux) Subscribe(types ...interface{}) Subscription {
 		for _, t := range types {
 			rtyp := reflect.TypeOf(t)
 			oldsubs := mux.subm[rtyp]
+			if find(oldsubs, sub) != -1 {
+				panic(fmt.Sprintf("event: duplicate type %s in Subscribe", rtyp))
+			}
 			subs := make([]*muxsub, len(oldsubs)+1)
 			copy(subs, oldsubs)
 			subs[len(oldsubs)] = sub
 			mux.subm[rtyp] = subs
 		}
 	}
-	mux.mutex.Unlock()
 	return sub
 }
 

event/event_test.go

@@ -60,6 +60,21 @@ func TestUnsubscribeUnblockPost(t *testing.T) {
 	}
 }
 
+func TestSubscribeDuplicateType(t *testing.T) {
+	mux := new(TypeMux)
+	expected := "event: duplicate type event.testEvent in Subscribe"
+
+	defer func() {
+		err := recover()
+		if err == nil {
+			t.Errorf("Subscribe didn't panic for duplicate type")
+		} else if err != expected {
+			t.Errorf("panic mismatch: got %#v, expected %#v", err, expected)
+		}
+	}()
+	mux.Subscribe(testEvent(1), testEvent(2))
+}
+
 func TestMuxConcurrent(t *testing.T) {
 	rand.Seed(time.Now().Unix())
 	mux := new(TypeMux)