Don't manipulate listeners array when expired

cmd/version.go

@@ -1,4 +1,4 @@
 package cmd
 
 // Version - Wails version
-const Version = "v1.12.0-pre1"
+const Version = "v1.12.0-pre3"

lib/event/manager.go

@@ -18,6 +18,7 @@ type Manager struct {
 	log            *logger.CustomLogger
 	renderer       interfaces.Renderer // Messages will be dispatched to the frontend
 	wg             sync.WaitGroup
+	mu             sync.Mutex
 }
 
 // NewManager creates a new event manager with a 100 event buffer
@@ -42,12 +43,12 @@ func (e *Manager) PushEvent(eventData *messages.EventData) {
 // means it does not expire (default).
 type eventListener struct {
 	callback func(...interface{}) // Function to call with emitted event data
-	counter  int                  // Expire after counter callbacks. 0 = infinite
+	counter  uint                 // Expire after counter callbacks. 0 = infinite
 	expired  bool                 // Indicates if the listener has expired
 }
 
 // Creates a new event listener from the given callback function
-func (e *Manager) addEventListener(eventName string, callback func(...interface{}), counter int) error {
+func (e *Manager) addEventListener(eventName string, callback func(...interface{}), counter uint) error {
 
 	// Sanity check inputs
 	if callback == nil {
@@ -75,7 +76,30 @@ func (e *Manager) addEventListener(eventName string, callback func(...interface{
 // On adds a listener for the given event
 func (e *Manager) On(eventName string, callback func(...interface{})) {
 	// Add a persistent eventListener (counter = 0)
-	e.addEventListener(eventName, callback, 0)
+	err := e.addEventListener(eventName, callback, 0)
+	if err != nil {
+		e.log.Error(err.Error())
+	}
+}
+
+// Once adds a listener for the given event that will auto remove
+// after one callback
+func (e *Manager) Once(eventName string, callback func(...interface{})) {
+	// Add a persistent eventListener (counter = 0)
+	err := e.addEventListener(eventName, callback, 1)
+	if err != nil {
+		e.log.Error(err.Error())
+	}
+}
+
+// OnMultiple adds a listener for the given event that will trigger
+// at most <counter> times.
+func (e *Manager) OnMultiple(eventName string, callback func(...interface{}), counter uint) {
+	// Add a persistent eventListener (counter = 0)
+	err := e.addEventListener(eventName, callback, counter)
+	if err != nil {
+		e.log.Error(err.Error())
+	}
 }
 
 // Emit broadcasts the given event to the subscribed listeners
@@ -108,20 +132,24 @@ func (e *Manager) Start(renderer interfaces.Renderer) {
 				})
 
 				// Notify renderer
-				e.renderer.NotifyEvent(event)
+				err := e.renderer.NotifyEvent(event)
+				if err != nil {
+					e.log.Error(err.Error())
+				}
 
-				// Notify Go listeners
-				var listenersToRemove []*eventListener
+				e.mu.Lock()
 
 				// Iterate listeners
 				for _, listener := range e.listeners[event.Name] {
 
-					// Call listener, perhaps with data
-					if event.Data == nil {
-						go listener.callback()
-					} else {
-						unpacked := event.Data.([]interface{})
-						go listener.callback(unpacked...)
+					if !listener.expired {
+						// Call listener, perhaps with data
+						if event.Data == nil {
+							go listener.callback()
+						} else {
+							unpacked := event.Data.([]interface{})
+							go listener.callback(unpacked...)
+						}
 					}
 
 					// Update listen counter
@@ -133,15 +161,8 @@ func (e *Manager) Start(renderer interfaces.Renderer) {
 					}
 				}
 
-				// Remove expired listeners in place
-				if len(listenersToRemove) > 0 {
-					listeners := e.listeners[event.Name][:0]
-					for _, listener := range listeners {
-						if !listener.expired {
-							listeners = append(listeners, listener)
-						}
-					}
-				}
+				e.mu.Unlock()
+
 			case <-e.quitChannel:
 				e.running = false
 			}

lib/interfaces/eventmanager.go

@@ -6,6 +6,8 @@ import "github.com/wailsapp/wails/lib/messages"
 type EventManager interface {
 	PushEvent(*messages.EventData)
 	Emit(eventName string, optionalData ...interface{})
+	OnMultiple(eventName string, callback func(...interface{}), counter uint)
+	Once(eventName string, callback func(...interface{}))
 	On(eventName string, callback func(...interface{}))
 	Start(Renderer)
 	Shutdown()

lib/renderer/webview/webview.go

@@ -353,7 +353,9 @@ func _webviewDispatchGoCallback(index unsafe.Pointer) {
 	f = fns[uintptr(index)]
 	delete(fns, uintptr(index))
 	m.Unlock()
-	f()
+	if f != nil {
+		f()
+	}
 }
 
 //export _webviewExternalInvokeCallback
@@ -369,5 +371,7 @@ func _webviewExternalInvokeCallback(w unsafe.Pointer, data unsafe.Pointer) {
 		}
 	}
 	m.Unlock()
-	cb(wv, C.GoString((*C.char)(data)))
+	if cb != nil {
+		cb(wv, C.GoString((*C.char)(data)))
+	}
 }

runtime/events.go

@@ -19,6 +19,16 @@ func (r *Events) On(eventName string, callback func(optionalData ...interface{})
 	r.eventManager.On(eventName, callback)
 }
 
+// Once pass through
+func (r *Events) Once(eventName string, callback func(optionalData ...interface{})) {
+	r.eventManager.Once(eventName, callback)
+}
+
+// OnMultiple pass through
+func (r *Events) OnMultiple(eventName string, callback func(optionalData ...interface{}), counter uint) {
+	r.eventManager.OnMultiple(eventName, callback, counter)
+}
+
 // Emit pass through
 func (r *Events) Emit(eventName string, optionalData ...interface{}) {
 	r.eventManager.Emit(eventName, optionalData...)