From bc481ea784339e57b5f1bd6e67245597dd32765a Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Tue, 21 May 2019 15:56:56 +0200
Subject: [PATCH] ui/app: serialize event handling

The frame callback for macOS comes in from a different thread than
the UI thread. Serialize event handling to maintain the invariant
that only one event is processed at a time.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 ui/app/window.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/ui/app/window.go b/ui/app/window.go
index 3415d952..71533ee3 100644
--- a/ui/app/window.go
+++ b/ui/app/window.go
@@ -35,6 +35,8 @@ type Window struct {
 
 	events chan Event
 
+	eventLock sync.Mutex
+
 	mu           sync.Mutex
 	stage        Stage
 	size         image.Point
@@ -230,6 +232,8 @@ func (w *Window) contextDriver() interface{} {
 }
 
 func (w *Window) event(e Event) {
+	w.eventLock.Lock()
+	defer w.eventLock.Unlock()
 	w.mu.Lock()
 	needAck := false
 	needRedraw := false