Make sure UI methods get called on the main thread

webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m

 /*
  *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 45 matching lines @@
   CGSize _localVideoSize;
   CGSize _remoteVideoSize;
 }
 
 @synthesize delegate = _delegate;
 @synthesize localVideoView = _localVideoView;
 @synthesize remoteVideoView = _remoteVideoView;
 
 
 - (void)displayLogMessage:(NSString *)message {
-  _logView.string =
-      [NSString stringWithFormat:@"%@%@\n", _logView.string, message];
-  NSRange range = NSMakeRange(_logView.string.length, 0);
-  [_logView scrollRangeToVisible:range];
+  dispatch_async(dispatch_get_main_queue(), ^{
+    _logView.string =
+        [NSString stringWithFormat:@"%@%@\n", _logView.string, message];
+    NSRange range = NSMakeRange(_logView.string.length, 0);
+    [_logView scrollRangeToVisible:range];
+  });
 }
 
 #pragma mark - Private
 
 - (instancetype)initWithFrame:(NSRect)frame {
   if (self = [super initWithFrame:frame]) {
     [self setupViews];
   }
   return self;
 }
@@ skipping 326 matching lines @@
   _client = client;
 }
 
 #pragma mark - Private
 
 - (APPRTCMainView*)mainView {
   return (APPRTCMainView*)self.view;
 }
 
 - (void)showAlertWithMessage:(NSString*)message {
-  NSAlert* alert = [[NSAlert alloc] init];
-  [alert setMessageText:message];
-  [alert runModal];
+  dispatch_async(dispatch_get_main_queue(), ^{
+    NSAlert* alert = [[NSAlert alloc] init];
+    [alert setMessageText:message];
+    [alert runModal];
+  });
 }
 
 - (void)resetUI {
   [_remoteVideoTrack removeRenderer:self.mainView.remoteVideoView];
   [_localVideoTrack removeRenderer:self.mainView.localVideoView];
   _remoteVideoTrack = nil;
   _localVideoTrack = nil;
   [self.mainView.remoteVideoView renderFrame:nil];
   [self.mainView.localVideoView renderFrame:nil];
 }
 
 - (void)disconnect {
   [self resetUI];
   [_captureController stopCapture];
   _captureController = nil;
   [_client disconnect];
 }
 
 @end