ObjC: Always dispatch async in UIApplication status observer.

webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m

 /*
  *  Copyright 2016 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.
  */
 
 #include "RTCUIApplicationStatusObserver.h"
 
 #if defined(WEBRTC_IOS)
 
 #import <UIKit/UIKit.h>
 
+#include "webrtc/rtc_base/checks.h"
+
 @implementation RTCUIApplicationStatusObserver {
+  BOOL _initialized;
+  dispatch_block_t _initializeBlock;
   UIApplicationState _state;
 }
 
 + (instancetype)sharedInstance {
   static id sharedInstance;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
     sharedInstance = [[self alloc] init];
   });
 
@@ skipping 10 matching lines @@
                       _state = [UIApplication sharedApplication].applicationState;
                     }];
 
     [center addObserverForName:UIApplicationDidEnterBackgroundNotification
                         object:nil
                          queue:[NSOperationQueue mainQueue]
                     usingBlock:^(NSNotification *note) {
                       _state = [UIApplication sharedApplication].applicationState;
                     }];
 
-    dispatch_block_t initializeBlock = ^{
+    _initialized = NO;
+    _initializeBlock = dispatch_block_create(DISPATCH_BLOCK_INHERIT_QOS_CLASS, ^{
       _state = [UIApplication sharedApplication].applicationState;
-    };
+      _initialized = YES;
+    });
 
-    if ([NSThread isMainThread]) {
-      initializeBlock();
-    } else {
-      dispatch_sync(dispatch_get_main_queue(), initializeBlock);
-    }
+    dispatch_async(dispatch_get_main_queue(), _initializeBlock);
   }
 
   return self;
 }
 
 - (BOOL)isApplicationActive {
+  if (!_initialized) {
+    long ret =
+        dispatch_block_wait(_initializeBlock, dispatch_time(DISPATCH_TIME_NOW, 1.0 * NSEC_PER_SEC));
+    RTC_CHECK_EQ(ret, 0);

[kthelgason, 2017/08/23 13:25:46]

just a nit, but in the future be aware that the arguments to (D)CHECK_EQ are
reversed, i.e. RTC_CHECK_EQ(0, ret) for some stupid reason.

+  }
   return _state == UIApplicationStateActive;
 }
 
 @end
 
 #endif  // WEBRTC_IOS