ObjC: Always dispatch async in UIApplication status observer.

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

Index: webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
diff --git a/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m b/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
index 718aeca58b3860f5593fae738a1dd7d3938035f4..9eb735758127880dcfe0fddb3340408cf868117e 100644
--- a/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
+++ b/webrtc/sdk/objc/Framework/Classes/Common/RTCUIApplicationStatusObserver.m
@@ -15,6 +15,8 @@
 #import <UIKit/UIKit.h>
 
 @implementation RTCUIApplicationStatusObserver {
+  BOOL _initialized;
+  dispatch_block_t _initializeBlock;
   UIApplicationState _state;
 }
 
@@ -45,21 +47,22 @@
                       _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) {
+    dispatch_block_wait(_initializeBlock, DISPATCH_TIME_FOREVER);

[daniela-webrtc, 2017/08/23 08:54:10]

This will make the 'isApplicationActive' a blocking call.  Will it have
implications in other parts of the code?

[andersc, 2017/08/23 09:32:26]

Before, we blocked on initialization by doing a dispatch_sync to the main queue,
which was problematic. Now instead we block the calling queue if
`isApplicationActive` is called before the ApplicationStatusObserver is fully
initialized. It will block at most once, when calling it directly after
initialization, before the _initializationBlock has completed, but some blocking
is needed since we have to wait for the initialization to run on the main queue.

[kthelgason, 2017/08/23 11:37:39]

Maybe instead of blocking forever we should add a timeout and a RTC_CHECK so
that if this ever causes problems it will be easier to find than a deadlock.

[andersc, 2017/08/23 12:14:22]

That sounds like a good idea! Done.

+  }
   return _state == UIApplicationStateActive;
 }