Remove Crit::Scope lock by using atomic bool property

webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm

 /*
  *  Copyright 2015 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 60 matching lines @@
 // to be owned by an instance of AVFoundationVideoCapturer. The reason for this
 // because other webrtc objects own cricket::VideoCapturer, which is not
 // ref counted. To prevent bad behavior we do not expose this class directly.
 @interface RTCAVFoundationVideoCapturerInternal : NSObject
     <AVCaptureVideoDataOutputSampleBufferDelegate>
 
 @property(nonatomic, readonly) AVCaptureSession *captureSession;
 @property(nonatomic, readonly) dispatch_queue_t frameQueue;
 @property(nonatomic, readonly) BOOL canUseBackCamera;
 @property(nonatomic, assign) BOOL useBackCamera;  // Defaults to NO.
-@property(nonatomic, assign) BOOL isRunning;  // Whether the capture session is running.
+@property(atomic, assign) BOOL isRunning;  // Whether the capture session is running.
 @property(atomic, assign) BOOL hasStarted;  // Whether we have an unmatched start.
 
 // We keep a pointer back to AVFoundationVideoCapturer to make callbacks on it
 // when we receive frames. This is safe because this object should be owned by
 // it.
 - (instancetype)initWithCapturer:(webrtc::AVFoundationVideoCapturer *)capturer;
 - (AVCaptureDevice *)getActiveCaptureDevice;
 
 // Starts and stops the capture session asynchronously. We cannot do this
 // synchronously without blocking a WebRTC thread.
 - (void)start;
 - (void)stop;
 
 @end
 
 @implementation RTCAVFoundationVideoCapturerInternal {
   // Keep pointers to inputs for convenience.
   AVCaptureDeviceInput *_frontCameraInput;
   AVCaptureDeviceInput *_backCameraInput;
   AVCaptureVideoDataOutput *_videoDataOutput;
   // The cricket::VideoCapturer that owns this class. Should never be NULL.
   webrtc::AVFoundationVideoCapturer *_capturer;
   webrtc::VideoRotation _rotation;
   BOOL _hasRetriedOnFatalError;
-  BOOL _isRunning;
   BOOL _hasStarted;
   rtc::CriticalSection _crit;
 }
 
 @synthesize captureSession = _captureSession;
 @synthesize frameQueue = _frameQueue;
 @synthesize useBackCamera = _useBackCamera;
 @synthesize hasStarted = _hasStarted;

[magjed_webrtc, 2016/09/28 13:56:36]

So this @synthesize step isn't needed? Maybe remove it for the other variables
as well, in this CL or in a separate CL.

[tkchin_webrtc, 2016/09/28 14:17:37]

The approach we've gone in this codebase is to explicitly synthesize everything
instead of relying on auto-synthesis. It prevents cases where things are
accidentally added but never used.

[daniela-webrtc, 2016/09/28 14:38:42]

Can you elaborate a bit on this part? Wouldn't the compiler throw an error for
unused properties? Or am I misunderstanding your statement?

 
 // This is called from the thread that creates the video source, which is likely
 // the main thread.
 - (instancetype)initWithCapturer:(webrtc::AVFoundationVideoCapturer *)capturer {
   RTC_DCHECK(capturer);
   if (self = [super init]) {
     _capturer = capturer;
     // Create the capture session and all relevant inputs and outputs. We need
     // to do this in init because the application may want the capture session
     // before we start the capturer for e.g. AVCapturePreviewLayer. All objects
@@ skipping 85 matching lines @@
   }
   @synchronized(self) {
     if (_useBackCamera == useBackCamera) {
       return;
     }
     _useBackCamera = useBackCamera;
     [self updateSessionInputForUseBackCamera:useBackCamera];
   }
 }
 
-- (BOOL)isRunning {
-  rtc::CritScope cs(&_crit);
-  return _isRunning;
-}
-
-- (void)setIsRunning:(BOOL)isRunning {
-  rtc::CritScope cs(&_crit);
-  _isRunning = isRunning;
-}
-
 // Called from WebRTC thread.
 - (void)start {
   if (self.hasStarted) {
     return;
   }
   self.hasStarted = YES;
   [RTCDispatcher dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                                block:^{
 #if TARGET_OS_IPHONE
      // Default to portrait orientation on iPhone. This will be reset in
@@ skipping 107 matching lines @@
       [self handleFatalError];
     }
 #else
     [self handleFatalError];
 #endif
   }];
 }
 
 - (void)handleCaptureSessionDidStartRunning:(NSNotification *)notification {
   RTCLog(@"Capture session started.");
+
   self.isRunning = YES;
   [RTCDispatcher dispatchAsyncOnType:RTCDispatcherTypeCaptureSession
                                block:^{
     // If we successfully restarted after an unknown error, allow future
     // retries on fatal errors.
     _hasRetriedOnFatalError = NO;
   }];
 }
 
 - (void)handleCaptureSessionDidStopRunning:(NSNotification *)notification {
@@ skipping 389 matching lines @@
       buffer = rotated_buffer;
     }
   }
 
   OnFrame(cricket::WebRtcVideoFrame(buffer, rotation,
                                     translated_camera_time_us, 0),
           captured_width, captured_height);
 }
 
 }  // namespace webrtc