Mac QTKit Video Capture: Run QTCaptureSession teardown in UI thread, clean up -stopCapture use.

media/video/capture/mac/video_capture_device_qtkit_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "media/video/capture/mac/video_capture_device_qtkit_mac.h"
 
 #import <QTKit/QTKit.h>
 
 #include "base/debug/crash_logging.h"
 #include "base/logging.h"
@@ skipping 128 matching lines @@
     return YES;
   } else {
     // Remove the previously set capture device.
     if (!captureDeviceInput_) {
       // Being here means stopping a device that never started OK in the first
       // place, log it.
       [self sendLogString:[NSString
           stringWithUTF8String:"No video capture device set, on removal."]];
       return YES;
     }
-    if ([[captureSession_ inputs] count] > 0) {
-      // The device is still running.
-      [self stopCapture];
-    }
-    if ([[captureSession_ outputs] count] > 0) {
-      // Only one output is set for |captureSession_|.
-      DCHECK_EQ([[captureSession_ outputs] count], 1u);
-      id output = [[captureSession_ outputs] objectAtIndex:0];
-      [output setDelegate:nil];
-
-      // TODO(shess): QTKit achieves thread safety by posting messages to the
-      // main thread.  As part of -addOutput:, it posts a message to the main
-      // thread which in turn posts a notification which will run in a future
-      // spin after the original method returns.  -removeOutput: can post a
-      // main-thread message in between while holding a lock which the
-      // notification handler  will need.  Posting either -addOutput: or
-      // -removeOutput: to the main thread should fix it, remove is likely
-      // safer. http://crbug.com/152757
-      [captureSession_ performSelectorOnMainThread:@selector(removeOutput:)
-                                        withObject:output
-                                     waitUntilDone:YES];
-    }
+    // Tear down input and output, stop the capture and deregister observers.
+    [self stopCapture];
     [captureSession_ release];
     captureSession_ = nil;
     [captureDeviceInput_ release];
     captureDeviceInput_ = nil;
     return YES;
   }
 }
 
 - (BOOL)setCaptureHeight:(int)height
                    width:(int)width
@@ skipping 54 matching lines @@
     [notificationCenter addObserver:self
                            selector:@selector(handleNotification:)
                                name:QTCaptureSessionRuntimeErrorNotification
                              object:captureSession_];
     [captureSession_ startRunning];
   }
   return YES;
 }
 
 - (void)stopCapture {
-  if ([[captureSession_ inputs] count] == 1) {
-    [captureSession_ removeInput:captureDeviceInput_];
-    [captureSession_ stopRunning];
-  }
-
+  // QTKit achieves thread safety and asynchronous execution by posting messages
+  // to the main thread, e.g. -addOutput:. Both -removeOutput: and -removeInput:
+  // post a message to the main thread while holding a lock that the
+  // notification handler might need. To avoid a deadlock, we perform those
+  // tasks in the main thread. See bugs http://crbug.com/152757 and
+  // http://crbug.com/399792.
+  [self performSelectorOnMainThread:@selector(stopCaptureOnUIThread:)
+                         withObject:nil
+                      waitUntilDone:YES];
   [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 
+- (void)stopCaptureOnUIThread:(id)dummy {
+  if ([[captureSession_ inputs] count] > 0) {
+    [captureSession_ removeInput:captureDeviceInput_];
+    DCHECK_EQ([[captureSession_ inputs] count], 1u);
+    [captureSession_ stopRunning];
+  }
+  if ([[captureSession_ outputs] count] > 0) {
+    DCHECK_EQ([[captureSession_ outputs] count], 1u);
+    id output = [[captureSession_ outputs] objectAtIndex:0];
+    [output setDelegate:nil];
+    [captureSession_ removeOutput:output];
+  }
+}
+
 // |captureOutput| is called by the capture device to deliver a new frame.
 - (void)captureOutput:(QTCaptureOutput*)captureOutput
   didOutputVideoFrame:(CVImageBufferRef)videoFrame
      withSampleBuffer:(QTSampleBuffer*)sampleBuffer
        fromConnection:(QTCaptureConnection*)connection {
   [lock_ lock];
   if(!frameReceiver_) {
     [lock_ unlock];
     return;
   }
@@ skipping 86 matching lines @@
 
 - (void)sendLogString:(NSString*)message {
   DVLOG(1) << [message UTF8String];
   [lock_ lock];
   if (frameReceiver_)
     frameReceiver_->LogMessage([message UTF8String]);
   [lock_ unlock];
 }
 
 @end