Ensure that data is not overwritten in the audio input shared memory ring buffer that sits on the b…

media/audio/audio_device_thread.cc

 // 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.
 
 #include "media/audio/audio_device_thread.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/logging.h"
@@ skipping 165 matching lines @@
     // Avoid running Process() for the paused signal, we still need to update
     // the buffer index if |synchronized_buffers_| is true though.
     //
     // See comments in AudioOutputController::DoPause() for details on why.
     if (pending_data != kuint32max) {
       base::AutoLock auto_lock(callback_lock_);
       if (callback_)
         callback_->Process(pending_data);
     }
 
-    // Let the other end know which buffer we just filled.  The buffer index is
-    // used to ensure the other end is getting the buffer it expects.  For more
+    // The usage of |synchronized_buffers_| differs between input and output
+    // cases.
+    // Input:
+    // Let the other end know that we have read data, so that it can verify
+    // it doesn't overwrite any data before read. The |buffer_index| value is
+    // not used. For more details, see AudioInputSyncWriter::Write().
+    // Output:
+    // Let the other end know which buffer we just filled. The |buffer_index| is
+    // used to ensure the other end is getting the buffer it expects. For more
     // details on how this works see AudioSyncReader::WaitUntilDataIsReady().
     if (synchronized_buffers_) {
       ++buffer_index;
       size_t bytes_sent = socket_.Send(&buffer_index, sizeof(buffer_index));
       if (bytes_sent != sizeof(buffer_index))
         break;
     }
   }
 }
 
@@ skipping 20 matching lines @@
 }
 
 AudioDeviceThread::Callback::~Callback() {}
 
 void AudioDeviceThread::Callback::InitializeOnAudioThread() {
   MapSharedMemory();
   CHECK(shared_memory_.memory());
 }
 
 }  // namespace media.