Boost WaveOut thread priority for background audio.

media/audio/win/waveout_output_win.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/win/waveout_output_win.h"
 
 #include <windows.h>
 #include <mmsystem.h>
 #pragma comment(lib, "winmm.lib")
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
+#include "base/message_loop_proxy.h"
+#include "base/threading/platform_thread.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_util.h"
 #include "media/audio/win/audio_manager_win.h"
 
 namespace media {
 
 // Some general thoughts about the waveOut API which is badly documented :
 // - We use CALLBACK_EVENT mode in which XP signals events such as buffer
 //   releases.
 // - We use RegisterWaitForSingleObject() so one of threads in thread pool
@@ skipping 77 matching lines @@
                                 format_.Format.wBitsPerSample) / 8;
   format_.Format.nAvgBytesPerSec = format_.Format.nBlockAlign *
                                    format_.Format.nSamplesPerSec;
   if (params.channels() > kMaxChannelsToMask) {
     format_.dwChannelMask = kChannelsToMask[kMaxChannelsToMask];
   } else {
     format_.dwChannelMask = kChannelsToMask[params.channels()];
   }
   format_.SubFormat = KSDATAFORMAT_SUBTYPE_PCM;
   format_.Samples.wValidBitsPerSample = params.bits_per_sample();
+
+  // Boost thread priority.  Required for glitch free background audio.

[scherkus (not reviewing), 2012/11/30 22:13:34]

which thread is this?

the OS callback thread or a chrome-created thread?

do we need to call this every invocation of BufferCallback()?

[henrika (OOO until Aug 14), 2012/12/03 08:35:43]

Same question as Andrew.

[DaleCurtis, 2012/12/03 18:11:06]

Henrik, please see the old messages for full discussion, but this is the thread
we create in the audio manager, hence the dcheck.

+  DCHECK(manager_->GetMessageLoop()->BelongsToCurrentThread());
+  base::PlatformThread::SetThreadPriority(
+      GetCurrentThread(), base::kThreadPriority_RealtimeAudio);
 }
 
 PCMWaveOutAudioOutputStream::~PCMWaveOutAudioOutputStream() {
   DCHECK(NULL == waveout_);
 }
 
 bool PCMWaveOutAudioOutputStream::Open() {
   if (state_ != PCMA_BRAND_NEW)
     return false;
   if (BufferSize() * num_buffers_ > kMaxOpenBufferSize)
@@ skipping 292 matching lines @@
                                        buffer,
                                        sizeof(WAVEHDR));
       if (result != MMSYSERR_NOERROR)
         stream->HandleError(result);
       stream->pending_bytes_ += buffer->dwBufferLength;
     }
   }
 }
 
 }  // namespace media