Low-latency AudioInputStream implementation based on WASAPI for Windows.

media/audio/win/avrt_wrapper_win.h

+// Copyright (c) 2011 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.
+//
+// The AvrtWrapper class encapsulates the details needed to support MMCSS.

[scherkus (not reviewing), 2011/10/18 21:12:30]

out of curiosity does Avrt stand for anything?

[henrika (OOO until Aug 14), 2011/10/19 15:42:43]

It's a jolly good question and I actually don't know the correct answer. The
header and DLL are called avrt.h and avrt.dll and it is sometimes written AvRt.
There are lots of DLLs called av---.dll but I don't know what it stands for.

If I check the properties of avrt.dll, it states File Description "Multimedia
Realtime Runtime", hence Rt could be Realtime or Runtime I guess.

+//
+// The Multimedia Class Scheduler service (MMCSS) enables multimedia
+// applications to ensure that their time-sensitive processing receives
+// prioritized access to CPU resources. This service enables multimedia
+// applications to utilize as much of the CPU as possible without denying
+// CPU resources to lower-priority applications.
+// MMCSS requires Windows Vista or higher and that the Avrt DLL is loaded.
+//
+#ifndef MEDIA_AUDIO_WIN_AVRT_WRAPPER_WIN_H_
+#define MEDIA_AUDIO_WIN_AVRT_WRAPPER_WIN_H_
+
+#include <windows.h>
+#include <avrt.h>

[scherkus (not reviewing), 2011/10/18 21:12:30]

can <avrt.h> get moved into the .cc ?

doesn't look like it's explicitly required by the .h

[henrika (OOO until Aug 14), 2011/10/19 15:42:43]

Need it for AVRT_PRIORITY

+
+#include "base/basictypes.h"
+
+class AvrtWrapper {

[scherkus (not reviewing), 2011/10/18 21:12:30]

there's nothing in here that warrants a class -- it looks like you're using it
as a form of namespacing so how about using a namespace and static functions?

for example, what about:

namespace avrt {
bool Initialize();
bool RevertThreadCharacteristics(...);
HANDLE SetThreadCharacteristics(...);
bool SetThreadPriority(...);
}  // namespace avrt

WDYT?

[henrika (OOO until Aug 14), 2011/10/19 15:42:43]

Agree, and so does Tommi. Will refactor.

+ public:
+  AvrtWrapper() {}
+  ~AvrtWrapper() {}
+
+  // Loads the Avrt.dll which is available on Windows Vista and later.
+  bool Initialize();
+
+  // Function wrappers for the underlying MMCSS functions.
+  bool AvRevertMmThreadCharacteristics(HANDLE avrt_handle);
+  HANDLE AvSetMmThreadCharacteristics(const char* task_name, DWORD* task_index);
+  bool AvSetMmThreadPriority(HANDLE avrt_handle, AVRT_PRIORITY priority);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AvrtWrapper);
+};
+
+#endif  // MEDIA_AUDIO_WIN_AVRT_WRAPPER_WIN_H_
+

[scherkus (not reviewing), 2011/10/18 21:12:30]

nit: remove blank line

[henrika (OOO until Aug 14), 2011/10/19 15:42:43]

Done.