Low-latency AudioInputStream implementation based on WASAPI for Windows.

media/audio/win/avrt_wrapper_win.cc

+// 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.
+
+#include "base/logging.h"
+#include "media/audio/win/avrt_wrapper_win.h"
+
+namespace {
+  // Function pointers

[tommi, 2011/10/18 14:14:10]

don't indent this section

[henrika (OOO until Aug 14), 2011/10/18 14:56:49]

Done.

+  typedef BOOL (WINAPI *AvRevertMmThreadCharacteristicsFn)(HANDLE);
+  typedef HANDLE (WINAPI *AvSetMmThreadCharacteristicsFn)(LPCSTR, LPDWORD);
+  typedef BOOL (WINAPI *AvSetMmThreadPriorityFn)(HANDLE, AVRT_PRIORITY);
+
+  HMODULE g_avrt = NULL;
+  AvRevertMmThreadCharacteristicsFn g_revert_mm_thread_characteristics = NULL;
+  AvSetMmThreadCharacteristicsFn g_set_mm_thread_characteristics = NULL;
+  AvSetMmThreadPriorityFn g_set_mm_thread_priority = NULL;
+}
+
+bool AvrtWrapper::Initialize() {
+  if (!g_set_mm_thread_priority) {
+    // The avrt.dll is available on Windows Vista and later.
+    char path[MAX_PATH] = {0};
+    ExpandEnvironmentStringsA("%WINDIR%\\system32\\avrt.dll", path,
+        arraysize(path));
+    g_avrt = LoadLibraryA(path);
+    g_revert_mm_thread_characteristics =
+        reinterpret_cast<AvRevertMmThreadCharacteristicsFn>(
+            GetProcAddress(g_avrt, "AvRevertMmThreadCharacteristics"));
+    g_set_mm_thread_characteristics =
+        reinterpret_cast<AvSetMmThreadCharacteristicsFn>(
+            GetProcAddress(g_avrt, "AvSetMmThreadCharacteristicsA"));
+    g_set_mm_thread_priority = reinterpret_cast<AvSetMmThreadPriorityFn>(
+        GetProcAddress(g_avrt, "AvSetMmThreadPriority"));
+  }
+  return (g_avrt && g_revert_mm_thread_characteristics &&
+      g_set_mm_thread_characteristics  && g_set_mm_thread_priority);

[tommi, 2011/10/18 14:14:10]

only one space after g_set_mm_thread_characteristics

[henrika (OOO until Aug 14), 2011/10/18 14:56:49]

Done.

+}
+
+bool AvrtWrapper::AvRevertMmThreadCharacteristics(HANDLE avrt_handle) {
+  DCHECK(g_revert_mm_thread_characteristics);
+  return (g_revert_mm_thread_characteristics &&

[tommi, 2011/10/18 14:14:10]

nit: since you're using && you don't need the != FALSE bit

[henrika (OOO until Aug 14), 2011/10/18 14:56:49]

LOL

+      g_revert_mm_thread_characteristics(avrt_handle) != FALSE);
+}
+
+HANDLE AvrtWrapper::AvSetMmThreadCharacteristics(const char* task_name,
+                                                 DWORD* task_index) {
+  DCHECK(g_set_mm_thread_characteristics);
+  return (g_set_mm_thread_characteristics ?
+      g_set_mm_thread_characteristics(task_name, task_index) : NULL);
+}
+
+bool AvrtWrapper::AvSetMmThreadPriority(HANDLE avrt_handle,
+                                        AVRT_PRIORITY priority) {
+  DCHECK(g_set_mm_thread_priority);
+  return (g_set_mm_thread_priority &&
+      g_set_mm_thread_priority(avrt_handle, priority) != FALSE);
+}