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 "media/audio/win/avrt_wrapper_win.h"
+
+#include "base/logging.h"
+
+namespace avrt {
+
+// Function pointers
+typedef BOOL (WINAPI *AvRevertMmThreadCharacteristicsFn)(HANDLE);
+typedef HANDLE (WINAPI *AvSetMmThreadCharacteristicsFn)(LPCWSTR, 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 Initialize() {
+  if (!g_set_mm_thread_priority) {
+    // The avrt.dll is available on Windows Vista and later.
+    wchar_t path[MAX_PATH] = {0};
+    ExpandEnvironmentStrings(L"%WINDIR%\\system32\\avrt.dll", path,
+        arraysize(path));
+    g_avrt = LoadLibraryExW(path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH);
+    if (!g_avrt)
+      return false;
+
+    g_revert_mm_thread_characteristics =
+        reinterpret_cast<AvRevertMmThreadCharacteristicsFn>(
+            GetProcAddress(g_avrt, "AvRevertMmThreadCharacteristics"));
+    g_set_mm_thread_characteristics =
+        reinterpret_cast<AvSetMmThreadCharacteristicsFn>(
+            GetProcAddress(g_avrt, "AvSetMmThreadCharacteristicsW"));
+    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);
+}
+
+bool AvRevertMmThreadCharacteristics(HANDLE avrt_handle) {
+  DCHECK(g_revert_mm_thread_characteristics);
+  return (g_revert_mm_thread_characteristics &&
+          g_revert_mm_thread_characteristics(avrt_handle));
+}
+
+HANDLE AvSetMmThreadCharacteristics(const wchar_t* 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 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));
+}
+
+}  // namespace avrt