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"

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

this should go first

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

Done.

+
+namespace {
+// Function pointers
+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;
+}  // namespace
+
+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);

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

you may want to use the following instead:
::LoadLibraryEx(path, NULL, LOAD_WITH_ALTERED_SEARCH_PATH)

while unlikely, it'll ensure that the presence of a DLL named avrt.dll doesn't
get accidentally loaded if the library load path is somehow changed

also please use the unicode versions of this function -- I'm not sure what would
happen if %WINDIR% expanded to contain unicode characters!

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

Done.

+    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);
+}
+
+bool AvrtWrapper::AvRevertMmThreadCharacteristics(HANDLE avrt_handle) {
+  DCHECK(g_revert_mm_thread_characteristics);
+  return (g_revert_mm_thread_characteristics &&
+      g_revert_mm_thread_characteristics(avrt_handle));
+}
+
+HANDLE AvrtWrapper::AvSetMmThreadCharacteristics(const char* task_name,

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

should also be unicode

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

I would say "could be unicode" but OK ;-)

Changed.

+                                                 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));
+}