New task queueing primitive for async tasks: TaskQueue.

webrtc/base/task_queue_win.cc

Index: webrtc/base/task_queue_win.cc
diff --git a/webrtc/base/task_queue_win.cc b/webrtc/base/task_queue_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..5ae6d9275baaa9c8350f1750ad8a33eded540b11
--- /dev/null
+++ b/webrtc/base/task_queue_win.cc
@@ -0,0 +1,184 @@
+/*
+ *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/base/task_queue.h"
+
+#include <string.h>
+#include <unordered_map>
+
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+
+namespace rtc {
+namespace {
+#define WM_RUN_TASK WM_USER + 1
+#define WM_QUEUE_DELAYED_TASK WM_USER + 2
+
+DWORD g_queue_ptr_tls = 0;
+
+BOOL CALLBACK InitializeTls(PINIT_ONCE init_once, void* param, void** context) {
+  g_queue_ptr_tls = TlsAlloc();
+  return TRUE;
+}
+
+DWORD GetQueuePtrTls() {
+  static INIT_ONCE init_once = INIT_ONCE_STATIC_INIT;
+  InitOnceExecuteOnce(&init_once, InitializeTls, nullptr, nullptr);
+  return g_queue_ptr_tls;
+}
+
+struct ThreadStartupData {
+  Event* started;
+  void* thread_context;
+};
+
+void CALLBACK InitializeQueueThread(ULONG_PTR param) {
+  MSG msg;
+  PeekMessage(&msg, NULL, WM_USER, WM_USER, PM_NOREMOVE);
+  ThreadStartupData* data = reinterpret_cast<ThreadStartupData*>(param);
+  TlsSetValue(GetQueuePtrTls(), data->thread_context);
+  data->started->Set();
+}
+}  // namespace
+
+TaskQueue::TaskQueue(const char* queue_name)
+    : thread_(&TaskQueue::ThreadMain, this, queue_name) {
+  RTC_DCHECK(queue_name);
+  thread_.Start();
+  Event event(false, false);
+  ThreadStartupData startup = {&event, this};
+  RTC_CHECK(thread_.QueueAPC(&InitializeQueueThread,
+                             reinterpret_cast<ULONG_PTR>(&startup)));
+  event.Wait(Event::kForever);
+}
+
+TaskQueue::~TaskQueue() {
+  RTC_DCHECK(!IsCurrent());
+  while (!PostThreadMessage(thread_.GetThreadRef(), WM_QUIT, 0, 0)) {
+    RTC_CHECK(ERROR_NOT_ENOUGH_QUOTA == ::GetLastError());
+    Sleep(1);
+  }
+  thread_.Stop();
+}
+
+// static
+TaskQueue* TaskQueue::Current() {
+  return static_cast<TaskQueue*>(TlsGetValue(GetQueuePtrTls()));
+}
+
+// static
+bool TaskQueue::IsCurrent(const char* queue_name) {
+  TaskQueue* current = Current();
+  return current && current->thread_.name().compare(queue_name) == 0;
+}
+
+bool TaskQueue::IsCurrent() const {
+  return IsThreadRefEqual(thread_.GetThreadRef(), CurrentThreadRef());
+}
+
+void TaskQueue::PostTask(std::unique_ptr<QueuedTask> task) {
+  if (PostThreadMessage(thread_.GetThreadRef(), WM_RUN_TASK, 0,
+                        reinterpret_cast<LPARAM>(task.get()))) {
+    task.release();
+  }
+}
+
+void TaskQueue::PostDelayedTask(std::unique_ptr<QueuedTask> task,
+                                uint32_t milliseconds) {
+  WPARAM wparam;
+#if defined(_WIN64)
+  // GetTickCount() returns a fairly coarse tick count (resolution or about 8ms)
+  // so this compensation isn't that accurate, but since we have unused 32 bits
+  // on Win64, we might as well use them.
+  wparam = (static_cast<WPARAM>(::GetTickCount()) << 32) | milliseconds;
+#else
+  wparam = milliseconds;
+#endif
+  if (PostThreadMessage(thread_.GetThreadRef(), WM_QUEUE_DELAYED_TASK, wparam,
+                        reinterpret_cast<LPARAM>(task.get()))) {
+    task.release();
+  }
+}
+
+void TaskQueue::PostTaskAndReply(std::unique_ptr<QueuedTask> task,
+                                 std::unique_ptr<QueuedTask> reply,
+                                 TaskQueue* reply_queue) {
+  QueuedTask* task_ptr = task.release();
+  QueuedTask* reply_task_ptr = reply.release();
+  DWORD reply_thread_id = reply_queue->thread_.GetThreadRef();
+  PostTask([task_ptr, reply_task_ptr, reply_thread_id]() {
+    if (task_ptr->Run())
+      delete task_ptr;
+    // If the thread's message queue is full, we can't queue the task and will
+    // have to drop it (i.e. delete).
+    if (!PostThreadMessage(reply_thread_id, WM_RUN_TASK, 0,
+                           reinterpret_cast<LPARAM>(reply_task_ptr))) {
+      delete reply_task_ptr;
+    }
+  });
+}
+
+void TaskQueue::PostTaskAndReply(std::unique_ptr<QueuedTask> task,
+                                 std::unique_ptr<QueuedTask> reply) {
+  return PostTaskAndReply(std::move(task), std::move(reply), Current());
+}
+
+// static
+bool TaskQueue::ThreadMain(void* context) {
+  std::unordered_map<UINT_PTR, std::unique_ptr<QueuedTask>> delayed_tasks;
+
+  BOOL ret;
+  MSG msg;
+
+  while ((ret = GetMessage(&msg, nullptr, 0, 0)) != 0 && ret != -1) {
+    if (!msg.hwnd) {
+      switch (msg.message) {
+        case WM_RUN_TASK: {
+          QueuedTask* task = reinterpret_cast<QueuedTask*>(msg.lParam);
+          if (task->Run())
+            delete task;
+          break;
+        }
+        case WM_QUEUE_DELAYED_TASK: {
+          QueuedTask* task = reinterpret_cast<QueuedTask*>(msg.lParam);
+          uint32_t milliseconds = msg.wParam & 0xFFFFFFFF;
+#if defined(_WIN64)
+          // Subtract the time it took to queue the timer.
+          const DWORD now = GetTickCount();
+          DWORD post_time = now - (msg.wParam >> 32);
+          milliseconds =
+              post_time > milliseconds ? 0 : milliseconds - post_time;
+#endif
+          UINT_PTR timer_id = SetTimer(nullptr, 0, milliseconds, nullptr);
+          delayed_tasks.insert(std::make_pair(timer_id, task));
+          break;
+        }
+        case WM_TIMER: {
+          KillTimer(nullptr, msg.wParam);
+          auto found = delayed_tasks.find(msg.wParam);
+          RTC_DCHECK(found != delayed_tasks.end());
+          if (!found->second->Run())
+            found->second.release();
+          delayed_tasks.erase(found);
+          break;
+        }
+        default:
+          RTC_NOTREACHED();
+          break;
+      }
+    } else {
+      TranslateMessage(&msg);
+      DispatchMessage(&msg);
+    }
+  }
+
+  return false;
+}
+}  // namespace rtc