New task queueing primitive for async tasks: TaskQueue.

webrtc/base/task_queue.h

Index: webrtc/base/task_queue.h
diff --git a/webrtc/base/task_queue.h b/webrtc/base/task_queue.h
new file mode 100644
index 0000000000000000000000000000000000000000..162088b9cbd7a31ae86bf201fe44ed9a339426de
--- /dev/null
+++ b/webrtc/base/task_queue.h
@@ -0,0 +1,178 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_BASE_TASK_QUEUE_H_
+#define WEBRTC_BASE_TASK_QUEUE_H_
+
+#if defined(WEBRTC_POSIX) && !defined(WEBRTC_MAC)
+#define LIBEVENT_TASK_QUEUE
+#endif
+
+#include <list>
+#include <memory>
+
+#if defined(WEBRTC_MAC)
+#include <dispatch/dispatch.h>
+#endif
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/criticalsection.h"
+
+#if !defined(WEBRTC_MAC)
+#include "webrtc/base/platform_thread.h"
+#endif
+
+#if defined(LIBEVENT_TASK_QUEUE)
+struct event_base;
+struct event;
+#endif
+
+namespace rtc {
+
+class QueuedTask {
+ public:
+  QueuedTask() {}
+  virtual ~QueuedTask() {}
+
+  // Main routine that will run when the task is executed on the desired queue.
+  // The task should return |true| to indicate that it should be deleted or
+  // |false| to indicate that the queue should consider ownership of the task
+  // having been transferred.  Returning |false| can be useful if a task has
+  // re-posted itself to a different queue or is otherwise being re-used.
+  virtual bool Run() = 0;
+
+ private:
+  RTC_DISALLOW_COPY_AND_ASSIGN(QueuedTask);
+};
+
+// Simple implementation of QueuedTask for use with rtc::Bind and lambdas.
+template <class Closure>
+class ClosureTask : public QueuedTask {
+ public:
+  explicit ClosureTask(const Closure& closure) : closure_(closure) {}
+
+ private:
+  bool Run() override {
+    closure_();
+    return true;
+  }
+
+  Closure closure_;
+};
+
+// Implements a task queue that asynchronously executes tasks in a way that
+// guarantees that they're executed in FIFO order and tasks never overlap.
+// Tasks may always execute on the same worker thread and they may not.
+// To DCHECK that tasks are executing on a known task queue, use IsCurrent().
+class TaskQueue {

[perkj_webrtc, 2016/04/26 14:30:37]

please add usage exampled in the description.

[tommi, 2016/04/28 12:04:01]

Done.

+ public:
+  explicit TaskQueue(const char* queue_name);
+  // TODO(tommi): Implement move semantics?
+  ~TaskQueue();
+
+  static TaskQueue* Current();
+
+  // Used for DCHECKing the current queue.
+  static bool IsCurrent(const char* queue_name);
+  bool IsCurrent() const;
+
+  // TODO(tommi): For better debuggability, implement FROM_HERE.
+
+  // Ownership of the task is passed to PostTask.
+  void PostTask(std::unique_ptr<QueuedTask> task);
+  // TODO(tommi): Should we expose this variant publicly
+  // (or only the other one)?
+  void PostTaskAndReply(std::unique_ptr<QueuedTask> task,

[perkj_webrtc, 2016/04/26 14:30:37]

I vote for only the simple one until it is needed. Seems like it would be hard
to follow what is going on if you post a reply on a separate queue.

[tommi, 2016/04/28 12:04:01]

Done.

+                        std::unique_ptr<QueuedTask> reply,
+                        TaskQueue* reply_queue);
+  void PostTaskAndReply(std::unique_ptr<QueuedTask> task,
+                        std::unique_ptr<QueuedTask> reply);
+
+  void PostDelayedTask(std::unique_ptr<QueuedTask> task, uint32_t milliseconds);
+
+  template <class Closure>
+  void PostTask(const Closure& closure) {
+    PostTask(std::unique_ptr<QueuedTask>(new ClosureTask<Closure>(closure)));
+  }
+
+  template <class Closure>
+  void PostDelayedTask(const Closure& closure, uint32_t milliseconds) {
+    PostDelayedTask(
+        std::unique_ptr<QueuedTask>(new ClosureTask<Closure>(closure)),
+        milliseconds);
+  }
+
+  template <class Closure1, class Closure2>
+  void PostTaskAndReply(const Closure1& task,
+                        const Closure2& reply,
+                        TaskQueue* reply_queue) {
+    PostTaskAndReply(
+        std::unique_ptr<QueuedTask>(new ClosureTask<Closure1>(task)),
+        std::unique_ptr<QueuedTask>(new ClosureTask<Closure2>(reply)),
+        reply_queue);
+  }
+
+  template <class Closure1, class Closure2>
+  void PostTaskAndReply(const Closure1& task, const Closure2& reply) {
+    PostTaskAndReply(
+        std::unique_ptr<QueuedTask>(new ClosureTask<Closure1>(task)),
+        std::unique_ptr<QueuedTask>(new ClosureTask<Closure2>(reply)));
+  }
+
+ private:
+#if defined(LIBEVENT_TASK_QUEUE)
+  static bool ThreadMain(void* context);
+  static void OnWakeup(int socket, short flags, void* context);  // NOLINT
+  static void RunTask(int fd, short flags, void* context);       // NOLINT
+  static void RunTimer(int fd, short flags, void* context);      // NOLINT
+
+  class PostAndReplyTask;
+  class SetTimerTask;
+
+  void PrepareReplyTask(PostAndReplyTask* reply_task);
+  void ReplyTaskDone(PostAndReplyTask* reply_task);
+
+  struct QueueContext;
+
+  int wakeup_pipe_in_ = -1;
+  int wakeup_pipe_out_ = -1;
+  event_base* event_base_;
+  std::unique_ptr<event> wakeup_event_;
+  PlatformThread thread_;
+  rtc::CriticalSection pending_lock_;
+  std::list<std::unique_ptr<QueuedTask>> pending_ GUARDED_BY(pending_lock_);
+  std::list<PostAndReplyTask*> pending_replies_ GUARDED_BY(pending_lock_);
+#elif defined(WEBRTC_MAC)
+  struct QueueContext;
+  dispatch_queue_t queue_;
+  QueueContext* const context_;
+#elif defined(WEBRTC_WIN)
+  static bool ThreadMain(void* context);
+
+  class WorkerThread : public PlatformThread {
+   public:
+    WorkerThread(ThreadRunFunction func, void* obj, const char* thread_name)
+        : PlatformThread(func, obj, thread_name) {}
+
+    bool QueueAPC(PAPCFUNC apc_function, ULONG_PTR data) {
+      return PlatformThread::QueueAPC(apc_function, data);
+    }
+  };
+  WorkerThread thread_;
+#else
+#error not supported.
+#endif
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(TaskQueue);
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_TASK_QUEUE_H_