New task queueing primitive for async tasks: TaskQueue.

webrtc/base/task_queue_libevent.cc

+/*
+ *  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 <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "base/third_party/libevent/event.h"
+#include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
+#include "webrtc/base/task_queue_posix.h"
+#include "webrtc/base/timeutils.h"
+
+namespace rtc {
+using internal::GetQueuePtrTls;
+using internal::AutoSetCurrentQueuePtr;
+
+namespace {
+static const char kQuit = 1;
+static const char kRunTask = 2;
+
+struct TimerEvent {
+  explicit TimerEvent(std::unique_ptr<QueuedTask> task)
+      : task(std::move(task)) {}
+  ~TimerEvent() { event_del(&ev); }
+  event ev;
+  std::unique_ptr<QueuedTask> task;
+};
+
+bool SetNonBlocking(int fd) {
+  const int flags = fcntl(fd, F_GETFL);
+  RTC_CHECK(flags != -1);
+  return (flags & O_NONBLOCK) || fcntl(fd, F_SETFL, flags | O_NONBLOCK) != -1;
+}
+}  // namespace
+
+struct TaskQueue::QueueContext {
+  explicit QueueContext(TaskQueue* q) : queue(q), is_active(true) {}
+  TaskQueue* queue;
+  bool is_active;
+  // Holds a list of events pending timers for cleanup when the loop exits.
+  std::list<TimerEvent*> pending_timers_;
+};
+
+class TaskQueue::PostAndReplyTask : public QueuedTask {
+ public:
+  PostAndReplyTask(std::unique_ptr<QueuedTask> task,
+                   std::unique_ptr<QueuedTask> reply,
+                   TaskQueue* reply_queue)
+      : task_(std::move(task)),
+        reply_(std::move(reply)),
+        reply_queue_(reply_queue) {
+    reply_queue->PrepareReplyTask(this);
+  }
+
+  ~PostAndReplyTask() override {
+    CritScope lock(&lock_);
+    if (reply_queue_)
+      reply_queue_->ReplyTaskDone(this);
+  }
+
+  void OnReplyQueueGone() {
+    CritScope lock(&lock_);
+    reply_queue_ = nullptr;
+  }
+
+ private:
+  bool Run() override {
+    if (!task_->Run())
+      task_.release();
+
+    CritScope lock(&lock_);
+    if (reply_queue_)
+      reply_queue_->PostTask(std::move(reply_));
+    return true;
+  }
+
+  CriticalSection lock_;
+  std::unique_ptr<QueuedTask> task_, reply_;

[perkj_webrtc, 2016/04/26 14:30:38]

reply_ on separate line please

[tommi, 2016/04/28 12:04:02]

Done.

+  TaskQueue* reply_queue_ GUARDED_BY(lock_);
+};
+
+class TaskQueue::SetTimerTask : public QueuedTask {
+ public:
+  SetTimerTask(std::unique_ptr<QueuedTask> task, uint32_t milliseconds)
+      : task_(std::move(task)),
+        milliseconds_(milliseconds),
+        posted_(Time32()) {}
+
+ private:
+  bool Run() override {
+    // Compensate for the time that has passed since construction
+    // and until we got here.
+    uint32_t post_time = Time32() - posted_;

[perkj_webrtc, 2016/04/26 14:30:38]

Please check with nisse@ that we use the same clock methods (Time32())

[tommi, 2016/04/28 12:04:02]

Yes, I'm following those changes.  I might switch this to TimeMillis() (64bit)
after rebasing.

+    TaskQueue::Current()->PostDelayedTask(
+        std::move(task_),
+        post_time > milliseconds_ ? 0 : milliseconds_ - post_time);
+    return true;
+  }
+
+  std::unique_ptr<QueuedTask> task_;
+  const uint32_t milliseconds_;
+  const uint32_t posted_;
+};
+
+TaskQueue::TaskQueue(const char* queue_name)
+    : event_base_(event_base_new()),
+      wakeup_event_(new event()),
+      thread_(&TaskQueue::ThreadMain, this, queue_name) {
+  RTC_DCHECK(queue_name);
+  int fds[2];
+  RTC_CHECK(pipe(fds) == 0);
+  SetNonBlocking(fds[0]);
+  SetNonBlocking(fds[1]);
+  wakeup_pipe_out_ = fds[0];
+  wakeup_pipe_in_ = fds[1];
+  event_set(wakeup_event_.get(), wakeup_pipe_out_, EV_READ | EV_PERSIST,
+            OnWakeup, this);
+  event_base_set(event_base_, wakeup_event_.get());
+  event_add(wakeup_event_.get(), 0);
+  thread_.Start();
+}
+
+TaskQueue::~TaskQueue() {
+  RTC_DCHECK(!IsCurrent());
+  struct timespec ts;
+  char message = kQuit;
+  while (write(wakeup_pipe_in_, &message, sizeof(message)) != sizeof(message)) {
+    // The queue is full, so we have no choice but to wait and retry.
+    RTC_CHECK_EQ(EAGAIN, errno);
+    ts.tv_sec = 0;
+    ts.tv_nsec = 1000000;
+    nanosleep(&ts, nullptr);
+  }
+
+  thread_.Stop();
+
+  event_del(wakeup_event_.get());
+  close(wakeup_pipe_in_);
+  close(wakeup_pipe_out_);
+  wakeup_pipe_in_ = -1;
+  wakeup_pipe_out_ = -1;
+
+  for (auto* reply : pending_replies_)
+    reply->OnReplyQueueGone();
+  pending_replies_.clear();

[perkj_webrtc, 2016/04/26 14:30:38]

Who owns the PostAndReplyTasks? 

[tommi, 2016/04/28 12:04:02]

They are stored in |pending_| or, if they can't be posted, deleted inside of
PostTask().  In any event, ownership is transferred to PostTask, same as with
other tasks.

+
+  event_base_free(event_base_);
+}
+
+// static
+TaskQueue* TaskQueue::Current() {
+  QueueContext* ctx =
+      static_cast<QueueContext*>(pthread_getspecific(GetQueuePtrTls()));
+  return ctx ? ctx->queue : nullptr;
+}
+
+// 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) {
+  RTC_DCHECK(task.get());
+  // libevent isn't thread safe.  This means that we can't use methods such

[perkj_webrtc, 2016/04/26 14:30:38]

? Didn't you say you fixed that in libevent? 

[tommi, 2016/04/28 12:04:02]

I didn't make libevent thread safe but I did remove libevent's use of global
variables.  That made libevent usable without triggering tsan2 errors, from
multiple, single-threaded, threads. (hope that makes sense)

+  // as event_base_once to post tasks to the worker thread from a different
+  // thread.  However, we can use it when posting from the worker thread itself.
+  if (IsCurrent()) {
+    if (event_base_once(event_base_, -1, EV_TIMEOUT, &TaskQueue::RunTask,
+                        task.get(), nullptr) == 0) {
+      task.release();
+    }
+  } else {
+    QueuedTask* task_id = task.get();  // Only used for comparison.
+    {
+      CritScope lock(&pending_lock_);
+      pending_.push_back(std::move(task));
+    }
+    char message = kRunTask;
+    if (write(wakeup_pipe_in_, &message, sizeof(message)) != sizeof(message)) {
+      LOG(WARNING) << "Failed to queue task.";
+      CritScope lock(&pending_lock_);
+      pending_.remove_if([task_id](std::unique_ptr<QueuedTask>& t) {
+        return t.get() == task_id;
+      });
+    }
+  }
+}
+
+void TaskQueue::PostDelayedTask(std::unique_ptr<QueuedTask> task,
+                                uint32_t milliseconds) {
+  if (IsCurrent()) {
+    TimerEvent* timer = new TimerEvent(std::move(task));
+    evtimer_set(&timer->ev, &TaskQueue::RunTimer, timer);
+    event_base_set(event_base_, &timer->ev);
+    QueueContext* ctx =
+        static_cast<QueueContext*>(pthread_getspecific(GetQueuePtrTls()));
+    ctx->pending_timers_.push_back(timer);
+    timeval tv = {milliseconds / 1000, (milliseconds % 1000) * 1000};
+    event_add(&timer->ev, &tv);
+  } else {
+    PostTask(std::unique_ptr<QueuedTask>(
+        new SetTimerTask(std::move(task), milliseconds)));
+  }
+}
+
+void TaskQueue::PostTaskAndReply(std::unique_ptr<QueuedTask> task,
+                                 std::unique_ptr<QueuedTask> reply,
+                                 TaskQueue* reply_queue) {
+  std::unique_ptr<QueuedTask> wrapper_task(
+      new PostAndReplyTask(std::move(task), std::move(reply), reply_queue));
+  PostTask(std::move(wrapper_task));

[tommi, 2016/04/28 12:04:02]

Here is where ownership of PostAndReplyTasks is handed over to PostTask.

+}
+
+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) {
+  TaskQueue* me = static_cast<TaskQueue*>(context);
+
+  QueueContext queue_context(me);
+  pthread_setspecific(GetQueuePtrTls(), &queue_context);
+
+  while (queue_context.is_active)
+    event_base_loop(me->event_base_, 0);
+
+  pthread_setspecific(GetQueuePtrTls(), nullptr);
+
+  for (TimerEvent* timer : queue_context.pending_timers_)
+    delete timer;
+
+  return false;
+}
+
+// static
+void TaskQueue::OnWakeup(int socket, short flags, void* context) {  // NOLINT
+  QueueContext* ctx =
+      static_cast<QueueContext*>(pthread_getspecific(GetQueuePtrTls()));
+  RTC_DCHECK(ctx->queue->wakeup_pipe_out_ == socket);
+  char buf;
+  RTC_CHECK(sizeof(buf) == read(socket, &buf, sizeof(buf)));
+  switch (buf) {
+    case kQuit:
+      ctx->is_active = false;
+      event_base_loopbreak(ctx->queue->event_base_);
+      break;
+    case kRunTask: {
+      std::unique_ptr<QueuedTask> task;
+      {
+        CritScope lock(&ctx->queue->pending_lock_);
+        RTC_DCHECK(!ctx->queue->pending_.empty());
+        task = std::move(ctx->queue->pending_.front());
+        ctx->queue->pending_.pop_front();
+        RTC_DCHECK(task.get());
+      }
+      if (!task->Run())
+        task.release();
+      break;
+    }
+    default:
+      RTC_NOTREACHED();
+      break;
+  }
+}
+
+// static
+void TaskQueue::RunTask(int fd, short flags, void* context) {  // NOLINT
+  auto* task = static_cast<QueuedTask*>(context);
+  if (task->Run())
+    delete task;
+}
+
+// static
+void TaskQueue::RunTimer(int fd, short flags, void* context) {  // NOLINT
+  TimerEvent* timer = static_cast<TimerEvent*>(context);
+  if (!timer->task->Run())
+    timer->task.release();
+  QueueContext* ctx =
+      static_cast<QueueContext*>(pthread_getspecific(GetQueuePtrTls()));
+  ctx->pending_timers_.remove(timer);
+  delete timer;
+}
+
+void TaskQueue::PrepareReplyTask(PostAndReplyTask* reply_task) {
+  RTC_DCHECK(reply_task);
+  CritScope lock(&pending_lock_);
+  pending_replies_.push_back(reply_task);
+}
+
+void TaskQueue::ReplyTaskDone(PostAndReplyTask* reply_task) {
+  CritScope lock(&pending_lock_);
+  pending_replies_.remove(reply_task);
+}
+
+}  // namespace rtc