TaskScheduler [6] SchedulerWorkerThread

base/task_scheduler/worker_thread.cc

+// Copyright 2016 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/task_scheduler/worker_thread.h"
+
+#include <stddef.h>
+
+#include <utility>
+
+#include "base/logging.h"
+#include "base/task_scheduler/task_tracker.h"
+
+namespace base {
+namespace internal {
+
+scoped_ptr<WorkerThread> WorkerThread::CreateWorkerThread(
+    ThreadPriority thread_priority,
+    const GetWorkCallback& get_work_callback,
+    const RanTaskFromSequenceCallback& ran_task_from_sequence_callback,
+    TaskTracker* task_tracker) {
+  scoped_ptr<WorkerThread> worker_thread(
+      new WorkerThread(thread_priority, get_work_callback,
+                       ran_task_from_sequence_callback, task_tracker));
+
+  if (worker_thread->thread_handle_.is_null())
+    return scoped_ptr<WorkerThread>();
+  return worker_thread;
+}
+
+WorkerThread::~WorkerThread() {
+  DCHECK(should_exit_for_testing());
+}
+
+void WorkerThread::WakeUp() {
+  wake_up_event_.Signal();
+}
+
+void WorkerThread::JoinForTesting() {
+  should_exit_for_testing_ = true;
+  base::subtle::MemoryBarrier();
+  WakeUp();
+  PlatformThread::Join(thread_handle_);
+}
+
+WorkerThread::WorkerThread(
+    ThreadPriority thread_priority,
+    const GetWorkCallback& get_work_callback,
+    const RanTaskFromSequenceCallback& ran_task_from_sequence_callback,
+    TaskTracker* task_tracker)
+    : wake_up_event_(false, false),
+      get_work_callback_(get_work_callback),
+      ran_task_from_sequence_callback_(ran_task_from_sequence_callback),
+      task_tracker_(task_tracker) {
+  DCHECK(!get_work_callback_.is_null());
+  DCHECK(!ran_task_from_sequence_callback_.is_null());
+  DCHECK(task_tracker_);
+
+  static const size_t kDefaultStackSize = 0;
+  PlatformThread::CreateWithPriority(kDefaultStackSize, this, &thread_handle_,
+                                     thread_priority);
+}
+
+void WorkerThread::ThreadMain() {
+  // Wait for a wake-up.

[robliao, 2016/03/30 19:38:26]

Instead, consider commenting that all WorkerThreads start out sleeping.

[fdoray, 2016/03/30 19:56:37]

Done.

+  wake_up_event_.Wait();
+
+  while (!task_tracker_->shutdown_completed() && !should_exit_for_testing()) {
+    // Get the sequence containing the next task to execute.
+    scoped_refptr<Sequence> sequence = get_work_callback_.Run(this);
+
+    if (!sequence) {
+      // Wait for a wake-up.

[robliao, 2016/03/30 19:38:26]

Nit: Remove this comment.

[fdoray, 2016/03/30 19:56:37]

Done.

+      wake_up_event_.Wait();
+      continue;
+    }
+
+    // Peek the next task in |sequence| and try to run it.

[robliao, 2016/03/30 19:38:27]

Nit: This comment can be removed here as it just restates the code below. 

[fdoray, 2016/03/30 19:56:37]

Done.

+    task_tracker_->RunTask(sequence->PeekTask());
+
+    // Notify |ran_task_from_sequence_callback_| that this WorkerThread tried to
+    // run a Task from |sequence|.

[robliao, 2016/03/30 19:38:26]

Same here

[fdoray, 2016/03/30 19:56:37]

Done.

+    ran_task_from_sequence_callback_.Run(this, std::move(sequence));
+
+    // Calling WakeUp() guarantees that this WorkerThread will run Tasks from

[robliao, 2016/03/30 19:38:27]

This comment is worth keeping as it explains the reason this statement is here.

[fdoray, 2016/03/30 19:56:37]

Acknowledged.

+    // Sequences returned by |get_work_callback_| until the callback returns
+    // nullptr. Resetting |wake_up_event_| here doesn't break this invariant and
+    // avoids a useless loop iteration before going to sleep if WakeUp() is
+    // called while this WorkerThread is awake.
+    wake_up_event_.Reset();
+  }
+}
+
+}  // namespace internal
+}  // namespace base