Revert of Revert of Add a WorkerScheduler and a WebThreadImplForWorker

content/child/webthread_impl.cc

-// Copyright 2014 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.
-
-// An implementation of WebThread in terms of base::MessageLoop and
-// base::Thread
-
-#include "content/child/webthread_impl.h"
-
-#include "base/bind.h"
-#include "base/bind_helpers.h"
-#include "base/pending_task.h"
-#include "base/threading/platform_thread.h"
-#include "third_party/WebKit/public/platform/WebTraceLocation.h"
-
-namespace content {
-
-class WebThreadBase::TaskObserverAdapter
-    : public base::MessageLoop::TaskObserver {
- public:
-  TaskObserverAdapter(WebThread::TaskObserver* observer)
-      : observer_(observer) {}
-
-  void WillProcessTask(const base::PendingTask& pending_task) override {
-    observer_->willProcessTask();
-  }
-
-  void DidProcessTask(const base::PendingTask& pending_task) override {
-    observer_->didProcessTask();
-  }
-
-private:
-  WebThread::TaskObserver* observer_;
-};
-
-WebThreadBase::WebThreadBase() {
-}
-
-WebThreadBase::~WebThreadBase() {
-  for (auto& observer_entry : task_observer_map_) {
-    delete observer_entry.second;
-  }
-}
-
-void WebThreadBase::addTaskObserver(TaskObserver* observer) {
-  CHECK(isCurrentThread());
-  std::pair<TaskObserverMap::iterator, bool> result = task_observer_map_.insert(
-      std::make_pair(observer, static_cast<TaskObserverAdapter*>(NULL)));
-  if (result.second)
-    result.first->second = new TaskObserverAdapter(observer);
-  AddTaskObserverInternal(result.first->second);
-}
-
-void WebThreadBase::removeTaskObserver(TaskObserver* observer) {
-  CHECK(isCurrentThread());
-  TaskObserverMap::iterator iter = task_observer_map_.find(observer);
-  if (iter == task_observer_map_.end())
-    return;
-  RemoveTaskObserverInternal(iter->second);
-  delete iter->second;
-  task_observer_map_.erase(iter);
-}
-
-void WebThreadBase::AddTaskObserverInternal(
-    base::MessageLoop::TaskObserver* observer) {
-  base::MessageLoop::current()->AddTaskObserver(observer);
-}
-
-void WebThreadBase::RemoveTaskObserverInternal(
-    base::MessageLoop::TaskObserver* observer) {
-  base::MessageLoop::current()->RemoveTaskObserver(observer);
-}
-
-// RunWebThreadTask takes the ownership of |task| from base::Closure and
-// deletes it on the first invocation of the closure for thread-safety.
-// base::Closure made from RunWebThreadTask is copyable but Closure::Run
-// should be called at most only once.
-// This is because WebThread::Task can contain RefPtr to a
-// thread-unsafe-reference-counted object (e.g. WorkerThreadTask can contain
-// RefPtr to WebKit's StringImpl), and if we don't delete |task| here,
-// it causes a race condition as follows:
-// [A] In task->run(), more RefPtr's to the refcounted object can be created,
-//     and the reference counter of the object can be modified via these
-//     RefPtr's (as intended) on the thread where the task is executed.
-// [B] However, base::Closure still retains the ownership of WebThread::Task
-//     even after RunWebThreadTask is called.
-//     When base::Closure is deleted, WebThread::Task is deleted and the
-//     reference counter of the object is decreased by one, possibly from a
-//     different thread from [A], which is a race condition.
-// Taking the ownership of |task| here by using scoped_ptr and base::Passed
-// removes the reference counter modification of [B] and the race condition.
-// When the closure never runs at all, the corresponding WebThread::Task is
-// destructed when base::Closure is deleted (like [B]). In this case, there
-// are no reference counter modification like [A] (because task->run() is not
-// executed), so there are no race conditions.
-// See https://crbug.com/390851 for more details.
-//
-// static
-void WebThreadBase::RunWebThreadTask(scoped_ptr<blink::WebThread::Task> task) {
-  task->run();
-}
-
-void WebThreadBase::postTask(const blink::WebTraceLocation& location,
-                             Task* task) {
-  postDelayedTask(location, task, 0);
-}
-
-void WebThreadBase::postDelayedTask(const blink::WebTraceLocation& web_location,
-                                    Task* task,
-                                    long long delay_ms) {
-  tracked_objects::Location location(web_location.functionName(),
-                                     web_location.fileName(), -1, nullptr);
-  TaskRunner()->PostDelayedTask(
-      location,
-      base::Bind(RunWebThreadTask, base::Passed(make_scoped_ptr(task))),
-      base::TimeDelta::FromMilliseconds(delay_ms));
-}
-
-void WebThreadBase::enterRunLoop() {
-  CHECK(isCurrentThread());
-  CHECK(MessageLoop());
-  CHECK(!MessageLoop()->is_running());  // We don't support nesting.
-  MessageLoop()->Run();
-}
-
-void WebThreadBase::exitRunLoop() {
-  CHECK(isCurrentThread());
-  CHECK(MessageLoop());
-  CHECK(MessageLoop()->is_running());
-  MessageLoop()->Quit();
-}
-
-bool WebThreadBase::isCurrentThread() const {
-  return TaskRunner()->BelongsToCurrentThread();
-}
-
-blink::PlatformThreadId WebThreadImpl::threadId() const {
-  return thread_->thread_id();
-}
-
-WebThreadImpl::WebThreadImpl(const char* name)
-    : thread_(new base::Thread(name)) {
-  thread_->Start();
-}
-
-WebThreadImpl::~WebThreadImpl() {
-  thread_->Stop();
-}
-
-base::MessageLoop* WebThreadImpl::MessageLoop() const {
-  return nullptr;
-}
-
-base::SingleThreadTaskRunner* WebThreadImpl::TaskRunner() const {
-  return thread_->message_loop_proxy().get();
-}
-
-}  // namespace content