Revert of Revert of Add a WorkerScheduler and a WebThreadImplForWorker

content/child/webthread_base.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_base.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/pending_task.h"
+#include "base/threading/platform_thread.h"
+#include "content/child/scheduler/single_thread_idle_task_runner.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();
+}
+
+// static
+void WebThreadBase::RunWebThreadIdleTask(
+    scoped_ptr<blink::WebThread::IdleTask> idle_task,
+    base::TimeTicks deadline) {
+  idle_task->run((deadline - base::TimeTicks()).InSecondsF());
+}
+
+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::postIdleTask(const blink::WebTraceLocation& web_location,
+                                 IdleTask* idle_task) {
+  tracked_objects::Location location(web_location.functionName(),
+                                     web_location.fileName(), -1, nullptr);
+  IdleTaskRunner()->PostIdleTask(
+      location, base::Bind(&WebThreadBase::RunWebThreadIdleTask,
+                           base::Passed(make_scoped_ptr(idle_task))));
+}
+
+void WebThreadBase::postIdleTaskAfterWakeup(
+    const blink::WebTraceLocation& web_location,
+    IdleTask* idle_task) {
+  tracked_objects::Location location(web_location.functionName(),
+                                     web_location.fileName(), -1, nullptr);
+  IdleTaskRunner()->PostIdleTaskAfterWakeup(
+      location, base::Bind(&WebThreadBase::RunWebThreadIdleTask,
+                           base::Passed(make_scoped_ptr(idle_task))));
+}
+
+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();
+}
+
+}  // namespace content