content/child/webthread_impl.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // An implementation of WebThread in terms of base::MessageLoop and
   6 // base::Thread
   7
   8 #include "content/child/webthread_impl.h"
   9
  10 #include "base/bind.h"
  11 #include "base/bind_helpers.h"
  12 #include "base/message_loop/message_loop.h"
  13 #include "base/pending_task.h"
  14 #include "base/threading/platform_thread.h"
  15 #include "third_party/WebKit/public/platform/WebTraceLocation.h"
  16
  17 namespace content {
  18
  19 class WebThreadBase::TaskObserverAdapter
  20     : public base::MessageLoop::TaskObserver {
  21  public:
  22   TaskObserverAdapter(WebThread::TaskObserver* observer)
  23       : observer_(observer) {}
  24
  25   void WillProcessTask(const base::PendingTask& pending_task) override {
  26     observer_->willProcessTask();
  27   }
  28
  29   void DidProcessTask(const base::PendingTask& pending_task) override {
  30     observer_->didProcessTask();
  31   }
  32
  33 private:
  34   WebThread::TaskObserver* observer_;
  35 };
  36
  37 WebThreadBase::WebThreadBase() {
  38 }
  39
  40 WebThreadBase::~WebThreadBase() {
  41   for (auto& observer_entry : task_observer_map_) {
  42     delete observer_entry.second;
  43   }
  44 }
  45
  46 void WebThreadBase::addTaskObserver(TaskObserver* observer) {
  47   CHECK(isCurrentThread());
  48   std::pair<TaskObserverMap::iterator, bool> result = task_observer_map_.insert(
  49       std::make_pair(observer, static_cast<TaskObserverAdapter*>(NULL)));
  50   if (result.second)
  51     result.first->second = new TaskObserverAdapter(observer);
  52   AddTaskObserverInternal(result.first->second);
  53 }
  54
  55 void WebThreadBase::removeTaskObserver(TaskObserver* observer) {
  56   CHECK(isCurrentThread());
  57   TaskObserverMap::iterator iter = task_observer_map_.find(observer);
  58   if (iter == task_observer_map_.end())
  59     return;
  60   RemoveTaskObserverInternal(iter->second);
  61   delete iter->second;
  62   task_observer_map_.erase(iter);
  63 }
  64
  65 void WebThreadBase::AddTaskObserverInternal(
  66     base::MessageLoop::TaskObserver* observer) {
  67   base::MessageLoop::current()->AddTaskObserver(observer);
  68 }
  69
  70 void WebThreadBase::RemoveTaskObserverInternal(
  71     base::MessageLoop::TaskObserver* observer) {
  72   base::MessageLoop::current()->RemoveTaskObserver(observer);
  73 }
  74
  75 // RunWebThreadTask takes the ownership of |task| from base::Closure and
  76 // deletes it on the first invocation of the closure for thread-safety.
  77 // base::Closure made from RunWebThreadTask is copyable but Closure::Run
  78 // should be called at most only once.
  79 // This is because WebThread::Task can contain RefPtr to a
  80 // thread-unsafe-reference-counted object (e.g. WorkerThreadTask can contain
  81 // RefPtr to WebKit's StringImpl), and if we don't delete |task| here,
  82 // it causes a race condition as follows:
  83 // [A] In task->run(), more RefPtr's to the refcounted object can be created,
  84 //     and the reference counter of the object can be modified via these
  85 //     RefPtr's (as intended) on the thread where the task is executed.
  86 // [B] However, base::Closure still retains the ownership of WebThread::Task
  87 //     even after RunWebThreadTask is called.
  88 //     When base::Closure is deleted, WebThread::Task is deleted and the
  89 //     reference counter of the object is decreased by one, possibly from a
  90 //     different thread from [A], which is a race condition.
  91 // Taking the ownership of |task| here by using scoped_ptr and base::Passed
  92 // removes the reference counter modification of [B] and the race condition.
  93 // When the closure never runs at all, the corresponding WebThread::Task is
  94 // destructed when base::Closure is deleted (like [B]). In this case, there
  95 // are no reference counter modification like [A] (because task->run() is not
  96 // executed), so there are no race conditions.
  97 // See https://crbug.com/390851 for more details.
  98 //
  99 // static
 100 void WebThreadBase::RunWebThreadTask(scoped_ptr<blink::WebThread::Task> task) {
 101   task->run();
 102 }
 103
 104 void WebThreadBase::postTask(const blink::WebTraceLocation& location,
 105                              Task* task) {
 106   postDelayedTask(location, task, 0);
 107 }
 108
 109 void WebThreadBase::postDelayedTask(const blink::WebTraceLocation& web_location,
 110                                     Task* task,
 111                                     long long delay_ms) {
 112   tracked_objects::Location location(web_location.functionName(),
 113                                      web_location.fileName(), -1, nullptr);
 114   TaskRunner()->PostDelayedTask(
 115       location,
 116       base::Bind(RunWebThreadTask, base::Passed(make_scoped_ptr(task))),
 117       base::TimeDelta::FromMilliseconds(delay_ms));
 118 }
 119
 120 void WebThreadBase::enterRunLoop() {
 121   CHECK(isCurrentThread());
 122   CHECK(!MessageLoop()->is_running());  // We don't support nesting.
 123   MessageLoop()->Run();
 124 }
 125
 126 void WebThreadBase::exitRunLoop() {
 127   CHECK(isCurrentThread());
 128   CHECK(MessageLoop()->is_running());
 129   MessageLoop()->Quit();
 130 }
 131
 132 bool WebThreadBase::isCurrentThread() const {
 133   return TaskRunner()->BelongsToCurrentThread();
 134 }
 135
 136 blink::PlatformThreadId WebThreadImpl::threadId() const {
 137   return thread_->thread_id();
 138 }
 139
 140 WebThreadImpl::WebThreadImpl(const char* name)
 141     : thread_(new base::Thread(name)) {
 142   thread_->Start();
 143 }
 144
 145 WebThreadImpl::~WebThreadImpl() {
 146   thread_->Stop();
 147 }
 148
 149 base::MessageLoop* WebThreadImpl::MessageLoop() const {
 150   return thread_->message_loop();
 151 }
 152
 153 base::SingleThreadTaskRunner* WebThreadImpl::TaskRunner() const {
 154   return thread_->message_loop_proxy().get();
 155 }
 156
 157 WebThreadImplForMessageLoop::WebThreadImplForMessageLoop(
 158     scoped_refptr<base::SingleThreadTaskRunner> owning_thread_task_runner)
 159     : owning_thread_task_runner_(owning_thread_task_runner),
 160       thread_id_(base::PlatformThread::CurrentId()) {
 161 }
 162
 163 blink::PlatformThreadId WebThreadImplForMessageLoop::threadId() const {
 164   return thread_id_;
 165 }
 166
 167 WebThreadImplForMessageLoop::~WebThreadImplForMessageLoop() {
 168 }
 169
 170 base::MessageLoop* WebThreadImplForMessageLoop::MessageLoop() const {
 171   DCHECK(isCurrentThread());
 172   return base::MessageLoop::current();
 173 }
 174
 175 base::SingleThreadTaskRunner* WebThreadImplForMessageLoop::TaskRunner() const {
 176   return owning_thread_task_runner_.get();
 177 }
 178
 179 }  // namespace content