components/html_viewer/web_thread_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 "components/html_viewer/web_thread_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 html_viewer {
  18
  19 WebThreadBase::WebThreadBase() {}
  20 WebThreadBase::~WebThreadBase() {}
  21
  22 class WebThreadBase::TaskObserverAdapter
  23     : public base::MessageLoop::TaskObserver {
  24  public:
  25   TaskObserverAdapter(WebThread::TaskObserver* observer)
  26       : observer_(observer) {}
  27
  28   void WillProcessTask(const base::PendingTask& pending_task) override {
  29     observer_->willProcessTask();
  30   }
  31
  32   void DidProcessTask(const base::PendingTask& pending_task) override {
  33     observer_->didProcessTask();
  34   }
  35
  36 private:
  37   WebThread::TaskObserver* observer_;
  38 };
  39
  40 void WebThreadBase::addTaskObserver(TaskObserver* observer) {
  41   CHECK(isCurrentThread());
  42   std::pair<TaskObserverMap::iterator, bool> result = task_observer_map_.insert(
  43       std::make_pair(observer, static_cast<TaskObserverAdapter*>(NULL)));
  44   if (result.second)
  45     result.first->second = new TaskObserverAdapter(observer);
  46   base::MessageLoop::current()->AddTaskObserver(result.first->second);
  47 }
  48
  49 void WebThreadBase::removeTaskObserver(TaskObserver* observer) {
  50   CHECK(isCurrentThread());
  51   TaskObserverMap::iterator iter = task_observer_map_.find(observer);
  52   if (iter == task_observer_map_.end())
  53     return;
  54   base::MessageLoop::current()->RemoveTaskObserver(iter->second);
  55   delete iter->second;
  56   task_observer_map_.erase(iter);
  57 }
  58
  59 WebThreadImpl::WebThreadImpl(const char* name)
  60     : thread_(new base::Thread(name)),
  61       web_scheduler_(new WebSchedulerImpl(thread_->task_runner())) {
  62   thread_->Start();
  63 }
  64
  65 // RunWebThreadTask takes the ownership of |task| from base::Closure and
  66 // deletes it on the first invocation of the closure for thread-safety.
  67 // base::Closure made from RunWebThreadTask is copyable but Closure::Run
  68 // should be called at most only once.
  69 // This is because WebThread::Task can contain RefPtr to a
  70 // thread-unsafe-reference-counted object (e.g. WorkerThreadTask can contain
  71 // RefPtr to WebKit's StringImpl), and if we don't delete |task| here,
  72 // it causes a race condition as follows:
  73 // [A] In task->run(), more RefPtr's to the refcounted object can be created,
  74 //     and the reference counter of the object can be modified via these
  75 //     RefPtr's (as intended) on the thread where the task is executed.
  76 // [B] However, base::Closure still retains the ownership of WebThread::Task
  77 //     even after RunWebThreadTask is called.
  78 //     When base::Closure is deleted, WebThread::Task is deleted and the
  79 //     reference counter of the object is decreased by one, possibly from a
  80 //     different thread from [A], which is a race condition.
  81 // Taking the ownership of |task| here by using scoped_ptr and base::Passed
  82 // removes the reference counter modification of [B] and the race condition.
  83 // When the closure never runs at all, the corresponding WebThread::Task is
  84 // destructed when base::Closure is deleted (like [B]). In this case, there
  85 // are no reference counter modification like [A] (because task->run() is not
  86 // executed), so there are no race conditions.
  87 // See https://crbug.com/390851 for more details.
  88 static void RunWebThreadTask(scoped_ptr<blink::WebThread::Task> task) {
  89     task->run();
  90 }
  91
  92 void WebThreadImpl::postTask(const blink::WebTraceLocation& location,
  93                              Task* task) {
  94   postDelayedTask(location, task, 0);
  95 }
  96
  97 void WebThreadImpl::postDelayedTask(const blink::WebTraceLocation& web_location,
  98                                     Task* task,
  99                                     long long delay_ms) {
 100   tracked_objects::Location location(web_location.functionName(),
 101                                      web_location.fileName(), -1, nullptr);
 102   thread_->message_loop()->PostDelayedTask(
 103       location,
 104       base::Bind(RunWebThreadTask, base::Passed(make_scoped_ptr(task))),
 105       base::TimeDelta::FromMilliseconds(delay_ms));
 106 }
 107
 108 void WebThreadImpl::enterRunLoop() {
 109   CHECK(isCurrentThread());
 110   CHECK(!thread_->message_loop()->is_running());  // We don't support nesting.
 111   thread_->message_loop()->Run();
 112 }
 113
 114 void WebThreadImpl::exitRunLoop() {
 115   CHECK(isCurrentThread());
 116   CHECK(thread_->message_loop()->is_running());
 117   thread_->message_loop()->Quit();
 118 }
 119
 120 blink::WebScheduler* WebThreadImpl::scheduler() const {
 121   return web_scheduler_.get();
 122 }
 123
 124 bool WebThreadImpl::isCurrentThread() const {
 125   return thread_->thread_id() == base::PlatformThread::CurrentId();
 126 }
 127
 128 blink::PlatformThreadId WebThreadImpl::threadId() const {
 129   return thread_->thread_id();
 130 }
 131
 132 WebThreadImpl::~WebThreadImpl() {
 133   thread_->Stop();
 134 }
 135
 136 WebThreadImplForMessageLoop::WebThreadImplForMessageLoop(
 137     base::MessageLoopProxy* message_loop)
 138     : message_loop_(message_loop),
 139       web_scheduler_(new WebSchedulerImpl(message_loop_)) {
 140 }
 141
 142 void WebThreadImplForMessageLoop::postTask(
 143     const blink::WebTraceLocation& location,
 144     Task* task) {
 145   postDelayedTask(location, task, 0);
 146 }
 147
 148 void WebThreadImplForMessageLoop::postDelayedTask(
 149     const blink::WebTraceLocation& web_location,
 150     Task* task,
 151     long long delay_ms) {
 152   tracked_objects::Location location(web_location.functionName(),
 153                                      web_location.fileName(), -1, nullptr);
 154   message_loop_->PostDelayedTask(
 155       location,
 156       base::Bind(RunWebThreadTask, base::Passed(make_scoped_ptr(task))),
 157       base::TimeDelta::FromMilliseconds(delay_ms));
 158 }
 159
 160 void WebThreadImplForMessageLoop::enterRunLoop() {
 161   CHECK(isCurrentThread());
 162   // We don't support nesting.
 163   CHECK(!base::MessageLoop::current()->is_running());
 164   base::MessageLoop::current()->Run();
 165 }
 166
 167 void WebThreadImplForMessageLoop::exitRunLoop() {
 168   CHECK(isCurrentThread());
 169   CHECK(base::MessageLoop::current()->is_running());
 170   base::MessageLoop::current()->Quit();
 171 }
 172
 173 blink::WebScheduler* WebThreadImplForMessageLoop::scheduler() const {
 174   return web_scheduler_.get();
 175 }
 176
 177 bool WebThreadImplForMessageLoop::isCurrentThread() const {
 178   return message_loop_->BelongsToCurrentThread();
 179 }
 180
 181 blink::PlatformThreadId WebThreadImplForMessageLoop::threadId() const {
 182   return thread_id_;
 183 }
 184
 185 WebThreadImplForMessageLoop::~WebThreadImplForMessageLoop() {}
 186
 187 }  // namespace html_viewer