[Thread-safe] Apply base::Passed to WebThread::Task

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"
@@ skipping 42 matching lines @@
   base::MessageLoop::current()->RemoveTaskObserver(iter->second);
   delete iter->second;
   task_observer_map_.erase(iter);
 }
 
 WebThreadImpl::WebThreadImpl(const char* name)
     : thread_(new base::Thread(name)) {
   thread_->Start();
 }
 
+static void RunWebThreadTask(scoped_ptr<blink::WebThread::Task> task)

[dcheng, 2014/12/18 19:31:38]

This code is really subtle. Can we expand this comment to describe why this is
necessary instead of just referencing a bug?

Also, if this task never runs at all, won't it potentially still be destroyed on
the wrong thread?

[hiroshige, 2014/12/19 09:16:11]

Added comments.
Yes, |WebThread::Task| can be destoyed on any thread, but in that case there is
no race condition, as described in the comment I added.
I think deleting |WebThread::Task| (and thus its parameters including
|StringImpl|) on a different thread from the thread where the task is intended
to be executed is not a problem. (if there is any specific problem please let me
know...)

+// Take ownership of blink::WebThread::Task and delete it on first |run|

[nasko, 2014/12/18 17:53:25]

nit: Comment should be before the method starts.

[hiroshige, 2014/12/19 09:16:11]

Done.

+// for thread-safety. http://crbug.com/390851, Comment #19
+{

[nasko, 2014/12/18 17:53:25]

Brace goes on the same line as the method params ending.

[hiroshige, 2014/12/19 09:16:11]

Done.

+    task->run();
+}
+
 void WebThreadImpl::postTask(Task* task) {
   thread_->message_loop()->PostTask(
-      FROM_HERE, base::Bind(&blink::WebThread::Task::run, base::Owned(task)));
+      FROM_HERE,
+      base::Bind(RunWebThreadTask, base::Passed(scoped_ptr<Task>(task))));

[dcheng, 2014/12/18 19:31:38]

It's slightly shorter to use make_scoped_ptr.

[hiroshige, 2014/12/19 09:16:11]

Done.

 }
 
 void WebThreadImpl::postDelayedTask(Task* task, long long delay_ms) {
   thread_->message_loop()->PostDelayedTask(
       FROM_HERE,
-      base::Bind(&blink::WebThread::Task::run, base::Owned(task)),
+      base::Bind(RunWebThreadTask, base::Passed(scoped_ptr<Task>(task))),
       base::TimeDelta::FromMilliseconds(delay_ms));
 }
 
 void WebThreadImpl::enterRunLoop() {
   CHECK(isCurrentThread());
   CHECK(!thread_->message_loop()->is_running());  // We don't support nesting.
   thread_->message_loop()->Run();
 }
 
 void WebThreadImpl::exitRunLoop() {
@@ skipping 14 matching lines @@
   thread_->Stop();
 }
 
 WebThreadImplForMessageLoop::WebThreadImplForMessageLoop(
     scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner)
     : main_thread_task_runner_(main_thread_task_runner),
       thread_id_(base::PlatformThread::CurrentId()) {}
 
 void WebThreadImplForMessageLoop::postTask(Task* task) {
   main_thread_task_runner_->PostTask(
-      FROM_HERE, base::Bind(&blink::WebThread::Task::run, base::Owned(task)));
+      FROM_HERE,
+      base::Bind(RunWebThreadTask, base::Passed(scoped_ptr<Task>(task))));
 }
 
 void WebThreadImplForMessageLoop::postDelayedTask(Task* task,
                                                   long long delay_ms) {
   main_thread_task_runner_->PostDelayedTask(
       FROM_HERE,
-      base::Bind(&blink::WebThread::Task::run, base::Owned(task)),
+      base::Bind(RunWebThreadTask, base::Passed(scoped_ptr<Task>(task))),
       base::TimeDelta::FromMilliseconds(delay_ms));
 }
 
 void WebThreadImplForMessageLoop::enterRunLoop() {
   CHECK(isCurrentThread());
   // We don't support nesting.
   CHECK(!base::MessageLoop::current()->is_running());
   base::MessageLoop::current()->Run();
 }
 
 void WebThreadImplForMessageLoop::exitRunLoop() {
   CHECK(isCurrentThread());
   CHECK(base::MessageLoop::current()->is_running());
   base::MessageLoop::current()->Quit();
 }
 
 bool WebThreadImplForMessageLoop::isCurrentThread() const {
   return main_thread_task_runner_->BelongsToCurrentThread();
 }
 
 blink::PlatformThreadId WebThreadImplForMessageLoop::threadId() const {
   return thread_id_;
 }
 
 WebThreadImplForMessageLoop::~WebThreadImplForMessageLoop() {}
 
 }  // namespace content