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// Copyright 2013 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.
#ifndef CC_TREES_BLOCKING_TASK_RUNNER_H_
#define CC_TREES_BLOCKING_TASK_RUNNER_H_
#include <vector>
#include "base/location.h"
#include "base/memory/ref_counted.h"
#include "base/single_thread_task_runner.h"
#include "base/synchronization/lock.h"
#include "cc/base/cc_export.h"
namespace cc {
// This class wraps a SingleThreadTaskRunner but allows posted tasks to be
// run without a round trip through the message loop. This shortcutting
// removes guarantees about ordering. Tasks posted while the
// BlockingTaskRunner is in a capturing state will run in order, and tasks
// posted while the BlockingTaskRunner is /not/ in a capturing state will
// run in order, but the two sets of tasks will *not* run in order relative
// to when they were posted.
//
// To use this class, post tasks to the task runner returned by
// BlockingTaskRunner::current() on the thread you want the tasks to run.
// Hold a reference to the BlockingTaskRunner as long as you intend to
// post tasks to it.
//
// Then, on the thread from which the BlockingTaskRunner was created, you
// may instantiate a BlockingTaskRunner::CapturePostTasks. While this object
// exists, the task runner will collect any PostTasks called on it, posting
// tasks to that thread from anywhere. This CapturePostTasks object provides
// a window in time where tasks can shortcut past the MessageLoop. As soon
// as the CapturePostTasks object is destroyed (goes out of scope), all
// tasks that had been posted to the thread during the window will be exectuted
// immediately.
//
// Beware of re-entrancy, make sure the CapturePostTasks object is destroyed at
// a time when it makes sense for the embedder to call arbitrary things.
class CC_EXPORT BlockingTaskRunner
: public base::RefCountedThreadSafe<BlockingTaskRunner> {
public:
// Returns the BlockingTaskRunner for the current thread, creating one if
// necessary.
static scoped_refptr<BlockingTaskRunner> current();
// While an object of this type is held alive on a thread, any tasks
// posted to the thread will be captured and run as soon as the object
// is destroyed, shortcutting past the MessageLoop.
class CC_EXPORT CapturePostTasks {
public:
CapturePostTasks();
~CapturePostTasks();
private:
scoped_refptr<BlockingTaskRunner> blocking_runner_;
DISALLOW_COPY_AND_ASSIGN(CapturePostTasks);
};
// True if tasks posted to the BlockingTaskRunner will run on the current
// thread.
bool BelongsToCurrentThread() {
return task_runner_->BelongsToCurrentThread();
}
// Posts a task using the contained SingleThreadTaskRunner unless |capture_|
// is true. When |capture_| is true, tasks posted will be caught and stored
// until the capturing stops. At that time the tasks will be run directly
// instead of being posted to the SingleThreadTaskRunner.
bool PostTask(const tracked_objects::Location& from_here,
const base::Closure& task);
private:
friend class base::RefCountedThreadSafe<BlockingTaskRunner>;
explicit BlockingTaskRunner(
scoped_refptr<base::SingleThreadTaskRunner> task_runner);
virtual ~BlockingTaskRunner();
void SetCapture(bool capture);
scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
base::Lock lock_;
int capture_;
std::vector<base::Closure> captured_tasks_;
};
} // namespace cc
#endif // CC_TREES_BLOCKING_TASK_RUNNER_H_
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