third_party/WebKit/Source/platform/WebTaskRunner.h

// Copyright 2015 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 WebTaskRunner_h
#define WebTaskRunner_h

#include <memory>
#include "base/callback.h"
#include "base/location.h"
#include "base/single_thread_task_runner.h"
#include "platform/wtf/Compiler.h"
#include "platform/wtf/Functional.h"
#include "platform/wtf/RefCounted.h"
#include "platform/wtf/Time.h"
#include "public/platform/WebCommon.h"

namespace base {
class SingleThreadTaskRunner;
}

namespace blink {

// TaskHandle is associated to a task posted by
// WebTaskRunner::postCancellableTask or
// WebTaskRunner::postCancellableDelayedTask and cancels the associated task on
// TaskHandle::cancel() call or on TaskHandle destruction.
class BLINK_PLATFORM_EXPORT TaskHandle {
 public:
  // Returns true if the task will run later. Returns false if the task is
  // cancelled or the task is run already.
  // This function is not thread safe. Call this on the thread that has posted
  // the task.
  bool IsActive() const;

  // Cancels the task invocation. Do nothing if the task is cancelled or run
  // already.
  // This function is not thread safe. Call this on the thread that has posted
  // the task.
  void Cancel();

  TaskHandle();
  ~TaskHandle();

  TaskHandle(TaskHandle&&);
  TaskHandle& operator=(TaskHandle&&);

  class Runner;

 private:
  friend class WebTaskRunner;

  explicit TaskHandle(scoped_refptr<Runner>);
  scoped_refptr<Runner> runner_;
};

// The blink representation of a chromium SingleThreadTaskRunner.
class BLINK_PLATFORM_EXPORT WebTaskRunner
    : public base::SingleThreadTaskRunner {
 public:
  virtual bool PostDelayedTask(const base::Location&,
                               base::OnceClosure,
                               base::TimeDelta) = 0;

  // Returns a microsecond resolution platform dependant time source.
  // This may represent either the real time, or a virtual time depending on
  // whether or not the WebTaskRunner is associated with a virtual time domain
  // or a real time domain.
  virtual double MonotonicallyIncreasingVirtualTimeSeconds() const = 0;

  // Helpers for posting bound functions as tasks.

  // For same-thread posting. Must be called from the associated WebThread.
  void PostTask(const base::Location&, base::OnceClosure);

  // For same-thread cancellable task posting. Returns a TaskHandle object for
  // cancellation.
  WARN_UNUSED_RESULT TaskHandle PostCancellableTask(const base::Location&,
                                                    base::OnceClosure);
  WARN_UNUSED_RESULT TaskHandle
  PostDelayedCancellableTask(const base::Location&,
                             base::OnceClosure,
                             TimeDelta delay);

 protected:
  friend ThreadSafeRefCounted<WebTaskRunner>;
  WebTaskRunner() = default;
  virtual ~WebTaskRunner();

 private:
  DISALLOW_COPY_AND_ASSIGN(WebTaskRunner);
};

// For cross-thread posting. Can be called from any thread.
BLINK_PLATFORM_EXPORT void PostCrossThreadTask(WebTaskRunner&,
                                               const base::Location&,
                                               CrossThreadClosure);
BLINK_PLATFORM_EXPORT void PostDelayedCrossThreadTask(WebTaskRunner&,
                                                      const base::Location&,
                                                      CrossThreadClosure,
                                                      TimeDelta delay);

}  // namespace blink

#endif  // WebTaskRunner_h