text: // 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 BASE_THREADING_SEQUENCED_TASK_RUNNER_HANDLE_H_
  #define BASE_THREADING_SEQUENCED_TASK_RUNNER_HANDLE_H_
  
  #include "base/compiler_specific.h"
  #include "base/macros.h"
  #include "base/memory/ref_counted.h"
  #include "base/sequenced_task_runner.h"
  
  namespace base {
  
  class BASE_EXPORT SequencedTaskRunnerHandle {
   public:
    // Returns a SequencedTaskRunner which guarantees that posted tasks will only
    // run after the current task is finished and will satisfy a SequenceChecker.
    // It should only be called if IsSet() returns true (see the comment there for
    // the requirements).
    static scoped_refptr<SequencedTaskRunner> Get();
  
    // Returns true if one of the following conditions is fulfilled:
    // a) A SequencedTaskRunner has been assigned to the current thread by
    //    instantiating a SequencedTaskRunnerHandle.
    // b) The current thread has a ThreadTaskRunnerHandle (which includes any
    //    thread that has a MessageLoop associated with it), or
    // c) The current thread is a worker thread belonging to a SequencedWorkerPool
    //    *and* is currently running a sequenced task (note: not supporting
    //    unsequenced tasks is intentional: https://crbug.com/618043#c4).
    static bool IsSet();
  
    // Binds |task_runner| to the current thread.
    explicit SequencedTaskRunnerHandle(
        scoped_refptr<SequencedTaskRunner> task_runner);
    ~SequencedTaskRunnerHandle();
  
   private:
    scoped_refptr<SequencedTaskRunner> task_runner_;
  
    DISALLOW_COPY_AND_ASSIGN(SequencedTaskRunnerHandle);
  };
  
  }  // namespace base
  
  #endif  // BASE_THREADING_SEQUENCED_TASK_RUNNER_HANDLE_H_
  