text: // Copyright (c) 2012 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_WORKER_POOL_H_
  #define BASE_THREADING_WORKER_POOL_H_
  
  #include "base/base_export.h"
  #include "base/callback.h"
  #include "base/memory/ref_counted.h"
  
  namespace tracked_objects {
  class Location;
  }  // namespace tracked_objects
  
  namespace base {
  
  class TaskRunner;
  
  // This is a facility that runs tasks that don't require a specific thread or
  // a message loop.
  //
  // WARNING: This shouldn't be used unless absolutely necessary. We don't wait
  // for the worker pool threads to finish on shutdown, so the tasks running
  // inside the pool must be extremely careful about other objects they access
  // (MessageLoops, Singletons, etc). During shutdown these object may no longer
  // exist.
  class BASE_EXPORT WorkerPool {
   public:
    // This function posts |task| to run on a worker thread.  |task_is_slow|
    // should be used for tasks that will take a long time to execute.  Returns
    // false if |task| could not be posted to a worker thread.  Regardless of
    // return value, ownership of |task| is transferred to the worker pool.
    static bool PostTask(const tracked_objects::Location& from_here,
                         OnceClosure task,
                         bool task_is_slow);
  
    // Just like TaskRunner::PostTaskAndReply, except the destination
    // for |task| is a worker thread and you can specify |task_is_slow| just
    // like you can for PostTask above.
    static bool PostTaskAndReply(const tracked_objects::Location& from_here,
                                 OnceClosure task,
                                 OnceClosure reply,
                                 bool task_is_slow);
  
    // Return true if the current thread is one that this WorkerPool runs tasks
    // on.  (Note that if the Windows worker pool is used without going through
    // this WorkerPool interface, RunsTasksOnCurrentThread would return false on
    // those threads.)
    static bool RunsTasksOnCurrentThread();
  
    // Get a TaskRunner wrapper which posts to the WorkerPool using the given
    // |task_is_slow| behavior.
    static const scoped_refptr<TaskRunner>& GetTaskRunner(bool task_is_slow);
  };
  
  }  // namespace base
  
  #endif  // BASE_THREADING_WORKER_POOL_H_
  