base/threading/worker_pool.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_THREADING_WORKER_POOL_H_
   6 #define BASE_THREADING_WORKER_POOL_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/callback_forward.h"
  10 #include "base/memory/ref_counted.h"
  11
  12 class Task;
  13
  14 namespace tracked_objects {
  15 class Location;
  16 }  // namespace tracked_objects
  17
  18 namespace base {
  19
  20 class TaskRunner;
  21
  22 // This is a facility that runs tasks that don't require a specific thread or
  23 // a message loop.
  24 //
  25 // WARNING: This shouldn't be used unless absolutely necessary. Typically
  26 // (without calling ShutDownCleanly()), we don't wait for the worker pool
  27 // threads to finish on shutdown, so the tasks running inside the pool must be
  28 // extremely careful about other objects they access (MessageLoops, Singletons,
  29 // etc). During shutdown these object may no longer exist.
  30 class BASE_EXPORT WorkerPool {
  31  public:
  32   // This function posts |task| to run on a worker thread.  |task_is_slow|
  33   // should be used for tasks that will take a long time to execute.  Returns
  34   // false if |task| could not be posted to a worker thread.  Regardless of
  35   // return value, ownership of |task| is transferred to the worker pool.
  36   static bool PostTask(const tracked_objects::Location& from_here,
  37                        const base::Closure& task, bool task_is_slow);
  38
  39   // Just like TaskRunner::PostTaskAndReply, except the destination
  40   // for |task| is a worker thread and you can specify |task_is_slow| just
  41   // like you can for PostTask above.
  42   static bool PostTaskAndReply(const tracked_objects::Location& from_here,
  43                                const Closure& task,
  44                                const Closure& reply,
  45                                bool task_is_slow);
  46
  47   // Return true if the current thread is one that this WorkerPool runs tasks
  48   // on.  (Note that if the Windows worker pool is used without going through
  49   // this WorkerPool interface, RunsTasksOnCurrentThread would return false on
  50   // those threads.)
  51   static bool RunsTasksOnCurrentThread();
  52
  53   // Get a TaskRunner wrapper which posts to the WorkerPool using the given
  54   // |task_is_slow| behavior.
  55   static const scoped_refptr<TaskRunner>& GetTaskRunner(bool task_is_slow);
  56
  57   // Blocks until all worker threads quit cleanly. Please note that it ensures
  58   // that no worker threads are running after the method returns, but it doesn't
  59   // guarantee to process all queued pending tasks. This method may take a long
  60   // time. Please don't use it unless absolutely necessary, e.g., when we want
  61   // to unload the library containing the worker pool before process shutdown.
  62   static void ShutDownCleanly();
  63 };
  64
  65 }  // namespace base
  66
  67 #endif  // BASE_THREADING_WORKER_POOL_H_