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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. We don't wait
26 // for the worker pool threads to finish on shutdown, so the tasks running
27 // inside the pool must be extremely careful about other objects they access
28 // (MessageLoops, Singletons, etc). During shutdown these object may no longer
29 // 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 
58 }  // namespace base
59 
60 #endif  // BASE_THREADING_WORKER_POOL_H_
61