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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.h"
10 #include "base/memory/ref_counted.h"
11 
12 namespace tracked_objects {
13 class Location;
14 }  // namespace tracked_objects
15 
16 namespace base {
17 
18 class TaskRunner;
19 
20 // This is a facility that runs tasks that don't require a specific thread or
21 // a message loop.
22 //
23 // WARNING: This shouldn't be used unless absolutely necessary. We don't wait
24 // for the worker pool threads to finish on shutdown, so the tasks running
25 // inside the pool must be extremely careful about other objects they access
26 // (MessageLoops, Singletons, etc). During shutdown these object may no longer
27 // exist.
28 class BASE_EXPORT WorkerPool {
29  public:
30   // This function posts |task| to run on a worker thread.  |task_is_slow|
31   // should be used for tasks that will take a long time to execute.  Returns
32   // false if |task| could not be posted to a worker thread.  Regardless of
33   // return value, ownership of |task| is transferred to the worker pool.
34   static bool PostTask(const tracked_objects::Location& from_here,
35                        OnceClosure task,
36                        bool task_is_slow);
37 
38   // Just like TaskRunner::PostTaskAndReply, except the destination
39   // for |task| is a worker thread and you can specify |task_is_slow| just
40   // like you can for PostTask above.
41   static bool PostTaskAndReply(const tracked_objects::Location& from_here,
42                                OnceClosure task,
43                                OnceClosure reply,
44                                bool task_is_slow);
45 
46   // Return true if the current thread is one that this WorkerPool runs tasks
47   // on.  (Note that if the Windows worker pool is used without going through
48   // this WorkerPool interface, RunsTasksOnCurrentThread would return false on
49   // those threads.)
50   static bool RunsTasksOnCurrentThread();
51 
52   // Get a TaskRunner wrapper which posts to the WorkerPool using the given
53   // |task_is_slow| behavior.
54   static const scoped_refptr<TaskRunner>& GetTaskRunner(bool task_is_slow);
55 };
56 
57 }  // namespace base
58 
59 #endif  // BASE_THREADING_WORKER_POOL_H_
60