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1 // Copyright (c) 2010 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_WORKER_POOL_JOB_H_ | |
6 #define BASE_WORKER_POOL_JOB_H_ | |
7 #pragma once | |
8 | |
9 #include "base/basictypes.h" | |
10 #include "base/lock.h" | |
11 #include "base/message_loop_proxy.h" | |
12 #include "base/ref_counted.h" | |
13 #include "base/thread_checker.h" | |
14 | |
15 namespace base { | |
16 | |
17 // WARNING: Are you sure you want to use WorkerPool in the first place? The | |
18 // thread will _not_ be joined, so the job may still be running during shutdown. | |
19 // Global objects that are deleted by AtExitManager should not be accessed on | |
20 // the WorkerPool thread, otherwise there is potential for shutdown crashes. | |
21 // | |
22 // WorkerPoolJob is a helper class for implementing jobs that get created on an | |
23 // origin thread, get posted to run on a WorkerPool thread, and then run back on | |
24 // the origin thread upon completion. WorkerPoolJob also handles cancellation | |
25 // of a job which prevents it from calling back. Note that we use inheritance | |
26 // rather than composition here, since WorkerPoolJob also handles lifetime | |
27 // management via refcounting. | |
28 class WorkerPoolJob : public base::RefCountedThreadSafe<WorkerPoolJob> { | |
29 public: | |
30 // ScopedHandle is provided to automate cancellation of the WorkerPoolJob. | |
31 template <typename JobType> | |
32 class ScopedHandle { | |
33 public: | |
34 explicit ScopedHandle(JobType* job) : job_(job) {} | |
35 | |
36 ~ScopedHandle() { | |
37 if (!job_->canceled() && job_->state_ == RUNNING) | |
38 job_->CancelJob(); | |
39 } | |
40 | |
41 JobType* job() const { return job_.get(); } | |
42 | |
43 private: | |
44 const scoped_refptr<JobType> job_; | |
45 DISALLOW_COPY_AND_ASSIGN(ScopedHandle); | |
46 }; | |
47 | |
48 protected: | |
49 WorkerPoolJob(); | |
50 | |
51 // This may be deleted on the origin or worker thread. | |
52 virtual ~WorkerPoolJob(); | |
53 | |
54 // Starts the job. Will post itself to the WorkerPool, where it will invoke | |
55 // RunJob(). After RunJob() runs, it will post itself back to the origin | |
56 // thread, where it will invoke OnJobCompleted(). This can only be called | |
57 // once and must be called on the origin thread. | |
58 void StartJob(); | |
59 | |
60 // Cancels the job. OnJobCompleted() is guaranteed not to be called when this | |
61 // happens. May only be called once, and only on the origin thread. | |
62 void CancelJob(); | |
63 | |
64 // Returns true if CancelJob() has been called. | |
65 bool canceled() const; | |
66 | |
67 // NOTE(willchan): I've restricted this to unit tests only, primarily because | |
68 // I haven't found a good reason for allowing subtypes to access this. If | |
69 // there is a motivating reason to do so, I am open to it. | |
70 #if defined(UNIT_TEST) | |
71 scoped_refptr<MessageLoopProxy> origin_loop() const { | |
72 return origin_loop_; | |
73 } | |
74 | |
75 // Returns true if OnJobCompleted() has not been called yet. | |
76 bool is_running() const { | |
77 DCHECK(thread_checker_.CalledOnValidThread()); | |
78 DCHECK_NE(state_, NONE); | |
79 return state_ == RUNNING; | |
80 } | |
81 #endif // defined(UNIT_TEST) | |
82 | |
83 private: | |
84 friend class base::RefCountedThreadSafe<WorkerPoolJob>; | |
85 | |
86 // State machine, primarily for enforcing that certain events only happen | |
87 // once. Also lets us implement is_running(). | |
88 enum State { | |
89 NONE, | |
90 RUNNING, | |
91 DONE, | |
92 }; | |
93 | |
94 // API for subtypes to implement. | |
95 | |
96 // RunJob() runs on the worker thread. If CancelJob() is called on the origin | |
97 // thread , then it may never be invoked, but that's a race. | |
98 virtual void RunJob() = 0; | |
99 | |
100 // OnJobCompleted() runs on the origin thread. If CancelJob() is called, then | |
101 // it may never be invoked. | |
eroman
2011/01/05 01:24:52
This wording can be stronger. If CancelJob() was c
| |
102 virtual void OnJobCompleted() = 0; | |
103 | |
104 void RunJobOnWorkerPool(); | |
105 void CompleteJobOnOriginLoop(); | |
106 | |
107 ThreadChecker thread_checker_; | |
108 const scoped_refptr<MessageLoopProxy> origin_loop_; | |
109 | |
110 bool canceled_; | |
111 State state_; | |
112 | |
113 DISALLOW_COPY_AND_ASSIGN(WorkerPoolJob); | |
114 }; | |
115 | |
116 } // namespace base | |
117 | |
118 #endif // BASE_WORKER_POOL_JOB_H_ | |
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