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Side by Side Diff: base/threading/worker_pool_posix.h

Issue 1647803004: Move base to DEPS (Closed) Base URL: git@github.com:domokit/mojo.git@master
Patch Set: Created 4 years, 10 months ago
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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 // The thread pool used in the POSIX implementation of WorkerPool dynamically
6 // adds threads as necessary to handle all tasks. It keeps old threads around
7 // for a period of time to allow them to be reused. After this waiting period,
8 // the threads exit. This thread pool uses non-joinable threads, therefore
9 // worker threads are not joined during process shutdown. This means that
10 // potentially long running tasks (such as DNS lookup) do not block process
11 // shutdown, but also means that process shutdown may "leak" objects. Note that
12 // although PosixDynamicThreadPool spawns the worker threads and manages the
13 // task queue, it does not own the worker threads. The worker threads ask the
14 // PosixDynamicThreadPool for work and eventually clean themselves up. The
15 // worker threads all maintain scoped_refptrs to the PosixDynamicThreadPool
16 // instance, which prevents PosixDynamicThreadPool from disappearing before all
17 // worker threads exit. The owner of PosixDynamicThreadPool should likewise
18 // maintain a scoped_refptr to the PosixDynamicThreadPool instance.
19 //
20 // NOTE: The classes defined in this file are only meant for use by the POSIX
21 // implementation of WorkerPool. No one else should be using these classes.
22 // These symbols are exported in a header purely for testing purposes.
23
24 #ifndef BASE_THREADING_WORKER_POOL_POSIX_H_
25 #define BASE_THREADING_WORKER_POOL_POSIX_H_
26
27 #include <queue>
28 #include <string>
29
30 #include "base/basictypes.h"
31 #include "base/callback_forward.h"
32 #include "base/location.h"
33 #include "base/memory/ref_counted.h"
34 #include "base/memory/scoped_ptr.h"
35 #include "base/pending_task.h"
36 #include "base/synchronization/condition_variable.h"
37 #include "base/synchronization/lock.h"
38 #include "base/threading/platform_thread.h"
39 #include "base/tracked_objects.h"
40
41 class Task;
42
43 namespace base {
44
45 class BASE_EXPORT PosixDynamicThreadPool
46 : public RefCountedThreadSafe<PosixDynamicThreadPool> {
47 public:
48 class PosixDynamicThreadPoolPeer;
49
50 // All worker threads will share the same |name_prefix|. They will exit after
51 // |idle_seconds_before_exit|.
52 PosixDynamicThreadPool(const std::string& name_prefix,
53 int idle_seconds_before_exit);
54
55 // Indicates that the thread pool is going away. Stops handing out tasks to
56 // worker threads. Wakes up all the idle threads to let them exit.
57 void Terminate();
58
59 // Adds |task| to the thread pool.
60 void PostTask(const tracked_objects::Location& from_here,
61 const Closure& task);
62
63 // Worker thread method to wait for up to |idle_seconds_before_exit| for more
64 // work from the thread pool. Returns NULL if no work is available.
65 PendingTask WaitForTask();
66
67 private:
68 friend class RefCountedThreadSafe<PosixDynamicThreadPool>;
69 friend class PosixDynamicThreadPoolPeer;
70
71 ~PosixDynamicThreadPool();
72
73 // Adds pending_task to the thread pool. This function will clear
74 // |pending_task->task|.
75 void AddTask(PendingTask* pending_task);
76
77 const std::string name_prefix_;
78 const int idle_seconds_before_exit_;
79
80 Lock lock_; // Protects all the variables below.
81
82 // Signal()s worker threads to let them know more tasks are available.
83 // Also used for Broadcast()'ing to worker threads to let them know the pool
84 // is being deleted and they can exit.
85 ConditionVariable pending_tasks_available_cv_;
86 int num_idle_threads_;
87 TaskQueue pending_tasks_;
88 bool terminated_;
89 // Only used for tests to ensure correct thread ordering. It will always be
90 // NULL in non-test code.
91 scoped_ptr<ConditionVariable> num_idle_threads_cv_;
92
93 DISALLOW_COPY_AND_ASSIGN(PosixDynamicThreadPool);
94 };
95
96 } // namespace base
97
98 #endif // BASE_THREADING_WORKER_POOL_POSIX_H_
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