worker_pool_posix.h revision 3f50c38dc070f4bb515c1b64450dae14f316474e 
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// 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#pragma once
27
28#include <queue>
29#include <string>
30
31#include "base/basictypes.h"
32#include "base/ref_counted.h"
33#include "base/scoped_ptr.h"
34#include "base/synchronization/condition_variable.h"
35#include "base/synchronization/lock.h"
36#include "base/threading/platform_thread.h"
37
38class Task;
39
40namespace base {
41
42class PosixDynamicThreadPool
43    : public RefCountedThreadSafe<PosixDynamicThreadPool> {
44 public:
45  class PosixDynamicThreadPoolPeer;
46
47  // All worker threads will share the same |name_prefix|.  They will exit after
48  // |idle_seconds_before_exit|.
49  PosixDynamicThreadPool(const std::string& name_prefix,
50                         int idle_seconds_before_exit);
51  ~PosixDynamicThreadPool();
52
53  // Indicates that the thread pool is going away.  Stops handing out tasks to
54  // worker threads.  Wakes up all the idle threads to let them exit.
55  void Terminate();
56
57  // Adds |task| to the thread pool.  PosixDynamicThreadPool assumes ownership
58  // of |task|.
59  void PostTask(Task* task);
60
61  // Worker thread method to wait for up to |idle_seconds_before_exit| for more
62  // work from the thread pool.  Returns NULL if no work is available.
63  Task* WaitForTask();
64
65 private:
66  friend class PosixDynamicThreadPoolPeer;
67
68  const std::string name_prefix_;
69  const int idle_seconds_before_exit_;
70
71  Lock lock_;  // Protects all the variables below.
72
73  // Signal()s worker threads to let them know more tasks are available.
74  // Also used for Broadcast()'ing to worker threads to let them know the pool
75  // is being deleted and they can exit.
76  ConditionVariable tasks_available_cv_;
77  int num_idle_threads_;
78  std::queue<Task*> tasks_;
79  bool terminated_;
80  // Only used for tests to ensure correct thread ordering.  It will always be
81  // NULL in non-test code.
82  scoped_ptr<ConditionVariable> num_idle_threads_cv_;
83
84  DISALLOW_COPY_AND_ASSIGN(PosixDynamicThreadPool);
85};
86
87}  // namespace base
88
89#endif  // BASE_THREADING_WORKER_POOL_POSIX_H_
90