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/callback_forward.h" 31 #include "base/location.h" 32 #include "base/macros.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_ 99