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 <memory> 28 #include <queue> 29 #include <string> 30 31 #include "base/callback.h" 32 #include "base/location.h" 33 #include "base/macros.h" 34 #include "base/memory/ref_counted.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 namespace base { 42 43 class BASE_EXPORT PosixDynamicThreadPool 44 : public RefCountedThreadSafe<PosixDynamicThreadPool> { 45 public: 46 class PosixDynamicThreadPoolPeer; 47 48 // All worker threads will share the same |name_prefix|. They will exit after 49 // |idle_seconds_before_exit|. 50 PosixDynamicThreadPool(const std::string& name_prefix, 51 int idle_seconds_before_exit); 52 53 // Adds |task| to the thread pool. 54 void PostTask(const tracked_objects::Location& from_here, OnceClosure task); 55 56 // Worker thread method to wait for up to |idle_seconds_before_exit| for more 57 // work from the thread pool. Returns NULL if no work is available. 58 PendingTask WaitForTask(); 59 60 private: 61 friend class RefCountedThreadSafe<PosixDynamicThreadPool>; 62 friend class PosixDynamicThreadPoolPeer; 63 64 ~PosixDynamicThreadPool(); 65 66 // Adds pending_task to the thread pool. This function will clear 67 // |pending_task->task|. 68 void AddTask(PendingTask* pending_task); 69 70 const std::string name_prefix_; 71 const int idle_seconds_before_exit_; 72 73 Lock lock_; // Protects all the variables below. 74 75 // Signal()s worker threads to let them know more tasks are available. 76 // Also used for Broadcast()'ing to worker threads to let them know the pool 77 // is being deleted and they can exit. 78 ConditionVariable pending_tasks_available_cv_; 79 int num_idle_threads_; 80 TaskQueue pending_tasks_; 81 // Only used for tests to ensure correct thread ordering. It will always be 82 // NULL in non-test code. 83 std::unique_ptr<ConditionVariable> num_idle_threads_cv_; 84 85 DISALLOW_COPY_AND_ASSIGN(PosixDynamicThreadPool); 86 }; 87 88 } // namespace base 89 90 #endif // BASE_THREADING_WORKER_POOL_POSIX_H_ 91
