michael@0: // Copyright (c) 2009 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: //
michael@0: // The thread pool used in the Linux implementation of WorkerPool dynamically
michael@0: // adds threads as necessary to handle all tasks.  It keeps old threads around
michael@0: // for a period of time to allow them to be reused.  After this waiting period,
michael@0: // the threads exit.  This thread pool uses non-joinable threads, therefore
michael@0: // worker threads are not joined during process shutdown.  This means that
michael@0: // potentially long running tasks (such as DNS lookup) do not block process
michael@0: // shutdown, but also means that process shutdown may "leak" objects.  Note that
michael@0: // although LinuxDynamicThreadPool spawns the worker threads and manages the
michael@0: // task queue, it does not own the worker threads.  The worker threads ask the
michael@0: // LinuxDynamicThreadPool for work and eventually clean themselves up.  The
michael@0: // worker threads all maintain scoped_refptrs to the LinuxDynamicThreadPool
michael@0: // instance, which prevents LinuxDynamicThreadPool from disappearing before all
michael@0: // worker threads exit.  The owner of LinuxDynamicThreadPool should likewise
michael@0: // maintain a scoped_refptr to the LinuxDynamicThreadPool instance.
michael@0: //
michael@0: // NOTE: The classes defined in this file are only meant for use by the Linux
michael@0: // implementation of WorkerPool.  No one else should be using these classes.
michael@0: // These symbols are exported in a header purely for testing purposes.
michael@0: 
michael@0: #ifndef BASE_WORKER_POOL_LINUX_H_
michael@0: #define BASE_WORKER_POOL_LINUX_H_
michael@0: 
michael@0: #include <queue>
michael@0: #include <string>
michael@0: 
michael@0: #include "base/basictypes.h"
michael@0: #include "base/condition_variable.h"
michael@0: #include "base/lock.h"
michael@0: #include "base/platform_thread.h"
michael@0: #include "base/ref_counted.h"
michael@0: #include "base/scoped_ptr.h"
michael@0: 
michael@0: class Task;
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: class LinuxDynamicThreadPool
michael@0:     : public RefCountedThreadSafe<LinuxDynamicThreadPool> {
michael@0:  public:
michael@0:   class LinuxDynamicThreadPoolPeer;
michael@0: 
michael@0:   // All worker threads will share the same |name_prefix|.  They will exit after
michael@0:   // |idle_seconds_before_exit|.
michael@0:   LinuxDynamicThreadPool(const std::string& name_prefix,
michael@0:                          int idle_seconds_before_exit);
michael@0:   ~LinuxDynamicThreadPool();
michael@0: 
michael@0:   // Indicates that the thread pool is going away.  Stops handing out tasks to
michael@0:   // worker threads.  Wakes up all the idle threads to let them exit.
michael@0:   void Terminate();
michael@0: 
michael@0:   // Adds |task| to the thread pool.  LinuxDynamicThreadPool assumes ownership
michael@0:   // of |task|.
michael@0:   void PostTask(Task* task);
michael@0: 
michael@0:   // Worker thread method to wait for up to |idle_seconds_before_exit| for more
michael@0:   // work from the thread pool.  Returns NULL if no work is available.
michael@0:   Task* WaitForTask();
michael@0: 
michael@0:  private:
michael@0:   friend class LinuxDynamicThreadPoolPeer;
michael@0: 
michael@0:   const std::string name_prefix_;
michael@0:   const int idle_seconds_before_exit_;
michael@0: 
michael@0:   Lock lock_;  // Protects all the variables below.
michael@0: 
michael@0:   // Signal()s worker threads to let them know more tasks are available.
michael@0:   // Also used for Broadcast()'ing to worker threads to let them know the pool
michael@0:   // is being deleted and they can exit.
michael@0:   ConditionVariable tasks_available_cv_;
michael@0:   int num_idle_threads_;
michael@0:   std::queue<Task*> tasks_;
michael@0:   bool terminated_;
michael@0:   // Only used for tests to ensure correct thread ordering.  It will always be
michael@0:   // NULL in non-test code.
michael@0:   scoped_ptr<ConditionVariable> num_idle_threads_cv_;
michael@0: 
michael@0:   DISALLOW_COPY_AND_ASSIGN(LinuxDynamicThreadPool);
michael@0: };
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: #endif  // BASE_WORKER_POOL_LINUX_H_