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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// The thread pool used in the POSIX implementation of WorkerPool dynamically
// adds threads as necessary to handle all tasks. It keeps old threads around
// for a period of time to allow them to be reused. After this waiting period,
// the threads exit. This thread pool uses non-joinable threads, therefore
// worker threads are not joined during process shutdown. This means that
// potentially long running tasks (such as DNS lookup) do not block process
// shutdown, but also means that process shutdown may "leak" objects. Note that
// although PosixDynamicThreadPool spawns the worker threads and manages the
// task queue, it does not own the worker threads. The worker threads ask the
// PosixDynamicThreadPool for work and eventually clean themselves up. The
// worker threads all maintain scoped_refptrs to the PosixDynamicThreadPool
// instance, which prevents PosixDynamicThreadPool from disappearing before all
// worker threads exit. The owner of PosixDynamicThreadPool should likewise
// maintain a scoped_refptr to the PosixDynamicThreadPool instance.
//
// NOTE: The classes defined in this file are only meant for use by the POSIX
// implementation of WorkerPool. No one else should be using these classes.
// These symbols are exported in a header purely for testing purposes.
#ifndef BASE_THREADING_WORKER_POOL_POSIX_H_
#define BASE_THREADING_WORKER_POOL_POSIX_H_
#include <queue>
#include <string>
#include "base/callback_forward.h"
#include "base/location.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/pending_task.h"
#include "base/synchronization/condition_variable.h"
#include "base/synchronization/lock.h"
#include "base/threading/platform_thread.h"
#include "base/tracked_objects.h"
class Task;
namespace base {
class BASE_EXPORT PosixDynamicThreadPool
: public RefCountedThreadSafe<PosixDynamicThreadPool> {
public:
class PosixDynamicThreadPoolPeer;
// All worker threads will share the same |name_prefix|. They will exit after
// |idle_seconds_before_exit|.
PosixDynamicThreadPool(const std::string& name_prefix,
int idle_seconds_before_exit);
// Indicates that the thread pool is going away. Stops handing out tasks to
// worker threads. Wakes up all the idle threads to let them exit.
void Terminate();
// Adds |task| to the thread pool.
void PostTask(const tracked_objects::Location& from_here,
const Closure& task);
// Worker thread method to wait for up to |idle_seconds_before_exit| for more
// work from the thread pool. Returns NULL if no work is available.
PendingTask WaitForTask();
private:
friend class RefCountedThreadSafe<PosixDynamicThreadPool>;
friend class PosixDynamicThreadPoolPeer;
~PosixDynamicThreadPool();
// Adds pending_task to the thread pool. This function will clear
// |pending_task->task|.
void AddTask(PendingTask* pending_task);
const std::string name_prefix_;
const int idle_seconds_before_exit_;
Lock lock_; // Protects all the variables below.
// Signal()s worker threads to let them know more tasks are available.
// Also used for Broadcast()'ing to worker threads to let them know the pool
// is being deleted and they can exit.
ConditionVariable pending_tasks_available_cv_;
int num_idle_threads_;
TaskQueue pending_tasks_;
bool terminated_;
// Only used for tests to ensure correct thread ordering. It will always be
// NULL in non-test code.
scoped_ptr<ConditionVariable> num_idle_threads_cv_;
DISALLOW_COPY_AND_ASSIGN(PosixDynamicThreadPool);
};
} // namespace base
#endif // BASE_THREADING_WORKER_POOL_POSIX_H_