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