Nutshell.ThreadWorkerPool .Net线程池设计

功能描述：

1. 支持创建多个线程池，并统一管理
2. 支持不同线程池的容量控制，以及最少活动线程的设置
3. 支持不同线程池中活动线程的闲时设置，即线程空闲时间到期后即自动被回收

结构设计：

• ThreadWorkerPoolManager: 线程池管理器，用于统一创建，获取，销毁线程池，使用单例模式
• ThreadWorkerPool: 线程池，用于管理指定数量的线程，由ThreadWorkerPoolManager管理，自身无法创建与销毁
• TheadWorkerPoolItem: 线程池项，用于包装线程工作器，协助ThreadWorkerPool更好的管理线程，例如取出，放回，闲时的控制
• TheadWorker: 线程工作器，用于包装系统线程System.Threading.Thread，使其可以重复使用，减少Thrad创建和销毁的性能开销

　　结构关系图：

　　

 详细设计：

　　ThreadWoker

　　要点设计：

1. 完成一次任务后，System.Threading.Thread不能被系统销毁, 默认情况下new Thread(ThreadStart start).Start(), 当ThreadStart委托的任务完成后，系统将销毁该线程，也就是说创建一个System.Threading.Thread实例只能使用一次；为了使线程能被重复使用，ThreadWoker将使用 while+sleeping 的方式对系统线程进行包装，同时使用AutoResetEvent代替Thread.Sleep(timeout)来达到更佳的控制
2. 闲时设计，线程资源是极其宝贵的系统资源，如果线程池中存在大量的空闲线程这是一种浪费，极端情况下将影响系统的稳定性和工作效率；ThreadWorker将使用AutoResetEvent和事件通知的方式来代替在线程池中定期轮询检查的方式，每完成一个任务将重新开始空闲时间的计算，如果ThreadWorker在线程池中被取出，那么ThreadWorker空闲时间将永远不会到期，直到ThreadWorker被返回线程池后才重新开始空闲时间的计算

　　状态图：

　　

　　关键代码：

　　

        private void ThreadWorking()
        {
            while (_status != ThreadWorkerStatus.Abort)
            {
                //WaitOne 返回false表示等待超时，true接到取消等待的通知
                //这里利用AutoResetEvent.WaitOne的特性来设计闲时控制，false表示空闲到期，true表示新的任务开始
                if (!_waitEvent.WaitOne(_idleTime)) 
                {
                    if (!_isCanIdleExpired) //_isCanIdleExpired变量控制是否允许超时，例如被取出后将不能超时
                        continue;

                    _status = ThreadWorkerStatus.Abort;
                    _waitEvent.Close();
                    _waitEvent.Dispose();
                    if (OnIdleExpired != null)
                        OnIdleExpired(this, null); //空闲到期事件通知
                    return;
                }
                else if (_status == ThreadWorkerStatus.Abort)
                    return;

                try
                {
                    Working();
                }
                catch (Exception ex)
                {
                    _logger.TraceEvent(TraceEventType.Error, (int)TraceEventType.Error, ex.ToString());
                }
                finally
                {
                    _status = ThreadWorkerStatus.Idle;
                    if (OnWorkCompleted != null)
                        OnWorkCompleted(this, null); //任务完成事件通知
                }
            }
        }

　　　　 public void Work()
        {
            if (_status == ThreadWorkerStatus.Abort)
                throw new InvalidOperationException("this ThreadWorker was Abort!");

            if (_status == ThreadWorkerStatus.Working)
                throw new InvalidOperationException("this ThreadWorker was working, unable to duplicate work!");

            _status = ThreadWorkerStatus.Working;
            _waitEvent.Set(); //通知线程有个新的工作要开始
        }

　　ThreadWorkerPoolItem

　　要点设计：

1. 链接ThreadWorker和线程池，线程池通过ThreadWorkerPoolItem控制ThreadWorker在线程池的取出，放回，销毁
2. 通过订阅ThreadWorker的空闲到期事件OnIdleExpired，来完成线程池对线程的移除
3. 通过订阅ThreadWorker的任务完成事件OnWorkCompleted，来完成线程返回线程池的操作
4. 提供剩余空闲时间查询，来为线程池提供更优线程取出方案

　　完整代码：

    public sealed class ThreadWorkerPoolItem
    {
        private ThreadWorkerPoolItemStatus _status;
        private readonly ThreadWorkerBase _threadWorker;
        private readonly ThreadWorkerPoolBase _threadWorkerPool;
        private readonly int _idleTime;
        private DateTime _startIdleTime;

        internal ThreadWorkerPoolItem(ThreadWorkerPoolBase pool, ThreadWorkerBase threadWorker, ThreadWorkerPoolSettings poolSettings)
        {
            _threadWorkerPool = pool;
            _threadWorker = threadWorker;
            _threadWorker.OnIdleExpired += _threadWorker_OnIdleExpired;
            _threadWorker.OnWorkCompleted += _threadWorker_OnWorkCompleted;
            _threadWorker.Start();
            _status = ThreadWorkerPoolItemStatus.Idle;
            _idleTime = poolSettings.IdleTime;
        }

        void _threadWorker_OnWorkCompleted(object sender, EventArgs args)
        {
            _threadWorkerPool.Return(this);
        }

        void _threadWorker_OnIdleExpired(object sender, EventArgs args)
        {
            _threadWorkerPool.Remove(this);
        }

        internal ThreadWorkerPoolItemStatus Status
        {
            get
            {
                if (_threadWorker.Status == ThreadWorkerStatus.Abort || _status == ThreadWorkerPoolItemStatus.Abort)
                    return ThreadWorkerPoolItemStatus.Abort;

                return _status;
            }
        }

        internal int SurplusIdleTime
        {
            get
            {
                if (_status == ThreadWorkerPoolItemStatus.Take || _idleTime == -1)
                    return -1;

                int idledTime = (int)(_startIdleTime - DateTime.Now).TotalMilliseconds;
                if (idledTime >= _idleTime)
                    return 0;

                return idledTime;
            }
        }

        internal void SetTake()
        {
            _threadWorker.IsCanIdleExpried = false;
            _status = ThreadWorkerPoolItemStatus.Take;
        }

        internal void SetIdle()
        {
            _startIdleTime = DateTime.Now;
            _status = ThreadWorkerPoolItemStatus.Idle;
            _threadWorker.IsCanIdleExpried = true;
        }

        internal ThreadWorkerBase ThreadWorker
        {
            get { return _threadWorker; }
        }
    }

　　ThreadWorkerPool

　　要点设计：

1. 使用Lock配合ThreadWorkerPoolItem的状态来确保多线程下，每次取出的都是空闲的ThreadWorker
2. 取出的超时设计，由于线程池有容量控制，高并发下必然导致线程池满负荷，提供超时设置，有利于使用者自行控制满负荷情况下的处理;ThreadWorkerPool将使用while+sleeping的方式，同时使用AutoResetEvent代替Thread.Sleep(timeout)来达到更佳的控制，当一个线程被放回线程池时，另一等待获取者立即获取，而无需等待下一次轮询的到来

　　关键代码：

        protected bool TryTake(int timeout, out ThreadWorkerBase threadWorker)
        {
            threadWorker = null;
            lock (_takeLocker)
            {
                ThreadWorkerPoolItem worker = null;
                DateTime startWaitTime;
                while (!_isDestoryed)
                {
                    worker = _threadWorkerList.Where(e => e.Status == Core.ThreadWorkerPoolItemStatus.Idle).OrderByDescending(e => e.SurplusIdleTime).FirstOrDefault();
                    if (worker == null)
                    {
                        if (_threadWorkerList.Count < _settings.MaxThreadWorkerCount)
                        {
                            worker = this.CreatePoolItem(_threadWorkerList.Count + 1, _settings.IdleTime);
                            worker.SetTake();
                            _threadWorkerList.Add(worker);
                            threadWorker = worker.ThreadWorker;
                            return true;
                        }

                        startWaitTime = DateTime.Now;
                        if (!_takeWaitEvent.WaitOne(timeout))
                        {
                            threadWorker = null;
                            return false;
                        }

                        if (timeout != -1)
                        {
                            timeout = timeout - (int)(DateTime.Now - startWaitTime).TotalMilliseconds;
                            if (timeout <= 0)
                            {
                                threadWorker = null;
                                return false;
                            }
                        }
                        continue;
                    }

                    threadWorker = worker.ThreadWorker;
                    worker.SetTake();
                    return true;
                }

                threadWorker = null;
                return false;
            }
        }

        internal void Return(ThreadWorkerPoolItem item)
        {
            item.SetIdle();
            _takeWaitEvent.Set();
        }

　　ThreadWorkerPoolManager使用单例模式管理，代码过于简单这里就不贴了......

　　有兴趣的同学可以点击这里进行下载源码查看：Nutshell.ThreadWorkerPool.zip

　　github 开源地址: https://github.com/zcylife/Nutshell