作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

namespace RealitySimulation.Utils.Threading
{
    #region Using directives

    using System;
    using System.Collections.Generic;
    using System.Text;
    using System.Threading;

    #endregion

    /// <summary>
    /// 同步屏障.
    /// </summary>
    public interface ISyncBarrier
    {
        /// <summary>
        /// 获取正在有屏障处理的线程总数.
        /// </summary>
        /// <remarks>
        /// 改变线程总数,是一个同步操作.
        /// 请在确保没有任何线程使用当前
        /// 屏障(或初始化)时改动总数.如果已经有线
        /// 程使用屏障,请使用ExchangingThreads
        /// 异步更改线程的数量.
        /// </remarks>
        int TotalThreads { get;set;}
        /// <summary>
        /// 获取或者设置等待交换的线程数.
        /// </summary>
        /// <remarks>
        /// 可以通过交换向线程总数中
        /// 添加或者删除线程.
        /// 使用这种方法主要是因为
        /// 线程同步过程中,只能在
        /// 重建屏障的时候改变线程
        /// 总数.而其他时候将造成
        /// 同步的失败.
        /// 此值为正,意味着添加
        /// 线程,相反意味着删除
        /// 线程.
        /// 当交换完成,此值自动
        /// 置零.
        /// 此外,如果线程的减少
        /// 量大于当前线程总量,
        /// 直接将总量置零,而不
        /// 考虑余量.
        /// 注意,这是一个异步操作,
        /// 屏障可能不会立即实现
        /// 这个操作.请观察此值,
        /// 以确定是否进行添加.
        /// </remarks>
        int ExchangingThreads { get;set;}
        /// <summary>
        /// 获取当前被阻碍的线程数.
        /// </summary>
        int BarricadedThreads { get;}
        /// <summary>
        /// 穿越屏障.
        /// </summary>
        /// <remarks>
        /// 线程通过调用穿越屏障,
        /// 将对控制的安排交给屏障.
        /// 当逃离条件满足,也就是
        /// 到达线程数量已经达到
        /// 要求的数量,屏障将自动
        /// 开放,而线程在此时可以
        /// 穿越.当逃离条件尚未满
        /// 足,线程将在穿越屏障的
        /// 时候被屏障阻塞.
        /// </remarks>
        void Stride();
    }

    public class SyncBarrier:ISyncBarrier
    {
        protected int unbarricadedThreads = 0;
        protected int exchangingThreads = 0;

        protected int totalThreads = 0;

        public virtual int BarricadedThreads
        {
            get { return this.totalThreads - this.unbarricadedThreads; }
        }
        public virtual int TotalThreads
        {
            get { return this.totalThreads; }
            set { this.Rebuild(value); }
        }
        public virtual int ExchangingThreads
        {
            get { return this.exchangingThreads; }
            set { this.exchangingThreads = value; }
        }

        public SyncBarrier():this(1){}
        public SyncBarrier(int totalThreads)
        {
            this.Rebuild(totalThreads);
        }

        public virtual void Stride()
        {
            //Barrier is designed for threads, no thread takes no effect.
            //And single thread will not be barricaded.
            if (this.totalThreads > 0)
            {
                lock (this)
                {
                    if (this.unbarricadedThreads > 0)
                    {
                        this.unbarricadedThreads--;
                        //All threads arrived
                        if (this.unbarricadedThreads == 0)
                        {
                            //Rebuild first, then pulse the signal!
                            this.Rebuild(this.totalThreads+this.exchangingThreads);
                            Monitor.PulseAll(this);
                        }
                        else//Not all threads arrived.
                        {
                            Monitor.Wait(this);
                        }
                        //Threads escapes here.
                    }
                }
            }
        }

        protected virtual void Rebuild(int totalThreads)
        {
            this.unbarricadedThreads = this.totalThreads = totalThreads;
            this.exchangingThreads = 0;
        }
    }
}

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