在1971年，著名的计算机科学家艾兹格·迪科斯彻提出了一个同步问题，即假设有五台计算机都试图访问五份共享的磁带驱动器。稍后，这个问题被托尼·霍尔重新表述为哲学家就餐问题。这个问题可以用来解释死锁和资源耗尽。
哲学家就餐问题描述：五个哲学家围坐在一张圆桌周围，每个哲学家面前都有一盘通心粉。由于通心粉很光滑，所以需要两把叉子才能夹住，相邻两个盘子之间放有一把叉子。哲学家的生活中有两种交替活动时段：即吃饭和思考（一种抽象而已）。当一个哲学家觉得饿了时，他就试图分两次去取其左边和右边的叉子，每次拿到一把，但不分次序。如果成功地得到了两把叉子，就开始吃饭，吃完后放下叉子继续思考。问题是为哲学家写一段描述其行为的程序，且决不会死锁。
源码：
哲学家就餐问题// 在1971年，著名的计算机科学家艾兹格·迪科斯彻提出了一个同步问题，
// 即假设有五台计算机都试图访问五份共享的磁带驱动器。稍后，这个问
// 题被托尼·霍尔重新表述为哲学家就餐问题。这个问题可以用来解释死
// 锁和资源耗尽。
//
// 哲学家就餐问题描述：五个哲学家围坐在一张圆桌周围，每个哲学家面
// 前都有一盘通心粉。由于通心粉很光滑，所以需要两把叉子才能夹住，
// 相邻两个盘子之间放有一把叉子。哲学家的生活中有两种交替活动时段：
// 即吃饭和思考（一种抽象而已）。当一个哲学家觉得饿了时，他就试图
// 分两次去取其左边和右边的叉子，每次拿到一把，但不分次序。如果成功
// 地得到了两把叉子，就开始吃饭，吃完后放下叉子继续思考。问题是为
// 哲学家写一段描述其行为的程序，且决不会死锁。
//
// ************************************************************
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace DiningPhilosophers
{
/// <summary>
/// 哲学家就餐问题是现代操作系统中很经典的问题。
/// 一个哲学家的封装。
/// </summary>
public class Philosopher : WorkerThread
{
public const int READY = 0;
public const int EATING = 1;
public const int THINKING = 2;
public const int FINISHED = 3;
public Philosopher(object data) : base(data) { }
public delegate void StateSwitchedHandler(Object sender, StateSwitchedEventArgs args);
public event StateSwitchedHandler StateSwitch;
protected override void Run()
{
PhilosopherData pd = (PhilosopherData)Data;
Ran
dom rnd = new Random(pd.PhilosopherId);
StateSwitch(this, new StateSwitchedEventArgs(READY, pd));
WaitHandle[] forks = new WaitHandle[] { pd.LeftFork, pd.RightFork };
while (pd.TotalFood > 0)
{
// 如果两边的哲学家有拿着叉子的，则等待。
WaitHandle.WaitAll(forks);
// 否则，开始吃通心粉。
StateSwitch(this, new StateSwitchedEventArgs(EATING, pd));
// 饭吃掉一部分移除。
pd.TotalFood -= pd.AmountToEat;
Thread.Sleep(rnd.Next(100, 1000));// 模拟正在吃通心粉
StateSwitch(this, new StateSwitchedEventArgs(THINKING, pd));
// 放下左边和右边的叉子开始思考。
pd.RightFork.ReleaseMutex();
pd.LeftFork.ReleaseMutex();
Thread.Sleep(rnd.Next(100, 1000));// 模拟正在思考
}
// 至此，通信粉都吃完了。
StateSwitch(this, new StateSwitchedEventArgs(FINISHED, pd));
}
}
/// <summary>
/// 哲学家相当于一个线程，这是工作线程抽象类，作为对线程操作的封装。
/// </summary>
public abstract class WorkerThread
{
private object _threadData;
private Thread _rawThread;
public object Data
{
get { return _threadData; }
set { _threadData = value; }
}
public WorkerThread(object data)
{
_threadData = data;
}
public WorkerThread()
{
&
nbsp; _threadData = null;
}
public void Start()
{
_rawThread = new Thread(new ThreadStart(this.Run));
_rawThread.Start();
}
protected abstract void Run();
}
/// <summary>
/// 封装哲学家数据的结构。
/// </summary>
public struct PhilosopherData
{
public int PhilosopherId; // 代表哲学家
public Mutex RightFork; // 代表右边的叉子
public Mutex LeftFork; // 代表左边的叉子
public int AmountToEat; // 吃掉的通心粉
public int TotalFood; // 盘中的总的通心粉
}
/// <summary>
/// 事件：用来通知外部现在哲学家的状态。
/// </summary>
public class StateSwitchedEventArgs : EventArgs
{
public int type;
public PhilosopherData philosopherData;
public StateSwitchedEventArgs(int t, PhilosopherData pd)
{
type = t;
philosopherData = pd;
}
}
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
namespace DiningPhilosophers
{
class Program
{
static void Main(string[] args)
{
// 准备数据
Mutex[] forks = new Mutex[N];
for (int i = 0; i < N; i++)
{
forks[i] = new Mutex(false);// 开始时叉子放在桌子上，没有哲学家拿到。
}
Philosopher[] p = new Philosopher[N];
for (int i = 0; i < N; i++)
{
PhilosopherData pd;
pd.PhilosopherId = i;
pd.RightFork = forks[(i + 1) % N];// 右边的叉子编号
pd.LeftFork = forks[(i + N – 1) % N];// 左边的叉子编号
pd.AmountToEat = N_EAT;// 暂时大锅饭，大家都一样。
pd.TotalFood = N_TOTAL;// 暂时大锅饭，大家都一样。
p[i] = new Philosopher(pd);
p[i].StateSwitch +=
new Philosopher.StateSwitchedHandler(
(sender, data) =>
{
Console.WriteLine(“Philosopher:{0} IS {1}.“,
data.philosopherData.PhilosopherId,
TranslateState(data.type));
});
}
for (int i = 0; i < N; i++)
p[i].Start();
Console.ReadKey();
}
private static string TranslateState(int state)
{
switch (state)
{
case Philosopher.READY:
return “READY“;
case Philosopher.EATING:
return “EATING“;
case Philosopher.THINKING:
return “THINKING“;
case Philosopher.FINISHED:
return “FINISHED“;
default:
throw new Exception(“*NOT* FOUND.“);
}
}
public const int N = 5;// 哲学家或叉子数目。
public const int N_EAT = 2;// 每次吃掉的通心粉数量。
public const int N_TOTAL = 20;// 盘中通心粉总数。
}
}
运行结果：
Philosopher:0 IS READY.
Philosopher:0 IS EATING.
Philosopher:1 IS READY.
Philosopher:1 IS EATING.
Philosopher:3 IS READY.
Philosopher:2 IS READY.
Philosopher:4 IS READY.
Philosopher:1 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:4 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:1 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:2 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:2 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:3 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:2 IS EATING.
Philosopher:2 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:0 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:3 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:1 IS THINKING.
Philosopher:2 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:0 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:2 IS THINKING.
Philosopher:1 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:4 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:2 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:2 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:4 IS THINKING.
Philosopher:1 IS EATING.
Philosopher:1 IS THINKING.
Philosopher:4 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:3 IS EATING.
Philosopher:3 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:1 IS FINISHED.
Philosopher:4 IS THINKING.
Philosopher:0 IS THINKING.
Philosopher:3 IS EATING.Philosopher:2 IS EATING.
Philosopher:4 IS FINISHED.
Philosopher:2 IS THINKING.
Philosopher:3 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:3 IS FINISHED.
Philosopher:2 IS THINKING.
Philosopher:0 IS EATING.
Philosopher:0 IS THINKING.
Philosopher:2 IS EATING.
Philosopher:0 IS FINISHED.
Philosopher:2 IS THINKING.
Philosopher:2 IS FINISHED.