CSharp Semaphore 信号量

限制可同时访问某一资源或资源池的线程数

Semaphore sema = new Semaphore(x,y)
x: 线程池中空位数
y: 线程池的总数

WaitOne

阻止当前线程，直到当前线程的WaitHandle 收到信号

Release

退出信号量并返回前一个计数

示例

排队

using System.Threading;
public class Program
{
    static Semaphore sema = new Semaphore(5, 5);//线程池中无线程, 最多同时执行5个线程
    const int cycleNum = 9;
    static void Main(string[] args) 
    {
        for(int i = 0; i < cycleNum; i++)
        {
            Thread td = new Thread(new ParameterizedThreadStart(testFun));
            td.Name = string.Format("{0}",i.ToString());
            td.Start(td.Name);
        }
        Console.ReadKey();
    }
    public static void testFun(object obj)
    {
        sema.WaitOne();
        Console.WriteLine(obj.ToString() + "进入：" + DateTime.Now.ToString());
        Thread.Sleep(2000);
        Console.WriteLine(obj.ToString() + "离开：" + DateTime.Now.ToString());
        sema.Release();
    }
}

Leetcode打印零与奇偶数

输入：n = 5
输出：”0102030405”

using System.Threading;
public class ZeroEvenOdd {
    private int n;
    public Semaphore semaphore = new Semaphore(1, 1);//奇数偶数打印完解锁
    public Semaphore semaphore2 = new Semaphore(0, 1);//0打印完解锁打印奇数
    public Semaphore semaphore3 = new Semaphore(0, 1);//0打印完解锁打印偶数

    public ZeroEvenOdd(int n) {
        this.n = n;
    }

    // printNumber(x) outputs "x", where x is an integer.
    public void Zero(Action<int> printNumber) {
        for(int i=0;i<n;i++)
        {
            semaphore.WaitOne();      
            printNumber(0);
            if(i%2 == 0)
            {
                semaphore2.Release();
            }
            else
            {
                semaphore3.Release();
            }

        }
    }

    public void Even(Action<int> printNumber) {
        for(int i=2;i<=n;i=i+2)
        {
            semaphore3.WaitOne(); 
            printNumber(i);
            semaphore.Release();
        }

    }

    public void Odd(Action<int> printNumber) {
        for(int i=1;i<=n;i=i+2)
        {
            semaphore2.WaitOne(); 
            printNumber(i);
            semaphore.Release();
        }
    }
}