信号量透过一个计数器控制对共享资源的访问

package sync;

import java.util.concurrent.Semaphore;

/**
 * 公共数据
 * 
 */
class Shared {
	public static int count;
}

/**
 * 递减线程
 * 
 */
class DecThread implements Runnable {

	private Semaphore sem;
	private String name;

	DecThread(Semaphore sem, String name) {
		this.sem = sem;
		this.name = name;
		new Thread(this).start();
	}

	@Override
	public void run() {
		try {
			System.out.println(name + "：等待通行证..");
			sem.acquire();
			System.out.println(name + "：得到通行证");
			for (int i = 0; i < 5; i++) {
				Shared.count--;
				System.out.println(name + ":" + Shared.count);
				Thread.sleep(10);
			}
			sem.release();
			System.out.println(name + "释放通行证");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

/**
 * 递加线程
 * 
  */
class IncThread implements Runnable {

	private Semaphore sem;
	private String name;

	IncThread(Semaphore sem, String name) {
		this.sem = sem;
		this.name = name;
		new Thread(this).start();
	}

	@Override
	public void run() {
		try {
			System.out.println(name + "：等待通行证..");
			sem.acquire();
			System.out.println(name + "：得到通行证");
			for (int i = 0; i < 5; i++) {
				Shared.count++;
				System.out.println(name + ":" + Shared.count);
				Thread.sleep(10);
			}
			sem.release();
			System.out.println(name + "释放通行证");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

}

/**
 * 信号量通过一个计数器控制对共享资源的访问
 * 
 */
public class SemaphoreTest {
	public static void main(String[] args) {
		// 信号量通过一个计数器控制对共享资源的访问
		Semaphore sem = new Semaphore(1);
		// 新启线程，传入信号量
		new IncThread(sem, "Inc");
		new DecThread(sem, "Dec");
	}
}
//输出
Inc：等待通行证..
Inc：得到通行证
Dec：等待通行证..
Inc:1
Inc:2
Inc:3
Inc:4
Inc:5
Inc释放通行证
Dec：得到通行证
Dec:4
Dec:3
Dec:2
Dec:1
Dec:0
Dec释放通行证

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