博客

假如有十张票，现在需要三个窗口（线程）卖，代码如下：

package com.test.runnable;

class MyThread implements Runnable {
	private int ticket = 10;
	public void run() {
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000l);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

输出结果为：

ticket = 10

ticket = 9

ticket = 8

ticket = 7

ticket = 7

ticket = 7

ticket = 6

ticket = 5

ticket = 6

ticket = 4

ticket = 4

ticket = 3

ticket = 2

ticket = 1

ticket = 2

可以发现不止卖 了十张，所以要进行并发控制。

第一种办法，采用同步关键字

package com.test.runnable;

class MyThread implements Runnable {
	private int ticket = 10;
	synchronized public void run() {
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

可以发现输出结果为：

ticket = 10

ticket = 9

ticket = 8

ticket = 7

ticket = 6

ticket = 5

ticket = 4

ticket = 3

ticket = 2

ticket = 1

这样多个窗口卖票，就能正确了，

2.也可以采用原子变量

package com.test.runnable;

import java.util.concurrent.atomic.AtomicInteger;

class MyThread implements Runnable {
	private AtomicInteger ticket = new AtomicInteger(10);
	synchronized public void run() {
		while (ticket.get() > 0) {
			System.out.println("ticket = " + ticket.getAndAdd(-1));
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

3.采用信号量Semaphore

package com.test.runnable;

import java.util.concurrent.Semaphore;

class MyThread implements Runnable {
	final Semaphore semp = new Semaphore(1);
	private  int ticket = 10;
	public void run() {
		// 获取许可
        try {
			semp.acquire();
		} catch (InterruptedException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		// 访问完后，释放
        semp.release();
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

4.采用Lock

package com.test.runnable;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class MyThread implements Runnable {
	private Lock myLock = new ReentrantLock(); // 执行操作所需的锁对象
	private  int ticket = 10;
	public void run() {
		myLock.lock();
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		// 访问完后，释放
		myLock.unlock();
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

5.但不能采用volatile关键字，因为线程内变量的值更新依赖原值。

package com.test.runnable;

class MyThread implements Runnable {
	//private volatile int ticket = 10;
	private volatile int ticket = 10;
	public void run() {
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}