System.out.println 的多线程并发问题

标签：system.out.println   并发   多线程   

如下例子所示：

package xiaoye.java;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicLong;

public class Test
{
	public static void main(String[] args)
	{
		ExecutorService pool = Executors.newFixedThreadPool(2);
		Runnable t1 = new MyRunnable("张三", 2000);
		Runnable t2 = new MyRunnable("李四", 3600);
		Runnable t3 = new MyRunnable("王五", 2700);
		Runnable t4 = new MyRunnable("老张", 600);
		Runnable t5 = new MyRunnable("老牛", 1300);
		Runnable t6 = new MyRunnable("老朱", 800);
		//执行各个线程
		pool.execute(t1);
		pool.execute(t2);
		pool.execute(t3);
		pool.execute(t4);
		pool.execute(t5);
		pool.execute(t6);
		//关闭线程池
		pool.shutdown();
	}
}

class MyRunnable implements Runnable
{
	private static AtomicLong aLong = new AtomicLong(10000); //原子量，每个线程都可以自由操作
	private String name; //操作人
	private int data; //操作数

	MyRunnable(String name, int data)
	{
		this.name = name;
		this.data = data;
	}
	public void run()
	{
		Thread.yield();
		System.out.println(name + "执行了" + data + "，当前余额：" + aLong.addAndGet(data));
	}
}

对于 

System.out.println(name + "执行了" + data + "，当前余额：" + aLong.addAndGet(data));

System.out.println((new StringBuilder(String.valueOf(name))).append("执行了").append(data).append("，当前余额：").append(aLong.addAndGet(data)).toString());

    public void println(String x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }

实际上的执行过程是： 张三——李四——王五——老张——老牛——老朱，而实际上输出 张三 却是称为最后一个输出的。这是因为 张三 在或的锁之前被打断了。

如果我们想要输出正确的执行顺序，可以加一个显示锁：

package xiaoye.java;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Test {
	public static void main(String[] args) {
		ExecutorService pool = Executors.newFixedThreadPool(2);
		Lock lock = new ReentrantLock(false);
		Runnable t1 = new MyRunnable("张三", 2000, lock);
		Runnable t2 = new MyRunnable("李四", 3600, lock);
		Runnable t3 = new MyRunnable("王五", 2700, lock);
		Runnable t4 = new MyRunnable("老张", 600, lock);
		Runnable t5 = new MyRunnable("老牛", 1300, lock);
		Runnable t6 = new MyRunnable("老朱", 800, lock);
		// 执行各个线程
		pool.execute(t1);
		pool.execute(t2);
		pool.execute(t3);
		pool.execute(t4);
		pool.execute(t5);
		pool.execute(t6);
		// 关闭线程池
		pool.shutdown();
	}
}

class MyRunnable implements Runnable {
	private static AtomicLong aLong = new AtomicLong(10000); // 原子量，每个线程都可以自由操作
	private Lock lock;
	private String name; // 操作人
	private int data; // 操作数

	MyRunnable(String name, int data, Lock lock) {
		this.name = name;
		this.data = data;
		this.lock = lock;
	}

	public void run() {
		lock.lock();
		System.out.println(name + "执行了" + data + "，当前余额："
				+ aLong.addAndGet(data));
		lock.unlock();
	}
}

System.out.println 的多线程并发问题

标签：system.out.println   并发   多线程   

原文地址：http://blog.csdn.net/zq602316498/article/details/40398247