首页 > 代码库 > Java多线程系列五——列表类

Java多线程系列五——列表类

参考资料:

http://xxgblog.com/2016/04/02/traverse-list-thread-safe/

一些列表类及其特性

 类 线程安全 Iterator 特性 说明
Vector fail-fast 内部方法用synchronized修饰,因此执行效率较低

1. 线程安全的列表类并不意味着调用它的代码就一定线程安全

2. 只有CopyOnWriteArrayList能支持在遍历时修改列表元素

ArrayList fail-fast 在多线程环境中使用不当易出错
Collections.synchronizedList fail-fast Collections.synchronizedList可以得到线程安全的列表,与Vector类似
CopyOnWriteArrayList fail-safe 每个线程先复制一份并把地址指向新list,在新的list上操作,因此最终结果未必符合预期,适用于经常需要遍历但很少修改的场景

 以下代码模拟多线程环境下,各个类Iterator机制的表现

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Vector;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;

/**
 * http://xxgblog.com/2016/04/02/traverse-list-thread-safe/
 * 
 * @Description: 多线程操作列表
 */
public class ThreadListTest {
    public void multipleThreadArrayList(final List<Integer> list) throws InterruptedException {
        int count = 10;
        for (int i = 0; i < count; i++) {
            list.add(i);
        }
        CountDownLatch countDownLatch = new CountDownLatch(2);
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                for (Integer integer : list) {
                    System.out.println(integer);
                }
                countDownLatch.countDown();
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getId() + " remove " + list.remove(0));
                countDownLatch.countDown();
            }
        }).start();
        countDownLatch.await();
    }

    public static void main(String[] args) throws InterruptedException {
        ThreadListTest test = new ThreadListTest();
        List<Integer> list;
        list = new Vector<>();// Vector只保证内部方法线程安全
        list = new ArrayList<>();// ArrayList效率较Vector,但非线程安全
        list = Collections.synchronizedList(new ArrayList<>());// Collections.synchronizedList与Vector有异曲同工之妙
        list = new CopyOnWriteArrayList<>();// CopyOnWriteArrayList线程安全:每个线程先复制一份并把地址指向新list,在新的list上操作,因此最终结果未必符合预期

        test.multipleThreadArrayList(list);
        System.out.println(list.toString());
    }
}

 

Java多线程系列五——列表类