Java 多线程中CopyOnWriteArrayList并发读写操作范例

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#CopyOnWriteArrayList

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范例1：

package com.contoso;

import java.util.Random;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CopyOnWriteArrayListExample1 {

    /**
     * CopyOnWriteArrayList用来替换同步List对象
     *
     * 当读操作比写操作更频繁时，使用CopyOnWriteArrayList
     *
     * 每次修改列表时都创建一个新副本，只进行短暂地同步以确保数组内容的可见性
     *
     * 迭代器返回集合当前状态的快照
     *
     * 支持原子操作
     *
     */
    public static void useCopyOnWriteArrayList() {
        System.out.println("=== CopyOnWriteArrayList ===");
        ExecutorService executor = Executors.newCachedThreadPool();
        Random random = new Random();
        // 不会有ConcurrentModificationException异常抛出
        CopyOnWriteArrayList copyOnWriteArrayList = new CopyOnWriteArrayList<Integer>();

        for (int i = 0; i < 100; i++) {
            if (i % 3 == 0) {
                // 写操作
                executor.execute(() -> {
                    int value = random.nextInt(50);
                    System.err.println("Write " + value);
                    copyOnWriteArrayList.add(value);
                });
            } else {
                // 读操作
                executor.execute(() -> {
                    StringBuffer buffer = new StringBuffer();
                    for (Object value : copyOnWriteArrayList) {
                        buffer.append(value + " ");
                    }
                    System.out.println("Read " + buffer.toString());
                });
            }
        }

        executor.shutdown();
    }

    public static void main(String[] args) {
        useCopyOnWriteArrayList();
    }
}

run:
=== CopyOnWriteArrayList ===
Write 13
Read 13 
Read 13 
Read 13 
Read 13 
Read 13 
Read 13 
Write 35
Read 13 35 
Read 13 35 
Write 5
Read 13 35 5 
Write 1
Read 13 35 5 1 
Read 13 35 5 1 
Read 13 35 5 1 
Write 17
Read 13 35 5 1 17 
Read 13 35 5 1 17 
Write 40
Read 13 35 5 1 17 40 46 
Write 46
Write 49
Read 13 35 5 1 17 40 46 
Write 35
Read 13 35 5 1 17 40 46 49 35 2 
Write 2
Read 13 35 5 1 17 40 46 49 35 2 
Write 34
Read 13 35 5 1 17 40 46 49 35 2 34 
Read 13 35 5 1 17 40 46 49 35 2 34 
Write 35
Read 13 35 5 1 17 40 46 49 35 2 34 35 
Read 13 35 5 1 17 40 46 49 35 2 34 35 
Read 13 35 5 1 17 40 46 49 35 2 34 35 
Write 32
Read 13 35 5 1 17 40 46 49 35 2 34 35 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 
Read 13 35 5 1 17 40 46 49 35 2 34 
Write 42
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 
Write 26
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 
Write 10
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 
Write 9
Write 39
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 
Write 35
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 
Write 41
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 
Write 5
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 
Write 9
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 
Write 25
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 
Write 36
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 
Write 0
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 
Write 3
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 
Write 18
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 
Write 38
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 
Write 9
Write 0
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 
Write 0
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 
Write 21
Write 36
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 0 
Write 48
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 0 21 36 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 0 21 36 48 
Read 13 35 5 1 17 40 46 49 35 2 34 35 32 42 26 10 9 39 35 41 5 9 25 36 0 3 18 38 9 0 0 21 36 
BUILD SUCCESSFUL (total time: 0 seconds)