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  • 并发容器之CopyOnWriteArrayList

    测试案例:

    import lombok.extern.slf4j.Slf4j;
    import net.jcip.annotations.ThreadSafe;
    
    import java.util.List;
    import java.util.concurrent.*;
    
    @ThreadSafe
    @Slf4j
    public class CopyOnWriteListExample {
    
        // 请求总数
        public static int requestTotal = 2000;
    
        // 同时并发执行的线程数
        public static int threadTotal = 200;
    
        public static List<Integer> list = new CopyOnWriteArrayList<>();
    
        public static void main(String[] args) {
            ExecutorService executorService = Executors.newCachedThreadPool();
            final Semaphore semaphore = new Semaphore(threadTotal);
            final CountDownLatch countDownLatch = new CountDownLatch(requestTotal);
    
            for (int i=0;i<requestTotal;i++) {
                final int num = i;
                executorService.execute(() -> {
                    try {
                        semaphore.acquire();
                        add(num);
                        semaphore.release();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
    
                    countDownLatch.countDown();
                });
            }
    
            try {
                countDownLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
    
            executorService.shutdown();
    
            log.info("{}", list.size());
        }
    
        private static void add(int i) {
            list.add(i);
        }
    
    }

    add方法源码:

    public boolean add(E e) {
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] elements = getArray();
            int len = elements.length;
            // 数组copy
            Object[] newElements = Arrays.copyOf(elements, len + 1);
            // 新增对象添加到新copy的数组
            newElements[len] = e;
            // 引用指向新数据
            setArray(newElements);
            return true;
        } finally {
            lock.unlock();
        }
    }

    由此上可知,CopyOnWriteArrayList适合多读少写的场景

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  • 原文地址:https://www.cnblogs.com/Kevin-1992/p/12608342.html
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