线程安全性（一）原子性 AtomicLong & LongAdder

最新推荐文章于 2025-07-10 15:38:06 发布

乌鲁木齐001号程序员

最新推荐文章于 2025-07-10 15:38:06 发布

阅读量699

点赞数

CC 4.0 BY-SA版权

本文链接：https://blog.youkuaiyun.com/weixin_33669968/article/details/88889793

本文对比了LongAdder和AtomicLong两种并发计数器的优缺点，并通过示例代码展示了它们的应用场景。LongAdder采用热点数据分离技术提高并发性能，而AtomicLong则适用于简单的原子操作。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

LongAdder相对于AtomicLong的优势

LongAdder用到了热点数据分离技术，即对long型共享变量拆分成数组，多线程分别针对数组中的一段进行读写，最后再将数组合并long型共享变量；

LongAdder 缺点

并发更新的时候可能导致数据出现误差；

AtomicLong 示例

import com.example.concurrency.annotations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

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

@Slf4j
@ThreadSafe
public class AtomicExample2 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    public static AtomicLong count = new AtomicLong(0);

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal ; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("count:{}", count.get());
    }

    private static void add() {
        count.incrementAndGet();
        // count.getAndIncrement();
    }
}

LongAdder 示例

import com.example.concurrency.annotations.ThreadSafe;
import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.LongAdder;

@Slf4j
@ThreadSafe
public class AtomicExample3 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    public static LongAdder count = new LongAdder();

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal ; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("count:{}", count);
    }

    private static void add() {
        count.increment();
    }
}