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Java 多线程(五):锁(三)

Java 多线程(五):锁(三)

作者:Grey

原文地址:

博客园:Java 多线程(五):锁(三)

CSDN:Java 多线程(五):锁(三)

StampedLock

StampedLock其实是对读写锁的一种改进,它支持在读同时进行一个写操作,也就是说,它的性能将会比读写锁更快。

更通俗的讲就是在读锁没有释放的时候是可以获取到一个写锁,获取到写锁之后,读锁阻塞,这一点和读写锁一致,唯一的区别在于读写锁不支持在没有释放读锁的时候获取写锁

StampedLock 有三种模式:

  • 悲观读:允许多个线程获取悲观读锁。

  • 写锁:写锁和悲观读是互斥的。

  • 乐观读:无锁机制,类似于数据库中的乐观锁,它支持在不释放乐观读的时候是可以获取到一个写锁。

参考: 有没有比读写锁更快的锁?

示例代码:

悲观读 + 写锁:

package git.snippets.juc;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.StampedLock;
import java.util.logging.Logger;

// 悲观读 + 写锁
public class StampedLockPessimistic {
    private static final Logger log = Logger.getLogger(StampedLockPessimistic.class.getName());
    private static final StampedLock lock = new StampedLock();
    //缓存中存储的数据
    private static final Map<String, String> mapCache = new HashMap<>();
    //模拟数据库存储的数据
    private static final Map<String, String> mapDb = new HashMap<>();

    static {
        mapDb.put("zhangsan", "你好,我是张三");
        mapDb.put("sili", "你好,我是李四");
    }

    private static void getInfo(String name) {
        //获取悲观读
        long stamp = lock.readLock();
        log.info("线程名:" + Thread.currentThread().getName() + " 获取了悲观读锁" + "    用户名:" + name);
        try {
            if ("zhangsan".equals(name)) {
                log.info("线程名:" + Thread.currentThread().getName() + " 休眠中" + "    用户名:" + name);
                Thread.sleep(3000);
                log.info("线程名:" + Thread.currentThread().getName() + " 休眠结束" + "    用户名:" + name);
            }
            String info = mapCache.get(name);
            if (null != info) {
                log.info("在缓存中获取到了数据");
                return;
            }
        } catch (InterruptedException e) {
            log.info("线程名:" + Thread.currentThread().getName() + " 释放了悲观读锁");
            e.printStackTrace();
        } finally {
            //释放悲观读
            lock.unlock(stamp);
        }

        //获取写锁
        stamp = lock.writeLock();
        log.info("线程名:" + Thread.currentThread().getName() + " 获取了写锁" + "    用户名:" + name);
        try {
            //判断一下缓存中是否被插入了数据
            String info = mapCache.get(name);
            if (null != info) {
                log.info("获取到了写锁,再次确认在缓存中获取到了数据");
                return;
            }
            //这里是往数据库获取数据
            String infoByDb = mapDb.get(name);
            //将数据插入缓存
            mapCache.put(name, infoByDb);
            log.info("缓存中没有数据,在数据库获取到了数据");
        } finally {
            //释放写锁
            log.info("线程名:" + Thread.currentThread().getName() + " 释放了写锁" + "     用户名:" + name);
            lock.unlock(stamp);
        }
    }

    public static void main(String[] args) {
//线程1
        Thread t1 = new Thread(() -> {
            getInfo("zhangsan");
        });

        //线程2
        Thread t2 = new Thread(() -> {
            getInfo("lisi");
        });

        //线程启动
        t1.start();
        t2.start();

        //线程同步
        try {
            t1.join();
            t2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

乐观读:

package git.snippets.juc;

import java.util.concurrent.locks.StampedLock;
import java.util.logging.Logger;

// 乐观写
public class StampedLockOptimistic {
    private static final Logger log = Logger.getLogger(StampedLockOptimistic.class.getName());
    private static final StampedLock lock = new StampedLock();
    private static int num1 = 1;
    private static int num2 = 1;

    /**
     * 修改成员变量的值,+1
     *
     * @return
     */
    private static int sum() {
        log.info("求和方法被执行了");
        //获取乐观读
        long stamp = lock.tryOptimisticRead();
        int cnum1 = num1;
        int cnum2 = num2;
        log.info("获取到的成员变量值,cnum1:" + cnum1 + "   cnum2:" + cnum2);
        try {
            //休眠3秒,目的是为了让其他线程修改掉成员变量的值。
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //判断在运行期间是否存在写操作   true:不存在   false:存在
        if (!lock.validate(stamp)) {
            log.info("存在写操作!");
            //存在写锁
            //升级悲观读锁
            stamp = lock.readLock();
            try {
                log.info("升级悲观读锁");
                cnum1 = num1;
                cnum2 = num2;
                log.info("重新获取了成员变量的值=========== cnum1=" + cnum1 + "    cnum2=" + cnum2);
            } finally {
                //释放悲观读锁
                lock.unlock(stamp);
            }
        }
        return cnum1 + cnum2;
    }

    //使用写锁修改成员变量的值
    private static void updateNum() {
        long stamp = lock.writeLock();
        try {
            num1 = 2;
            num2 = 2;
        } finally {
            lock.unlock(stamp);
        }
    }


    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            int sum = sum();
            log.info("求和结果:" + sum);
        });
        t1.start();
        //休眠1秒,目的为了让线程t1能执行到获取成员变量之后
        Thread.sleep(1000);
        updateNum();
        t1.join();
        log.info("执行完毕");

    }

}

使用 StampedLock 的注意事项

  1. 看名字就能看出来StampedLock不支持重入锁。

  2. 它适用于读多写少的情况,如果不是这种情况,请慎用,性能可能还不如synchronized

  3. StampedLock的悲观读锁、写锁不支持条件变量。

  4. 千万不能中断阻塞的悲观读锁或写锁,如果调用阻塞线程的interrupt(),会导致cpu飙升,如果希望StampedLock支持中断操作,请使用readLockInterruptibly(悲观读锁)与writeLockInterruptibly(写锁)。

CountDownLatch

类似门闩的概念,可以替代join,但是比join灵活,因为一个线程里面可以多次countDown,但是join一定要等线程完成才能执行。

其底层原理是:调用await()方法的线程会利用AQS排队,一旦数字减为0,则会将AQS中排队的线程依次唤醒。

代码如下:

package git.snippets.juc;

import java.util.concurrent.CountDownLatch;

/**
 * CountDownLatch可以用Join替代
 */
public class CountDownLatchAndJoin {
    public static void main(String[] args) {
        useCountDownLatch();
        useJoin();
    }

    public static void useCountDownLatch() {
        // use countdownlatch
        long start = System.currentTimeMillis();
        Thread[] threads = new Thread[100000];
        CountDownLatch latch = new CountDownLatch(threads.length);

        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Thread(() -> {
                int result = 0;
                for (int i1 = 0; i1 < 1000; i1++) {
                    result += i1;
                }
                // System.out.println("Current thread " + Thread.currentThread().getName() + " finish cal result " + result);
                latch.countDown();
            });
        }
        for (Thread thread : threads) {
            thread.start();
        }
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        long end = System.currentTimeMillis();

        System.out.println("end latch down, time is " + (end - start));

    }

    public static void useJoin() {
        long start = System.currentTimeMillis();

        // use join
        Thread[] threads = new Thread[100000];

        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Thread(() -> {
                int result = 0;
                for (int i1 = 0; i1 < 1000; i1++) {
                    result += i1;
                }
                // System.out.println("Current thread " + Thread.currentThread().getName() + " finish cal result " + result);
            });
        }
        for (Thread thread : threads) {
            thread.start();
        }
        for (Thread thread : threads) {
            try {
                thread.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        long end = System.currentTimeMillis();

        System.out.println("end join, time is " + (end - start));
    }
}

CyclicBarrier

类似栅栏,类比:满了20个乘客就发车 这样的场景。

比如:一个程序可能收集如下来源的数据:

  1. 数据库

  2. 网络

  3. 文件

程序可以并发执行,用线程操作1,2,3,然后操作完毕后再合并, 然后执行后续的逻辑操作,就可以使用CyclicBarrier

代码如下:

package git.snippets.juc;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

/**
 * CyclicBarrier示例:满员发车
 *
 * @author <a href="mailto:410486047@qq.com">Grey</a>
 * @since 1.8
 */
public class CyclicBarrierTest {
    public static void main(String[] args) {
        CyclicBarrier barrier = new CyclicBarrier(20, () -> {
            System.out.println("满了20,发车");
        });
        for (int i = 0; i < 100; i++) {
            new Thread(() -> {
                try {
                    barrier.await();
                } catch (InterruptedException | BrokenBarrierException e) {
                    e.printStackTrace();
                }
            }).start();
        }
    }
}

Semaphore

表示信号量,有如下两个操作:

s.acquire() 信号量减1

s.release()信号量加1

到 0 以后,就不能执行了,这个可以用于限流

底层原理是:如果没有线程许可可用,则线程阻塞,并通过 AQS 来排队,可以通过release()方法来释放许可,当某个线程释放了某个许可后,会从 AQS 中正在排队的第一个线程依次开始唤醒,直到没有空闲许可。

Semaphore 使用示例:有N个线程来访问,我需要限制同时运行的只有信号量大小的线程数。

代码如下:

package git.snippets.juc;

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

/**
 * Semaphore用于限流
 */
public class SemaphoreUsage {
    public static void main(String[] args) {
        Semaphore semaphore = new Semaphore(1);
        new Thread(() -> {
            try {
                semaphore.acquire();
                TimeUnit.SECONDS.sleep(2);
                System.out.println("Thread 1 executed");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                semaphore.release();
            }
        }).start();

        new Thread(() -> {
            try {
                semaphore.acquire();
                TimeUnit.SECONDS.sleep(2);
                System.out.println("Thread 2 executed");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                semaphore.release();
            }
        }).start();
    }
}

Semaphore可以有公平非公平的方式进行配置。

SemaphoreCountDownLatch的区别?

Semaphore 是信号量,可以做限流,限制 n 个线程并发,释放一个线程后就又能进来一个新的线程。

CountDownLatch 是闭锁,带有阻塞的功能,必须等到 n 个线程都执行完后,被阻塞的线程才能继续往下执行。

Guava RateLimiter

采用令牌桶算法,用于限流

示例代码如下

package git.snippets.juc;

import com.google.common.util.concurrent.RateLimiter;
import java.util.List;
import java.util.concurrent.Executor;

/**
 * @author <a href="mailto:410486047@qq.com">Grey</a>
 * @date 2021/4/21
 * @since
 */
public class RateLimiterUsage {
    //每秒只发出2个令牌
    static final RateLimiter rateLimiter = RateLimiter.create(2.0);
    static void submitTasks(List<Runnable> tasks, Executor executor) {
        for (Runnable task : tasks) {
            rateLimiter.acquire(); // 也许需要等待
            executor.execute(task);
        }
    }
}

注:上述代码需要引入 Guava 包

Phaser(Since jdk1.7)

遗传算法,可以用这个结婚的场景模拟: 假设婚礼的宾客有 5 个人,加上新郎和新娘,一共 7 个人。 我们可以把这 7 个人看成 7 个线程,有如下步骤要执行。

  1. 到达婚礼现场

  2. 吃饭

  3. 离开

  4. 拥抱(只有新郎和新娘线程可以执行)

每个阶段执行完毕后才能执行下一个阶段,其中拥抱阶段只有新郎新娘这两个线程才能执行。

以上需求,我们可以通过 Phaser 来实现,具体代码和注释如下:

package git.snippets.juc;

import java.util.Random;
import java.util.concurrent.Phaser;
import java.util.concurrent.TimeUnit;

public class PhaserUsage {
    static final Random R = new Random();
    static WeddingPhaser phaser = new WeddingPhaser();

    static void millSleep() {
        try {
            TimeUnit.MILLISECONDS.sleep(R.nextInt(1000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        // 宾客的人数
        final int guestNum = 5;
        // 新郎和新娘
        final int mainNum = 2;
        phaser.bulkRegister(mainNum + guestNum);
        for (int i = 0; i < guestNum; i++) {
            new Thread(new Person("宾客" + i)).start();
        }
        new Thread(new Person("新娘")).start();
        new Thread(new Person("新郎")).start();
    }

    static class WeddingPhaser extends Phaser {
        @Override
        protected boolean onAdvance(int phase, int registeredParties) {
            switch (phase) {
                case 0:
                    System.out.println("所有人到齐");
                    return false;
                case 1:
                    System.out.println("所有人吃饭");
                    return false;
                case 2:
                    System.out.println("所有人离开");
                    return false;
                case 3:
                    System.out.println("新郎新娘拥抱");
                    return true;
                default:
                    return true;
            }
        }
    }

    static class Person implements Runnable {
        String name;

        Person(String name) {
            this.name = name;
        }

        @Override
        public void run() {
            // 先到达婚礼现场
            arrive();
            // 吃饭
            eat();
            // 离开
            leave();
            // 拥抱,只保留新郎和新娘两个线程可以执行
            hug();
        }

        private void arrive() {
            millSleep();
            System.out.println("name:" + name + " 到来");
            phaser.arriveAndAwaitAdvance();
        }

        private void eat() {
            millSleep();
            System.out.println("name:" + name + " 吃饭");
            phaser.arriveAndAwaitAdvance();
        }

        private void leave() {
            millSleep();
            System.out.println("name:" + name + " 离开");
            phaser.arriveAndAwaitAdvance();
        }

        private void hug() {
            if ("新娘".equals(name) || "新郎".equals(name)) {
                millSleep();
                System.out.println("新娘新郎拥抱");
                phaser.arriveAndAwaitAdvance();
            } else {
                phaser.arriveAndDeregister();
            }
        }
    }
}

Exchanger

用于线程之间交换数据,exchange()方法是阻塞的,所以要两个exchange行为都执行到才会触发交换。

package git.snippets.juc;

import java.util.concurrent.Exchanger;
import java.util.concurrent.TimeUnit;

/**
 * Exchanger用于两个线程之间交换变量
 */
public class ExchangerUsage {
    static Exchanger<String> semaphore = new Exchanger<>();

    public static void main(String[] args) {

        new Thread(() -> {
            String s = "T1";
            try {
                s = semaphore.exchange(s);
                TimeUnit.SECONDS.sleep(2);
                System.out.println("Thread 1(T1) executed, Result is " + s);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }).start();

        new Thread(() -> {
            String s = "T2";
            try {
                s = semaphore.exchange(s);
                TimeUnit.SECONDS.sleep(2);
                System.out.println("Thread 2(T2) executed, Result is " + s);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }).start();
    }
}

LockSupport

其他锁的底层用的是AQS

原先让线程等待需要wait/await,现在仅需要LockSupport.park()

原先叫醒线程需要notify/notifyAll,现在仅需要LockSupport.unpark(), LockSupport.unpark()还可以叫醒指定线程,

示例代码:

package git.snippets.juc;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;

/**
 * 阻塞指定线程,唤醒指定线程
 */
public class LockSupportUsage {
    public static void main(String[] args) {
        Thread t = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    if (i == 5) {
                        LockSupport.park();
                    }
                    if (i == 8) {
                        LockSupport.park();
                    }
                    TimeUnit.SECONDS.sleep(1);
                    System.out.println(i);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
        // unpark可以先于park调用
        //LockSupport.unpark(t);
        try {
            TimeUnit.SECONDS.sleep(8);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        LockSupport.unpark(t);
        System.out.println("after 8 seconds");
    }
}

实现一个监控元素的容器

实现一个容器,提供两个方法

// 向容器中增加一个元素
void add(T t);
// 返回容器大小
int size();

有两个线程,线程1添加10个元素到容器中,线程2实现监控元素的个数,当个数到5个时,线程2给出提示并结束

方法 1. 使用wait + notify实现

方法 2. 使用CountDownLatch实现

方法 3. 使用LockSupport实现

代码如下:

package git.snippets.juc;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;

// 实现一个容器,提供两个方法,add,size,有两个线程,
// 线程1添加10个元素到容器中,
// 线程2实现监控元素的个数,
// 当个数到5个时,线程2给出提示并结束
public class MonitorContainer {

    public static void main(String[] args) {

        useLockSupport();
        // useCountDownLatch();
        // useNotifyAndWait();
    }


    /**
     * 使用LockSupport
     */
    private static void useLockSupport() {
        System.out.println("use LockSupport...");
        Thread adder;
        List<Object> list = Collections.synchronizedList(new ArrayList<>());
        Thread finalMonitor = new Thread(() -> {
            LockSupport.park();
            if (match(list)) {
                System.out.println("filled 5 elements size is " + list.size());
                LockSupport.unpark(null);
            }
        });
        adder = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                increment(list);
                if (match(list)) {
                    LockSupport.unpark(finalMonitor);
                }
            }
        });
        adder.start();
        finalMonitor.start();
    }

    /**
     * 使用CountDownLatch
     */
    private static void useCountDownLatch() {
        System.out.println("use CountDownLatch...");
        List<Object> list = Collections.synchronizedList(new ArrayList<>());
        CountDownLatch latch = new CountDownLatch(5);
        Thread adder = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                increment(list);
                if (i <= 4) {
                    latch.countDown();
                }
            }
        });
        Thread monitor = new Thread(() -> {
            try {
                latch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            if (match(list)) {
                System.out.println("filled 5 elements");
            }
        });
        adder.start();
        monitor.start();
    }

    /**
     * notify + wait 实现
     */
    private static void useNotifyAndWait() {
        System.out.println("use notify and wait...");
        List<Object> list = Collections.synchronizedList(new ArrayList<>());
        final Object o = new Object();
        Thread adder = new Thread(() -> {
            synchronized (o) {
                for (int i = 0; i < 10; i++) {
                    increment(list);
                    if (match(list)) {
                        o.notify();
                        try {
                            o.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
                System.out.println("add finished");
                o.notify();
            }
        });
        Thread monitor = new Thread(() -> {
            synchronized (o) {
                if (match(list)) {
                    System.out.println("5 elements added " + list.size());
                    o.notify();
                    try {
                        o.wait();
                        System.out.println("monitor finished");
                        o.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                }
            }
        });
        adder.start();
        monitor.start();
    }

    /**
     * 只要是5的倍数,就循环打印
     */
    private static void useNotifyAndWaitLoop() {
        List<Object> list = Collections.synchronizedList(new ArrayList<>());
        final Object o = new Object();
        Thread adder = new Thread(() -> {
            synchronized (o) {
                for (; ; ) {
                    increment(list);
                    if (match(list)) {
                        o.notify();
                        try {
                            o.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });
        Thread monitor = new Thread(() -> {
            synchronized (o) {
                while (true) {
                    if (match(list)) {
                        System.out.println("filled 5 elements");
                    }
                    o.notify();
                    try {
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        });
        adder.start();
        monitor.start();
    }

    private static void increment(List<Object> list) {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        list.add(new Object());
        System.out.println("list add the ele, size is " + list.size());
    }

    private static boolean match(List<Object> list) {
        return list.size() % 5 == 0;
    }
}

生产者消费者问题

写一个固定容量的同步容器,拥有putget方法,以及getCount方法,能够支持 2 个生产者线程以及 10 个消费者线程的阻塞调用。

方法 1. 使用wait/notifyAll

方法 2. ReentrantLockCondition,本质就是等待队列

package git.snippets.juc;

import java.util.LinkedList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

// 写一个固定容量的同步容器,拥有put和get方法,以及getCount方法,能够支持2个生产者线程以及10个消费者线程的阻塞调用。
public class ProducerAndConsumer {
    public static void main(String[] args) {
        // MyContainerByCondition container = new MyContainerByCondition(100);
        MyContainerByNotifyAndWait container = new MyContainerByNotifyAndWait(100);
        for (int i = 0; i < 25; i++) {
            new Thread(container::get).start();
        }
        for (int i = 0; i < 20; i++) {
            new Thread(() -> container.put(new Object())).start();
        }
    }
}

// 使用ReentrantLock的Condition
class MyContainerByCondition {
    static ReentrantLock lock = new ReentrantLock();
    final int MAX;
    private final LinkedList<Object> list = new LinkedList<>();
    Condition consumer = lock.newCondition();
    Condition producer = lock.newCondition();

    public MyContainerByCondition(int limit) {
        this.MAX = limit;
    }

    public void put(Object object) {
        lock.lock();
        try {
            while (getCount() == MAX) {
                System.out.println("container is full");
                try {
                    producer.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            list.add(object);
            consumer.signalAll();
            System.out.println("contain add a object, current size " + getCount());

        } finally {
            lock.unlock();
        }

    }

    public Object get() {
        lock.lock();
        try {
            while (getCount() == 0) {
                try {
                    System.out.println("container is empty");
                    consumer.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            Object object = list.removeFirst();
            producer.signalAll();

            System.out.println("contain get a object, current size " + getCount());
            return object;
        } finally {
            lock.unlock();
        }

    }

    public synchronized int getCount() {
        return list.size();
    }
}

// 使用synchronized的wait和notifyAll
class MyContainerByNotifyAndWait {
    LinkedList<Object> list = null;
    final int limit;

    MyContainerByNotifyAndWait(int limit) {
        this.limit = limit;
        list = new LinkedList<>();
    }

    synchronized int getCount() {
        return list.size();
    }

    // index 从0开始计数
    synchronized Object get() {
        while (list.size() == 0) {
            System.out.println("container is empty");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        Object o = list.removeFirst();

        System.out.println("get a data");
        this.notifyAll();
        return o;
    }

    synchronized void put(Object data) {
        while (list.size() > limit) {
            System.out.println("container is full , do not add any more");
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        list.add(data);

        System.out.println("add a data");
        this.notifyAll();
    }
}

说明

本文涉及到的所有代码和图例

图例

代码

更多内容见:Java 多线程

参考资料

实战Java高并发程序设计(第2版)

深入浅出Java多线程

多线程与高并发-马士兵

Java并发编程实战

Java中的共享锁和排他锁(以读写锁ReentrantReadWriteLock为例)

【并发编程】面试官:有没有比读写锁更快的锁?

图解Java多线程设计模式

posted @ 2022-09-11 17:37  Grey Zeng  阅读(310)  评论(0编辑  收藏  举报