实现一个自己的类ReentrantLock

最新推荐文章于 2022-04-13 21:13:31 发布

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本文详细介绍了一种自定义的ReentrantLock实现方法，通过继承AbstractQueuedSynchronizer来控制锁的状态，并提供了完整的锁操作，包括lock、tryLock、unlock等。同时，还提供了一个测试类用于验证自定义锁的功能。

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import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 *
 * 实现一个自己的类ReentrantLock
 */
public class SelfLock implements Lock {
    //state=1表示获取到了锁，state=0表示这个锁当前没有线程拿到
    private static class Sync extends AbstractQueuedSynchronizer {
        //是否占用
        protected boolean isHeldExclusively() {
            return getState()==1;
        }
        protected boolean tryAcquire(int arg) {
            if(compareAndSetState(0,1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }
        protected boolean tryRelease(int arg) {
            if(getState()==0) {
                throw new UnsupportedOperationException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }
        Condition newCondition() {
            return new ConditionObject();
        }
    }

    private final Sync sycn = new Sync();

    @Override
    public void lock() {
        sycn.acquire(1);

    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sycn.acquireInterruptibly(1);

    }

    @Override
    public boolean tryLock() {
        return sycn.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sycn.tryAcquireNanos(1, unit.toNanos(time));
    }

    @Override
    public void unlock() {
        sycn.release(1);

    }

    @Override
    public Condition newCondition() {
        return sycn.newCondition();
    }
}

import java.util.concurrent.TimeUnit;

/**
 * 线程休眠辅助工具类
 */
public class SleepTools {
    /**
     * 按秒休眠
     * @param seconds 秒数
     */
    public  static final void second(int seconds){
        try {
            TimeUnit.SECONDS.sleep(seconds);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 按毫秒数休眠
     * @param millis 毫秒数
     */
    public static final void milli(int millis){
        try {
            TimeUnit.MILLISECONDS.sleep(millis);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

/**
 *
 * 测试类似ReentrantLock的锁
 */
public class TestMyLock {
    public void test() {
        final Lock lock = new SelfLock();
        
        class Worker extends Thread {
            public void run() {
                while (true) {
                    lock.lock();
                    try {
                       SleepTools.second(1);
                        System.out.println(Thread.currentThread().getName());
                        SleepTools.second(1);
                    } finally {
                        lock.unlock();
                    }
                    SleepTools.second(2);
                }
            }
        }
        // 启动10个子线程
        for (int i = 0; i < 10; i++) {
            Worker w = new Worker();
            w.setDaemon(true);
            w.start();
        }
        // 主线程每隔1秒换行
        for (int i = 0; i < 10; i++) {
           SleepTools.second(1);
            System.out.println();
        }
    }

    public static void main(String[] args) {
        TestMyLock testMyLock = new TestMyLock();
        testMyLock.test();
    }
}