手写Lockl锁

可分为三步：

　　1.实现Lock类；

　　2.实现lock()

　　3.实现unlock()

　　

以下图形象的表示抢锁与释放锁过程

　　

 

 

相关代码如下：

package myLock;

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.LockSupport;

/**
 * 简单描述
 *
 * @author lijie
 * @data 2021/5/11 22:17
 */
public class JieLock implements Lock {
    // 房卡，用来登记线程
    AtomicReference<Thread> owners = new AtomicReference<>();
    // 队列（此队列安全+高效）。用来存放没有抢到锁的线程
    LinkedBlockingQueue<Thread> waiters = new LinkedBlockingQueue<>();

    @Override
    public void lock() {
        while (!owners.compareAndSet(null, Thread.currentThread())) {
            // 若抢不到锁，则等待
            waiters.add(Thread.currentThread());
            // 让当前线程阻塞
            LockSupport.park();
            // 当不阻塞时，从队列中将该线程移除
            waiters.remove(Thread.currentThread());
        }

    }

    @Override
    public void lockInterruptibly() throws InterruptedException {

    }

    @Override
    public boolean tryLock() {
        return false;
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return false;
    }

    @Override
    public void unlock() {
        // 只有持有锁的线程才可以释放锁
        if (owners.compareAndSet(Thread.currentThread(), null)) {
            for (Thread waiter : waiters) {
                LockSupport.unpark(waiter);
            }
        } else {
        }
    }

    @Override
    public Condition newCondition() {
        return null;
    }
}

进行测试：

　　

package myLock;

/**
 * 简单描述
 *
 * @author lijie
 * @data 2021/5/11 22:35
 */
public class TestLock {
    int i = 10000;
    JieLock lock = new JieLock();
    public void order(){
        lock.lock();
        try {
            i--;
        } finally {
            lock.unlock();

        }
    }

    public static void main(String[] args) throws InterruptedException {
        TestLock lock1 = new TestLock();
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    lock1.order();
                }
            }).start();
        }
        // 等待线程执行完操作
        Thread.sleep(2000);
        System.out.println(lock1.i);
    }

}