利用CAS构造一个TryLock自定义显示锁

CAS--campareAndSet

自定义异常

package com.dwz.atomicApi;

public class GetLockException extends Exception {
    public GetLockException() {
        super();
    }
    
    public GetLockException(String message) {
        super(message);
    }
}

自定义锁

package com.dwz.atomicApi;

import java.util.concurrent.atomic.AtomicInteger;

public class CompareAndSetLock {
    private final AtomicInteger value = new AtomicInteger(0);
    //保证锁是由同一个线程释放
    private Thread lockedThread;
    
    public void tryLock() throws GetLockException {
        boolean success = value.compareAndSet(0, 1);
        if(!success) {
            throw new GetLockException("Get the lock failed!");
        } else {
            lockedThread = Thread.currentThread();
        }
    }
    
    public void unlock() {
        if(0 == value.get()) {
            return;
        }
        
        if(lockedThread == Thread.currentThread()) {
            value.compareAndSet(1, 0);
        }
    }
}

测试代码

package com.dwz.atomicApi;
/**
 * synchronized在加锁后如果当前业务执行时间太长，后面的对象抢不到锁会一直等待
 *     在此我们加一个快速失败的场景，使用CAS自定义的一个显示锁
 */
public class AtomicIntegerDetailsTest2 {
    private final static CompareAndSetLock lock = new CompareAndSetLock();
    public static void main(String[] args) {
        for(int i = 0; i < 5; i++) {
            new Thread() {
                @Override
                public void run() {
                    try {
                        doSomething2();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } catch (GetLockException e) {
                        e.printStackTrace();
                    }
                };
            }.start();
        }
    }
    
    private static void doSomething() throws InterruptedException {
        synchronized (AtomicIntegerDetailsTest2.class) {
            System.out.println(Thread.currentThread().getName() + " get the lock");
            Thread.sleep(100000L);
        }
    }
    
    private static void doSomething2() throws InterruptedException, GetLockException {
        try {
            lock.tryLock();
            System.out.println(Thread.currentThread().getName() + " get the lock");
            Thread.sleep(100000L);
        } finally {
            lock.unlock();
        }
    }
}

附加：

CAS轻量级锁，带来一个严重问题，ABA问题

 详解解决CAS机制中ABA问题的AtomicStampedReference