Java ReentrantLock锁

1. 什么是ReentrantLock？

ReentrantLock称为可重入锁，或者中心锁。

ReentrantLock加锁后需要手动解锁。

2.ReentrantLock的使用

方法	含义	备注
lock	加锁	加锁以后不会自动解锁，需要手动解锁(unlock)。当一个线程lock以后，其他线程lock时，会加入等待队列。
unlock	解锁	释放锁，和一般和lock成对使用
tryLock	尝试申请锁	尝试加锁，申请失败不加入等待队列。如果锁被占用，则加锁失败，返回false。

验证

/**
 * 测试ReentrantLock尝试加锁
 *
 * @author zhouronghua
 * @time 2021/6/30 5:58 下午
 */
public class TestReentrantTryLock {

    /**
     * ReentrantLock
     */
    private final ReentrantLock reentrantLock = new ReentrantLock();

    /**
     * 加锁处理
     *
     * @author zhouronghua
     * @time 2021/6/30 6:00 下午
     */
    private void lockProcessor() {
        try {
            System.out.println(Thread.currentThread().getName() + " 获得ReentrantLock锁");
            reentrantLock.lock();
            try {
                TimeUnit.SECONDS.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            reentrantLock.unlock();
            System.out.println(Thread.currentThread().getName() + " lockProcessor释放ReentrantLock锁");
        }
    }

    /**
     * 尝试申请锁处理
     *
     * @author zhouronghua
     * @time 2021/6/30 6:00 下午
     */
    private void tryLockProcessor() {
        System.out.println(Thread.currentThread().getName() + " 尝试申请ReentrantLock锁");
        boolean isLockSuccess = false;
        while (true) {
            try {
                isLockSuccess = reentrantLock.tryLock();
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " 申请ReentrantLock锁" + (isLockSuccess ? "成功" : "失败"));
                if (isLockSuccess) {
                    break;
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (isLockSuccess) {
                    reentrantLock.unlock();
                    System.out.println(Thread.currentThread().getName() + " tryLockProcessor释放ReentrantLock锁");
                }
            }
        }

    }

    /**
     * main入口
     *
     * @param args 参数
     * @author zhouronghua
     * @time 2021/6/30 5:59 下午
     */
    public static void main(String[] args) {
        TestReentrantTryLock tryLock = new TestReentrantTryLock();
        new Thread(tryLock::lockProcessor, "thread 1").start();
        new Thread(tryLock::tryLockProcessor, "thread 2").start();
    }
}

只有lock释放以后，tryLock才成功。

thread 1 获得ReentrantLock锁
thread 2 尝试申请ReentrantLock锁
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁失败
thread 1 lockProcessor释放ReentrantLock锁
thread 2 申请ReentrantLock锁失败
thread 2 申请ReentrantLock锁成功
thread 2 tryLockProcessor释放ReentrantLock锁