ReentrantLock

1 特点

• 可中断
• 可以设置超时时间
• 可以设置为公平锁
• 支持多个条件变量

2 基本语法

   ReentrantLock lock = new ReentrantLock();
   // 获取锁
   lock.lock();
   try {
       // 临界区
   } finally {
       // 释放锁
       lock.unlock();
   }

3 可重入

	static ReentrantLock lock = new ReentrantLock();

    public static void main(String[] args) throws InterruptedException {
        lock.lock();
        try {
            log.info("main...");
            method1();
        } finally {
            lock.unlock();
        }

    }

    static void method1() {
        lock.lock();
        try {
            log.info("method1...");
            method2();
        } finally {
            lock.unlock();
        }
    }

    static void method2() {
        lock.lock();
        try {
            log.info("method2...");
        } finally {
            lock.unlock();
        }
    }

3 可打断

	static ReentrantLock lock = new ReentrantLock();

    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            try {
                // 如果没有竞争 此方法会获取lock锁
                // 如果有竞争 就进入阻塞队列 可以被其他线程用interrupt打断
                log.info("t1 start get lock..");
                lock.lockInterruptibly();
            } catch (InterruptedException e) {
                log.info("t1 dont get lock..");
                e.printStackTrace();
                return;
            }

            try {
                log.info("t1 get lock..");
            } finally {
                lock.unlock();
            }
        }, "t1");

        lock.lock();
        t1.start();

        TimeUnit.SECONDS.sleep(1);
        t1.interrupt();
    }

4 锁超时

	static ReentrantLock lock = new ReentrantLock();

    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            log.info("t1 start get lock..");
            if (!lock.tryLock()) {
                log.info("t1 dont get lock..");
                return;
            }
//            try {
//                if (!lock.tryLock(1, TimeUnit.SECONDS)) {
//                    log.info("t1 dont get lock..");
//                    return;
//                }
//            } catch (InterruptedException e) {
//                log.info("t1 dont get lock..");
//                e.printStackTrace();
//                return;
//            }
            try {
                log.info("t1 get lock..");
            } finally {
                lock.unlock();
            }
        });

        lock.lock();
        t1.start();
    }

5 公平锁

锁的竞争不再是随意的了，相对来说就是公平的（先到先得）

6 条件变量

Condition condition = lock.newCondition();
        
 condition.await();
 
 condition.signal();
 
 condition.signalAll();