JUC学习之同步锁和闭锁

分手后的思念是犯贱 2022-05-19 04:41 210阅读 0赞

一、同步锁（Lock）：同步锁是一个显示锁，需要通过 lock() 上锁，通过 unlock() 释放锁

public class Test { 
    
        public static void main(String[] args) throws ExecutionException, InterruptedException {
            Ticket ticket = new Ticket();
            new Thread(ticket, "1号窗口").start();
            new Thread(ticket, "2号窗口").start();
            new Thread(ticket, "3号窗口").start();
        }
    }
    
    class Ticket implements Runnable {
    
        private int tickets = 100;
        private Lock lock = new ReentrantLock();
    
        @Override
        public void run() {
            // 加锁
            lock.lock();
            try {
                while (tickets > 0) {
                    Thread.sleep(100);
                    System.out.println(Thread.currentThread().getName() + " 完成售票，余票为：" + --tickets);
                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                // 释放锁
                lock.unlock();
            }
        }
    }

二、闭锁（CountDownLatch）：在要完成某些运算时，只有其它线程的运算全部运行完毕，当前运算才继续下去。

例如：计算线程的执行时间

public class Test { 
    
        public static void main(String[] args) {
            // 闭锁计数器和其它线程数一样
            final CountDownLatch latch = new CountDownLatch(5);
            LatchDemo ld = new LatchDemo(latch);
    
            long start = System.currentTimeMillis();
            for (int i = 0; i < 5; i++) {
                // 其它运算线程开始执行
                new Thread(ld).start();
            }
            try {
                // 主线程等待其它线程全部执行完，才继续下去，算出线程执行时间
                latch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            long end = System.currentTimeMillis();
            System.out.println("耗时：" + (end - start));
        }
    }
    
    // 其它运算线程
    class LatchDemo implements Runnable {
        private CountDownLatch latch;
    
        LatchDemo(CountDownLatch latch) {
            this.latch = latch;
        }
    
        @Override
        public void run() {
            synchronized (this) {
                try {
                    for (int i = 0; i < 50000; i++) {
                        if (i % 2 == 0) {
                            System.out.println(i);
                        }
                    }
                } finally {
                    // 闭锁每次减一
                    latch.countDown();
                }
            }
        }
    }