Java Lock锁练习 (2024.8.12)

        LockExercise

package LockExercise20240812;public class LockExercise {public static void main(String[] args) {// Synchronized同步代码块或同步方法通过锁对象解决了数据安全的问题，但是并没有清晰的看见在何处上锁和解锁，// 所以说在JDK5之后提供了一个新的锁对象Lock，可以清晰地表达如何上锁和解锁// Lock是一个接口，不能直接实例化，可以通过其实现类ReentrantLock进行实例化// ReentrantLock() 创建一个ReentrantLock对象// void lock() 上锁// void unlock() 解锁SellTickets st = new SellTickets();Thread thread1 = new Thread(st, "窗口1");Thread thread2 = new Thread(st, "窗口2");Thread thread3 = new Thread(st, "窗口3");thread1.start();thread2.start();thread3.start();}
}

        SellTickets

package LockExercise20240812;import java.util.concurrent.locks.ReentrantLock;public class SellTickets implements Runnable {private static int tickets = 100;private static ReentrantLock lock = new ReentrantLock();@Overridepublic void run() {while (true) {lock.lock();try {if (tickets <= 0) {break;} else {try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}tickets--;System.out.println(Thread.currentThread().getName() + ": 正在卖第" + (100 - tickets) + "张票");}} finally {lock.unlock();}}}
}//package LockExercise20240812;
//
//import java.util.concurrent.locks.ReentrantLock;
//
//public class SellTickets implements Runnable {
//    private static int tickets = 100;
//    private static ReentrantLock lock = new ReentrantLock();
//
//    @Override
//    public void run() {
//        while (true) {
//            lock.lock();
//            if (tickets <= 0) {
//                return;
//            } else {
//                try {
//                    Thread.sleep(100);
//                } catch (InterruptedException e) {
//                    e.printStackTrace();
//                }
//                tickets--;
//                System.out.println(Thread.currentThread().getName() + ": 正在卖第" + (100 - tickets) + "张票");
//            }
//            lock.unlock();
//        }
//    }
//}// 将unlock方法写在了if - else之外，假如tickets的值小于等于0，线程会直接返回而不会释放锁，
// 这可能导致其他线程无法获取锁（因为其他线程已经进入循环了，在等待那把锁，假如一直没有就会陷入死锁状态）从而进入死锁状态