ReentrantLock

Posted 2022-05-25 han6

package com.dh.test;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

public class ReentrantLockTest 
    // 参考：https://www.cnblogs.com/takumicx/p/9338983.html
    // ReentrantLock 可重入锁   有lock必须有对应的unlock
    // ReentrantLock  公平锁FairSync()  非公平锁NonfairSync()  非公平锁性能更好，但是当有足够多的的线程时，可能会造成饥饿问题(长时间获取不到锁)
    // ReentrantLock lockInterruptibly() 可响应中断。 如下造成死锁时，中断thread1，可让thread2正常执行
    // ReentrantLock tryLock()  可选择时间参数，表示等待指定时间，无参表示立即返回获取锁的结果：true表示获取锁成功,false表示获取锁失败
    // 线程间通信，Object的wait/notify方法   ReentrantLock可newCondition() ,利用condition的await/single()来进行线程间通信，await会释放当前锁。


    static ReentrantLock lock1 = new ReentrantLock();
    static ReentrantLock lock2 = new ReentrantLock();
    static ReentrantLock lock3 = new ReentrantLock();
    static ReentrantLock lock4 = new ReentrantLock();

    public static void main(String[] args) throws InterruptedException 
        Thread thread1 = new Thread(new MyThread(lock1, lock2));
        Thread thread2 = new Thread(new MyThread(lock2, lock1));
        thread1.start();
        thread2.start();
        thread1.interrupt();

        Thread.sleep(100);

        Thread try1 = new Thread(new TryLockThread(lock3, lock4));
        Thread try2 = new Thread(new TryLockThread(lock4, lock3));
        try1.start();
        try2.start();
    

    //响应中断的代码示例：lockInterruptibly()
    static class MyThread implements Runnable 
        ReentrantLock lock1;
        ReentrantLock lock2;

        public MyThread(ReentrantLock lock1, ReentrantLock lock2) 
            this.lock1 = lock1;
            this.lock2 = lock2;
        

        @Override
        public void run() 
            try 
                lock1.lockInterruptibly();
                Thread.sleep(10);
                lock2.lockInterruptibly();
             catch (InterruptedException e) 
                e.printStackTrace();
             finally 
                lock1.unlock();
                lock2.unlock();
            
        
    

    static class TryLockThread implements Runnable 
        ReentrantLock lock1;
        ReentrantLock lock2;

        public TryLockThread(ReentrantLock lock1, ReentrantLock lock2) 
            this.lock1 = lock1;
            this.lock2 = lock2;
        

        @Override
        public void run() 

            try 
                while (!lock1.tryLock()) 
                    TimeUnit.MILLISECONDS.sleep(10);
                
                while (!lock2.tryLock()) 
                    lock1.unlock();
                    TimeUnit.MILLISECONDS.sleep(10);
                
                System.out.println("tryLock==线程执行完毕");
             catch (InterruptedException e) 
                e.printStackTrace();
             finally 
                lock1.unlock();
                lock2.unlock();