互斥锁简单介绍

可重入锁意思是object.lock()获取锁后，可以再次使用object.lock()获取锁，如果发生了死锁就不是可重入锁

公平锁就是排队买票，不公平锁就是插队买票

锁实现的基本原理

1.需要一个state变量，标记锁的状态，state至少要有两个值，0,1，对state变量的操作，使用CAS保证线程安全

2.需要记录当前是哪个线程持有锁

3.需要底层支持对一个线程进行阻塞或者唤醒操作

4.需要有一个队列维护所有阻塞的线程，这个队列的要求必须是线程安全的无所队列，需要使用到CAS

有关ReentrantLock实现互斥锁

案例代码

package com.java.test.lock;
 
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
 
/**
 * @author yourheart
 * @Description
 * @create 2023-01-15 17:31
 */
public class ReentrantLockService {
 
    private ReentrantLock reentrantLock = new ReentrantLock();
    private Condition condition = reentrantLock.newCondition();
    private List<String> arrayList = new ArrayList<>();
 
    public void addItems(){
        try {
            reentrantLock.lock();
            if (arrayList.size() <= 0) {
                arrayList.add("买票");
                System.out.println("addItems -- > 开始等待删除车票");
                condition.await();
            }
            System.out.println("addItems -- > 执行完了");
        } catch (Exception e) {
 
        } finally {
            reentrantLock.unlock();
        }
 
    }
 
    public void removeItems() {
        try {
            reentrantLock.lock();
            if (arrayList.size() >= 0) {
                arrayList.remove(0);
                System.out.println("removeItems -- > 车票已删除");
                condition.signal();
            }
            System.out.println("removeItems -- > 执行完了");
        } catch (Exception e) {
 
        } finally {
            reentrantLock.unlock();
        }
    }
}

package com.java.test.lock;
 
import org.junit.Test;
 
/**
 * @author yourheart
 * @Description
 * @create 2023-01-15 17:12
 */
public class ReentrantLockTest {
 
    @Test
    public void test() throws InterruptedException {
 
        ReentrantLockService lockService=new ReentrantLockService();
 
        new Thread(()->{
            lockService.addItems();
        }).start();
 
        new Thread(()->{
            lockService.removeItems();
        }).start();
 
        while (true){
 
        }
 
 
    }
 
 
 
}