java高并发系列 – 第33篇：怎么演示公平锁和非公平锁? | Java入门教程_springboot基础教程_springcloud

这是java高并发系列第33篇文章。

环境：jdk1.8。

今天群里面刚有有人在问这块的东西，那就拿出来说一下。

本文主要用juc中的ReentrantLock来说一下公平锁和非公平锁的东西。

先理解一下什么是公平锁、非公平锁？

公平锁和非公平锁体现在别人释放锁的一瞬间，如果前面已经有排队的，新来的是否可以插队，如果可以插队表示是非公平的，如果不可用插队，只能排在最后面，是公平的方式。

示例

测试公平锁和非公平锁的时候，可以这么来：在主线程中先启动一个t1线程，在t1里面获取锁，获取锁之后休眠一会，然后在主线中启动10个father线程去排队获取锁，然后在t1中释放锁代码的前面一步再启动一个线程，在这个线程内部再创建10个son线程，去获取锁，看看后面这10个son线程会不会排到上面10个father线程前面去，如果会表示插队了，说明是非公平的，如果不会，表示排队执行的，说明是公平的方式，示例代码如下：
```java
package com.itsoku.chat32;

import lombok.extern.slf4j.Slf4j;

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

/**

```
 //非公平锁
 test1(false);
 TimeUnit.SECONDS.sleep(4);
 log.info("------------------------------");
 //公平锁
 test1(true);
```
}

public static void test1(boolean fair) throws InterruptedException {
```
 ReentrantLock lock = new ReentrantLock(fair);
 Thread t1 = new Thread(() -> {
     lock.lock();
     try {
         log.info("start");
         TimeUnit.SECONDS.sleep(3);
         new Thread(() -> {
             m1(lock, "son");
         }).start();
         log.info("end");
     } catch (InterruptedException e) {
         e.printStackTrace();
     } finally {
         lock.unlock();
     }
 });
 t1.setName("t1");
 t1.start();
 TimeUnit.SECONDS.sleep(1);
 m1(lock, "father");
```
}

public static void m1(ReentrantLock lock, String threadPre) {
```
 for (int i = 0; i < 10; i++) {
     Thread thread = new Thread(() -> {
         lock.lock();
         try {
             log.info("获取到锁!");
         } finally {
             lock.unlock();
         }
     });
     thread.setName(threadPre + "-" + i);
     thread.start();
 }
```
}
}
```
输出：
```
10:16:02.132 [t1] INFO com.itsoku.chat32.Demo8 - start
10:16:05.135 [t1] INFO com.itsoku.chat32.Demo8 - end
10:16:05.135 [father-0] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.136 [father-1] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.136 [father-2] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.136 [son-2] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.136 [father-3] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.137 [father-4] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.137 [father-5] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.137 [son-5] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.137 [father-6] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.137 [father-7] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.137 [father-8] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [father-9] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [son-0] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [son-1] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [son-3] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [son-4] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [son-6] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.138 [son-7] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.139 [son-8] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:05.139 [son-9] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:07.129 [main] INFO com.itsoku.chat32.Demo8 - ------------------------------
10:16:07.129 [t1] INFO com.itsoku.chat32.Demo8 - start
10:16:10.130 [t1] INFO com.itsoku.chat32.Demo8 - end
10:16:10.130 [father-0] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.130 [father-1] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.130 [father-2] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.131 [father-3] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.131 [father-4] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.131 [father-5] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.131 [father-6] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.132 [father-7] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.132 [father-8] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.132 [father-9] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.132 [son-1] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.132 [son-0] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.132 [son-2] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.133 [son-4] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.133 [son-3] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.133 [son-5] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.133 [son-6] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.133 [son-7] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.133 [son-8] INFO com.itsoku.chat32.Demo8 - 获取到锁!
10:16:10.135 [son-9] INFO com.itsoku.chat32.Demo8 - 获取到锁!
```