公平锁和非公平锁的性能对比

写在最前面：

默认看到这的大神们都懂什么是公平锁和非公平锁

废话不多说，直接上代码：

package org.sino.multith.lock;

import lombok.extern.slf4j.Slf4j;
import org.sino.util.ThreadUtil;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 案例说明：
 * 使用公平锁和非公平锁进行3个售票员（3线程）卖10w张票所需的时间
 *
 */
@Slf4j
public class FairUnFairDemo {
    static ExecutorService executorService = ThreadUtil.newCpuThreadPool();

    public static void main(String[] args) throws InterruptedException {
        int ticketCount = 100000;
        int threadCount = 12;

        Ticket fairTicket = new Ticket(ticketCount, Boolean.TRUE);
        CountDownLatch fairCdl = new CountDownLatch(threadCount);
        log.info("------------------------------- 公平锁开始 ----------------------------------------");
        long start = System.currentTimeMillis();
        for (int i = 1; i <= threadCount; i++) {
            new Thread(()->{
                while(fairTicket.sale()) {

                }
                fairCdl.countDown();
            }, "FairLock" + i).start();
        }
        fairCdl.await(); 
        long end = System.currentTimeMillis();
　　　　 log.info("一共耗费：" + (end - start) + " ms");
        log.info("------------------------------- 公平锁结束 ----------------------------------------");
        

        Ticket unfairTicket = new Ticket(ticketCount, Boolean.FALSE);
        CountDownLatch unfairCdl = new CountDownLatch(threadCount);
        log.info("------------------------------- 非公平锁开始 ----------------------------------------");
        start = System.currentTimeMillis();
        for (int i = 1; i <= threadCount; i++) {
            new Thread(()->{
                while (unfairTicket.sale()) {

                }
                unfairCdl.countDown();
            }, "UnFairLock" + i).start();
        }
        unfairCdl.await();
        end = System.currentTimeMillis();
　　　　　log.info("一共耗费：" + (end - start) + " ms");
        log.info("------------------------------- 非公平锁开始 ----------------------------------------");
    }
}

@Slf4j
class Ticket {
    private int ticketCount;
    private ReentrantLock lock;

    public Ticket(int ticketCount, boolean fair) {
        this.ticketCount = ticketCount;
        // false为非公平锁，true为公平锁
        this.lock = new ReentrantLock(fair);
    }

    /**
     * 还有票，返回true，没票了返回false
     *
     * @return
     */
    public boolean sale () {
        lock.lock();
        try {
            if(ticketCount > 0) {
                ticketCount --;
                // log.info(" --> 卖出第：\t" + (ticketCount --) + " 还剩下：" + ticketCount);
            }
            if(ticketCount == 0) {
                // log.info(" --> \t还剩下：" + ticketCount);
            }
            return ticketCount != 0;
        } finally {
            lock.unlock();
        }
    }
}

运行结果：

在10w票的运行结果：

 

 在100w票的运行结果：

 

  在1000w票的运行结果：

 

 

结论：

在高并发的场景下，公平锁的性能远低于非公平锁