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
原文地址:http://www.cnblogs.com/sinoknots/p/16816706.html
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