HashMap 1.8的源码分析三
线程安全问题:
在添加时候并没有进行安全考虑,枷锁
所以是线程不安全的,接下来进行代码测试;
package com.mmall.concurrency.example.commonUnsafe; import com.mmall.concurrency.annoations.NotThreadSafe; import lombok.extern.slf4j.Slf4j; import java.util.HashMap; import java.util.Map; import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; public class HashMapExample { // 请求总数 public static int clientTotal = 5000; // 同时并发执行的线程数 public static int threadTotal = 200; private static Map<Integer, Integer> map = new HashMap<>(); public static void main(String[] args) throws Exception { ExecutorService executorService = Executors.newCachedThreadPool(); final Semaphore semaphore = new Semaphore(threadTotal); final CountDownLatch countDownLatch = new CountDownLatch(clientTotal); for (int i = 0; i < clientTotal; i++) { final int count = i; executorService.execute(() -> { try { semaphore.acquire(); update(count); semaphore.release(); } catch (Exception e) { log.error("exception" , e); } countDownLatch.countDown(); }); } countDownLatch.await(); executorService.shutdown(); System.out.println(map.size()); log.info("size:{}" , map.size()); } private static void update(int i) { map.put(i, i); } }
运行三次:
所以hashmap是线程不安全的,那么我们在代码里面怎么还要用呢,我们只是局部使用,并没有在多线程环境下使用,所以并不会出现线程安全问题
笔记转移,由于在有道云的笔记转移,写的时间可能有点久,如果有错误的地方,请指正