利用CountDownLatch和Semaphore测试案例

package com.cxy;

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;

/**
 * Created by Administrator on 2019/4/10.
 */
public class CxyDemo {
    // 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);
    }

}

hashmap不是一个线程安全的类,上面就是对其进行测试

执行结果:

再执行一次:

可见不是线程安全的,

package com.cxy;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.*;

/**
 * Created by Administrator on 2019/4/10.
 */
public class CxyDemo {
    // 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<>();
    private static ConcurrentHashMap<Integer, Integer> map = new ConcurrentHashMap<>();

    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);
    }

}

测试concurrentHashmap,可以知道是线程安全的

package com.cxy;

import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.concurrent.*;

/**
 * Created by Administrator on 2019/4/10.
 */
public class CxyDemo {
    // 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<>();
   // private static ConcurrentHashMap<Integer, Integer> map = new ConcurrentHashMap<>();
    private static Map<Integer, Integer> map = new Hashtable<>();

    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);
    }

}

hashtable也是线程安全:

总结:通过semaphore来模拟线程数,然后通过countdownlatch线程计数器来计算执行的线程,这样可以来模拟高并发测试