ConcurrenthashMap如何实现并发操作

Question

请教一个问题，

首先在ConcurrenthashMap中预置10万条测试数据

1，我如何使用一个线程对ConcurrenthashMap作操作，先get(key)，接着remove(key)，直到所有数据remove，记录一下所有时间

2，我如何使用多个线程(3个线程)对ConcurrenthashMap作上面同样的操作，我需要得到两种处理方式所使用的时间

希望能给我简单的demo，谢谢了，小弟线上等待。。。

Answer 1

public class ConcurrentHashMapTest {

/**
 * @param args
 * @throws InterruptedException 
 */
public static void main(String[] args) throws InterruptedException {
    ConcurrentHashMap<Integer,String> map = new ConcurrentHashMap<Integer,String>();
    for(int i=0;i<10*10000;i++){
        map.put(i, String.valueOf(i));
    }

    System.out.println("prepare test data of 10w");

    new Consumer(map,1).start();

    Thread.sleep(1000);
    ConcurrentHashMap<Integer,String> map1 = new ConcurrentHashMap<Integer,String>();
    for(int i=0;i<10*10000;i++){
        map1.put(i, String.valueOf(i));
    }
    for(int i=0;i<3;i++){
        new Consumer(map1,2).start(); 
    }

}

}
class Consumer extends Thread{
ConcurrentHashMap map;
int which;
public Consumer(ConcurrentHashMap map,int which){
this.map = map;
this.which = which;
}
@Override
public void run() {
long start = System.currentTimeMillis();
for(Integer key : map.keySet()){
map.get(key);
map.remove(key);
}
System.out.println("The "+which+" cost "+(System.currentTimeMillis()-start)+"ms");
}

}

执行三次,发现单线程性能cost比较稳定，3个线程会有波动，按照最长时间的线程来看，有可能性能还不如single的，可见concurrenthashmap对于同步处理还是有一定的开销的
prepare test data of 10w for 1
The 1 cost 18ms
prepare test data of 10w for 2
The 2 cost 13ms
The 2 cost 14ms
The 2 cost 12ms

prepare test data of 10w for 1
The 1 cost 18ms
prepare test data of 10w for 2
The 2 cost 20ms
The 2 cost 19ms
The 2 cost 16ms

prepare test data of 10w for 1
The 1 cost 18ms
prepare test data of 10w for 2
The 2 cost 14ms
The 2 cost 13ms
The 2 cost 16ms