ThreadLocalPerformance.java

package ch4.s3;

import java.util.Random;
import java.util.concurrent.*;

public class ThreadLocalPerformance {
    public static final int GEN_COUNT = 10000000;
    public static final int THREAD_COUNT = 4;
    static ExecutorService exe = Executors.newFixedThreadPool(THREAD_COUNT);
    public static Random rnd = new Random(123);

    public static ThreadLocal<Random> tRnd = new ThreadLocal<Random>(){

        protected Random initialValue() {
            return new Random(123);
        }
    };

    public static class RndTask implements Callable<Long>{
        private int mode = 0;
        public RndTask(int mode){
            this.mode = mode;
        }
        public Random getRandom(){
            if(mode == 0){
                return rnd;
            } else if (mode == 1){
                return tRnd.get();
            } else{
                return null;
            }
        }

        public Long call() throws Exception {
            long b =System.currentTimeMillis();
            for(long i=0;i<GEN_COUNT;i++){
                getRandom().nextInt();
            }
            long e =System.currentTimeMillis();
            System.out.println(Thread.currentThread().getName() + " spend" + (e-b) + "ms");
            return e - b;
        }
    }

    public static void main(String []args) throws ExecutionException, InterruptedException {
        Future<Long>[] futs = new Future[THREAD_COUNT];
        for(int i=0;i<THREAD_COUNT;i++){
            futs[i] = exe.submit(new RndTask(0));
        }
        long totaltime = 0;
        for(int i=0;i<THREAD_COUNT;i++){
            totaltime += futs[i].get();
        }
        System.out.println("多线程访问同一个Random实例："+ totaltime + "ms");

        for(int i=0;i<THREAD_COUNT;i++){
            futs[i] = exe.submit(new RndTask(1));
        }
        totaltime = 0;
        for(int i=0;i<THREAD_COUNT;i++){
            totaltime += futs[i].get();
        }
        System.out.println("使用ThreadLocal包装Random实例："+ totaltime + "ms");
        exe.shutdown();
    }
}