线程池之固定大小线程池FixedThreadPool

                                                线程池之固定大小线程池FixedThreadPool

package src.main.java.com.qqjx.thread;


import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
/*
* 《Java并发编程实战》中Brian和合著者们为线程池大小的优化
*  提供了不少中肯的建议 这点非常重要 如果线程池中线程的数量过多
*  最终它们会竞争稀缺的处理器和内存资源,浪费大量的时间在上下文切换上
*  如果线程的数目过少,正如你的应用所面临的情况 处理器的一些核数可能无法
*  充分利用
* */
public class T09_FixedThreadPool {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        long start = System.currentTimeMillis();
        getPrime(1, 200000);
        long end = System.currentTimeMillis();
        System.out.println(end - start);

        final int cpuCoreNum = 4;

        ExecutorService service = Executors.newFixedThreadPool(cpuCoreNum);

        MyTask t1 = new MyTask(1, 80000); //1-5 5-10 10-15 15-20
        MyTask t2 = new MyTask(80001, 130000);
        MyTask t3 = new MyTask(130001, 170000);
        MyTask t4 = new MyTask(170001, 200000);

        Future<List<Integer>> f1 = service.submit(t1);
        Future<List<Integer>> f2 = service.submit(t2);
        Future<List<Integer>> f3 = service.submit(t3);
        Future<List<Integer>> f4 = service.submit(t4);

        start = System.currentTimeMillis();
        f1.get();
        f2.get();
        f3.get();
        f4.get();
        end = System.currentTimeMillis();
        System.out.println(end - start);
    }

    static class MyTask implements Callable<List<Integer>> {
        int startPos, endPos;

        MyTask(int s, int e) {
            this.startPos = s;
            this.endPos = e;
        }

        @Override
        public List<Integer> call() throws Exception {
            List<Integer> r = getPrime(startPos, endPos);
            return r;
        }

    }

    static boolean isPrime(int num) {
        for(int i=2; i<=num/2; i++) {
            if(num % i == 0) return false;
        }
        return true;
    }

    static List<Integer> getPrime(int start, int end) {
        List<Integer> results = new ArrayList<>();
        for(int i=start; i<=end; i++) {
            if(isPrime(i)) results.add(i);
        }

        return results;
    }
}

    源码
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

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