package com.basic;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;

/**
 * @program JavaBooks
 * @description: 并行计算的小例子
 * @author: mf
 * @create: 2020/01/01 14:26
 */

public class T24 {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        List<Integer> results = getPrime(1, 200000);
        long end = System.currentTimeMillis();
        System.out.println(end - start);

        System.out.println(Runtime.getRuntime().availableProcessors());// 看看自己的cpu几核

        // 但算了， 还是取4把
        final int cpuCoreNum = 4;

        ExecutorService service = Executors.newFixedThreadPool(cpuCoreNum);

        MyTask t1 = new MyTask(1, 80000);
        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);

        service.shutdown();
    }

    static class MyTask implements Callable<List<Integer>> {

        int startPos, endPos;

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

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


    /**
     * 判断该数是否为质数
     * @param num
     * @return
     */
    private static boolean isPrime(int num) {
        for (int i = 2; i <= num / 2; i++) {
            if (num % i == 0) return false;
        }
        return true;
    }

    /**
     * 在一定范围内的质数
     * @param start
     * @param end
     * @return
     */
    private 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;
    }
}