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;

}

}