java多线程：Thread、Runnable、Future以及CompleteFuture

Future<T>是一种任务，可以使用CompleteFuture<T>代替Future<T>。

 

CompleteFuture<T>的介绍：

https://blog.csdn.net/qq_34562093/article/details/90209520

https://www.cnblogs.com/TS86/p/18205735

 

 

package com.example.demo.basicSE;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;

// Future<T> f = executorService.submit(new Callable<T>)，但f.get()是阻塞的（CompletableFuture.get()也是阻塞的）
// 一般使用CompletableFuture替代Future：https://blog.csdn.net/qq_34562093/article/details/90209520
// CompletionService和CompletableFuture（按照任务完成的先后顺序获取任务的结果）

public class threads {
    
    public static void _future() throws InterruptedException, ExecutionException{
        List<Integer> list = List.of(1, 2, 3, 4, 5);

        ExecutorService executorService = Executors.newFixedThreadPool(5);
        List<Future<Integer>> futures = new ArrayList<>();
        for (int i : list) {
            Future<Integer> future = executorService.submit(new createSqre(i));
            futures.add(future);
        }

        List<Integer> res = new ArrayList<>();
        for(Future<Integer> f:futures){
            int t = f.get();
            res.add(t);
        }

        for(int i:res){
            System.out.println(i);
        }
        // shutdown()只是关闭了外部的submit()，线程池内部未执行完的还会继续跑
        executorService.shutdown();
        try {
            // shutdownNow()立即停止线程池，正在跑的和等待的都停止了，但风险较大
            // awaitTermination()后外部可以继续submit()进线程池。当前线程阻塞直到所有已提交任务跑完/超时/线程Interrupt()。
            // 使用awaitTermination()来等待线程池中所有任务都执行完毕
            if(!executorService.awaitTermination(60, TimeUnit.SECONDS)){
                executorService.shutdownNow();
            }
        } catch (Exception e) {
            // TODO: handle exception
            executorService.shutdownNow();
            Thread.currentThread().interrupt();
        }
    }

    public static int math_square(int x){
        return x*x;
    }
    public static void _completeFuture(){
        List<Integer> l = List.of(1,2,3,4,5);
        // supplyAsync()异步处理
        List<CompletableFuture<Integer>> futures = l.stream().map(i->CompletableFuture.supplyAsync(()->math_square(i))).collect(Collectors.toList());
        // allof()等待所有future执行完成
        CompletableFuture<Void> aCompletableFuture = CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]));
        // 等待所有任务完成
        aCompletableFuture.join();
        List<Integer> ans = futures.stream().map(f->{
            try {
                return f.get();
            } catch (Exception e) {
                throw new IllegalStateException(e);
                // TODO: handle exception
            }
        }).collect(Collectors.toList());
        ans.forEach(System.out::println);
    }

    public static void main(String[] args) throws InterruptedException, ExecutionException {
        // _future();
        _completeFuture();
    }

}

class createSqre implements Callable<Integer>{
    private int n;
    createSqre(int a){this.n = a;}

    @Override
    public Integer call() throws Exception {
        return n*n;
    }
}