线程之Callable，Future，CompletionService

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ThreadCallAndFuture {

    /**
     * 线程的返回值
     */
    public static void main(String[] args) {

        /*
         * 一个线程调用另一个线程的返回值
         * 要想拿到返回值的这个过程需要等待
         */
//        ExecutorService executorService = Executors.newSingleThreadExecutor();
//        Future<String> future = executorService.submit(new Callable<String>(){
//
//            @Override
//            public String call() throws Exception {
//                Thread.sleep(1000);
//                return "hello word";
//            }
//            
//        });
//        
//        System.out.println("waiting for result...");
//        try {
//            System.out.println("result is : "+future.get());
//        } catch (InterruptedException e) {
//            e.printStackTrace();
//        } catch (ExecutionException e) {
//            e.printStackTrace();
//        }
        
        
        /*
         * 上例似乎在实际中是没太大的用处的
         * 下例是一个收割事例
         * 就好像有一些菜田，那个先熟，先收割那个
         * 有一些线程，当那个线程有返回值就获得那个返回值
         * CompletionService接口
         */
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        CompletionService<Integer> completionService = new ExecutorCompletionService<Integer>(executorService);
        for(int i=0;i<10;i++){
            final int flag = i;
            completionService.submit(new Callable<Integer>() {
                @Override
                public Integer call() throws Exception {
                    Thread.sleep(new Random().nextInt(5000));
                    return flag;
                }
            });
        }
        
        
        for(int i=0;i<10;i++){
            try {
                System.out.println(completionService.take().get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
        
    }

}