JUC-FutureTask

得到别的线程任务的返回值

import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

@Slf4j
public class FutureExample {
    static  class MyCallable implements Callable<String> {
        @Override
        public String call() throws Exception{
            log.info("do something in callable");
            Thread.sleep(500);
            return "Done";
        }
    }
    public static void main(String[] args) throws Exception{
        ExecutorService executorService= Executors.newCachedThreadPool();
        Future<String> future= executorService.submit(new MyCallable());//提交任务
        log.info("do something in main");
        Thread.sleep(1000);
        String result=future.get();
        log.info("result:{}",result);
    }
}

　　

import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

@Slf4j
public class FutureTaskExample {
    public static void main(String[] args) throws Exception{
        FutureTask<String> futureTask=new FutureTask<String>(new Callable<String>() {
            @Override
            public String call() throws Exception {
                log.info("do something in callable");
                Thread.sleep(500);
                return "Done";
            }
        });

        new Thread(futureTask).start();
        log.info("do something in main");
        Thread.sleep(1000);
        String result=futureTask.get();
        log.info("result:{}",result);
    }
}

　　

实现代码示例：

import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
@Slf4j
public class ForJoinTaskExample extends RecursiveTask<Integer>{
    public static final int threshold=2;
    private int start;
    private  int end;

    public ForJoinTaskExample(int start,int end){
        this.start=start;
        this.end=end;
    }
    @Override
    protected Integer compute(){
        int sum=0;
        //如果任务足够小，就计算
        boolean canCompute=(end-start)<=threshold;
        if(canCompute){
            for(int i=start;i<=end;i++){
                sum+=i;
            }
        }else {
            //如果任务大于阀值，就分裂成两个子任务计算
            int middle=(start+end)/2;

            ForJoinTaskExample leftTask=new ForJoinTaskExample(start,middle);
            ForJoinTaskExample rightTask=new ForJoinTaskExample(middle+1,end);

            //执行子任务
            leftTask.fork();
            rightTask.fork();

            //等待任务执行结束合并结果
            int leftResult=leftTask.join();
            int rightResult=rightTask.join();

            //合并子任务
            sum=leftResult+rightResult;
        }
        return sum;
    }

    public static void main(String[] args) {
        ForkJoinPool forkJoinPool=new ForkJoinPool();
        //生成一个计算任务1+2+3+4
        ForJoinTaskExample task=new ForJoinTaskExample( 1,100);
        //执行一个任务
        Future<Integer> result=forkJoinPool.submit(task);
        try{
            log.info("result:{}",((ForkJoinTask) result).get());
        }catch (Exception e){
            log.error("exception",e);
        }
    }
}

　　

线程安全，用于生产消费者模式。

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