FutureTask、Fork/Join、 BlockingQueue

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(5000);
            return "Done";
        }
    }
 
    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        Future<String> future = executorService.submit(new MyCallable());
        log.info("do something in main");
        //Thread.sleep(10000);
        log.info("这里不阻塞，可以继续异步执行");
        String result = future.get(); //get方法会发生阻塞，如果判断任务是否执行完成使用isDone()方法
        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(5000);
                return "Done";
            }
        });
 
        new Thread(futureTask).start();
        log.info("do something in main");
        Thread.sleep(1000);
        String result = futureTask.get();
        log.info("result：{}", result);
    }
}

import lombok.extern.slf4j.Slf4j; 
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
 
@Slf4j
public class ForkJoinTaskExample extends RecursiveTask<Integer> {
 
    public static final int threshold = 2;
    private int start;
    private int end;
 
    public ForkJoinTaskExample(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任务
        boolean canCompute = (end - start) <= threshold;
        if (canCompute) {
            for (int i = start; i <= end; i++) {
                sum += i;
            }
        } else {
            // 如果任务大于阈值，就分裂成两个子任务计算
            int middle = (start + end) / 2;
            ForkJoinTaskExample leftTask = new ForkJoinTaskExample(start, middle);
            ForkJoinTaskExample rightTask = new ForkJoinTaskExample(middle + 1, end);
 
            // 执行子任务
            leftTask.fork();
            rightTask.fork();
 
            // 等待任务执行结束合并其结果
            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，计算1+2+3+4
        ForkJoinTaskExample task = new ForkJoinTaskExample(1, 100);
 
        //执行一个任务
        Future<Integer> result = forkjoinPool.submit(task);
 
        try {
            log.info("result:{}", result.get());
        } catch (Exception e) {
            log.error("exception", e);
        }
    }
}