futureTask RunnableFuture Future 三者关系认知

最新推荐文章于 2023-08-05 11:39:56 发布

原创

最新推荐文章于 2023-08-05 11:39:56 发布 · 394 阅读

0 ·

CC 4.0 BY-SA版权

鹿少年

文章标签：

#多线程

本文详细剖析FutureTask与ExecutorService协作，通过实例演示Future.get()获取结果的机制，解释为何submit返回null及多任务执行顺序。涉及的关键步骤包括任务提交、线程池调度与执行。

对于这三者首先我们看下源码，之后在分别写几个demo讲解下用法：

public interface RunnableFuture<V> extends Runnable, Future<V> {
     void run();
}

public class FutureTask<V> implements RunnableFuture<V> {}

public interface Future<V> {
    boolean cancel(boolean mayInterruptIfRunning);
    V get(long timeout, TimeUnit unit)throws InterruptedException, ExecutionException, TimeoutException;
    V get() throws InterruptedException, ExecutionException;
 }

关系一目了然，我们首先使用下FutureTask ，下面简单写一个demo

  FutureTask<Boolean> futureTask = new FutureTask<>(() -> false);
        ExecutorService executor = Executors.newSingleThreadExecutor();
        Future<Boolean> future = (Future<Boolean>) executor.submit(futureTask);
        try {
            System.out.println("future:"+future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        try {
            boolean rs = futureTask.get(1, TimeUnit.MINUTES);
            System.out.println(rs);
        } catch (InterruptedException e) {
            System.out.println("执行被中断");
            e.printStackTrace();
        } catch (ExecutionException e) {
            System.out.println("执行过程出错");
            e.printStackTrace();
        } catch (TimeoutException e) {
            System.out.println("时间超时");
            e.printStackTrace();
        }finally {
            executor.shutdown();
        }
    }

输出结果：

future:null
false

为什么 Future<Boolean> future = (Future<Boolean>) executor.submit(futureTask); 拿不到执行结果呢，我们知道 executor.submit（）如果执行的是runable接口方法返回值是null,下面改写下代码：

  FutureTask<Boolean> futureTask = new FutureTask<>(() -> false);
        ExecutorService executor = Executors.newSingleThreadExecutor();

        Future<Boolean> future = executor.submit(() -> true);
        executor.execute(futureTask);
        executor.submit(futureTask);
        try {
            System.out.println("future:"+future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        try {
            boolean rs = futureTask.get(3, TimeUnit.SECONDS);