并发编程005 --- future &&futureTask

Future

用于异步计算，可以获取异步计算结果、取消异步任务、判断任务是否被取消、是否执行完成。

1、get

get()用于获取异步计算结果，如果计算未完成，则阻塞当前线程，直到计算完成

task类

public class CallableTask implements Callable<String> {

    @Override
    public String call() throws InterruptedException {
        System.out.println(Thread.currentThread().getName() + " start.");
        Thread.sleep(3000);
        System.out.println(Thread.currentThread().getName() + " finished.");
        return "Callable Task return.";
    }
}

测试类：

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService service = Executors
                .newFixedThreadPool(1, new ThreadFactoryBuilder().setNameFormat("test-%d").build());

        Future<String> future = service.submit(new CallableTask());
        System.out.println("calc result: " + future.get());

        System.out.println("Master run finished.");


        service.shutdownNow();
    }

执行结果：

 get(time, timeunit)，表示等待有限度，如果超过指定时间未完成，抛出超时异常

测试类：

    public static void main(String[] args) throws ExecutionException, InterruptedException, TimeoutException {
        ExecutorService service = Executors
                .newFixedThreadPool(1, new ThreadFactoryBuilder().setNameFormat("test-%d").build());

        Future<String> future = service.submit(new CallableTask());
        System.out.println("calc result: " + future.get(2, TimeUnit.SECONDS));

        System.out.println("Master run finished.");


        service.shutdownNow();
    }

执行结果： 可以看到，主进程抛出异常，线程执行完成

2、cancel

用来取消任务执行。如果任务执行完成，或者已经取消，或者由于未知原因不能取消，返回false；

如果任务未开始，则返回true，并且任务永远不能被执行；

如果任务已经开始执行，并且mayInterruptIfRunning指定为true，则中断该任务，否则允许任务执行完成    ----- 这里有点疑问，明天确认下

场景1：任务执行完成后取消任务，返回false

源码：

    public static void main(String[] args) throws ExecutionException, InterruptedException, TimeoutException {
        ExecutorService service = Executors
                .newFixedThreadPool(1, new ThreadFactoryBuilder().setNameFormat("test-%d").build());

        Future<String> future = service.submit(new CallableTask());
        Thread.sleep(4000);

        System.out.println("Future is cancel succeed? " + future.cancel(false));

        System.out.println("Master run finished.");


        service.shutdownNow();
    }

执行结果：

 场景2：任务执行中，返回true

    public static void main(String[] args) throws ExecutionException, InterruptedException, TimeoutException {
        ExecutorService service = Executors
                .newFixedThreadPool(1, new ThreadFactoryBuilder().setNameFormat("test-%d").build());

        Future<String> future = service.submit(new CallableTask());
        Thread.sleep(1000);

        System.out.println("Future is cancel succeed? " + future.cancel(false));

        System.out.println("Master run finished.");


        service.shutdownNow();
    }

执行结果：

 3、isCanceled

 任务执行完成之前被取消，返回true

4、isDone

 任务被终止、被取消、出现异常，该方法均会返回true