JUC 一 FutureTask

java.util.concurrent

public class FutureTask<V> implements RunnableFuture<V>

简介

FutureTask提供了对Future的基本实现，可以调用方法去开始和取消一个Callable，可以查询Callable是否完成并且获取计算结果。

只有当Callable完成时才能获取到Callable结果，一旦计算完成，计算将不能被重启或者被取消

源码分析

AbstractExecutorService.submit（Callable <T> task）（此方法是线程池的执行逻辑）：

    public Future<?> submit(Runnable task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<Void> ftask = newTaskFor(task, null);
        execute(ftask);
        return ftask;
    }

    public <T> Future<T> submit(Runnable task, T result) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task, result);
        execute(ftask);
        return ftask;
    }

    public <T> Future<T> submit(Callable<T> task) {
        if (task == null) throw new NullPointerException();
        RunnableFuture<T> ftask = newTaskFor(task);
        execute(ftask);
        return ftask;
    }

    protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
        return new FutureTask<T>(runnable, value);
    }

    public FutureTask(Runnable runnable, V result) {
        this.callable = Executors.callable(runnable, result);
        this.state = NEW;       // ensure visibility of callable
    }

Future：

    public interface Future<V> {

        //尝试取消当前任务的执行。
        //如果任务已经启动，参数mayInterruptIfRunning将决定任务是否应该中断执行该任务的线程，以尝试中断该任务。
        boolean cancel(boolean mayInterruptIfRunning);

        //如果任务在正常结束之前被被取消返回true
        boolean isCancelled();

        //正常结束、异常或者被取消导致任务完成，将返回true
        boolean isDone();

        //等待任务结束，然后获取结果，如果任务在等待过程中被中断将抛出异常
        V get() throws InterruptedException, ExecutionException;

        //任务最多在给定时间内完成并返回结果，如果没有在给定时间内完成任务将抛出TimeoutException。
        V get(long timeout, TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException;
    }

RunnableFuture：

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

FutureTask：

    public FutureTask(Callable<V> callable) {
        if (callable == null)
            throw new NullPointerException();
        this.callable = callable;
        this.state = NEW;       // ensure visibility of callable
    }

    public FutureTask(Runnable runnable, V result) {
        this.callable = Executors.callable(runnable, result);
        this.state = NEW;       // ensure visibility of callable
    }