java 多线程知识梳理3

Callable Runable和Future FutureTask的使用

1 先看看接口定义

public interface Runnable {

    public abstract void run();//定义为void，和thread一样，无法返回执行结果

}

public interface Callable<V> {

    /**

     * Computes a result, or throws an exception if unable to do so.

     *

     * @return computed result

     * @throws Exception if unable to compute a result

     */

    V call() throws Exception;//返回入参类型的执行结果

}

2 调用，针对这两种类型的接口通过ExecutorService执行。

<T> Future<T> submit(Callable<T> task);

<T> Future<T> submit(Runnable task, T result);

Future<?> submit(Runnable task);

Future就是对于具体的Runnable或者Callable任务的执行结果进行取消、查询是否完成、获取结果。

Future接口定义：

public interface Future<V> {

    boolean cancel(boolean mayInterruptIfRunning);//取消任务，如果成功就返回true

    boolean isCancelled();

    boolean isDone();

    V get() throws InterruptedException, ExecutionException;//获取任务执行结果，如果没有就阻塞

    V get(long timeout, TimeUnit unit)

        throws InterruptedException, ExecutionException, TimeoutException;

}

FutureTask:

public class FutureTask<V> implements RunnableFuture<V>

public interface RunnableFuture<V> extends Runnable, Future<V> {

    void run();

}

是Future的唯一实现类，实现了Future的功能，同时增加了线程执行完成后回调的功能。

  public FutureTask(Runnable runnable, V result) {
        sync = new Sync(Executors.callable(runnable, result));
    }

    public boolean isCancelled() {
        return sync.innerIsCancelled();
    }

    public boolean isDone() {
        return sync.innerIsDone();
    }

    public boolean cancel(boolean mayInterruptIfRunning) {
        return sync.innerCancel(mayInterruptIfRunning);
    }
    public V get() throws InterruptedException, ExecutionException {
        return sync.innerGet();
    }
    public V get(long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException {
        return sync.innerGet(unit.toNanos(timeout));
    }

    protected void done() { }//当线程执行完成后，调用该方法。可以实现自己的FutureTask类，实现该方法
    protected void set(V v) {
        sync.innerSet(v);
    }
    protected void setException(Throwable t) {
        sync.innerSetException(t);

    public void run() {
        sync.innerRun();
    }

    protected boolean runAndReset() {
        return sync.innerRunAndReset();
    }