java并发编程学习之线程池-AbstractExecutorService(二)

摘要：抽象类，实现了的接口。将任务封装成提交任务主要方法在任务是否超时超时时间任务书用于存放结果的，先完成的放前面。

AbstractExecutorService抽象类，实现了ExecutorService的接口。

将任务封装成FutureTask

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

提交任务

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

主要方法在doInvokeAny

//tasks任务
//timed是否超时
//nanos超时时间
private  T doInvokeAny(Collection> tasks,
                              boolean timed, long nanos)
    throws InterruptedException, ExecutionException, TimeoutException {
    if (tasks == null)
        throw new NullPointerException();
    int ntasks = tasks.size();//任务书
    if (ntasks == 0)
        throw new IllegalArgumentException();
    ArrayList> futures = new ArrayList>(ntasks);
    //用于存放结果的，先完成的放前面。所以第一个任务没完成的时候，会继续提交后续任务
    ExecutorCompletionService ecs =
        new ExecutorCompletionService(this);

    try {     
        //异常信息
        ExecutionException ee = null;
        //过期时间
        final long deadline = timed ? System.nanoTime() + nanos : 0L;
        Iterator> it = tasks.iterator();//获取第一个任务
        提交任务
        futures.add(ecs.submit(it.next()));
        --ntasks;//因为提交了一个，任务数-1
        int active = 1;//正在执行的任务

        for (;;) {
            Future f = ecs.poll();
            if (f == null) {//第一个没完成
                if (ntasks > 0) {//还有没提交的任务
                    --ntasks;//任务数-1
                    futures.add(ecs.submit(it.next()));//提交任务
                    ++active;//正在执行的任务+1
                }
                else if (active == 0)//当前没任务了，但是都失败了，异常被捕获了
                    break;
                else if (timed) {
                    f = ecs.poll(nanos, TimeUnit.NANOSECONDS);//等待
                    if (f == null)//返回空，超时抛出异常，结束
                        throw new TimeoutException();
                    nanos = deadline - System.nanoTime();//剩余时间
                }
                else
                    f = ecs.take();//阻塞等待获取
            }
            if (f != null) {//说明已经执行完
                --active;//任务数-1
                try {
                    return f.get();//返回执行结果
                } catch (ExecutionException eex) {
                    ee = eex;
                } catch (RuntimeException rex) {
                    ee = new ExecutionException(rex);
                }
            }
        }

        if (ee == null)
            ee = new ExecutionException();
        throw ee;

    } finally {
        //取消其他任务，毕竟第一个结果已经返回了
        for (int i = 0, size = futures.size(); i < size; i++)
            futures.get(i).cancel(true);
    }
}

public  T invokeAny(Collection> tasks)
    throws InterruptedException, ExecutionException {
    try {
        return doInvokeAny(tasks, false, 0);
    } catch (TimeoutException cannotHappen) {
        assert false;
        return null;
    }
}

public  T invokeAny(Collection> tasks,
                       long timeout, TimeUnit unit)
    throws InterruptedException, ExecutionException, TimeoutException {
    return doInvokeAny(tasks, true, unit.toNanos(timeout));
}

返回所有任务的结果

public  List> invokeAll(Collection> tasks)
    throws InterruptedException {
    if (tasks == null)
        throw new NullPointerException();
    ArrayList> futures = new ArrayList>(tasks.size());//
    boolean done = false;
    try {
        for (Callable t : tasks) {//封装任务，并提交
            RunnableFuture f = newTaskFor(t);
            futures.add(f);
            execute(f);
        }
        for (int i = 0, size = futures.size(); i < size; i++) {
            Future f = futures.get(i);
            if (!f.isDone()) {
                try {
                    f.get();//阻塞，等待结果
                } catch (CancellationException ignore) {
                } catch (ExecutionException ignore) {
                }
            }
        }
        done = true;
        return futures;
    } finally {
        if (!done)//有异常，取消
            for (int i = 0, size = futures.size(); i < size; i++)
                futures.get(i).cancel(true);
    }
}

public  List> invokeAll(Collection> tasks,
                                     long timeout, TimeUnit unit)
    throws InterruptedException {
    if (tasks == null)
        throw new NullPointerException();
    long nanos = unit.toNanos(timeout);
    ArrayList> futures = new ArrayList>(tasks.size());
    boolean done = false;
    try {
        for (Callable t : tasks)
            futures.add(newTaskFor(t));

        final long deadline = System.nanoTime() + nanos;
        final int size = futures.size();

        // Interleave time checks and calls to execute in case
        // executor doesn"t have any/much parallelism.
        
        for (int i = 0; i < size; i++) {
            execute((Runnable)futures.get(i));
            nanos = deadline - System.nanoTime();
            if (nanos <= 0L)
                return futures;//每个提交都要判断，超时了返回Future
        }

        for (int i = 0; i < size; i++) {
            Future f = futures.get(i);
            if (!f.isDone()) {
                if (nanos <= 0L)
                    return futures;
                try {
                    f.get(nanos, TimeUnit.NANOSECONDS);
                } catch (CancellationException ignore) {
                } catch (ExecutionException ignore) {
                } catch (TimeoutException toe) {
                    return futures;
                }
                nanos = deadline - System.nanoTime();
            }
        }
        done = true;
        return futures;
    } finally {
        if (!done)
            for (int i = 0, size = futures.size(); i < size; i++)
                futures.get(i).cancel(true);
    }
}