java併發編程學習之線程池-AbstractExecutorService(二)

AbstractExecutorService抽象類，實現了ExecutorService的接口。

newTaskFor

將任務封裝成FutureTask

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

submit

提交任務

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;
}

invokeAny

主要方法在doInvokeAny

//tasks任務
//timed是否超時
//nanos超時時間
private <T> T doInvokeAny(Collection<? extends Callable<T>> tasks,
                              boolean timed, long nanos)
    throws InterruptedException, ExecutionException, TimeoutException {
    if (tasks == null)
        throw new NullPointerException();
    int ntasks = tasks.size();//任務書
    if (ntasks == 0)
        throw new IllegalArgumentException();
    ArrayList<Future<T>> futures = new ArrayList<Future<T>>(ntasks);
    //用於存放結果的，先完成的放前面。因此第一個任務沒完成的時候，會繼續提交後續任務
    ExecutorCompletionService<T> ecs =
        new ExecutorCompletionService<T>(this);

    try {     
        //異常信息
        ExecutionException ee = null;
        //過時時間
        final long deadline = timed ? System.nanoTime() + nanos : 0L;
        Iterator<? extends Callable<T>> it = tasks.iterator();//獲取第一個任務
        提交任務
        futures.add(ecs.submit(it.next()));
        --ntasks;//由於提交了一個，任務數-1
        int active = 1;//正在執行的任務

        for (;;) {
            Future<T> f = ecs.poll();
            if (f == null) {//第一個沒完成
                if (ntasks > 0) {//還有沒提交的任務
                    --ntasks;//任務數-1
                    futures.add(ecs.submit(it.next()));//提交任務
                    ++active;//正在執行的任務+1
                }
                else if (active == 0)//當前沒任務了，可是都失敗了，異常被捕獲了
                    break;
                else if (timed) {
                    f = ecs.poll(nanos, TimeUnit.NANOSECONDS);//等待
                    if (f == null)//返回空，超時拋出異常，結束
                        throw new TimeoutException();
                    nanos = deadline - System.nanoTime();//剩餘時間
                }
                else
                    f = ecs.take();//阻塞等待獲取
            }
            if (f != null) {//說明已經執行完
                --active;//任務數-1
                try {
                    return f.get();//返回執行結果
                } catch (ExecutionException eex) {
                    ee = eex;
                } catch (RuntimeException rex) {
                    ee = new ExecutionException(rex);
                }
            }
        }

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

    } finally {
        //取消其餘任務，畢竟第一個結果已經返回了
        for (int i = 0, size = futures.size(); i < size; i++)
            futures.get(i).cancel(true);
    }
}

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

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

invokeAll

返回全部任務的結果

public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
    throws InterruptedException {
    if (tasks == null)
        throw new NullPointerException();
    ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());//
    boolean done = false;
    try {
        for (Callable<T> t : tasks) {//封裝任務，並提交
            RunnableFuture<T> f = newTaskFor(t);
            futures.add(f);
            execute(f);
        }
        for (int i = 0, size = futures.size(); i < size; i++) {
            Future<T> f = futures.get(i);
            if (!f.isDone()) {
                try {
                    f.get();//阻塞，等待結果
                } catch (CancellationException ignore) {
                } catch (ExecutionException ignore) {
                }
            }
        }
        done = true;
        return futures;
    } finally {
        if (!done)//有異常，取消
            for (int i = 0, size = futures.size(); i < size; i++)
                futures.get(i).cancel(true);
    }
}

public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                     long timeout, TimeUnit unit)
    throws InterruptedException {
    if (tasks == null)
        throw new NullPointerException();
    long nanos = unit.toNanos(timeout);
    ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
    boolean done = false;
    try {
        for (Callable<T> 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;//每一個提交都要判斷，超時了返回Future
        }

        for (int i = 0; i < size; i++) {
            Future<T> 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);
    }
}