Executor 上的 AsyncTask 和 PriorityBlockingQueue 实现问题

在浪潮中这个问题 https://stackoverflow.com/questions/12039596/asynctask-on-executor-and-priorityblockingqueue并有许多提示另一个 https://stackoverflow.com/questions/7792767/priority-threadpoolexecutor-in-java-android，我正在尝试实现一个AsyncTask具有可以确定优先级的任务的变体。

In my CustomAsyncTask我的课程有：

public abstract class CustomAsyncTask<Params, Progress, Result> {

    private static int CORE_POOL_SIZE = 1;
    private static int MAXIMUM_POOL_SIZE = 1;

    private static final int KEEP_ALIVE = 1;

    private static final ThreadFactory sThreadFactory = new ThreadFactory() {
        private final AtomicInteger mCount = new AtomicInteger(1);

        public Thread newThread(Runnable r) {
            return new Thread(r, "CustomAsyncTask #" + mCount.getAndIncrement());
        }
    };

    private static final BlockingQueue<DownloadTask> pPoolWorkQueue =
            new PriorityBlockingQueue<DownloadTask>(10, new DownloadTasksComparator());

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static Executor PRIORITY_THREAD_POOL_EXECUTOR
            = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
                    TimeUnit.SECONDS, (PriorityBlockingQueue) pPoolWorkQueue, sThreadFactory);

   //...
}

比较器：

public class DownloadTasksComparator implements Comparator<DownloadTask> {

    @Override
    public int compare(DownloadTask arg0, DownloadTask arg1) {
        int res;

        if (arg0 == null && arg1 == null) {
            res = 0;
        } else if (arg0 == null) {
            res = -1;
        } else if (arg1 == null) {
            res = 1;
        }

        res = arg0.getPriority() - arg1.getPriority();

        return res;
    }
}

In the DownloadTask类扩展CustomAsyncTask我有一个priority整数字段和getPriority() method.

我将任务执行称为：

DownloadTask dt = new DownloadTask(..., PRIORITY_NORMAL, ...);
dt.executeOnExecutor(CustomAsyncTask.PRIORITY_THREAD_POOL_EXECUTOR);

这是可行的：如果池大小为 1，则下载将被一项一项地执行；如果池大小为 2，等等。

注意：优先级整数具有任意值：

public static final int PRIORITY_HIGH = 10;
public static final int PRIORITY_NORMAL = 1;

但如果我将任务称为：

DownloadTask dt = new DownloadTask(..., PRIORITY_HIGH, ...);
dt.executeOnExecutor(CustomAsyncTask.PRIORITY_THREAD_POOL_EXECUTOR);

我有一个java.lang.ClassCastException: my.pkg.name.CustomAsyncTask$3 cannot be cast to my.pkg.name.DownloadTask

and then

at my.pkg.name.DownloadTasksComparator.compare(DownloadTasksComparator.java:1)
at java.util.concurrent.PriorityBlockingQueue.siftUpUsingComparator(PriorityBlockingQueue.java:334)
at java.util.concurrent.PriorityBlockingQueue.offer(PriorityBlockingQueue.java:447)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1295)
at my.pkg.name.CustomAsyncTask.executeOnExecutor(CustomAsyncTask.java:494)
at my.pkg.name.GetDownloadTaskListener$1.finishDownload(GetDownloadTaskListener.java:180)
at my.pkg.name.DownloadTask.onPostExecute(DownloadTask.java:330)
at my.pkg.name.DownloadTask.onPostExecute(DownloadTask.java:1)
at my.pkg.name.CustomAsyncTask.finish(CustomAsyncTask.java:536)
at my.pkg.name.CustomAsyncTask.access$0(CustomAsyncTask.java:532)
at my.pkg.name.CustomAsyncTask$InternalHandler.handleMessage(CustomAsyncTask.java:549)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)

全部来自AndroidRuntime

我真的没有任何线索...

EDIT：此时，我已经封装了一个小型 Eclipse 项目，该项目以与较大应用程序完全相同的方式实现事物，并且遇到了相同的问题。它借用CustomAsyncTaskComparator and CustomAsyncTask逐字。没有给出视觉反馈。应用程序的进度只是一些 LogCat 输出。但它给出了想法。当两个以上的任务排队时，应用程序 FC。

https://www.dropbox.com/s/lrg4kscgw3f1xwr/ConcurrentTest.tar.gz https://www.dropbox.com/s/lrg4kscgw3f1xwr/ConcurrentTest.tar.gz

CustomAsyncTask, like AsyncTask，使用static queue. 一切目前，该队列中的内容将贯穿您的DownloadTasksComparator。然而，DownloadTasksComparator仅适用于DownloadTask。只要你只使用DownloadTask，而不是其他子类CustomAsyncTask， 你会好起来的。但是，显然您还有其他一些匿名内部类扩展CustomAsyncTask，这不是一个DownloadTask.

Make CustomAsyncTask be abstract，有一个getPriority()方法作为abstract方法。改名DownloadTasksComparator to CustomAsyncTaskComparator并进行比较CustomAsyncTask实例。然后，你的其他子类CustomAsyncTask需要实施自己的getPriority()方法，使它们能够与DownloadTask工作队列中的实例。