Question

我有一个列表，其中包含我想用Android的DownloadManager下载的图像的URL。这是一个非常基本的设计，用于定义从列表中删除对象然后调用DownloadManager的AsyncTask子类。我的问题是如何处理AsyncTasks的并行性时，每个都将list.get(curentIndex)。为了清楚起见，我希望每个任务（将在Executor上运行，因此在其他任务中运行，而不仅仅是主线程）以原子方式运行

将从列表中删除对象
将增加索引

Answer 1

这通常是同步问题。有很多方法可以解决这个问题。我会建议一些事情：

// Your index. Defaulted at 0. Thread safe Integer wrapper object.
// All set/get operations are guaranteed atomical.
AtomicInteger mIndex = new AtomicInteger(0);

// Your list. This is thread-safe. All mutative operations
// are atomical, and properly locked. The list is copied on each write.
// This solution, though it does what it needs to do, is SLOW. Don't use for
// large lists.
CopyOnWriteArrayList<Object> mList = ... ;

// Your async task. Maybe more of them.
AsyncTask mTask = ...;

// Anything here that should be thread safe.
ensurePrerequisites(mTask);

// Execute on thread pool to make sure they're parallel.
// CAUTION: You will still get only (CPU_CORE_COUNT + 1) max parallel tasks.
mTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);


public void synchronized ensurePrerequisites(AsyncTask task) {
     // I assume you want to pass the values into the task.
     int idx = mIndex.getAndIncrement();
     task.setIndex(idx);
     task.setObject(mList.remove(idx));
}

使AsyncTasks自动运行

1 个答案: