Tape 是一组跟队列相关的工具类，同时也适用于 Android 平台。

示例代码：

/** Listener for starting the upload service when the queue has tasks. */
public class ImageQueueServiceListener implements ObjectQueue.Listener {
  private final Context context;

  public ImageQueueServiceStarter(Context context) {
    this.context = context;
  }

  @Override public void onAdd(ObjectQueue, ImageUploadTask task) {
    context.startService(new Intent(context, ImageQueueService.class));
  }

  @Override public void onRemove(ObjectQueue) {}
}

/** Service which iterates through pending upload tasks one-by-one. */
public class ImageQueueService extends Service implements ImageUploadTask.Callback {
  private TaskQueue queue;
  private boolean running;

  @Override public void onCreate() {
    super.onCreate();
    // Obtain TaskQueue here (e.g., through injection)
  }

  @Override public int onStartCommand(Intent intent, int flags, int startId) {
    executeNext();
    return START_STICKY;
  }

  public void executeNext() {
    if (running) return; // Only one task at a time.
    ImageUploadTask task = queue.peek();
    if (task != null) {
      task.execute(this);
      running = true;
      return;
    }
    stopSelf(); // We're done for now.
  }

  @Override public void imageUploadComplete() {
    running = false;
    queue.remove();
    executeNext();
  }
}

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