code: public void onUploadTaskError(long rid) {
          if (LOG) {
              Log.d(TAG, "Upload #" + rid + " error");
          }
          QueueItem queueItem = findItem(rid);
          if (queueItem == null) {
              if (LOG) {
                  Log.d(TAG, "- Nothing found");
              }
              return;
          }
  
          if (!queueItem.isStarted) {
              return;
          }
  
          queueItem.taskRef.send(PoisonPill.INSTANCE);
          queueItem.isStopped = true;
          queueItem.isStarted = false;
  
          ArrayList<UploadFileCallback> clist = callbacks.get(rid);
          if (clist != null) {
              for (final UploadFileCallback callback : clist) {
                  im.actor.runtime.Runtime.dispatch(() -> callback.onNotUploading());
              }
          }
  
          queueItem.requestActor.send(new UploadError(rid));
  
          checkQueue();
      }
docs: Queue processing