过一个pass就停止不动了，内存占用着，但是cpu和gpu都为0了，就一直不动了

[bjkite]

经确认，是在reader的实现中使用了 paddle.reader.xmap_readers的原因，去掉不用就不会出现
代码如下：

   def reader():
        UNK = word_id_dict['<UNK>']
        with open(file_name) as file:
            count = 0
            for line in file:
                image_path,image_tag = line.strip().split("\t")
                words = image_tag.decode('utf-8', 'ignore').strip().split()
                if len(words) < min_sentence_length or len(
                        words) > max_sentence_length:
                    continue
                ids = [word_id_dict.get(w, UNK) for w in words]
                ids.append(word_id_dict['<EOS>'])
                target = ids[:]
                target.append(word_id_dict['<EOS>'])
                count += 1
                yield image_path, ids[:], target[:]

    return paddle.reader.xmap_readers(image_mapper, reader,
                                     1, buffered_size)