fix memory leak bug
fix memory leak bug

apache/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa,apache/incubator-singa