国家自然科学基金91118007;国家“八六三”高技术研究发展计划项目基金2012AA011205;计算机软件新技术国家重点实验室开放课题项目基金ZZKT2013B09资助.This work is supported by the National Natural Science Foundation of China91118007;the National High Technology Research and Development Program 863 Program of China2012AA011205;the Open Foundation of State Key Laboratory for Novel Software Technology in Nanjing UniversityZZKT2013B09