tree b07e7a6e579268d85d2fe9be9db7f1657ffd27a2
parent 716addcf42043787ce9bf4337f122170fefc7883
author Zhenkai Zhu <zhenkai@cs.ucla.edu> 1338956317 -0700
committer Zhenkai Zhu <zhenkai@cs.ucla.edu> 1338956317 -0700

add mutex for thread safety