volatile keyword fixes gcc compile error
volatile keyword fixes gcc compile error

jianqiao/incubator-quickstep,cramja/incubator-quickstep,UWQuickstep/quickstep,jianqiao/incubator-quickstep,cramja/incubator-quickstep,UWQuickstep/quickstep,cramja/incubator-quickstep,zuyu/incubator-quickstep,UWQuickstep/quickstep,hbdeshmukh/incubator-quickstep,zuyu/incubator-quickstep,UWQuickstep/quickstep,cramja/incubator-quickstep,zuyu/incubator-quickstep,jianqiao/incubator-quickstep,UWQuickstep/quickstep,hbdeshmukh/incubator-quickstep,hbdeshmukh/incubator-quickstep,hbdeshmukh/incubator-quickstep,jianqiao/incubator-quickstep,zuyu/incubator-quickstep