关于进程调度的理解很nice的一个例子 干货如下: http://wenku.baidu.com/link?url=74dsAPYkhVmeTnlI76_7aoYVK8lSX383cg5wjc5TxTSX6-sZcFmlTj8-KXYDMIJLBUnRRQ9D_YYiqcp7EhP1KO6Ieh-Yo9SUWL_XbYHKOey