Add a context manager to the useful read/writer lock.
Add a context manager to the useful read/writer lock.

junneyang/taskflow,junneyang/taskflow,citrix-openstack-build/taskflow,jimbobhickville/taskflow,citrix-openstack-build/taskflow,jimbobhickville/taskflow,jessicalucci/TaskManagement,pombredanne/taskflow-1,varunarya10/taskflow,pombredanne/taskflow-1,varunarya10/taskflow,openstack/taskflow,jessicalucci/TaskManagement,openstack/taskflow