[JDEV] How to get current number of users?

[Yanming Xiao]

Write a new JSM component containing a  function similiar to
that of "js_users_gc (user.c) , which is a heart-beat callback function
installed in jsm.c:

void jsm(instance i, xmlnode x)
{
   ...

register_beat(j_atoi(xmlnode_get_tag_data(si->config,"usergc"),60),js_users_
gc,(void *)si);
}

-Yanming