Path: utzoo!attcan!uunet!zephyr.ens.tek.com!uw-beaver!mit-eddie!bloom-beacon!erik.UUCP!randy
From: randy@erik.UUCP (Randy Brown)
Newsgroups: comp.windows.x
Subject: X client as RPC server
Message-ID: <9010252039.AA04627@erik.uucp>
Date: 25 Oct 90 20:39:09 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 45

Last June there was a brief exchange on the question of using an X
client as an RPC server.  I saved the bit below, which I am reposting to
forestall the inevitable requests.  I am interested to know if anyone
has further experience, particularly with a solution based on Xt rather
than Xview.  ... Randy Brown (uunet!erik!rbrown)

from Don Bennett <dpb@frame.com> (408)433-3311 Frame Technology
> rpcListen(client_data, source, id)
> caddr_t client_data;
> int *source;
> XtInputId *id;
> {
>     svc_getreq(1 << *source);
> }
> 
> main()
> {
>     int fd;
> 
>     svc_register(transp, ...);
>     fd = transp->xp_sock;
>     XtAppAddInput(_XtDefaultAppContext(), fd, XtInputReadMask, rpcListen, 0);
>     XtMainLoop();
> }

from David Brownell <db@east.sun.com> (508) 671-0348
> It's worth noting that this posted solution works only for UDP RPCs.
> That is, if you use TCP for simpler semantics, more data than the
> default of 8 Kbytes, or better error reporting, this doesn't work.
> 
> Also, this uses the obsolete svc_getreq() call, which is limited
> to 32 file descriptors.  More recent UNIXes have a much higher
> limit -- this should use svc_getreqset() instead, which handles
> many more file descriptors.
> 
> The issue with TCP is that the RPC library needs to allocate and
> deallocate file descriptors dynamically.  To handle this within
> Xt, the input callback for the tcp-based SVCXPRT must diff the RPC
> file descriptors in svc_fdset before and after it calls svc_getreqset(),
> invoking XtAppAddInput (or XtAddInput) on new file descriptors and
> calling XtRemoveInput() one ones that've disappeared.
> 
> The upcoming release of XView will do this for you automatically if
> you ask, so that you won't have to scour the innards of the window
> system and notifier documentation to find out how to do this!