Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!wiley!news
From: doug@ridley.coyote.trw.com (Doug Rudoff)
Newsgroups: comp.unix.questions
Subject: How can a server tell if a client is gone?
Message-ID: <26DAAE36.74D6@wilbur.coyote.trw.com>
Date: 28 Aug 90 17:47:34 GMT
Sender: news@wilbur.coyote.trw.com (News Software)
Reply-To: rudoff@mdi.com
Organization: Mobile Data International
Lines: 33

I am writing an application that uses a client-server model. I want the
server to be able to tell if the client has disappeared unexpectedly.

I have been using RPC for interprocess communication on a Sun3 and Sun4
running 4.0.3.

What would be ideal would be an RPC call that tells you if a server's
client still exists. In the not too descriptive man page on RPC, I
don't see a function that does what I want.

I did try having the client register an RPC service, and have the
server every so often check to see if it could make a connection to
the client's service (and then destroy the connection). This only
worked if I used a tcp protocal (using udp, the server thought the
client was there all the time, regardless of whether it was really
there or not). However, after a couple of successful verifications of
the client's presence, the server's call to clnt_create() would lock
up in connect(). In reading the man page for connect(), I can't figure
out why it would lock up.

The problem of determining if a client still exists seems to me to be
a common thing that needs to be done. Is there a simple way to do it
with ANY type of IPC? Now, I am using RPC, but its underlying basis is
sockets, so some help relating to sockets could be useful.

Also, the Sun manuals on RPC leave a lot to be desired. Does anyone
know of anything more informitive? (My most important question is what
happens to a registed service if its process dies?)
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Doug Rudoff            Mobile Data International   Bothell, WA
(206) 487-5937         rudoff@mdi.com, uunet!mdisea!rudoff
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