RE: Example socket program to send data to a non IBM i device

All the manual socket programming I did is now 17 years old, and I used Scott Klements guides as a starting point. I remember having issues with my client program getting stuck. I switched to a non blocking model, and that code is still running today with no issues with the client side.

https://www.scottklement.com/rpg/socktut/nonblocking.html


-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxxxxxxxx] On Behalf Of a4g atl
Sent: Wednesday, February 20, 2019 1:16 PM
To: Midrange Systems Technical Discussion
Subject: Re: Example socket program to send data to a non IBM i device

Has anyone been able to change the send timeout values? I tried changing the SO_SNDTIMEO constant value from 70 to 10, but this has not made a difference.

I need to get the timeout changed to 3 to 5 seconds.

Darryl Freinkel.


On Wed, Feb 20, 2019 at 9:27 AM a4g atl <a4ginatl2@xxxxxxxxx> wrote:

Scott is correct. We have equipment that may not be online all the
time and in this instance, the program is waiting for the response.

At this point the "default" timeout is somewhere in the regions of 3
to 5 minutes before dropping back to my code. I am working to reduce
this to 3 seconds, today.

This is a major issue here as we have between 5 and 100 devices and
for those not responding, it delays the entire process as its a single
threaded process. 20 devices being offline results in a delay of 60 minutes.

TIA

Darryl


On Tue, Feb 19, 2019 at 1:26 PM Scott Klement
<midrange-l@xxxxxxxxxxxxxxxx>
wrote:

Alan,

I'd like to reply to some of the things in your message, I'll put my
comments inline.

The hanging thing is a new one. Are other people using this socket

server?

It doesn't sound like the socket server is not responding, it
sounds

like

you are connecting and then being hung up.

"Socket" is a set of routines that can be used for many different
things... I assume this example is TCP?

It is an extremely frequent issue with TCP that they "hang" when a
firewall is blocking the connection, or when the network connection
gets broken, etc. TCP is meant to be completely reliable, so the
receiving side will send acknowledgements of the data received, and
the sender will re-send anything that wasn't acknowledged, basically
it'll get stuck re-sending indefinitely if it gets no response.

For that reason, you should always implement a time out mechanism in
a TCP application.

Normally socket attempts to make a connection. That connection is
either accepted or rejected. If there is nothing to connect to it
just returns

an

error.

...but that error can only be received if the network connection is
open and working. If something is blocking it (a firewall, or
something like an unplugged cable, power turned off, etc... anything
that would prevent the error message being sent back) instead of an
error, you'll sit and wait indefinitely.


If by "socket server" (hate that term) you don't mean a TCP server
but you mean something else, then my comments above may not apply.
It'd help me out a lot if you'd be more specific rather than using
terms like "socket server" or "socket client". Say TCP if you mean
TCP. If you can be even more specific (like Telnet, FTP, HTTP, SMTP,
PPTP, etc) then please do.
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