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

Hi Darryl,

Those constants are just mnemonics ;-)   Changing that won't change the timeout value, and SO_SNDTIMEO doesn't apply to the standard socket API, anyway.

There are two ways to do timeouts in socket programming:

1) You can use signals, such as the alarm() API with SIGALRM to interrupt a socket call after a given time period.  This is quick and dirty, but doesn't work everywhere (some jobs block signals).

2) You can use non-blocking sockets together with the select() API.  (technically you can do this with blocking as well, but its not as robust.)   This is the best way, but its more work.

Unfortunately the articles I wrote about this are no longer online (when iProDeveloper.com/SystemiNetwork.com was taken down, all of my articles went with it.)  Otherwise I'd give you a link.

-SK


On 2/20/2019 1:15 PM, a4g atl wrote:

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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