LNET UDP - problemm with connection
lazarus / 38-Networking and Web Programming

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jardigital · 2013-08-16 15:26

Hi,

I have a problem.
I have a program that needs to communicate with multiple devices via
UDP. I use LNET package.
Everything is fine if all devices are turned on and connected to the
Ethernet.

But if I some device turn it off or unplug from ethernet.
I will send a UDP packet.
The device is not responding. Nothing comes back, then try again to
communicate the same or another device.
using for example
Code: [Select]Net.Connect ('192 .168.1.161 ', 8888)the application
hangs for about 2 seconds.

note:
(When the device receives a UDP packet, UDP packet is sent back to
confirm receipt.)


If after sending the first packet (if nothing comes back), then I wait
two seconds after sending, after this time I send next packet then
program don't  freeze.

The problem is that it is impossible for any problem to wait 2
seconds. The program has with other devices communicate quickly
without stopping. Delay 2 seconds is too long.

Does anyone know where the problem might be?

Code for sending is very simple.:
Code: [Select]FNet.Connect('192.168.1.80', 8888);
FNet.SendMessage('hello');  nothing else.
for sendig packets i use timer.
thanks Robert

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Almindor · 2013-09-10 17:03

lNet in UDP doesn't really do anything when you do a connect, it only
sets a structure. The only thing which could block is the DNS
resolution which is still blocking, but it shouldn't attempt that when
you provide an IP address.

Can you try and use a debug build and step into the connect command to
see? If it goes to netDB and blocks there then that's the DNS problem
and we'll need to find out why it didn't try to use the ip-address
directly.

Ales