Lnet SendAfterError
lazarus / 38-Networking and Web Programming

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Jake012345 · 2020-05-11 13:23

Hello!

I wrote a program with Lnet and I use private declared sockets (so not
the aSocket).
And when one of my sockets errored, nothing happens, but after that,
if server send any message to any socket, It's (the server) crashing
with SIGSEGV error.
What can I do for avoid this problem?

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MarkMLl · 2020-05-11 13:38

Well to start with, you can keep an eye on topics you've started on
the same subject.

https://forum.lazarus.freepascal.org/index.php/topic,49675.msg361162.h
tml#msg361162

MarkMLl

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Jake012345 · 2020-05-11 15:22

That's good, but I can't solve my problem wit it...

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MarkMLl · 2020-05-11 17:50

Have you tried contacting the authors yet? I suspect that I'm about
the last person to do any maintenance on it (I very gingerly added a
bit of extra functionality to the Telnet client) but I don't think
there's anybody who really understands how it works.

MarkMLl

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jiaxing2 · 2020-05-11 18:16

Quote from: MarkMLl on May 11, 2020, 07:50:06 pmHave you tried
contacting the authors yet? I suspect that I'm about the last person
to do any maintenance on it (I very gingerly added a bit of extra
functionality to the Telnet client) but I don't think there's anybody
who really understands how it works.

MarkMLl

I don't think this would help. One of my discipline is don't use
abandonware.

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MarkMLl · 2020-05-11 19:19

Quote from: jiaxing2 on May 11, 2020, 08:16:31 pmQuote from: MarkMLl
on May 11, 2020, 07:50:06 pmHave you tried contacting the authors yet?
I suspect that I'm about the last person to do any maintenance on it
(I very gingerly added a bit of extra functionality to the Telnet
client) but I don't think there's anybody who really understands how
it works.

I don't think this would help. One of my discipline is don't use
abandonware.

I agree, but he might possibly have more success getting in contact
with them than the other people who've tried over the last few years-
including myself.

I don't know the history of lnet, or why it's packaged by itself under
utils/fppkg. However for very limited use it's handy not having to
specify an external package... most of the networking stuff I do is
non-standard so I write on top of the Berkeley Sockets API but I'd
rather not have to reimplement something like Telnet unless I really
had to.

In any event, if OP carries on tinkering with it he's going to be the
Local Expert :-)

MarkMLl

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Almindor · 2020-05-12 15:59

Quote from: Jake012345 on May 11, 2020, 03:23:45 pmHello!

I wrote a program with Lnet and I use private declared sockets (so not
the aSocket).
And when one of my sockets errored, nothing happens, but after that,
if server send any message to any socket, It's (the server) crashing
with SIGSEGV error.
What can I do for avoid this problem?

I haven't had time to go over your code properly yet but from what I
see you're using the TLComponent classes wrong.

Sockets are created as needed on a listening TLTcp. You get the
OnAccept event with the socket in it. You're not supposed to "own" the
socket object but just keep a reference to it which you get from these
events.

You also need to handle OnError events properly and consider any
socket that gets reported in the OnError event as invalid from that
point on. What I suspect is happening with your code is that you set
your socket in your socket array (which is fine in itself, you're just
keeping a reference) but then you do not handle either OnError or
OnDisconnect properly and do not remove this reference from your list.

Then when you try to send something you include that "invalid" socket
in the list you try to send to causing a SIGSEGV because the
underlayng object (the TLSocket value) has been removed by TLTcp since
it disconnected or error-ed out.