Sockets / fpAccept break signal
lazarus / 38-Networking and Web Programming

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marcodor · 2015-03-26 16:08

Hello,

Trying to write a socket server using Sockets unit.
Everything it's OK till now, but some questions appears.

Server initialize socket and are waiting for client connections.
Later it create a new thread for each new socket connection to handle
client.
This is done in an infinite cycle repeat/until:

Code: [Select]function TUSocketServer.Start: Boolean;
const Sal: TSockLen = SizeOf(TInetSockAddr);
var A, B: TInetSockAddr;
begin
  FLink := fpSocket(AF_INET, SOCK_STREAM, 0);
  if FLink = S_FAIL then Exit(False);
  A.sin_family := AF_INET;
  A.sin_port := NToHs(FPort);
  A.sin_addr.s_addr:= 0;
  if fpBind(FLink, @A, Sal) = S_FAIL then Exit(False);
  if fpListen(FLink, 1) = S_FAIL then Exit(False);
  repeat
    if fpAccept(FLink, @B, @Sal) = S_FAIL then begin Write('ACP');
Exit(False); end;
    // <<< Handle new connection
  until false;
end;


The question is: How to stop server waiting for new connections,
terminate main thread, disconnect connected clients and free resources
in a graceful way?

For example on Windows / COM Port communication there is a possibility
to signal "waiting" state using Events and Signals.
I'm looking for something similar in socket handling that also works
on Linux platform.

Thanks in advice!

-
  Dorin

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marcodor · 2015-03-26 16:36

I found a way using KillThread, is this only option available?

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engkin · 2015-03-26 16:43

The thread loop should be:
Code: [Select]  while not Terminated do
...

TThread has both Terminated and Terminate.

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marcodor · 2015-03-26 16:48

engkin,

fpAccept function wait unlimited time until some socket connection is
established.
Calling Thread.Terminate and check for Terminated won't help here,
because "hang" is inside fpAccept function.

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engkin · 2015-03-26 17:40

This is just my assumption. Turning the socket into non-blocking
*might* take it out of FpAccept and allow you to tear it down with
fpshutdown and CloseSocket.

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marcodor · 2015-03-26 18:09

Engkin,

Lol, i need blocking model. Controlled Query->Answer. Like in http/sql
protocol.
Non-blocking when you receive something while sending something and
you don't know exactly what you receive is not a solution for me. Non-
blocking is used in other cases.

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marcodor · 2015-03-26 18:13

I decided to put just "fpAccept" cycle in a separate thread and use
later KillThread to stop it.
Will report about success.

By the way, calling KillThread while Thread executing a small critical
section make it wait a bit of nanoseconds till thread exit that
section? or kill it immediately in an barbarian cruel way?

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engkin · 2015-03-26 18:19

Barbarian way.

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marcodor · 2015-03-26 18:36

Ah, just found a solution from Remy Lebeau, Indy author, here
Thanks, Engkin for quick answers! I'm new in FP world

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engkin · 2015-03-26 20:34

Thanks for sharing that solution, and welcome to FPC/Lazarus forum.