[fpc-pascal] SSocket: TSocketServer.StopAccepting

[Johann Glaser]

Hi!

I'm using the SSocket unit with TSocketServer (and TInetServer) for
TCP/IP communication in a multi-threaded application. To listen (and
accept) connections from a client the method StartAccepting is called.
This is a blocking function.

To quit the server I call StopAccepting. The implementation just sets a
variable which is checked by StartAccepting.

There are two problems:
1) If using the TSocketStream in blocking mode, the accept() call used
by StartAccepting does not return at all, so StopAccepting is somewhat
useless here.
2) In non-blocking mode the internal variable is checked periodically,
but not really often, so race conditions with Destroy can happen.

In both cases, when I want to quit my program, there is no safe way to
stop accepting at the socket, except from OnConnect (as shown e.g.
in /packages/fcl-base/examples/isocksvr.pp).

So there are some ideas to solve this.

First: Send a SIGTERM to this thread, accept() will return with EINTR,
which should then be checked for in TInetServer.Accept,
TUnixServer.Accept, ... and generate a special exception which is then
again checked for in TSocketServer.StartAccepting which simply exits the
loop.

Second: Do a dummy connect to myself and check for FAccepting directly
after Accept returns and then leave the loop. I prefer this one. OTOH
this depends on knowing one's own address and allowing this connection
by the firewall rules.

In any case, I suggest that StopAccepting really waits and only returns
after StartAccepting has finished. This also must be used in Destroy.
Here we have to take care for the case if StopAccepting is called from
OnConnect.

Did I miss something? Do you have other ideas? If you agree with my
idea, I'll implement the changes and send a patch for that.

Bye
  Hansi