Re: [Cppcms-users] Simple long polling application has memory leaks (sockets left in CLOSE_WAIT state indefinitely)

[Cody S. <cod...@gu...>]

Artyom Beilis <artyom.beilis@...> writes:

> 
> The problem is that detecting that the connection isn't alive isn't 
reliable.
> 
> Especially when working via webserver and fastcgi/scgi.
> 
> You always need to have timeouts on connections especially long-
polling
> ones.
> 
> For example if you know that client resubmits request every 10 seconds
> (also I'd suggest
> to increase it) put your own 10 seconds timeout as well as you know 
that the
> client will disconnect so why to keep one alive.
> 
> Always manage timeouts on asynchronous requests.
> 
> Artyo
> 
> >
> > The problem arises in an ajax function called "listen()", which 
makes an
> > ajax POST request to the server and waits until the server has 
responded
> > or 10 seconds have passed, at which point it will fire up another 
"long-
> > polling" request.  However, each of these requests remains open in 
the
> > case that they time out, and then the lighttpd server refuses any 
more
> > connections after too many requests have been issued.  I'm not sure 
what
> > I'm doing wrong with my long-polling approach, but for some reason,
> > these sockets are not getting closed and I've been unable to 
determine
> > why after 2 days of investigating.
> >
> >

Thanks, that seems to really address the heart of the issue.

Just for clarification: async_on_peer_reset isn't automagically tracking
the client timeout and performing some cleanup?  I think that was the 
fundamental assumption that I had that went wrong.  I expected that in 
this code:

  void listen()
  {
      booster::shared_ptr<cppcms::http::context> context = 
release_context();
      waiters_.insert(context);
      context->async_on_peer_reset(
          std::bind(
              &chat::remove_context,
              this,
              context));
  }

the callback passed into async_on_peer_reset would get called on client
timeout.  The documentation here: 
http://cppcms.com/cppcms_ref/latest/classcppcms_1_1http_1_1context.html#
a0f6fe53deabd90fee0ced81a8df6404e
seems to indicate that that is a valid expectation.


P.S. Sorry for blowing up the thread above with repeat submissions; I 
thought gmane may have dropped my post.  I'll be more patient this time
;)  Also, thanks for the framework and all your hard work; I'm having a
great time jumping into web dev. and C++ with your tool!