Re: [libmicrohttpd] race condition on 0.9.73

[José Bollo]

Hi Evgeny, Hi all,

Firstly, protecting MHD_run made the job, the crash disappears and
valgrind is happy. Thank you for that efficient support.

Secundly, I'm still seeing and investigating an issue. Sometime, the
queued response (MHD_queue_response) is not sent. Here again, I think
that it is a race condition. The issue is surely on my side.

Then some responses to your questions below.

[snip]

> >>>
> >>>   flags = MHD_USE_EPOLL
> >>>                   | MHD_ALLOW_UPGRADE
> >>>                   | MHD_USE_TCP_FASTOPEN
> >>>                   | MHD_USE_NO_LISTEN_SOCKET
> >>>                   | MHD_ALLOW_SUSPEND_RESUME;  
> >>
> >> Do you use suspend/resume of connections?  
> > 
> > yes for websocket upgrade but it is not relevant in the case.  
> 
> Don't you use MHD built-in "upgrade" functions?

Good question. I had not noticed before: I have both options
MHD_ALLOW_UPGRADE and MHD_ALLOW_SUSPEND_RESUME. When I first
implemented websocket using MHD, I used the suspend/resume behaviour.
Is it still needed? I am now using MHD_create_response_for_upgrade for
that purpose.

However, at the moment, the program suspend the connection for the time
it processes the request. That is the reason way MHD_run were called
from multiple threads.

[snip]

> Please share you results.
> We are close to releasing the next MHD version and want to make sure 
> there are no know bugs in the code.

Still investigating one issue.

> I'm wondering, why do you run the same MHD instance in different
> threads? Every MHD_run() processes *all* connections served by
> particular MHD instance. This looks like work duplication (or
> multiplication). If you process specific connections by each thread
> and you add connections to MHD by MHD_add_connection(), just use
> thread-specific MHD instance so you will always know which
> connections are processed by MHD_run().

I could answer but here is what I prefer to write.

I also think that if every one made same choices the world would be
peaceful. But new problems, new solutions, new men, new ideas, ... Why
have you written MHD in C and not in PASCAL?