Re: [libmicrohttpd] race condition on 0.9.73

[Evgeny Grin]

On 23.09.2021 18:43, José Bollo wrote:
> > For sure you can run MHD with "external poll" mode, but you must
> > ensure that only single thread is calling MHD_run() at any given
> > moment of time.
>
> Okay, that is a good hint, thanks. I'm going to first track concurrent
> use of MHD_run. FYI, I tried the latest git and got the same issue.
>
> > If you want to call several copies of MHD_run(), make sure that you
> > have individual copies of MHD for each thread (start MHD by
> > MHD_start_daemon() for every thread).
>
> I don't want that, because it implies differents port I suppose.

Even if MHD is doing internal accept(), you still can use 
MHD_OPTION_LISTENING_ADDRESS_REUSE parameter to bind to the same port. 
Or provide your own socket.
However as I can see below, it's not applicable for your case as you are 
not using MHD to listen for new connections.


> > Alternatively, you can use MHD with its own threading mode. MHD can
> > run treads per connection or use thread pool.
> >
> > Can you give more details how you use MHD? Which flags are used?
>
>         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?

> > Why do you use external threads instead of MHD internal treads?
>
> The program has a job scheduler that manages threads on its own. It
> also serves other protocols that HTTP(S).

It is still hard to see where is the problem. Actually responses are 
thread-safe and shouldn't create any such kind of problems.

Could you share you access handler callback code?
Where do you generate responses?
Where do you queue responses?

--
Evgeny

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