Re: [lwip-users] Handle multiple connections using netconn API?

[address@hidden]

Am 19.11.2021 um 17:38 schrieb Grant Edwards:
> For the past few days, I've been trying to figure out the netconn API
> equivalent for select/poll, and I haven't been able to come up with
> anything.
>
> How does a single server thread handle multiple TCP or UDP
> "connections" using the netconn API?
>
> If you use a callback to wake the server thread, how do you avoid a
> race condition when data arrives just after it has serviced all the
> connections but before the server thread blocks?
>
> Handling the recv data in the callback seems like a bad idea, since
> that presumably is done in the tcpip thread's context. Handling the
> recv data may take a considerable amount of time and needs to be done
> at a low priority so that it doesn't interfere with other
> time-critical traffic.
>
> Isn't there some way to handle this without switching to the socket
> API?

Of course there is a way: "just" implement the same callback + select
behaviour as in the socket API. This is, however, not included in the
lwIP code, you'll have to do that yourself.

In theory, we could probably move the callback/select code from the
socket layer to the netconn layer. However, since noone has requested
this yet, noone worked on this, yet.

Regards,
Simon

> One answer is to create a server thread for each new connection, and
> then use blocking recv calls. But, that's not possible in my RTOS:
> threads can't be created dynamically. They have to be declared
> statically at compile time. [Yes, that's a pain.]
>
> In my system sys_thread_new() doesn't actually "create" a thread. It
> searches the static table of threads and starts the thread with a
> matching entry point.
>
> Thanks...
>
> --
> Grant
>
>
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