Re: [lwip-users] When and how often are mtx/sem/mox new() and free() called?

[address@hidden]

Am 10.11.2021 um 22:45 schrieb Grant Edwards:
> Another porting question, I'm afraid.
>
> In deciding how to implement new/free operations for mailboxes,
> semaphores, and mutexes, it would be helpful if I had some idea of
> when and how often they are called.
>
> Are execution times for these functions going to noticeably affect
> performance of things like a small web server and MQTT client?
>
> Or should I do things using a simple and obviously correct method.
>
> I tend toward the latter unless warned beforehand that something is in
> a time-critical path.

- allocation of mutexes is only done when initializing lwIP
- allocation/deallocation of mboxes is done when initializing lwIP *and*
when creating/closing a socket
- allocation/deallocation of semaphores is done when creating/closing a
socket and when calling sys_msleep()

BUT: allocation/deallocation of sempahores is also done:
- for many API calls (from an application thread into the tcpip-thread)
or tcpip_calback when LWIP_TCPIP_CORE_LOCKING==0
- for select and for DNS API calls (like gethostbyname etc) when
LWIP_NETCONN_SEM_PER_THREAD==0

Note that LWIP_NETCONN_SEM_PER_THREAD==1 needs thread-local storage
support. Also, sys_msleep() isn't really broadly used but could probably
be somehow converted to use LWIP_NETCONN_SEM_PER_THREAD, too.

Overall, this doesn't look time-critical to me (unless you are making
heavy use of netconn/sockets and explicitly change
LWIP_TCPIP_CORE_LOCKING from its default setting 1 to 0).

Regards,
Simon