Re: [lwip-users] sys_arch_mbox_fetch() implementation for FreeRTOS

[address@hidden]

Am 20.06.2022 um 11:22 schrieb massimiliano cialdi via lwip-users:
> hello,
>
> I am using lwip 2.1.3 and contrib 2.1.0.
> in the ports/freertos/sys_arch.c file there is the sys_arch_mbox_fetch()
> function, in which there is the timeout_ms parameter.
> Given the name I expect the sys_arch_mbox_fetch() function to be
> blocking for a maximum time corresponding to timeout_ms milliseconds.
> I see this piece of code, though:
>
>    if (!timeout_ms) {
>      /* wait infinite */
>      ret = xQueueReceive(mbox->mbx, &(*msg), portMAX_DELAY);
>      LWIP_ASSERT("mbox fetch failed", ret == pdTRUE);
>    } else {
>
> I wonder why I should wait infinitely if I set the timeout to 0 (so I
> want it non-blocking)? is this a bug?

See the documentation of that parameter in sys.h:
@param timeout maximum time (in milliseconds) to wait for a message (0 =
wait forever)

It's a bit unfortunate, but it has been like that since forever (0 =
wait forever). The code uses sys_arch_mbox_tryfetch() when it does not
want to block at all.

> In fact, it happens to me occasionally (I have yet to figure out the
> conditions) that even though I have the timeout set to 0, re-read with
> lwip_getsockopt(SO_RCVTIMEO), the task blocks indefinitely while waiting
> for a message in the queue.

That would be odd. Please report a fix if you find one.

Regards,
Simon