Re: [PATCH 1/5] cobalt/events: add auto-clear feature

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka <jan.kiszka@siemens.com> writes:

> On 06.04.22 17:56, Philippe Gerum via Xenomai wrote:
>> From: Philippe Gerum <rpm@xenomai.org>
>> 
>> The current implementation does not atomically consume+clear the event
>> set to be received by the waiter(s), which makes it useless for
>> anything but a plain one-time latch due to the race window this opens
>> with a consume[A]->signal[B]->clear[A] sequence.
>> 
>> To address this issue, let's provide the auto-clear feature with
>> __cobalt_event_wait().
>> 
>> This change affects the ABI by adding the auto-clear mode as an opt-in
>> feature, enabled by passing COBALT_EVENT_AUTOCLEAR to
>> cobalt_event_init().
>> 
>
> Makes sense, but shouldn't autoclear be rather the default then? Which
> users are affected? None in-tree so far?
>

There is one user in copperplate:
https://source.denx.de/Xenomai/xenomai/-/blob/28158391258eea52650856bef5d3ed6ebaaf813b/lib/copperplate/eventobj.c#L87

which indirectly affects rt_event_signal() from the alchemy API:
https://source.denx.de/Xenomai/xenomai/-/blob/28158391258eea52650856bef5d3ed6ebaaf813b/lib/alchemy/event.c#L453

Nobody raised the issue so far with alchemy, which is why I refrained
from turning the autoclear mode on by default so far. This is debatable,
since no documentation explains the limitation on usage caused by not
having the autoclear mode set.

-- 
Philippe.