Re: [Xenomai-core] [PATCH 2/9] Switch to handle-based fast mutex owners

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> Jan Kiszka wrote:
>>> To improve robustness of the fast mutex implementation in POSIX (and
>>> later on in native), it is better to track the mutex owner by handle
>>> instead of kernel object pointer. Therefore, this patch changes
>>> __xn_sys_current (xeno_set_current) so that it returns
>>> xnthread_handle(current_thread). It furthermore converts the POSIX mutex
>>> implementation to pick up and store the lock owner as handle in the
>>> kernel/user-shared mutex. Finally it ensures that all skins (except for
>>> RTDM which must not mess around with foreign skins anyway) add their
>>> threads to the registry so that at least anonymous handles are
>>> available.
>>>
>>> As the value stored in the mutex variable is now an integer, we can
>>> switch over to xnarch_atomic_t, removing all atomic_intptr users.
>> The current implementation allows RTDM threads to use POSIX skin
>> mutexes. I do not see why this should change.
> 
> Such mixup might technically be possible now. But there is neither a
> need nor does it make the resulting driver more portable. I don't want
> to introduce needless thread registration to RTDM just to cover
> theoretical use cases that should not exist in the first place.
> 
> Nevertheless, some sanity check will have to be added to the
> to-be-written generic xnsynch support to catch missing thread handles.
> That make sense for checking future skin implementation as well.

That is overhead in the hot path, whereas adding the thread registration
takes place in a non hot path.

-- 
                                                 Gilles.