On 08/26/2011 08:19 PM, Jan Kiszka wrote:
> On 2011-08-26 20:07, Gilles Chanteperdrix wrote:
>> On 08/26/2011 03:05 PM, Jan Kiszka wrote:
>>> On 2011-08-26 14:34, Gilles Chanteperdrix wrote:
>>>> Hi,
>>>> I think it is about time we release Xenomai 2.6.0. Has anyone anything
>>>> pending (maybe Alex)? Should we release an -rc first?
>>> No patches ATM, but [1] is still an open bug - a bug that affects the ABI.
>>> Jan
>>> [1] http://thread.gmane.org/gmane.linux.real-time.xenomai.devel/8343
>> I had forgotten about this one. So, the only real problem is if a
>> SCHED_NOTOTHER thread switches to SCHED_OTHER, this appears to be a
>> corner case, so, I wonder if you should not simply add a special
>> treatment, only for this corner case.
>> What I have in mind is keeping a list of xnsynch in kernel-space (this
>> basically means having an xnholder_t more in the xnsynch structure), and
>> when we trip the corner case (thread with SCHED_FIFO switches to
>> SCHED_OTHER), walk the list to find how many xnsynch the thread is the
>> owner, we have that info in kernel-space, and set the refcnt accordingly.
>> Or does it still sound overkill?
> Mmh, need to think about it. Yeah, we do not support
> PTHREAD_MUTEX_INITIALIZER, so we do not share that part of the problem
> with futexes.

Actually, we could implement PTHREAD_MUTEX_INITIALIZER: when the magic
is wrong, just issue a pthread_mutex_init syscall, and try locking
again. But the problem is that this particular call to
pthread_mutex_lock would be much heavier than locking an initialized
mutex for reasons which are not obvious (besides, we would have to
handle concurrency by some way, like having a pthread_once_t in
pthread_mutex_t). I find not having PTHREAD_MUTEX_INITIALIZER more
clear, even if this makes us not really posix compliant.

> If we have all objects and can explore ownership, we can also implement
> robust mutexes this way, i.e. waiter signaling when the owner dies.
> Jan


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