Re: [Xenomai-core] Fwd: problem in pthread_mutex_lock/unlock

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

Gilles Chanteperdrix wrote:
> Nero Fernandez wrote:
>> On Fri, Jun 18, 2010 at 7:42 PM, Gilles Chanteperdrix
>> <gilles.chanteperdrix@xenomai.org
>> <mailto:gilles.chanteperdrix@xenomai.org>> wrote:
>>
>>     Nero Fernandez wrote:
>>     > Hi,
>>     >
>>     > Please find an archive attached, containing :
>>     >  - a program for testing context-switch-latency using posix-APIs
>>     >    for native linux kernel and xenomai-posix-skin (userspace).
>>     >  - Makefile to build it using xenomai
>>
>>     Your program is very long to tell fast. But it seems you are using the
>>     mutex as if they were recursive. Xenomai posix skin mutexes used to be
>>     recursive by default, but no longer are.
>>
>>     Also note that your code does not check the return value of the posix
>>     skin services, which is a really bad idea.
>>
>>     --
>>                                                Gilles.
>>
>>
>> Thanks for the prompt response.
>>
>> Could you explain  'recursive usage of mutex' a little further?
>> Are the xenomai pthread-mutexes very different in behaviour than regular
>> posix mutexes?
> 
> The posix specification does not define the default type of a mutex. So,
>  in short, the behaviour of a "regular posix mutex" is unspecified.
> However, following the principle of least surprise, Xenomai chose, like
> Linux, to use the "normal" type by default.
> 
> What is the type of a posix mutex is explained in many places, starting
> with Xenomai API documentation. So, no, I will not repeat it here.

Actually, that is not your problem. However, you do not check the return
value of posix services, which is a bad idea. And indeed, if you check
it you will find your error: a thread which does not own a mutex tries
to unlock it.

Sorry, mutex are not semaphore, this is invalid, and Xenomai returns an
error in such a case.

-- 
					    Gilles.