Re: [Xenomai-help] Interprocess Mutex

[Philippe Gerum <rpm@xenomai.org>]

Adrian Boeing wrote:
> Hi Gilles, thanks for the reply.
> 
> In my test (pseudo) code with rt_mutex:
> (without bind):
> int main() {

   err = rt_task_shadow(...);

>  err = rt_mutex_create(&mutex_desc,0);
>  err =  rt_mutex_acquire(&mutex_desc,TM_INFINITE); //fails with -1!
> }
> (with bind):
> int main() {


   err = rt_task_shadow(...);

>  err = rt_mutex_create(&Kmutex_desc,"bob");
>  err = rt_mutex_bind(&mutex_desc,"bob",TM_INFINITE);
>  err =  rt_mutex_acquire(&mutex_desc,TM_INFINITE); //fails with -1!
> }
> 
> Both of these fail to acquire the mutex with "EPERM" :: (this service
> was called from a context which cannot be given the ownership of the mutex).
> 
> Is there something special I need to do in order to do this in user space?
>

Those Xenomai syscalls are only available to Xenomai threads; rt_task_shadow()
turns a regular Linux pthread into a Xenomai-enabled RT thread. rt_task_shadow()
has to be called once when you don't want to spawn a new RT task using the
rt_task_create() interface, but promote the current Linux pthread to the Xenomai
real-time domain. In short, it associates a Xenomai task control block to the
underlying Linux task, so that both Xenomai and Linux schedulers can handle it.

> Thanks,
> -Adrian
> 
> On Thu, Nov 20, 2008 at 9:48 PM, Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org
> <mailto:gilles.chanteperdrix@xenomai.org>> wrote:
> 
> 
>     Adrian Boeing wrote:
>     > Hi,
>     >
>     > Is it possible to create an inter-process mutex between kernel
>     space and
>     > user space?
>     > If so, how is this done with the native API?
>     >
>     > The system has one real-time kernel process which communicates
>     with other
>     > processes via shared memory.
> 
>     See rt_mutex_bind:
>     http://www.xenomai.org/documentation/branches/v2.4.x/html/api/group__mutex.html#g39b3a0e7f6f6ee41b8068ed59e25d1d1
>     or, for the posix skin, pthread_mutexattr_setpshared:
>     http://www.xenomai.org/documentation/branches/v2.4.x/html/api/group__posix__mutex.html#g73bd8697b91e0ee9a63c30052ac9f72f
>     Note that for sharing a mutex with the posix skin, the pthread_mutex_t
>     structure needs to reside on a shared memory.
> 
>     --
>                        Gilles.
> 
> 
> 
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-- 
Philippe.