Re: [Xenomai-help] mutex locking

[Jan Kiszka <jan.kiszka@domain.hid>]

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Tobias Bär wrote:
> Hi all,
> 
> my question is about the right way to lock and inquire a mutex. At time, my code looks like this:
> 
> 
> rt_mutex_inquire(&mutex,TM_NONBLOCK);
> 
> if(info.lockcnt == 0) 
> {
>       rt_mutex_lock(&write_mutex,TM_NONBLOCK);
> 
>       // do sth.
> 
>       rt_mutex_unlock(&mutex);
> }
> 
> 
> What happens if anyone locks the mutex between my "rt_mutex_inquire(...)" and my "if(info.lockcnt == 0)" ?
> 
> Is this the standard way to lock and inquire a mutex?
> 

Try this, it's safe from such races:

/* returns -EWOULDBLOCK if the mutex is locked */
if (rt_mutex_lock(&write_mutex,TM_NONBLOCK) == 0)
{
      // do sth.

      rt_mutex_unlock(&mutex);
}

Jan


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