Subj : Re: Shared Mutex Ownership
To   : comp.programming.threads
From : Sebastien Decugis
Date : Wed Jan 05 2005 04:41 am

zeddicus76 wrote:

>I have an app that uses shared memory alongside other apps.  I create
>mutexes with the pthread_mutexattr_setpshared(, &attr,
>PTHREAD_PROCESS_SHARED) attribute.
>
>If the owner of the mutex dies (seg fault in this instance), my other
>app can not lock that mutex.  Is there anyway to force ownership once
>an app that owns the mutex dies?
>
>What recovery options are available?  How do other people handle this
>case?
>Would there be a better method with the 2.6 kernel?
>  
>
Hi!

The feature you need is called "robust mutex". When a thread or process 
dies while holding a mutex, one of the waiter for that mutex is woken up 
and the call for pthread_mutex_lock returns an error code which tells 
that an owner died.

This feature is not (yet?) implemented in the standard glibc for 
GNU/Linux systems, but a project exists which implements this behavior 
on top of the NTPL. It indeeds imply deep changes in the libc and in the 
kernel (there are 2 different patchs to apply).

This project is located at http://developer.osdl.org/dev/robustmutexes/ 
and is very active.

I hope this helps...

-------------------------------
Sebastien DECUGIS
NPTL Test & Trace Project
http://nptl.bullopensouce.org/

.