Re: Breaking out of pthread_mutex_lock

[Darren Hart <dvhltc@us.ibm.com>]

On Thu, 2008-05-29 at 16:46 -0700, Stephen Hemminger wrote:
> On Thu, 29 May 2008 23:41:55 +0000
> Darren Hart <dvhltc@us.ibm.com> wrote:
> 
> > I find I need to be able to break out of the blocked state while waiting
> > to acquire a pthread_mutex.  I'm using PI mutexes and want to continue
> > to do so.  As I understand it, I can't use a signal to break out of the
> > lock as the man pages states:
> > 
> > "If a signal is delivered to a thread waiting for a mutex,  upon  return
> > from  the  signal handler the thread shall resume waiting for the mutex
> > as if it was not interrupted."
> > 
> > and that pthread_mutex_lock will not return EINTR.  I had considered
> > using cond variables, but I don't think they will provide the same PI
> > behavior (since the threads are not blocked on the mutex while awaiting
> > the pthread_cond_signal - right?).
> > 
> > I'm sure I'm not the first to want to do this, does anyone know of a
> > common best practice for accomplishing such a thing?
> > 
> 
> setjmp/longjmp?

Stephen,

Hrmm... I confess to not having made use of them before.  I read up a
bit, and don't see right off how they would help in this situation.  I
assume you're suggesting the longjmp be used in a signal handler while
the thread is blocked on the mutex - where would it jump to, and how
would I ensure the integrity of the pthread_mutex structure (which
thinks my thread is waiting for it) ?

-- 
Darren Hart
Real-Time Linux Team
IBM Linux Technology Center