Re: [Valgrind-users] valgrind pthreads mutex bug

[Igmar P. <mai...@jd...>]

On Fri, 29 May 2003, Jeremy Fitzhardinge wrote:

> They're already useless for that; I'm guessing you really want to be
> using condition variables, which have the behaviour you're looking for. 
> With any luck, they synchronization code is only in one or two places...

I don't agree, they're used to protect global variables from having 
multiple threads messing with then :

pthread_mutex_lock(&mutex);

for (....;...;...) {
	/* Walk linked list*/
        .....
}
pthread_mutex_unlock(&mutex);

This works fine, at least in my app with at least 5 threads running, not 
counting incoming connections.

I use rwlocks whenever I can, that means you must be able to read a 
datastructure without modifying it.
cond. variables are the way to go when it comes to thread synchronisation, 
I use them to process an application shutdown.

I've seen weird things happening when valgrind monitors threads, including 
the SIGFPE's flying around :). I'll see if I can reproduce it again, I 
know what happened when those things started.

> > > The bug is that Valgrind should flag this as an error.
> > 
> > The whole cinelerra (quite a huge program) is based upon this kind of
> > behaviour. It uses mutexes in order to synchronize 'data delivery':
> 
> That's exactly what a condvar is for.

Indeed. Mutexes can't be used for that.
 
> > So my question is... would it be possible for Valgrind to support this
> > bugous behaviour by some switch or something?
> 
> If you come up with a patch we can look at it.  But I think your time
> would be better spent fixing the code: what you're asking is equivalent
> to "but my program always uses memory after it has been freed, and it
> works fine without Valgrind".
> 
> > The problem is that cinelerra works just fine if it is run without
> > valgrind... 
> 
> Oh yes. Have you tried it with NPTL?

That requires kernel patching and a complete glibc rebuild :)

Just to wonder OT : Can both LinuxThreads and NTPL be build into the same 
glibc ??

> 
>     J



	Igmar