[Insight-developers] RE: itkParallelSparseFieldLevelSetImageFilterTest.

[Miller, James V (Research)]

Josh, 

Does a pthread semaphore provide an API to adjust the semaphore value 
by more than 1?  Some of these Win32 condition variable implementations
require incrementing the semaphore by more than 1.  I am trying to decide
whether to much the itkSemaphore class with this or just put in straight
Win32 code in the condition variable.

I tried (a port of) the boost condition variable and it also deadlocked.
I am going to try one of Schmidt's solutions now.

Jim



> -----Original Message-----
> From: Joshua Cates [mailto:cates at sci . utah . edu]
> Sent: Tuesday, August 26, 2003 12:49 PM
> To: Miller, James V (Research)
> Cc: Insight-Developers; Suyash P. Awate
> Subject: RE: itkParallelSparseFieldLevelSetImageFilterTest.
> 
> 
> Hi Jim,
> 
> Yes there is a well known race condition between the mutex 
> unlock and the
> wait on the semaphore.  Our implementation is supposed to avoid this
> condition (hard to explain in email just now...), but I agree 
> that it is
> suspicious because windows is the only platform that uses the code in
> question.  One of the many things that makes windows so 
> special is that it
> provides neither barrier class nor condition variable implementations.
> 
> I'm still having trouble, however, convincing myself that the barrier
> class could ever encounter this race condition.  But, as you 
> point out,
> this stuff is tricky.
> 
> I just found an interesting reference on implementing 
> condition variables
> on win32.  Have not had time yet to go through it, but looks 
> like it gives
> some concrete solutions and analysis of the windows problem:
> 
>  http://www . cs . wustl . edu/~schmidt/win32-cv-1 . html
> 
> Maybe we can simply choose one of these Schmidt-Pyarali 
> implementations
> for windows.  I'm stressed for time this week, but I can try 
> to look at it
> tonight or maybe tomorrow. Let me know what you think.
> 
> thanks,
> 
> Josh.
> 
> 
> ______________________________
>  Josh Cates			
>  Scientific Computing and Imaging Institute
>  University of Utah
>  Email: cates at sci . utah . edu
>  Phone: (801) 587-7697
>  URL:   http://www . sci . utah . edu/~cates
> 
> 
> On Tue, 26 Aug 2003, Miller, James V (Research) wrote:
> 
> > Josh,
> > 
> > I think the problem with the Barrier is in the condition 
> variable. I dug
> > around the net and found a lot of threads on the "incorrect ways of
> > implementing condition variables".  My conclusion is that 
> this is very
> > tricky.  My best guess right now is that the trouble spot is in
> > ConditionVariable::Wait().  From what I read on the net, if 
> the unlocking of
> > the external mutex and waiting on the semaphore are 
> performed as an atomic
> > operation, then another another thread can jump in between the
> > mutex.Unlock() and m_Semaphore.Down() calls.
> > 
> > There is a condition variable implementation in the boost 
> libraries.  I was
> > thinking of looking at that to see if the manner in which 
> they implemented
> > condition variables would work for ITK.  In the boost 
> implementation, then
> > keep an explicit queue of whose waiting (rather than using 
> the OS) for part
> > of the implementation.
> > 
> > Jim
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: Joshua Cates [mailto:cates at sci . utah . edu]
> > > Sent: Monday, August 25, 2003 6:29 PM
> > > To: Miller, James V (CRD)
> > > Cc: Insight-Developers; Suyash P. Awate
> > > Subject: itkParallelSparseFieldLevelSetImageFilterTest.
> > > 
> > > 
> > > Hi Jim,
> > > 
> > > We added some additional testing to itkBarrierTest.cxx and 
> > > managed to get
> > > failure (timeouts) on several Windows platforms.  Looks like 
> > > there is a
> > > bug somewhere in the Windows implementation.  I will try 
> to debug this
> > > locally on my Borland build.  In the meantime, I've removed 
> > > the offending
> > > code for itkBarrierTest so as not to slow down continuous builds.
> > > 
> > > Josh.
> > > 
> > > ______________________________
> > >  Josh Cates			
> > >  Scientific Computing and Imaging Institute
> > >  University of Utah
> > >  Email: cates at sci . utah . edu
> > >  Phone: (801) 587-7697
> > >  URL:   http://www . sci . utah . edu/~cates
> > > 
> > > 
> > 
>