[Insight-users] Re: Insight-users Digest, Vol 43, Issue 7

[Gaëtan Lehmann]

Hi Julia,


Le 5 nov. 07 à 21:07, Julia Smith a écrit :

> 3.4.0
> I haven't built it yet, but did take a look at itkLightObject. Now   
> UnRegister does correct multi-threading thing of _not_  referencing  
> a volatile value outside a semaphore, SetRegister() should do the  
> same thing. It's just not thread safe to check values modifiable by  
> another context. A race condition persists if one thread sets a  
> reference count to zero and another decrements it to zero, both may  
> attempt to delete the same piece of memory. A true pain to debug.

You're right, we can still have a race condition. The following  
version of SetReferenceCount() should do the correct job:

void
LightObject
::SetReferenceCount(int ref)
{
   m_ReferenceCountLock.Lock();
   m_ReferenceCount = ref;
   m_ReferenceCountLock.Unlock();

   if ( ref <= 0) // <--- changes here
     {
     delete this;
     }
}

I'm rebuilding ITK with that change, and will commit it if all the  
test are OK.

However, contrary to UnRegister(), I think we are talking about an  
already highly dangerous method, which shouldn't be used excepted in  
a few (rare) cases.
Do you have seen that problem in java wrappers?

Thanks a lot for your efforts to fix that problem.

Gaëtan


>
> void
> LightObject
> ::UnRegister() const
> {
>   m_ReferenceCountLock.Lock();
>   int tmpReferenceCount = --m_ReferenceCount;
>   m_ReferenceCountLock.Unlock();
>
>   // ReferenceCount in now unlocked.  We may have a race condition
>   // to delete the object.
>   if ( tmpReferenceCount <= 0)
>     {
>     delete this;
>     }
> }
>
>
> void
> LightObject
> ::SetReferenceCount(int ref)
> {
>   m_ReferenceCountLock.Lock();
>   m_ReferenceCount = ref;
>   m_ReferenceCountLock.Unlock();
>
>   if ( m_ReferenceCount <= 0)
>     {
>     delete this;
>     }
> }
>
>
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org
> http://www.itk.org/mailman/listinfo/insight-users

--
Gaëtan Lehmann
Biologie du Développement et de la Reproduction
INRA de Jouy-en-Josas (France)
tel: +33 1 34 65 29 66    fax: 01 34 65 29 09
http://voxel.jouy.inra.fr



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