[Insight-developers] LightObject race condition fix

[Gaëtan Lehmann]

Hi,

Julia Smith has reported a weird race conditions some days ago,  
discovered while using java. I have patched the LightObject's code to  
avoid it, while changing as less as possible the code to avoid  
involuntary breakage.


Index: Code/Common/itkLightObject.cxx
===================================================================
RCS file: /cvsroot/Insight/Insight/Code/Common/itkLightObject.cxx,v
retrieving revision 1.34
diff -u -r1.34 itkLightObject.cxx
--- Code/Common/itkLightObject.cxx      4 Apr 2007 20:04:10  
-0000       1.34
+++ Code/Common/itkLightObject.cxx      10 Jul 2007 18:41:08 -0000
@@ -150,12 +150,12 @@
::UnRegister() const
{
    m_ReferenceCountLock.Lock();
-  m_ReferenceCount--;
+  int tmpReferenceCount = --m_ReferenceCount;
    m_ReferenceCountLock.Unlock();

    // ReferenceCount in now unlocked.  We may have a race condition
    // to delete the object.
-  if ( m_ReferenceCount <= 0)
+  if ( tmpReferenceCount <= 0)
      {
      delete this;
      }
Index: Code/Common/itkLightObject.h
===================================================================
RCS file: /cvsroot/Insight/Insight/Code/Common/itkLightObject.h,v
retrieving revision 1.33
diff -u -r1.33 itkLightObject.h
--- Code/Common/itkLightObject.h        6 Feb 2006 22:01:56  
-0000       1.33
+++ Code/Common/itkLightObject.h        10 Jul 2007 18:41:08 -0000
@@ -114,7 +114,7 @@
    virtual void PrintTrailer(std::ostream& os, Indent indent) const;

    /** Number of uses of this object by other objects. */
-  mutable int m_ReferenceCount;
+  volatile mutable int m_ReferenceCount;
    /** Mutex lock to protect modification to the reference count */
    mutable SimpleFastMutexLock m_ReferenceCountLock;


All the tests are OK.
If no one disagree, I'd like to put the changes in the repository.

Julia has proposed more changes to unsure nothing bad can be done,  
like attempting to delete an object twice.
I think they should be reviewed and (hopefully) adopted at the  
beginning of the next release cycle.

Gaëtan


--
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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