BUG: fixed concurrant writes to an ivar found by Thread Sanitizer

Multiple threads call this method which all write to this->m_ANTSAssociate simultaneously. At least they are writing the same thing, but it's still undefined behaviour without any mutex or similar protection. Used std::call_once to ensure only one writer actually writes.

Modules/Registration/Metricsv4/include/itkANTSNeighborhoodCorrelationImageToImageMetricv4GetValueAndDerivativeThreader.h

@@ -24,6 +24,7 @@
 #include "itkConstNeighborhoodIterator.h"
 
 #include <deque>
+#include <mutex>
 
 namespace itk
 {
@@ -299,6 +300,7 @@ class ITK_TEMPLATE_EXPORT ANTSNeighborhoodCorrelationImageToImageMetricv4GetValu
   /** Internal pointer to the metric object in use by this threader.
    *  This will avoid costly dynamic casting in tight loops. */
   TNeighborhoodCorrelationMetric * m_ANTSAssociate;
+  std::once_flag                   m_ANTSAssociateOnceFlag;
 };
 
 

Modules/Registration/Metricsv4/include/itkANTSNeighborhoodCorrelationImageToImageMetricv4GetValueAndDerivativeThreader.hxx

@@ -33,12 +33,14 @@ ANTSNeighborhoodCorrelationImageToImageMetricv4GetValueAndDerivativeThreader<TDo
     const ThreadIdType                                                                         threadId)
 {
   /* Store the casted pointer to avoid dynamic casting in tight loops. */
-  this->m_ANTSAssociate = dynamic_cast<TNeighborhoodCorrelationMetric *>(this->m_Associate);
-  if (this->m_ANTSAssociate == nullptr)
+  auto associate = dynamic_cast<TNeighborhoodCorrelationMetric *>(this->m_Associate);
+  if (associate == nullptr)
   {
     itkExceptionMacro("Dynamic casting of associate pointer failed.");
   }
 
+  std::call_once(this->m_ANTSAssociateOnceFlag, [this, &associate]() { this->m_ANTSAssociate = associate; });
+
   VirtualPointType   virtualPoint;
   MeasureType        metricValueResult = NumericTraits<MeasureType>::ZeroValue();
   MeasureType        metricValueSum = NumericTraits<MeasureType>::ZeroValue();
@@ -50,15 +52,15 @@ ANTSNeighborhoodCorrelationImageToImageMetricv4GetValueAndDerivativeThreader<TDo
   DerivativeType & localDerivativeResult = this->m_GetValueAndDerivativePerThreadVariables[threadId].LocalDerivatives;
 
   /* Create an iterator over the virtual sub region */
-  // this->m_ANTSAssociate->InitializeScanning( virtualImageSubRegion, scanIt, scanMem, scanParameters );
+  // associate->InitializeScanning( virtualImageSubRegion, scanIt, scanMem, scanParameters );
   this->InitializeScanning(virtualImageSubRegion, scanIt, scanMem, scanParameters);
 
   /* Iterate over the sub region */
   scanIt.GoToBegin();
   while (!scanIt.IsAtEnd())
   {
     /* Get the virtual point */
-    this->m_ANTSAssociate->TransformVirtualIndexToPhysicalPoint(scanIt.GetIndex(), virtualPoint);
+    associate->TransformVirtualIndexToPhysicalPoint(scanIt.GetIndex(), virtualPoint);
 
     /* Call the user method in derived classes to do the specific
      * calculations for value and derivative. */