From a93ca65723ca734e851f775d8b04f616f9492c54 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?D=C5=BEenan=20Zuki=C4=87?= <dzenan.zukic@kitware.com>
Date: Fri, 20 Jul 2018 17:57:24 -0400
Subject: [PATCH] ENH: emit a useful error message with small threaded regions

---
 include/itkRecursiveLineYvvGaussianImageFilter.hxx | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/itkRecursiveLineYvvGaussianImageFilter.hxx b/include/itkRecursiveLineYvvGaussianImageFilter.hxx
index 9892a3f..6a37d86 100644
--- a/include/itkRecursiveLineYvvGaussianImageFilter.hxx
+++ b/include/itkRecursiveLineYvvGaussianImageFilter.hxx
@@ -331,6 +331,14 @@ RecursiveLineYvvGaussianImageFilter< TInputImage, TOutputImage >
 
   const unsigned int ln = region.GetSize()[this->m_Direction];
 
+  if ( ln < 4 )
+    {
+    itkExceptionMacro( "The number of pixels along direction "
+      << this->m_Direction
+      << " in this work-unit image region is less than 4."
+      << " Note: TBBMultiThreader can divide small regions into really small pieces.");
+    }
+
   RealType *inps = nullptr;
   RealType *outs = nullptr;
   RealType *scratch = nullptr;