From ddaffa10fa8ae07d05867a729c5de12008e3ffea Mon Sep 17 00:00:00 2001
From: Bradley Lowekamp <blowekamp@mail.nih.gov>
Date: Fri, 22 May 2026 17:04:36 +0000
Subject: [PATCH] BUG: Honor StopOptimization from IterationEvent in v4
 optimizers

Add an immediate m_Stop check after InvokeEvent(IterationEvent()) in
ExhaustiveOptimizerv4, PowellOptimizerv4, and
OnePlusOneEvolutionaryOptimizerv4. Previously these optimizers would
continue advancing after an observer called StopOptimization() (or
StopWalking()) during IterationEvent, making it impossible to halt
from a callback.

This is the companion change to cf929f2ca7 which added the same
pattern to the GradientDescentOptimizerv4 family. All v4 optimizers
now consistently stop before taking another step when Stop is
requested from an IterationEvent observer.
---
 .../Optimizersv4/include/itkExhaustiveOptimizerv4.hxx      | 4 ++++
 .../include/itkOnePlusOneEvolutionaryOptimizerv4.hxx       | 7 +++++++
 .../Numerics/Optimizersv4/include/itkPowellOptimizerv4.hxx | 6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/Modules/Numerics/Optimizersv4/include/itkExhaustiveOptimizerv4.hxx b/Modules/Numerics/Optimizersv4/include/itkExhaustiveOptimizerv4.hxx
index e7a1c84abce..3b1f32b3f0b 100644
--- a/Modules/Numerics/Optimizersv4/include/itkExhaustiveOptimizerv4.hxx
+++ b/Modules/Numerics/Optimizersv4/include/itkExhaustiveOptimizerv4.hxx
@@ -134,6 +134,10 @@ ExhaustiveOptimizerv4<TInternalComputationValueType>::ResumeWalking()
                                << "@ index " << this->GetCurrentIndex() << " value is " << m_CurrentValue;
 
     this->InvokeEvent(IterationEvent());
+    if (m_Stop)
+    {
+      break;
+    }
     this->AdvanceOneStep();
     this->m_CurrentIteration++;
   }
diff --git a/Modules/Numerics/Optimizersv4/include/itkOnePlusOneEvolutionaryOptimizerv4.hxx b/Modules/Numerics/Optimizersv4/include/itkOnePlusOneEvolutionaryOptimizerv4.hxx
index 7d464af752b..bc12b7e7951 100644
--- a/Modules/Numerics/Optimizersv4/include/itkOnePlusOneEvolutionaryOptimizerv4.hxx
+++ b/Modules/Numerics/Optimizersv4/include/itkOnePlusOneEvolutionaryOptimizerv4.hxx
@@ -257,6 +257,13 @@ OnePlusOneEvolutionaryOptimizerv4<TInternalComputationValueType>::StartOptimizat
     }
 
     this->InvokeEvent(IterationEvent());
+    if (m_Stop)
+    {
+      m_StopConditionDescription.str("");
+      m_StopConditionDescription << this->GetNameOfClass() << ": "
+                                 << "StopOptimization() called";
+      break;
+    }
     itkDebugMacro("Current position: " << this->GetCurrentPosition());
   }
   if (this->m_CurrentIteration >= m_MaximumIteration)
diff --git a/Modules/Numerics/Optimizersv4/include/itkPowellOptimizerv4.hxx b/Modules/Numerics/Optimizersv4/include/itkPowellOptimizerv4.hxx
index a511067cf84..9804b4be4ff 100644
--- a/Modules/Numerics/Optimizersv4/include/itkPowellOptimizerv4.hxx
+++ b/Modules/Numerics/Optimizersv4/include/itkPowellOptimizerv4.hxx
@@ -498,6 +498,12 @@ PowellOptimizerv4<TInternalComputationValueType>::StartOptimization(bool /* doOn
     }
 
     this->InvokeEvent(IterationEvent());
+    if (m_Stop)
+    {
+      m_StopConditionDescription << "StopOptimization() called";
+      this->InvokeEvent(EndEvent());
+      return;
+    }
   }
 
   m_StopConditionDescription << "Maximum number of iterations exceeded. "