ENH: Make ElastixMain database creation + loading components thread safe

Common/GTesting/CMakeLists.txt

@@ -1,5 +1,6 @@
 add_executable(CommonGTest
   elxBaseComponentGTest.cxx
+  elxElastixMainGTest.cxx
   elxTransformIOGTest.cxx
   itkComputeImageExtremaFilterGTest.cxx
   )

Common/GTesting/elxElastixMainGTest.cxx

@@ -0,0 +1,45 @@
+/*=========================================================================
+ *
+ *  Copyright UMC Utrecht and contributors
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *        http://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// First include the header file to be tested:
+#include "elxElastixMain.h"
+
+#include <gtest/gtest.h>
+
+
+// Tests retrieving the component data base and a component creator in parallel.
+GTEST_TEST(ElastixMain, GetComponentDatabaseAndCreatorInParallel)
+{
+  const elx::xoutManager manager("", false, false);
+
+#pragma omp parallel for
+  for (auto i = 0; i <= 9; ++i)
+  {
+    const auto creator = elx::ElastixMain::GetComponentDatabase().GetCreator("Elastix", 1);
+    EXPECT_NE(creator, nullptr);
+    EXPECT_NE(creator, elx::ComponentDatabase::PtrToCreator{});
+
+    if (creator != nullptr)
+    {
+      const auto elxComponent = creator();
+      EXPECT_NE(elxComponent, nullptr);
+      EXPECT_NE(elxComponent, itk::Object::Pointer{});
+      EXPECT_NE(dynamic_cast<elx::ElastixBase *>(elxComponent.GetPointer()), nullptr);
+    }
+  }
+}

Components/Transforms/WeightedCombinationTransform/elxWeightedCombinationTransform.hxx

@@ -280,8 +280,7 @@ WeightedCombinationTransformElastix<TElastix>::LoadSubTransforms(void)
     /** Create a SubTransform. */
     typename ObjectType::Pointer subTransform;
     PtrToCreator                 testcreator = nullptr;
-    testcreator =
-      this->GetElastix()->GetComponentDatabase()->GetCreator(subTransformName, this->m_Elastix->GetDBIndex());
+    testcreator = ElastixMain::GetComponentDatabase().GetCreator(subTransformName, this->m_Elastix->GetDBIndex());
 
     // Note that ObjectType::Pointer() yields a default-constructed SmartPointer (null).
     subTransform = testcreator ? testcreator() : typename ObjectType::Pointer();

Core/ComponentBaseClasses/elxTransformBase.hxx

@@ -19,6 +19,7 @@
 #define elxTransformBase_hxx
 
 #include "elxTransformBase.h"
+#include "elxElastixMain.h"
 #include "elxTransformIO.h"
 
 #include "itkPointSet.h"
@@ -548,7 +549,7 @@ TransformBase<TElastix>::ReadInitialTransformFromConfiguration(
 
   /** Create an InitialTransform. */
   const PtrToCreator testcreator =
-    this->GetElastix()->GetComponentDatabase()->GetCreator(initialTransformName, this->m_Elastix->GetDBIndex());
+    ElastixMain::GetComponentDatabase().GetCreator(initialTransformName, this->m_Elastix->GetDBIndex());
   const ObjectType::Pointer initialTransform = (testcreator == nullptr) ? nullptr : testcreator();
 
   const auto elx_initialTransform = dynamic_cast<Self *>(initialTransform.GetPointer());

Core/Install/elxComponentLoader.cxx

@@ -87,10 +87,7 @@ ComponentLoader::ComponentLoader()
  * ****************** Destructor *********************************
  */
 
-ComponentLoader::~ComponentLoader()
-{
-  this->UnloadComponents();
-}
+ComponentLoader::~ComponentLoader() = default;
 
 
 /**
@@ -160,22 +157,4 @@ ComponentLoader::LoadComponents(void)
 
 } // end LoadComponents
 
-
-/**
- * ****************** UnloadComponents ****************************
- */
-
-void
-ComponentLoader::UnloadComponents()
-{
-  /**
-   * This function used to be more useful when we still used .dll's.
-   */
-
-  // Not necessary I think:
-  // this->m_ComponentDatabase = 0;
-
-} // end UnloadComponents
-
-
 } // end namespace elastix

Core/Install/elxComponentLoader.h

@@ -63,10 +63,6 @@ class ComponentLoader : public itk::Object
   int
   LoadComponents(void);
 
-  /** Function to unload components. */
-  void
-  UnloadComponents(void);
-
 protected:
   /** Standard constructor and destructor. */
   ComponentLoader();

Core/Kernel/elxElastixBase.cxx

@@ -132,7 +132,6 @@ ElastixBase::ElastixBase()
 {
   /** Initialize. */
   this->m_Configuration = nullptr;
-  this->m_ComponentDatabase = nullptr;
   this->m_DBIndex = 0;
 
   /** The default output precision of elxout is set to 6. */

Core/Kernel/elxElastixBase.h

@@ -198,14 +198,6 @@ class ElastixBase
     return this->m_DBIndex;
   }
 
-
-  /** Functions to get/set the ComponentDatabase
-   * The component database contains pointers to functions
-   * that create components.
-   */
-  elxGetObjectMacro(ComponentDatabase, ComponentDatabaseType);
-  elxSetObjectMacro(ComponentDatabase, ComponentDatabaseType);
-
   /** Get the component containers.
    * The component containers store components, such as
    * the metric, in the form of an itk::Object::Pointer.
@@ -397,9 +389,8 @@ class ElastixBase
   ElastixBase();
   ~ElastixBase() override = default;
 
-  ConfigurationPointer     m_Configuration;
-  DBIndexType              m_DBIndex;
-  ComponentDatabasePointer m_ComponentDatabase;
+  ConfigurationPointer m_Configuration;
+  DBIndexType          m_DBIndex;
 
   FlatDirectionCosinesType m_OriginalFixedImageDirection;
 

Core/Kernel/elxElastixMain.cxx

@@ -25,6 +25,7 @@
 #endif
 
 #include "elxElastixMain.h"
+#include "elxComponentLoader.h"
 
 #include "elxMacro.h"
 #include "itkPlatformMultiThreader.h"
@@ -182,12 +183,27 @@ ElastixMain::ElastixMain()
 
 
 /**
- * ****************** Initialization of static members *********
+ * ****************** GetComponentDatabase *********
  */
 
-// Both s_CDB and s_ComponentLoader are defaulted-constructed to null.
-ElastixMain::ComponentDatabasePointer ElastixMain::s_CDB;
-ElastixMain::ComponentLoaderPointer   ElastixMain::s_ComponentLoader;
+const ComponentDatabase &
+ElastixMain::GetComponentDatabase(void)
+{
+  // Improved thread-safety by using C++11 "magic statics".
+  static const auto componentDatabase = [] {
+    const auto componentDatabase = ComponentDatabase::New();
+    const auto componentLoader = ComponentLoader::New();
+    componentLoader->SetComponentDatabase(componentDatabase);
+
+    if (componentLoader->LoadComponents() != 0)
+    {
+      xout["error"] << "Loading components failed" << std::endl;
+    }
+    return componentDatabase;
+  }();
+  return *componentDatabase;
+}
+
 
 /**
  * ********************** Destructor ****************************
@@ -338,7 +354,6 @@ ElastixMain::Run(void)
 
   /** Set some information in the ElastixBase. */
   this->GetElastixBase()->SetConfiguration(this->m_Configuration);
-  this->GetElastixBase()->SetComponentDatabase(this->s_CDB);
   this->GetElastixBase()->SetDBIndex(this->m_DBIndex);
 
   /** Populate the component containers. ImageSampler is not mandatory.
@@ -635,32 +650,18 @@ ElastixMain::InitDBIndex(void)
       }
     }
 
-    /** Load the components. */
-    if (this->s_CDB.IsNull())
+    /** Get the DBIndex from the ComponentDatabase. */
+    this->m_DBIndex = GetComponentDatabase().GetIndex(this->m_FixedImagePixelType,
+                                                      this->m_FixedImageDimension,
+                                                      this->m_MovingImagePixelType,
+                                                      this->m_MovingImageDimension);
+    if (this->m_DBIndex == 0)
     {
-      int loadReturnCode = this->LoadComponents();
-      if (loadReturnCode != 0)
-      {
-        xout["error"] << "Loading components failed" << std::endl;
-        return loadReturnCode;
-      }
+      xout["error"] << "ERROR:" << std::endl;
+      xout["error"] << "Something went wrong in the ComponentDatabase" << std::endl;
+      return 1;
     }
 
-    if (this->s_CDB.IsNotNull())
-    {
-      /** Get the DBIndex from the ComponentDatabase. */
-      this->m_DBIndex = this->s_CDB->GetIndex(this->m_FixedImagePixelType,
-                                              this->m_FixedImageDimension,
-                                              this->m_MovingImagePixelType,
-                                              this->m_MovingImageDimension);
-      if (this->m_DBIndex == 0)
-      {
-        xout["error"] << "ERROR:" << std::endl;
-        xout["error"] << "Something went wrong in the ComponentDatabase" << std::endl;
-        return 1;
-      }
-    } // end if s_CDB!=0
-
   } // end if m_Configuration->Initialized();
   else
   {
@@ -727,55 +728,6 @@ ElastixMain::GetTotalNumberOfElastixLevels(void)
 } // end GetTotalNumberOfElastixLevels()
 
 
-/**
- * ********************* LoadComponents **************************
- *
- * Store the install function of each component in the
- * component database.
- */
-
-int
-ElastixMain::LoadComponents(void)
-{
-  /** Create a ComponentDatabase. */
-  if (this->s_CDB.IsNull())
-  {
-    this->s_CDB = ComponentDatabaseType::New();
-  }
-
-  /** Create a ComponentLoader and set the database. */
-  if (this->s_ComponentLoader.IsNull())
-  {
-    this->s_ComponentLoader = ComponentLoaderType::New();
-    this->s_ComponentLoader->SetComponentDatabase(s_CDB);
-  }
-
-  /** Load the components. */
-  return this->s_ComponentLoader->LoadComponents();
-
-} // end LoadComponents()
-
-
-/**
- * ********************* UnloadComponents **************************
- */
-
-void
-ElastixMain::UnloadComponents(void)
-{
-  s_CDB = nullptr;
-  s_ComponentLoader->SetComponentDatabase(nullptr);
-
-  if (s_ComponentLoader)
-  {
-    s_ComponentLoader->UnloadComponents();
-  }
-
-  s_ComponentLoader = nullptr;
-
-} // end UnloadComponents()
-
-
 /**
  * ************************* GetElastixBase ***************************
  */
@@ -806,7 +758,7 @@ ElastixMain::CreateComponent(const ComponentDescriptionType & name)
 {
   /** A pointer to the New() function. */
   PtrToCreator testcreator = nullptr;
-  testcreator = this->s_CDB->GetCreator(name, this->m_DBIndex);
+  testcreator = GetComponentDatabase().GetCreator(name, this->m_DBIndex);
 
   // Note that ObjectPointer() yields a default-constructed SmartPointer (null).
   ObjectPointer testpointer = testcreator ? testcreator() : ObjectPointer();

Core/Kernel/elxElastixMain.h

@@ -19,7 +19,6 @@
 #define elxElastixMain_h
 
 #include "elxComponentDatabase.h"
-#include "elxComponentLoader.h"
 
 #include "elxElastixBase.h"
 #include "itkParameterMapInterface.h"
@@ -169,10 +168,6 @@ class ElastixMain : public itk::Object
   typedef ComponentDatabaseType::ImageDimensionType       ImageDimensionType;
   typedef ComponentDatabaseType::IndexType                DBIndexType;
 
-  /** Typedef for class that populates a ComponentDatabase. */
-  typedef ComponentLoader              ComponentLoaderType;
-  typedef ComponentLoaderType::Pointer ComponentLoaderPointer;
-
   /** Typedef that is used in the elastix dll version. */
   typedef itk::ParameterMapInterface::ParameterMapType ParameterMapType;
 
@@ -315,31 +310,14 @@ class ElastixMain : public itk::Object
   virtual void
   SetMaximumNumberOfThreads(void) const;
 
-  /** Functions to get/set the ComponentDatabase. */
-  static ComponentDatabase *
-  GetComponentDatabase(void)
-  {
-    return s_CDB.GetPointer();
-  }
-
-
-  static void
-  SetComponentDatabase(ComponentDatabase * arg)
-  {
-    if (s_CDB != arg)
-    {
-      s_CDB = arg;
-    }
-  }
-
+  /** Function to get the ComponentDatabase. */
+  static const ComponentDatabase &
+  GetComponentDatabase(void);
 
   /** GetTransformParametersMap */
   virtual ParameterMapType
   GetTransformParametersMap(void) const;
 
-  static void
-  UnloadComponents(void);
-
 protected:
   ElastixMain();
   ~ElastixMain() override;
@@ -383,11 +361,6 @@ class ElastixMain : public itk::Object
 
   FlatDirectionCosinesType m_OriginalFixedImageDirection;
 
-  static ComponentDatabasePointer s_CDB;
-  static ComponentLoaderPointer   s_ComponentLoader;
-  virtual int
-  LoadComponents(void);
-
   /** InitDBIndex sets m_DBIndex by asking the ImageTypes
    * from the Configuration object and obtaining the corresponding
    * DB index from the ComponentDatabase.