ENH: Add backwards compatibility for Get/SetNumberOfThreads

SetNumberOfThreads() should be called on
processObject->GetMultiThreader()->SetMaximumNumberOfThreads().
But processObject->SetNumberOfWorkUnits() is usually desired now.

Change-Id: I20d95b343765dbdb4472d07a3eb5b7f2458800b5

Documentation/ITK5MigrationGuide.md

@@ -138,7 +138,9 @@ this->AfterThreadedGenerateData();
 
 Get/Set GlobalMaximumNumberOfThreads and GlobalDefaultNumberOfThreads
 now reside in `MultiThreaderBase`. With a warning, they are still
-available in `PlatformMultiThreader`.
+available in `PlatformMultiThreader`. The common case of
+`innerFilter->SetNumberOfThreads(1);` should be replaced by
+`innerFilter->SetNumberOfWorkUnits(1);`.
 
 To transition to the new threading model, it is usually enough to rename
 `ThreadedGenerateData` into `DynamicThreadedGenerateData`, remove the

Modules/Core/Common/include/itkProcessObject.h

@@ -443,6 +443,18 @@ class ITKCommon_EXPORT ProcessObject:public Object
   itkSetClampMacro(NumberOfWorkUnits, ThreadIdType, 1, ITK_MAX_THREADS);
   itkGetConstReferenceMacro(NumberOfWorkUnits, ThreadIdType);
 
+#if !defined( ITK_LEGACY_REMOVE ) || defined( ITKV4_COMPATIBILITY )
+  itkLegacyMacro(void SetNumberOfThreads(ThreadIdType count))
+  {
+    this->SetNumberOfWorkUnits(count);
+  }
+
+  itkLegacyMacro(ThreadIdType GetNumberOfThreads() const)
+  {
+    return this->GetNumberOfWorkUnits();
+  }
+#endif // !ITK_LEGACY_REMOVE
+
   /** Return the multithreader used by this class. */
   MultiThreaderType * GetMultiThreader() const
   { return m_MultiThreader; }

Modules/Numerics/Optimizersv4/include/itkObjectToObjectOptimizerBase.h

@@ -182,12 +182,26 @@ class ITK_TEMPLATE_EXPORT ObjectToObjectOptimizerBaseTemplate : public Object
   itkGetConstReferenceMacro(DoEstimateScales, bool);
   itkBooleanMacro(DoEstimateScales);
 
-  /** Set the number of threads to use when threading.
-   * The default is the global default number of threads
-   * returned from itkMultiThreader. */
+  /** Set the number of work units to use when threading.
+   * The default is the global default number of work units
+   * decided in the constructor of the MultiThreader. */
   virtual void SetNumberOfWorkUnits( ThreadIdType number );
 
-  /** Get the number of threads set to be used. */
+#if !defined( ITK_LEGACY_REMOVE )
+  /** Set the number of work units to use when threading.
+   *
+   * NOTE: deprecated. Use SetNumberOfWorkUnits() */
+  itkLegacyMacro( virtual void SetNumberOfThreads( ThreadIdType number ) )
+  {
+    return this->SetNumberOfWorkUnits( number );
+  }
+  itkLegacyMacro( virtual const ThreadIdType& GetNumberOfThreads() const )
+  {
+    return this->m_NumberOfWorkUnits;
+  }
+#endif // !ITK_LEGACY_REMOVE
+
+  /** Get the number of work units set to be used. */
   itkGetConstReferenceMacro( NumberOfWorkUnits, ThreadIdType );
 
   /** Return current number of iterations. */

Modules/Registration/Metricsv4/include/itkImageToImageMetricv4.h

@@ -457,6 +457,34 @@ class ITK_TEMPLATE_EXPORT ImageToImageMetricv4
   virtual void SetMaximumNumberOfWorkUnits( const ThreadIdType workUnits );
   virtual ThreadIdType GetMaximumNumberOfWorkUnits() const;
 
+#if !defined ( ITK_LEGACY_REMOVE )
+  /** Get number of threads to used in the the most recent
+   * evaluation.  Only valid after GetValueAndDerivative() or
+   * GetValue() has been called.
+   *
+   * NOTE: deprecated. Use GetNumberOfWorkUnitsUsed() */
+  itkLegacyMacro( virtual ThreadIdType GetNumberOfThreadsUsed() const )
+  {
+    return this->GetNumberOfWorkUnitsUsed();
+  }
+
+  /** Set number of threads to use. This the maximum number of threads to use
+   * when multithreaded.  The actual number of threads used (may be less than
+   * this value) can be obtained with \c GetNumberOfWorkUnitsUsed.
+   *
+   * NOTE: deprecated. Use SetMaximumNumberOfWorkUnits() and
+   * GetMaximumNumberOfWorkUnits() */
+  itkLegacyMacro( virtual void SetMaximumNumberOfThreads( const ThreadIdType count ) )
+  {
+    this->SetMaximumNumberOfWorkUnits(count);
+  }
+  itkLegacyMacro( virtual ThreadIdType GetMaximumNumberOfThreads() const )
+  {
+    return this->GetMaximumNumberOfWorkUnits();
+  }
+#endif // !ITK_LEGACY_REMOVE
+
+
   /**
     * Finalize the per-thread components for computing
     * metric.  Some threads can accumulate their data