ENH: Use get_schedaffin to determine number of threads

Modules/Core/Common/CMake/itkCheckHasSchedGetAffinity.cxx

@@ -0,0 +1,31 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  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
+ *
+ *         https://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.
+ *
+ *=========================================================================*/
+
+#include <sched.h>
+
+int
+main(void)
+{
+
+  cpu_set_t mask;
+
+  sched_getaffinity(0, sizeof(cpu_set_t), &mask);
+  CPU_COUNT(&mask);
+
+  return 0;
+}

Modules/Core/Common/CMakeLists.txt

@@ -101,6 +101,10 @@ try_compile(
   ${CMAKE_CURRENT_SOURCE_DIR}/CMake/itkCheckHasFenvtStructMember.cxx
   COMPILE_DEFINITIONS -DITK_CHECK_FENV_T_CW)
 
+try_compile(
+        ITK_HAS_SCHED_GETAFFINITY ${ITK_BINARY_DIR}
+        ${CMAKE_CURRENT_SOURCE_DIR}/CMake/itkCheckHasSchedGetAffinity.cxx)
+
 #-----------------------------------------------------------------------------
 # Make default visibility as an option for generated export header
 

Modules/Core/Common/src/itkConfigure.h.in

@@ -190,4 +190,6 @@
 #  endif
 #endif
 
+#cmakedefine ITK_HAS_SCHED_GETAFFINITY
+
 #endif //itkConfigure_h

Modules/Core/Common/src/itkMultiThreaderBase.cxx

@@ -46,6 +46,10 @@
 #include <cctype>
 #include <utility> // For move.
 
+#if defined(ITK_HAS_SCHED_GETAFFINITY)
+#  include <sched.h>
+#endif
+
 #if defined(ITK_USE_TBB)
 #  include "itkTBBMultiThreader.h"
 #endif
@@ -334,15 +338,23 @@ MultiThreaderBase::GetGlobalDefaultNumberOfThreads()
 ThreadIdType
 MultiThreaderBase::GetGlobalDefaultNumberOfThreadsByPlatform()
 {
+#if defined(ITK_HAS_SCHED_GETAFFINITY)
+  cpu_set_t mask;
+  if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) != -1)
+  {
+    return static_cast<ThreadIdType>(CPU_COUNT(&mask));
+  }
+#endif
+
 #if defined(ITK_LEGACY_REMOVE)
   return std::thread::hardware_concurrency();
 #endif
 
 #if defined(ITK_USE_PTHREADS)
   ThreadIdType num;
 
-  // Default the number of threads to be the number of available
-  // processors if we are using pthreads()
+// Default the number of threads to be the number of available
+// processors if we are using pthreads()
 #  ifdef _SC_NPROCESSORS_ONLN
   num = static_cast<ThreadIdType>(sysconf(_SC_NPROCESSORS_ONLN));
 #  elif defined(_SC_NPROC_ONLN)
@@ -371,7 +383,7 @@ MultiThreaderBase::GetGlobalDefaultNumberOfThreadsByPlatform()
 #else
   return 1;
 #endif
-}
+} // namespace itk
 
 MultiThreaderBase::Pointer
 MultiThreaderBase::New()