Add module ProcessorCount.cmake (#11302)

Credit goes to David Cole ( http://www.kitware.com/blog/home/post/63 ).

Also add a script-based test of the new module.

Signed-off-by: Michael Wild <themiwi@users.sourceforge.net>

Modules/ProcessorCount.cmake

@@ -0,0 +1,60 @@
+# - ProcessorCount(var)
+# Determine the number of processors/cores and save value in ${var}
+#
+# Sets the variable named ${var} to the number of physical cores available on
+# the machine if the information can be determined. Otherwise it is set to 0.
+# Currently this functionality is only implemented for Windows, Mac OS X and
+# Unix systems providing getconf or the /proc/cpuinfo interface (e.g. Linux).
+
+# A more reliable way might be to compile a small C program that uses the CPUID
+# instruction, but that again requires compiler support or compiling assembler
+# code.
+
+#=============================================================================
+# Copyright 2002-2009 Kitware, Inc.
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distributed this file outside of CMake, substitute the full
+#  License text for the above reference.)
+
+function(ProcessorCount var)
+  # Unknown:
+  set(count 0)
+
+  if(WIN32)
+    # Windows:
+    set(count "$ENV{NUMBER_OF_PROCESSORS}")
+  elseif(APPLE)
+    # Mac:
+    find_program(ProcessorCount_cmd_sysctl sysctl
+      PATHS /usr/sbin)
+    if(ProcessorCount_cmd_sysctl)
+      execute_process(COMMAND ${ProcessorCount_cmd_sysctl} -n hw.ncpu
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+        OUTPUT_VARIABLE count)
+    endif()
+  else()
+    find_program(ProcessorCount_cmd_getconf getconf)
+    if(ProcessorCount_cmd_getconf)
+      # Linux and other systems with getconf:
+      execute_process(COMMAND ${ProcessorCount_cmd_getconf} _NPROCESSORS_ONLN
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+        OUTPUT_VARIABLE count)
+    else()
+      # Linux and other systems with /proc/cpuinfo:
+      set(cpuinfo_file /proc/cpuinfo)
+      if(EXISTS "${cpuinfo_file}")
+        file(STRINGS "${cpuinfo_file}" procs REGEX "^processor.: [0-9]+$")
+        list(LENGTH procs count)
+      endif()
+    endif()
+  endif()
+
+  set(${var} ${count} PARENT_SCOPE)
+endfunction()

Tests/CMakeTests/CMakeLists.txt

@@ -27,6 +27,7 @@ AddCMakeTest(String "")
 AddCMakeTest(Math "")
 AddCMakeTest(CMakeMinimumRequired "")
 AddCMakeTest(CompilerIdVendor "")
+AddCMakeTest(ProcessorCount "")
 
 AddCMakeTest(FileDownload "")
 set_property(TEST CMake.FileDownload PROPERTY

Tests/CMakeTests/ProcessorCountTest.cmake.in

@@ -0,0 +1,9 @@
+include(ProcessorCount)
+
+ProcessorCount(processor_count)
+message("processor_count='${processor_count}'")
+
+if(processor_count EQUAL 0)
+  message(FATAL_ERROR "could not determine number of processors
+- Additional code needed in ProcessorCount.cmake?")
+endif()