From af94ba2dfbd9f195bc39127c12b1844f248335fb 2008-06-24 00:29:58
From: Fernando Perez <Fernando.Perez@berkeley.edu>
Date: 2008-06-24 00:29:58
Subject: [PATCH] Add num_cpus() functions to detect total number of CPUs active.

---

diff --git a/IPython/genutils.py b/IPython/genutils.py
index 2cc19c0..4bc418d 100644
--- a/IPython/genutils.py
+++ b/IPython/genutils.py
@@ -27,9 +27,11 @@ try:
 except ImportError:
     pass
 import os
+import platform
 import re
 import shlex
 import shutil
+import subprocess
 import sys
 import tempfile
 import time
@@ -2041,6 +2043,55 @@ def wrap_deprecated(func, suggest = '<nothing>'):
                       stacklevel = 2)
         return func(*args, **kwargs)
     return newFunc
-    
-#*************************** end of file <genutils.py> **********************
 
+
+def _num_cpus_unix():
+    """Return the number of active CPUs on a Unix system."""
+    return os.sysconf("SC_NPROCESSORS_ONLN")
+
+
+def _num_cpus_darwin():
+    """Return the number of active CPUs on a Darwin system."""
+    p = subprocess.Popen(['sysctl','-n','hw.ncpu'],stdout=subprocess.PIPE)
+    return p.stdout.read()
+
+
+def _num_cpus_windows():
+    """Return the number of active CPUs on a Windows system."""
+    return os.environ.get("NUMBER_OF_PROCESSORS")
+
+
+def num_cpus():
+   """Return the effective number of CPUs in the system as an integer.
+
+   This cross-platform function makes an attempt at finding the total number of
+   available CPUs in the system, as returned by various underlying system and
+   python calls.
+
+   If it can't find a sensible answer, it returns 1 (though an error *may* make
+   it return a large positive number that's actually incorrect).
+   """
+   
+   # Many thanks to the Parallel Python project (http://www.parallelpython.com)
+   # for the names of the keys we needed to look up for this function.  This
+   # code was inspired by their equivalent function.
+
+   ncpufuncs = {'Linux':_num_cpus_unix,
+                'Darwin':_num_cpus_darwin,
+                'Windows':_num_cpus_windows,
+                # On Vista, python < 2.5.2 has a bug and returns 'Microsoft'
+                # See http://bugs.python.org/issue1082 for details.
+                'Microsoft':_num_cpus_windows,
+                }
+
+   ncpufunc = ncpufuncs.get(platform.system(),
+                            # default to unix version (Solaris, AIX, etc)
+                            _num_cpus_unix)
+
+   try:
+       ncpus = max(1,int(ncpufunc()))
+   except:
+       ncpus = 1
+   return ncpus
+
+#*************************** end of file <genutils.py> **********************