I want to know the number of CPUs on the local machine using Python. The result should be user/real as output by time(1) when called with an optimally scaling userspace-only program.

解决方案

If you're interested into the number of processors available to your current process, you have to check cpuset first. Otherwise (or if cpuset is not in use), multiprocessing.cpu_count() is the way to go in Python 2.6 and newer. The following method falls back to a couple of alternative methods in older versions of Python:

import os

import re

import subprocess

def available_cpu_count():

""" Number of available virtual or physical CPUs on this system, i.e.

user/real as output by time(1) when called with an optimally scaling

userspace-only program"""

# cpuset

# cpuset may restrict the number of *available* processors

try:

m = re.search(r'(?m)^Cpus_allowed:\s*(.*)$',

open('/proc/self/status').read())

if m:

res = bin(int(m.group(1).replace(',', ''), 16)).count('1')

if res > 0:

return res

except IOError:

pass

# Python 2.6+

try:

import multiprocessing

return multiprocessing.cpu_count()

except (ImportError, NotImplementedError):

pass

# https://github.com/giampaolo/psutil

try:

import psutil

return psutil.cpu_count() # psutil.NUM_CPUS on old versions

except (ImportError, AttributeError):

pass

# POSIX

try:

res = int(os.sysconf('SC_NPROCESSORS_ONLN'))

if res > 0:

return res

except (AttributeError, ValueError):

pass

# Windows

try:

res = int(os.environ['NUMBER_OF_PROCESSORS'])

if res > 0:

return res

except (KeyError, ValueError):

pass

# jython

try:

from java.lang import Runtime

runtime = Runtime.getRuntime()

res = runtime.availableProcessors()

if res > 0:

return res

except ImportError:

pass

# BSD

try:

sysctl = subprocess.Popen(['sysctl', '-n', 'hw.ncpu'],

stdout=subprocess.PIPE)

scStdout = sysctl.communicate()[0]

res = int(scStdout)

if res > 0:

return res

except (OSError, ValueError):

pass

# Linux

try:

res = open('/proc/cpuinfo').read().count('processor\t:')

if res > 0:

return res

except IOError:

pass

# Solaris

try:

pseudoDevices = os.listdir('/devices/pseudo/')

res = 0

for pd in pseudoDevices:

if re.match(r'^cpuid@[0-9]+$', pd):

res += 1

if res > 0:

return res

except OSError:

pass

# Other UNIXes (heuristic)

try:

try:

dmesg = open('/var/run/dmesg.boot').read()

except IOError:

dmesgProcess = subprocess.Popen(['dmesg'], stdout=subprocess.PIPE)

dmesg = dmesgProcess.communicate()[0]

res = 0

while '\ncpu' + str(res) + ':' in dmesg:

res += 1

if res > 0:

return res

except OSError:

pass

raise Exception('Can not determine number of CPUs on this system')