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# Copyright 2015-2019 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2
import re
__all__ = ["get_cpu_count", "makeopts_to_job_count"]
# Before you set out to change this function, figure out what you're really
# asking:
#
# - How many CPUs exist in this system (e.g. that the kernel is aware of?)
# This is 'getconf _NPROCESSORS_CONF' / get_nprocs_conf(3)
# In modern Linux, implemented by counting CPUs in /sys/devices/system/cpu/
#
# - How many CPUs in this system are ONLINE right now?
# This is 'getconf _NPROCESSORS_ONLN' / get_nprocs(3)
# In modern Linux, implemented by parsing /sys/devices/system/cpu/online
#
# - How many CPUs are available to this program?
# This is 'nproc' / sched_getaffinity(2), which is implemented in modern
# Linux kernels by querying the kernel scheduler; This might not be available
# in some non-Linux systems!
#
# - How many CPUs are available to this thread?
# This is pthread_getaffinity_np(3)
#
# As a further warning, the results returned by this function can differ
# between runs, if altered by the scheduler or other external factors.
def get_cpu_count():
"""
Try to obtain the number of CPUs available to this process.
@return: Number of CPUs or None if unable to obtain.
"""
try:
import os
# This was introduced in Python 3.3 only, but exists in Linux
# all the way back to the 2.5.8 kernel.
# This NOT available in FreeBSD!
return len(os.sched_getaffinity(0))
except (ImportError, NotImplementedError, AttributeError):
pass
try:
import multiprocessing
return multiprocessing.cpu_count()
except (ImportError, NotImplementedError):
return None
def makeopts_to_job_count(makeopts):
"""
Parse the job count (-jN) from MAKEOPTS. Python version of
bin/isolated-functions.sh's ___makeopts_jobs().
@return: Number of jobs to run or number of CPUs if none set.
"""
if not makeopts:
return get_cpu_count()
jobs = re.match(r".*(j|--jobs=\s)\s*([0-9]+)", makeopts)
if not jobs:
return get_cpu_count()
return jobs.groups()[1]
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