| # Copyright 2015-2019 Gentoo Authors |
| # Distributed under the terms of the GNU General Public License v2 |
| |
| __all__ = ['get_cpu_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 |
