"""
CPU Detection
"""
# Parallel Python Software: http://www.parallelpython.com
# Copyright (c) 2005-2008, Vitalii Vanovschi
# All rights reserved.
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#    * Redistributions of source code must retain the above copyright notice,
#      this list of conditions and the following disclaimer.
#    * Redistributions in binary form must reproduce the above copyright
#      notice, this list of conditions and the following disclaimer in the
#      documentation and/or other materials provided with the distribution.
#    * Neither the name of the author nor the names of its contributors
#      may be used to endorse or promote products derived from this software
#      without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
# THE POSSIBILITY OF SUCH DAMAGE.

######
# This is from ParallelPython (the pp.py file).

import os
import subprocess

def ncpus():
    """
    Detects the number of effective CPUs in the system.

    EXAMPLES::

        sage: sage.parallel.ncpus.ncpus()  # random output -- depends on machine.
        2
    """
    # Support Sage environment variable SAGE_NUM_THREADS
    # NOTE: while doctesting, this is forced to be 2 by the
    # sage-runtests script
    try:
        n = os.environ["SAGE_NUM_THREADS"]
    except KeyError:
        pass
    else:
        return int(n)

    #for Linux, Unix and MacOS
    if hasattr(os, "sysconf"):
        if "SC_NPROCESSORS_ONLN" in os.sysconf_names:
            #Linux and Unix
            ncpus = os.sysconf("SC_NPROCESSORS_ONLN")
            if isinstance(ncpus, int) and ncpus > 0:
                return ncpus
        else:
            #MacOS X
            #deprecated: return int(os.popen2("sysctl -n hw.ncpu")[1].read())
            process = subprocess.Popen("sysctl -n hw.ncpu", shell=True, stdin=subprocess.PIPE, stdout = subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
            return int(process.stdout.read())
    #for Windows
    if "NUMBER_OF_PROCESSORS" in os.environ:
        ncpus = int(os.environ["NUMBER_OF_PROCESSORS"])
        if ncpus > 0:
            return ncpus
    #return the default value
    return 1
