Get real number of cpus on machine, ignoring any quotas/limits.

Machine.cs

namespace Utilities
{
    using System;
    using System.Diagnostics;
    using System.Runtime.InteropServices;

    public static class Machine
    {
        private const int MaximumNumberOfCpus = 128;
        private static int? _processorCount;

        /// <summary>
        /// Returns the actual processor counts on the machine.
        /// This was needed in docker because Environment.ProcessorCount was returning the cpu value taking into account
        /// CPU limits set.
        /// In order to check how many cpus actually exist on the machine, we loop from 0 to 127, asking libc to give us
        /// the affinity of the current process to the cpuIndex. If the operation succeeds and we get a result, cpu exists
        /// if it returns -1 then the operatin failed and cpu doesn't exist.
        /// </summary>
        public static int ProcessorCount
        {
            get
            {
                if (_processorCount.HasValue)
                {
                    return _processorCount.Value;
                }

                if (!RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
                {
                    _processorCount = Environment.ProcessorCount;
                    return Environment.ProcessorCount;
                }
                else
                {
                    ulong count = 0;
                    ulong result = 0;
                    while (LibC.sched_getaffinity(Process.GetCurrentProcess().Id, (IntPtr)count, ref result) != 0 && count < MaximumNumberOfCpus)
                    {
                        count++;
                    }

                    _processorCount = Math.Max((int)count, 1);
                }

                return _processorCount.Value;
            }
        }
    }

    internal static class LibC
    {
        private const string DllName = "libc";

        /// <summary>
        /// Calls libc sched_getaffinity https://linux.die.net/man/2/sched_getaffinity
        /// </summary>
        /// <param name="pid">The pid to get the affinity for</param>
        /// <param name="cpuSetSize">Value passed is the index of the cpu</param>
        /// <param name="affinityResult">The affinity of the current process to the cpu specified</param>
        /// <returns>-1 on error, 0 on success</returns>
        [DllImport(DllName)]
        internal static extern int sched_getaffinity(int pid, IntPtr cpuSetSize, ref ulong affinityResult);
    }
}