Question

I already found a solution for “Most unixes” via cat /proc/cpuinfo, but a pure-Ruby solution would be nicer.

Answer 1

I am currently using this, which covers all os.
https://github.com/grosser/parallel/blob/master/lib/parallel.rb#L63

  def self.processor_count
    case RbConfig::CONFIG['host_os']
    when /darwin9/
      `hwprefs cpu_count`.to_i
    when /darwin/
      ((`which hwprefs` != '') ? `hwprefs thread_count` : `sysctl -n hw.ncpu`).to_i
    when /linux/
      `cat /proc/cpuinfo | grep processor | wc -l`.to_i
    when /freebsd/
      `sysctl -n hw.ncpu`.to_i
    when /mswin|mingw/
      require 'win32ole'
      wmi = WIN32OLE.connect("winmgmts://")
      cpu = wmi.ExecQuery("select NumberOfCores from Win32_Processor") # TODO count hyper-threaded in this
      cpu.to_enum.first.NumberOfCores
    end
  end