Detect number of CPUs installed

Question

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

Answer 1

As of Ruby version 2.2.3, the etc module in Ruby's stdlib offers an nprocessors method which returns the number of processors. The caveat to this, is that if ruby is relegated to a subset of CPU cores, Etc.nprocessors will only return the number of cores that Ruby has access to. Also, as seanlinsley pointed out, this will only return virtual cores instead of physical cores, which may result in a disparity in the expected value.

require 'etc' p Etc.nprocessors #=> 4 

Answer 2

EDIT: Now rails ships with concurrent-ruby as a dependency so it's probably the best solution;

$ gem install concurrent-ruby $ irb irb(main):001:0> require 'concurrent' => true irb(main):002:0> Concurrent.processor_count => 8 irb(main):003:0> Concurrent.physical_processor_count => 4 

see http://ruby-concurrency.github.io/concurrent-ruby/master/Concurrent.html for more info. Because it does both physical and logical cores, it's better than the inbuilt Etc.nprocessors.

and here is the previous answer;

$ gem install facter $ irb irb(main):001:0> require 'facter' => true irb(main):002:0> puts Facter.value('processors')['count'] 4 => nil irb(main):003:0>  

This facter gem is the best if you want other facts about the system too, it's not platform specific and designed to do this exact thing.

UPDATE: updated to include Nathan Kleyn's tip on the api change.