jruby_start_up.rb

# A simple way to measure start-up time from inside Java application
#  credits:
#   - https://stackoverflow.com/questions/39321345/how-do-i-measure-jvm-startup-time
#
#  How to run:
#
#    0. install JRuby (brew, rvm, etc.) e.g. `rvm install jruby-9.2.11.1`
#    1. download this script
#    2. in the shell run `for i in {1..10}; do ruby jruby_start_up.rb; done | awk '{ total += $1; count++ } END { print total/count }'`
#       => 1673.9

require 'java'

java_import java.lang.System
java_import java.lang.management.ManagementFactory

current_time = System.currentTimeMillis
vm_start_time = ManagementFactory.getRuntimeMXBean.getStartTime

# For debug:
# puts "System info JRUBY_OPTS='#{ENV['JRUBY_OPTS']}'"
# puts "#{(current_time - vm_start_time)} ms"

puts "#{(current_time - vm_start_time)}"