show the effects of stack size on ruby's performance

gdb_stack_size.rb

#!/usr/bin/env ruby

require "benchmark"

bit64 = 1.size == 8

open('gdb-script', 'w') do |f|
  f.puts <<-EOS
  p ((unsigned int)rb_gc_stack_start - (unsigned int)$#{bit64 ? 'r' : 'e'}sp)
  detach
  quit
  EOS
end

def stack(size = 200, n = 0, &blk)
  unless n >= size
    stack(size, n+1, &blk)
  else
    yield
  end
end

def run_test
  0.step(500, 100) do |size|
    stack(size) do
      ss = %x"gdb -q -x gdb-script `which ruby` #{$$} 2>/dev/null"[/\$1 = (\d+)/m, 1]
      puts "Ruby stack: #{"%4d" % size} Stack size: #{"%10d" % ss} bytes"
      puts(Benchmark.measure { 10_000.times { stack(10) { ss.size } } })
    end
  end
end

puts "Without thread:"
run_test

puts
puts "With stopped thread:"
t1 = Thread.new { Thread.stop }
run_test

puts
t2 = Thread.new { loop { stack(10) { Thread.current } } }
puts "With active thread: (n.b. stack size lies!)"
run_test