Strange behavior of Ruby's GC. ## Careful !! The following script requires ~40Mb of your virtual memory address space.

ruby_gc_goes_wild.rb

## Careful !!
# The following script requires ~40Mb of your virtual memory address space.

vm_before = File.read("/proc/#{$$}/status").match(/^VmSize:\s*(\d*)/)[1].to_i

def vm_used(vm_before)
  File.read("/proc/#{$$}/status").match(/^VmSize:\s*(\d*)/)[1].to_i - vm_before
end

# w block
def gsub_w(s)
  ["la ", "ko "].each{ |t| s.gsub!(/#{t}/){ "" } }
end

# w/o block
def gsub_wo(s)
  ["la ", "ko "].each{ |t| s.gsub!(/#{t}/, "") }
end

########
#
# str_gsub() without using block
p [:before_string_build, vm_used(vm_before)]
s = ""
3495253.times { |i| s << "la " } #  ~10 Mb
3495253.times { |i| s << "ko " } #  ~10 Mb
p [:after_string_build, vm_used(vm_before)]


p [:before_gsub_wo_block, vm_used(vm_before)]
gsub_wo(s)

# VmSize goes wild here !!!!
p [:after_gsub_wo_block, vm_used(vm_before)]

GC.start

########
#
# str_gsub() using block
p [:before_string_build, vm_used(vm_before)]
s = ""
3495253.times { |i| s << "la " } #  ~10 Mb
3495253.times { |i| s << "ko " } #  ~10 Mb
p [:after_string_build, vm_used(vm_before)]

p [:before_gsub_wo_block, vm_used(vm_before)]
gsub_w(s)
p [:after_gsub_wo_block, vm_used(vm_before)]


p [:end, vm_used(vm_before)]