From: Ron M <rm_rails@...>
Date: 2007-07-20T07:07:22+09:00
Subject: Array flatten memory "leak"?

After I use "flatten" on a big array; the garbage collector
seems to get pretty forgetful of what memory it's allowed
to free up.

In both of the following scripts, the first two lines
create an array of many arrays; and then flatten them
back into a flat array.

In both cases, the memory after creating this array
the scripts use about 20MB.   After that, they
repeatedly pack and unpack an array.   The script that
used "flatten" keeps growing quickly until it used
about 1/4 GB of memory.   The script that flattened
the array by hand stays right about at 20MB.

What could it be about flatten that makes the
garbage collector fail to see that it could be
re-using the memory of the pack/unpack loop?


#########################################################################
#  This unexpectedly grows to 200+MB.
#########################################################################
a = (1..200000).map{|x| [x.to_s]};a.length
b = a.flatten.map{|x| x.to_i} ; b.length
puts `grep VmSize /proc/#{$$}/status`           ######## under 20 MB
(1..100).each{|x| b.pack("I*").unpack("I*");}
puts `grep VmSize /proc/#{$$}/status`           ######## WHOA GREW TO 1/4 GB.


#########################################################################
#  This stays at 20MB
#########################################################################
a = (1..200000).map{|x| [x.to_s]};a.length
b = a.map{|x| x[0].to_i} ; b.length
puts `grep VmSize /proc/#{$$}/status`         ######## under 20 MB
(1..100).each{|x| b.pack("I*").unpack("I*");}
puts `grep VmSize /proc/#{$$}/status`         ######## still 20 MB