Rails - May 2006 - Image format gotcha

I''ve been doing a lot of testing witn RMagick lately, in view of
reports
that it leaks memory. I''m happy to report that RMagick doesn''t
seem to
leak at all, when used as directed -- that is, when you remember to set 
the image variable to nil and call GC.start manually after you''re done 
with an image.

BUT -- one ImageMagick format seems to be leaky! I was using the native 
"MPC" format to store an intermediate image for processing, since 
(according to the ImageMagick docs) it maps directly into memory and 
should be very quick-loading. I kept seeing big increases in 
virtual-memory allocation every time I used that image. The problem went 
away when I changed the format of the intermediate file to anything else 
(PNG, JPG).

Here''s the quickie script I sent to Timothy Hunter demonstrating the 
problem. I''ve only tested it on a Mac (OS 10.4.6), so it might be 
OS-specific. You might have to change the ps command -- what you''re 
interested in is virtual memory allocation.

--Al Evans

-----

#!/usr/bin/env ruby

require ''RMagick''
include Magick

# name of original photo without extension
def photo_basename(name)
  name.gsub(/\.\w+$/i, '''')
end

def make_image_cache(pic_file_name)
  img = Image.read(pic_file_name).first
  img.strip!.change_geometry("1024x1024") { |cols, rows, img|
    img.resize!(cols, rows)
  }
  img.write("#{photo_basename(pic_file_name)}.MPC")
  img = nil
  GC.start
end

def make_image_workfile(pic_file_name)
  img = Image.read("#{photo_basename(pic_file_name)}.MPC").first
  img.strip!.change_geometry("640x512") { |cols, rows, img|
    img.resize!(cols, rows)
  }
  img.write("#{photo_basename(pic_file_name)}_work.JPG") {
self.quality
= 50 }
  img = nil
  GC.start
end

while true
  make_image_cache(ARGV[0])
  make_image_workfile(ARGV[0])
  puts `ps -l | grep ruby`
  sleep(10)
end

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