[Rubycocoa-talk] I just don't understand RubyCocoa Garbage Collection

[Duncan M. <du...@on...>]

Sorry, yet more woes from me.

I've pretty much given up being able to write PDF directly from  
RubyCocoa without leaking badly (CGImageSourceRefs, can't live with  
'em, can't dispose of 'em), and as my customers are passing 200 pages  
of 300 DPI images for me to write to a PDF, this is a big problem.

So I've moved the PDF rendering into an Objective-C class, and then  
load and use that class from my RubyCocoa class, passing in  
NSImageRepresentations. But I still leak. In the end it boils down to  
the following test

#!/usr/bin/env ruby
require 'test/unit'
require 'osx/cocoa'

include OSX

OSX::NSApplication.sharedApplication

NSBundle.bundleWithPath('build/Debug/VelOCRaptorShared.bundle').load

class QuartzPDFWriterTest < Test::Unit::TestCase
	
	def test_NSImage
		1.upto(10000) do |i|
			p i
			image = NSImage.alloc.initWithContentsOfFile 'testdata/pot pourri/ 
blood.jpg'
			#ObjectSpace.garbage_collect
		end
	end
end

If I don't garbage collect, this code will run from the console until  
the process has consumed all available memory and started sucking  
disk. If I un-comment the garbage_collect, it sits happily at 30MB or  
so of real memory.

As a Java guy I expected not to have to second-guess when GC would be  
a good idea, but here it seems that Ruby just doesn't try to GC in the  
hard loop. Is this due to the green threads, or am I missing something  
fundamental here? When does Ruby start a GC in normal code?

Cheers

Duncan