Re: Garbage collection - was Beginner with Cocoa

FROM : Scott Thompson
DATE : Mon Mar 24 18:36:39 2008

On Mar 24, 2008, at 10:30 AM, colo wrote:

> In Ruby GC just works dandy without thought. Why is it so different 
> in Cocoa Obj2.0?


Conceptually, it's not much different. In implementation, however, 
they are two separate garbage collectors and they don't play well 
together. The problem crops up when you try to mix the two using 
RubyCococa in a single application.

Right now RubyCocoa allows you to work with Objective-C objects 
through the Ruby interpreter and it uses retain/release mechanisms to 
manage the life-cycle of the Objective-C objects.  To put it another 
way, if you are using Ruby as your development language, you don't 
have to worry about retain and release because the RubyCocoa library 
does it for you.

However, that memory management is done in the RubyCocoa framework not 
at the level of the Ruby garbage collector. The Ruby garbage collector 
is not at all aware of the Objective-C garbage collector (and vice 
versa).  As a result, it might be possible for one garbage collector 
to sweep away objects that the other garbage collector things should 
be "live".  That's not good.

To integrate the two, someone would have to rewrite the internals of 
the Ruby interpreter and add in special case code for Objective-C 
objects.  That kind of a rewrite sounds Hard(tm) on many levels.  Not 
the least of which is the fact that interpreter is shared across many 
platforms and environments and mucking with it's guts could have far-
reaching and unexpected consequences.

Regardless of the reasons, however, the fact remains that if you are 
going to write a Cocoa application that uses the RubyCocoa bridge to 
talk to some Ruby code in Leopard. The Cocoa application cannot use 
the Objective-C 2.0 garbage collector.

> What kinda of real headaches will I have jumping into osx programing
> compared to ruby ?



It kinda depends on what you mean by "OS X Programming".

Well, if you want to do "Pure" Ruby programming (including Rails) on 
Mac OS X, I doubt you are likely to run into many headaches.  For 
everything I've tried,  which I must admit is not much compared to 
what's possible, Ruby "just works" on Mac OS X.

If  "OS X Programming"  means writing Coco applications, then, the 
RubyCocoa bridge will allow you write Cocoa applications in Ruby. 
However, be forewarned that there are some headaches in integrating 
the two.  Those headaches might make learning Cocoa through Ruby 
unattractive for the Cocoa novice.  My opinion (and apparently the 
opinions of others) is that you would be better off learning the Cocoa 
framework through the Objective-C APIs first, and then applying that 
knowledge to Ruby, than you would be trying to learn the Cocoa 
framework through Ruby from square one.  YMMV

If you are familiar with Cocoa and "familiar enough" with Ruby then 
I've found RubyCocoa particularly useful in two instances:

1. Quickly prototyping some object designs.  If I'm trying to put 
together an object hierarchy or some object interactions, I will often 
prototype them in Ruby and play with their interfaces and such (I used 
to use Squeak/Smalltalk for that, but with ALL due respect to the 
Squeak folks, Ruby takes up less screen real estate).

2. Exploring new APIs and new parts of Cocoa.  I used Ruby to learn 
some more about the Scripting Bridge and the "Publish and Subscribe" 
frameworks.  Mostly because I was curious about them.  Again, the 
ability to quickly throw together some... er... half-baked code in 
Ruby and then poke at it with irb was pretty handy.

And to be fair, my understanding, though I have no experience with 
these other languages, is that you can do the same thing with other 
languages.  Most notably, I've heard of support in FScript, Python, 
Perl (by using CamelBones).

Does that answer your question?