From: Brian Candler <B.Candler@...>
Date: 2003-04-14T01:51:49+09:00
Subject: Re: Need IO Optimization help

On Mon, Apr 14, 2003 at 01:34:42AM +0900, gabriele renzi wrote:
> >You can eliminate the extra argument by doing
> >
> >     mycounter = mycounter.succ
> 
> well I suppose his point is that not using Fixnum you can have
> Counter.succ!, without the need for an assignment , written directly
> in C,  possibly faster..
> (and though possibly low level optimized as in "inc reg" vs "add
> reg,1"  )

I don't think you'll get anywhere close to where that would make any
difference. The big overhead is in the dispatch to .succ or .succ! where the
interpreter has to walk through the chain of object classes and superclasses
to find the correct method to call. Once you have invoked a method and got a
return 'VALUE', storing that value in a local variable is minimal cost.

You might be able to optimise this using Polymorphic Inline Caches (Google
will give you some papers on this), but in the general case I don't think
you'll ever be able to get as far as "inc reg" without some extremely
serious data-flow analysis. If you'd like to try writing a Ruby to C (or
C++) converter, I think you'll get the picture :-)

The problems include:

- any method you call could decide to redefine any method of any other
object (including Fixnum#+ and Fixnum#succ) at any time.

- any method which you pass a block to, can keep a copy of that block and
call it at any time in the future

In fact it's hard enough even to answer the question "at what point is this
object no longer referenced?" that Ruby does mark-and-sweep periodic garbage
collection rather than disposing of objects as soon as they are no longer
used.

Regards,

Brian.