Re: Objective-C and Smalltalk; speed of message send

[Richard Frith-Macdonald]

On 19 Aug 2004, at 15:24, Adrian Robert wrote:

> On Aug 18, 2004, at 3:49 PM, Marcel Weiher wrote:
>
> > Whoa, an NSDictionary is a pretty heavy-weight item, especially 
> > compared to a simple 2D array!  Why not stick with the 2D array, if I 
> > may ask?  After all, one of the point of Objective-C is that it *is* 
> > C.
> >
> > >  We decided to use NSStrings as the keys.
> >
> > Also potentially fairly heavy, though a common choice.  I remember 
> > people complaining about NSString's performance compared to char* 
> > when Foundation was introduced.  However, NSString is really for 
> > "human readable" text, whereas char* is often more for "tokens", or 
> > really just byte-sequences.
> >
> > >  To maintain a backwards bridge, we took the old 2D access indices 
> > > and turned them into a string. And then stored/set them in the 
> > > NSMutableDictionary via those. The performance was not impressive.
> >
> > I wouldn't expect it to be.  NS(Mutable)Dictionary is pretty slow.  
> > One issue is that it copies its keys.  Arrrggghh.

Not really a big issue ... if the key is a constant string, a copy is 
just a retain.  If it's not constance, failing to copy would be a 
significant bug.

> While it's good to have the raw C capabilities there for extreme 
> cases, it's NOT much good having a nice, high-level API if it's so 
> slow you end up dropping back to mid-level C (with all of its tedium 
> and error-proneness) much of the time.  I'm going to get in trouble 
> here for talking instead of sending code ;), but it seems like the 
> class NSString and at least the plist classes NSDictionary and NSArray 
> ought to be as optimized as well as they can possibly be.  These are 
> used everywhere in the libraries and in applications, and effort in 
> this direction should pay off handsomely.  I'm sure much has been done 
> already, but perhaps there is still some reasonably low-hanging fruit 
> remaining?

I'm sure there are always possibilities, but I think NSArray and 
NSDictionary are actually pretty fast.  NSString is more of a problem.

> I realize there are things that just have to be done for correct 
> behavior (e.g., hash key copying), but I just don't see how any 
> Smalltalk environment should be able to match Objective-C in 
> performance for a straightforward application of strings and 
> dictionaries.  We ought to look at these implementations (if any have 
> source available) and see what techniques they are using.

Maybe ... I think that most likely the main problem is using 
stringWithFormat:
That method is slow for a variety of reasons (it's probably faster now 
than when the smalltalk test was done),
not least the fact that it uses the autorelease mechanism.  Autorelease 
is fundamentally pretty slow, and a
good garbage collection system would perform better.  However, 
retain/release/autorelease is the way
things are currently done.