Re: [Jscheme-user] DynamicVariable proposal

[Ken A. <kan...@bb...>]

I just made the changes for this.
The Gabriel benchmarks show a 3% improvement.
I should have tried your benchmark.

Toby,
Can you test serialization and see if your patch is still needed.

k

At 11:08 PM 7/15/2004 -0400, Timothy John Hickey wrote:

>On Jul 9, 2004, at 2:55 PM, Ken Anderson wrote:
>
>>Tim,
>>Let me know what you think of this proposal.
>>
>>Currently a DynamicVariable has 3 fields
>>Symbol name
>>DynamicEnvironment dynamicenv - used to look up value in hash table.
>>Object storedDynamicValue         - only used during serialization.
>>
>>A DynamicEnvironment, DE, maps symbols to values.
>>So every time we evaluate a DV, we do a hash lookup.
>>
>>I'd like to propose we
>>1. put the DV's value in the storedDynamicValue field
>>2. remove the dynamicenv field.
>>3. Change DE to map from Symbol -> DV.
>I agree. I'd thought about this optimization before and it makes great sense.
>
>>This means the DE will intern the DV for a symbol, but it can use its current hashtable to do that.  getBindings and importBindings would have to clone all the DV's (or could they be shared?).
>I think they could be shared. Modules are assumed to be locked (i.e. you can't change the bindings
>of toplevel symbols) and so there would be no need to clone.
>>
>>The advantage is we'd get rid of a runtime hash lookup for every global value.
>Yes. I tried to see whether this would make a dramatic difference by comparing two
>expressions which differ only in their use of globally defined symbols:
>
>> (define fib
>   (lambda (n)
>       (if (< n 3) 1 (+ 1 (fib (- n 1)) (fib (- n 2))))))
>
>> (define fib2
>  (let ((+ +) (- -) (< <))
>   (lambda(n)
>     (if (< n 3) 1 (+ 1 (fib (- n 1)) (fib (- n 2)))))))
>
>> (time (fib  25) 1)
>(150049 (986 msec) (20776 bytes))
>
>> (time (fib2 25) 1)
>(150049 (916 msec) (3288 bytes))
>
>Here the code in the closure of fib2 uses only local variables
>and hence should be doing four fewer hash table lookups for
>each procedure call, but I don't see much in the way of time
>differences....
>
>I really expected a bigger time difference. The regular approach gets
>152K procedure calls per second (on a Powerbook G4 with jdk1.4)
>and the fancier approach gets 163K pc/sec which is about a 7% improvement.
>
>---Tim---