On Mar 21, 2010, at 11:18 PM, Stéphane Ducasse wrote:
>>
>> The reason why the #isInmemory checks are there at all is the following:
>>
>> -> they used imageSegements (and before, the ObjectOut stuff) to swap
>> out objecs to disk
>> -> Now if you access the class, it is loaded again.
>> -> doing anything that looks at "all classes" would load the classes.
>> (all of them)
>> -> this includes things like "Object subclasses". or "Smalltalk
>> classNames".
>> -> e.g. Openign a browser would load all classes.
>> -> so we put #isInMemory everywhere
>
> Yes I know that :)
> Now I was wondering what adrian meant.
>
>> -> this of course means that #subclasses would just return those that
>> by chance are
>> in memory... I don't understand how that can work. Honestly :-)
>>
>> I think we shoud remove all that stuff and do it "for real". c.f. Loom.
>
> probably.
so I was wondering: what exactly is bad in swapping in all classes when opening
a browser?
1) no need to swap in *everything*. Classe are large because they
reference *lots* of methods (which in turn reference
lots of literals).
But most cases where we iterate over all classes we will not touch
the methods (other than when we *want*
the methods).
=> be fine grained. Loading all classes does not imply
loading all methodDictcs.
2) If I am interested in all classes, I am interested in all classes.
Give them to me!
And get rid of them as soon as I am not interested anymore
=> on-demand loading is half of the story.
On-No-Demand-*Unloading* is needed, too.
This means, when developing, we will have all classes (or at
least parts of them) in memory.
(*because we look at them*). But in Deployment, the working set
of objects will be different, and
only those classes that are needed for *execution* will stay in
memory.
3) Intelligent caching. Of course we don't load objects one-by-one, we
will have an intelligent cache.
We will do intelligent pre-fetching, too, to not have to go to
disk for each object when it's clear that
probably we will load more that just that one object (or it's
cheap to load more).
But that is orthogonal and invisible.
Marcus
--
Marcus Denker -- http://www.marcusdenker.de
INRIA Lille -- Nord Europe. Team RMoD.
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