[self-interest] Re: Clustering in Self ?
David.Ungar at Eng.Sun.COM
Mon Mar 6 21:55:30 UTC 2000
two small points:
The Self transporter (I think) does support the modules as orthogonal
to classes view a bit better than Smalltalk, although ST does have
If the original question was about objects in memory, of course the
VM does put all the data for a given object in one place, and the
old-space collector does tend to move related objects together. This
was studied for Smalltalk while I was at Berkeley and there are some
(hard-to-find) papers about it.
We called it "offline reorganization" since in those days it was so
slow you couldn't wait for it.
At 6:25 PM -0300 3/6/00, Jecel Assumpcao Jr. wrote:
>José Baltasar García Perez-Schofield wrote:
>> I do apologise because of interrupt this "low-level, implementation"
>> discussion, but I have a philosphycal question about Self.
>> The matter is that Self can be considered a persistent language since
>> it has its objects "living" in the Self world among executions of the
>> Self environment.
>> In many persistent languages, clustering techniques are applied to the
>> persistent store (the world in Self), grouping together objects that are
>> close one each other.
>> (1) For example, "close" can be defined in terms of inheritance
>> relations, or in terms of objects pointed by another objects ... or even
>> combinations of this two considerations.
>> The question is: does Self follow any of this techniques ?
>There are currently two views of a Self world on disk:
> A) a single large binary file called the Snapshot that is
>memory dump of a running system
> B) a set of text files which are managed by a program called "the
>There is no clustering in A, while in B you explicitly group together objects
>or slots into named "modules". There is a second level of organization in this
>case since modules can include submodules.
>I have worked on alternative designs which would divide the binary Snapshot
>into several "clusters". The Squeak people have just introduced "image
>segments" into their system.
>> The central matter of the question is that, as far as I know, hte
>> minimal unit of storage in Self is the slot, so, apparently, the "object
>> semantic", is lost.
>That is the case for the transporter. But for a Snapshot (either the current
>monolithic one or one made up of small clusters) you would not be
>able to split
>an object into anything smaller.
>Before Self 4.0, programming was done by typing expressions directly at the
>prompt or into files using any text editor. You would then load these files to
>create or change the objects. Like the FileIns in Smalltalk, different files
>could make changes to the same objects. So you tended to group in a
>all of the changes (adding slots, mostly) related to a single project. You
>might need to add a method 'isPrime' to 'traits integer' to make your project
>work, for example. Then there would be one slot (namely 'isPrime') that would
>not be found in the 'integer.self' source file as you would expect but in the
>'myProject.self' file instead. Note that this is not unique to Self
>has always been like this.
>When Dave created the transporter, he wanted to support this "tradition". So
>you can tag different slots in a single objects as belonging to different
>modules (and so as being saved to different text files).
>> Are the slots of the same object grouped together, for example ?
>Even in the transporter, the default is to make all slots in an object belong
>to a single module. But they don't have to be grouped together.
>In a system that stores *live* objects to disk (which the text file
>representations mostly certainly are not, no matter how hard they try to fake
>it) then objects must be the smallest grouping unit. This creates some hard
>problems in terms of the work of different programmers combining in a usefull
>way, but I don't see any way to avoid them.
>On a related issue, you might find the work on "object grouping" at page fault
>time that the Mushroom people (including Mario Wolczko - see his
>pages about it
>at http://www.sun.com/research/people/mario/mushroom/index.html) very
>I hope this helps,
>Its easy. Its fun. Best of all, its free.
>-- Check out your group's private Chat room
Sun Microsystems Laboratories
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