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ImageSegment [WAS] getting rid of Symbol >> new: ?

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Mariano Martinez Peck

ImageSegment [WAS] getting rid of Symbol >> new: ?

On Thu, Dec 10, 2009 at 1:59 AM, Sheridan Mahoney <[hidden email]> wrote:

Adrian Lienhard wrote:
>
>
> On Dec 8, 2009, at 12:08 , Mariano Martinez Peck wrote:
>
>> On Fri, Dec 4, 2009 at 12:05 PM, Adrian Lienhard <[hidden email]>
>> wrote:
>
>> When you are creating your root of objects and you put symbols
>> inside, they
>> are not put in ourPointers but in ByteArray.
>> This is due to the fact that the only object who is pointing to that
>> symbol
>> is inside the segment ?
>
> To be precise, the symbols are also pointed to by the symbol table,
> but only by weak references. Since image segments use the GC mark
> logic, these pointers are not considered.
>
>

Martin and I had been working towards the idea that ImageSegments should
never create non-Canonical symbols,

what does non-Canonical mean ?

and the user should not have to use
manual techniques to preserve symbols they are interested in keeping alive.

+9999 agree.

I ended up getting stuck however, in trying to discover what process
ImageSegment
goes through while it is installing objects - ImageSegment #install has a
call to an
unimplemented method #readFromFileWithSymbols which it seems it should be
using, but isn't....(wha' the?)

yes. We should try to look in the old squeak images (like 3.6). I tried to make it work, but my machine seems to be too new :(

Does someone has an old squeak running and has this method implemented?

install
"This operation retrieves the segment if necessary from file storage,
installs it in memory, and replaces (using become:) all the root stubs with
the reconstructed roots of the segment."

| newRoots |
state = #onFile ifTrue: [self readFromFile].
state = #onFileWithSymbols ifTrue: [self readFromFileWithSymbols.
endMarker := segment nextObject. "for enumeration of objects"
endMarker == 0 ifTrue: [endMarker := 'End' clone]].
(state = #active) | (state = #imported) ifFalse: [self errorWrongState].
newRoots := self loadSegmentFrom: segment outPointers: outPointers.
state = #imported
ifTrue: ["just came in from exported file"
arrayOfRoots := newRoots]
ifFalse: [
arrayOfRoots elementsForwardIdentityTo: newRoots].
state := #inactive.
Beeper beepPrimitive

I think the next step in this trajectory is to trace is how the state is
getting
set - right now it is kind of a mystery...

Easy, see the senders of onFileWithSymbols.There are 4, but the more important is writeToFileWithSymbols which is also called by writeToFileWithSymbols:

So, if you don't use any of those messages, the state never would be onFileWithSymbols.

Try to write a test using that message and you will probably get the DNU.

In addition, as you said, the user shouldn't even be care about this method. He should just send the message "writeToDisk". I have the same impression with the classes. When you store in a segment a class, you must also put the metaclass. And I think this can be automatically be done by ImageSegment instead of the user.

Does this seem reasonable?

Thanks,

Sheri

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Sheridan Mahoney

Re: ImageSegment [WAS] getting rid of Symbol >> new: ?

Mariano Martinez Peck wrote

> Martin and I had been working towards the idea that ImageSegments should
> never create non-Canonical symbols,

what does non-Canonical mean ?

I will give you my understanding, with the hope that others more knowledgeable will add to this
if it is off the mark...

Canonical means :
"reduced to the simplest and most significant form possible without loss of generality"

In the context of Symbols in Smalltalk, each Symbol has only one instance, and it is the
canonical instance for all references. So a non-canonical Symbol is usually one for which there
is more than one instance.

My old programming textbook described the Smalltalk language as the canonical example for OO languages...

HTH, and
Cheers,

Sheri