This sounds like it could be useful for packaging a minimal system VM and
image for PDAs.
It sounds like this is independent of the "shrink" words built in.  How
well do they play together?
S

At 08:54 PM 10/6/99 -0800, you wrote:
>Folks -
>
>It has been half a year since we introduced imageSegments to Squeak
(updates 756 and 760 in March of this year.  In case you have not followed
this, here is a summary...
>
>ImageSegments are created by a primitive operation that very quickly
identifies what objects are reachable for a given set of roots, and by no
other path.  The primitive also copies the objects into a WordArray in the
same form as they exist in the Squeak image itself, and copies into an
Array all of the pointers from the segment into the rest of Squeak (ie the
parts that are reachable from the outside).  Naturally there is an inverse
operation that will recreate the entire structure in a twinkle from the
segment.
>
>If you put these two operations together, you get a high-performance
deepCopy operation.  If you save the imageSegments on a local file, you get
application overlaying, and if you send that file far away and read it into
another image, you have export/import of Squeak worlds.  They are fast.
They are compact.  AND, they are platform-independent!  Imagine a DLL that
you can use on Windows or a Mac or a bare chip.
>
>Of course there is more to this technology.  For instance to swap out a
segment, you must replace all its roots by ImageSegmentRootStubs.  These
are special objects that will retrieve their segment if any message is sent
to them, and even if they are classes and a message is sent to one of their
instances.  Also, if you export an image segment, special work must be done
when importing it to reconcile the outpointers with the state of the
receiving system.  That work comprises much of the intelligence of
SmartReferenceStreams. [more info in class comments to ImageSegment,
ImageSegmentRootStub and SmartReferenceStream]
>
>That's the background.  Ted Kaehler and I will be writing a paper on
ImageSegments and their associated technology later this year.  But that's
not why I'm writing this message.  The reason is that we have been beating
on this code heavily in the last month, we have found a number of bugs, we
have fixed them, and we now deem that ImageSegments are ready for serious
test.
>
>To become a tester of ImageSegments you will need to do two things:  back
up all your work (duh), and get a new copy of the Squeak VM.  There is one
for the Mac PPC available now in the Squeak 2.5 folder at UIUC, called:
>
>	SqueakVM2.5cPPC.sea
>
>Hopefully we will have others out soon for the other platforms.  Any
Squeak with updates through 1523 should be capable of producing the
interpreter file.
>
>For our first real test of ImageSegments, we have implemented swapping of
morphic projects.  Thus, if you have an up-to-date image with a lot of
(morphic) projects in it, you can open the preferences panel and set
#projectsSentToDisk to true.  Thereafter, every time you change projects,
it will bring in the new project and send out up to two others.  Soon all
your projects will be on disk, and your kernel image will be smaller.  To
write all projects initially in one long pause (not necessary) do this:
>
>	Project storeAllInSegments.
>
>We have been testing this on a 70MB version of an image that Alan uses for
a lot of his presentations.  After segmentation the image is only 18MB, and
there is a companion folder of segments ranging from 20K up to 8MB, and
totalling 52MB (natch).
>
>Key to the effectiveness of this technique is that there be no pointers
from "the outside" into the morphic world that comprises the project.
Anything pointed to directly or indirectly other than by the roots of the
world will be excluded from the segment and will thus not get swapped out.
>
>Note that if you start using imageSegments, a folder will appear on your
disk named imageName_segs.  If you move or rename your image, this folder
must accompany it and remain named correspondingly.
>
>Have fun testing this, but remember:  You are testing.  This is a kernel
mechanism -- if one bit is wrong your system will crash.  But we just found
the last bug today.  We think.
>
>Enjoy
>	- Dan (and Ted)
>
>PS:  Prior users of ImageSegments will definitely want to get the new VM.
If you experienced problems in the past, it is likely things will work
better now.  We did find two fatal bugs in the last two weeks.
>
>
>
>
Serg Koren
VisualNewt Software
Serg at VisualNewt.com
http://www.VisualNewt.com