Hello list

Hello list,

my name is Marc Hanisch, I'm from Germany and I recently joined the
list. I'm new to GNU Smalltalk but was curious about the language,
because every time I heard about cool features of a programming
language (like Ruby) they said: this feature came from Smalltalk :-)

I'm familiar with C-like languages (C, Java and most of the time PHP
but Ruby too) and playing around with GNU Smalltalk is very exciting.

At the moment I'm a bit confused about images vs. files. I'm
accustomed to work with files with my favorite texteditor in PHP and
this works in Smalltalk, too. But what is the advantage of images?
And to be honestly, the GNU Smalltalk documentation is not the best
and clearly one...

So maybe someone can show me the advantages of images or why to use them...

Best regards,
Marc

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> At the moment I'm a bit confused about images vs. files. I'm
> accustomed to work with files with my favorite texteditor in PHP and
> this works in Smalltalk, too. But what is the advantage of images?

I think this post

    http://gbracha.blogspot.com/2009/10/image-problem.html

shows the advantages and disadvantages of images pretty well.

In GNU Smalltalk, the image is used mostly as a cache of preloaded
packages.  It allows very fast startup because all the code is already
compiled and converted to objects (instances of Class, CompiledMethod,
etc.).  See also

    http://smalltalk.gnu.org/faq/37

which expands a bit on this topic.

> And to be honestly, the GNU Smalltalk documentation is not the best
> and clearly one...

What did you find confusing, exactly?

Paolo

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Hello Paolo,

thank your for the hints...

2010/5/20 Paolo Bonzini <[hidden email]>:
I'm currently editing my class files with an editor. Implies the use
of images, that I have to edit my classes inside of gst? Or can I mix
both approaches?

>
>> And to be honestly, the GNU Smalltalk documentation is not the best
>> and clearly one...
>
> What did you find confusing, exactly?

The users guide is somewhat undidactic. There are no words about the
differences between the standard and GNU Smalltalk (for example the
braces in methods, the different initialisation of instance and class
variables (instanceVariableNames, classVariableNames etc)) in the
introduction. This makes it hard for new users :-)

Therefore the class-reference is fantastic :-D

Best regards,
Marc

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On 05/20/2010 10:18 AM, Marc Hanisch wrote:
People who edit their classes inside GST will have to answer. :-)

But yes, you can in general mix both approaches.  The most common way is
to make an image with some packages preloaded (e.g. Seaside or Iliad)
and then you load your code into it.  That's much faster than waiting
for GST to reload code from the entire web framework (and dependent
packages) everytime.

Thanks.  The tutorial is supposed to be a bit more complete about that,
but it's not optimal (and a cross-reference would help).

Paolo

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On Thu, 20 May 2010 08:16:48 +0200
Marc Hanisch <[hidden email]> wrote:

> Hello list,

Hello Marc,

have you read Canol's book?

http://www.canol.info/books/computer_programming_using_gnu_smalltalk/

s.

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Stefan Schmiedl wrote

Hello Marc,

have you read Canol's book?

http://www.canol.info/books/computer_programming_using_gnu_smalltalk/

Although the book might answer some other newbie questions of Marc, it does not mention about the image system, yet. Hopefully, second edition will cover more Smalltalk (and GNU Smalltalk, in particular) specific topics like images, packages, VisualGST etc.

> Although the book might answer some other newbie questions of Marc, it does
> not mention about the image system, yet. Hopefully, second edition will
> cover more Smalltalk (and GNU Smalltalk, in particular) specific topics like
> images, packages, VisualGST etc.

Actually, I think that only three people could answer about how to use
images with GST, and that does not include me (which is a good thing,
since I cannot be considered omniscient...).  That's of course Berto,
Nicolas and Sebastien since they used GST in production.

All I know is that Berto is using Postgres for his data, while the two
Odyssey people are using images and ObjectDumper as their primary
persistence strategies.  I imagine their handling of images is pretty
different, though all three of them are using gst-remote.

So if any of you could write a blog post about how to use images for
GST apps that would be really great.

Paolo

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Hi guys,

> So if any of you could write a blog post about how to use images for
> GST apps that would be really great.

Sure, I can do it, but I think our use of images is pretty specific to
web applications.
I'll try to write more details in a blog post, but the basic idea is
that we load all our packages and save the image with a bash script like

echo "PackageLoader fileInPackage: '...'. ObjectMemory snapshot:
'foo.im'" | gst

This way we can start gst with all our packages very quickly.
Then we start the image with loaded packages with gst-remote.

We don't use the image itself as persistence, instead we save all our
data in binary (using ObjectDumper) or xml format. This means we always
have all our data loaded in memory and that we save the entire database
each time. We can afford it since we don't have too much data, and for
small applications I think it works fine. Of course if you have 40Gb of
data, it may not work for you.

Another interesting use of images for us, since we have one image and db
per website, is to stop gst-remote and make a snapshot (this time with
all data loaded) when all sessions expire. Then we would restart them
for the next request. We didn't try it in production yet, but our
experiments seem quite conclusive.

Cheers,
Nico

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