New subject: [ANN] ExperimentalBit [WAS] Re: Out of the box primitives for bit in ObjectHeader?

22 Dec 2011

      Hi guys. Last days I needed to migrate some old code I used to have in the
VM for tracing objects usage. Luc Fabresse wanted also to be able to set
and get the value of a bit in the object header to do some experiments.
So...we thought it was a good idea to make it abstract an public. So....the
following is only one morning work we did together with Luc, so don't
expect that much. What we did is to do a very small change in the VM to use
one free bit in the object header, and then we coded 3 primitives: one to
get the value, one to set it and one to unmark all objects. The idea is
that you can use this code and give semantics to the bit. This is just for
experimenting and prototypes, not for production code since such bit in the
object header may not be available.
To download:
Gofer it
    url: 'http://ss3.gemstone.com/ss/ExperimentalBit';
    package: 'ConfigurationOfExperimentalBit';
load.
Now.... you can read ConfigurationOfExperimentalBit  class comment:
---------------
ExperimentalBit is a small facade for setting and getting the value of a
bit in the Object Header. It requires a special VM which supports the
primitives to set and get the value of such bit. You can get a already
compiled MacOSX VM from: https://gforge.inria.fr/frs/download.php/30042/
CogMTVM-ExperimentalBit.zip. For more details read class comment of
ExperimentalBitHandler.
If you already have a compiled VM with the required primitives, then you
can just load the image side part evaluating:
((Smalltalk at: #ConfigurationOfExperimentalBit) project version: '1.0')
load.
If you want to build a VM with the primitives we need, you need to download:
((Smalltalk at: #ConfigurationOfExperimentalBit) project version: '1.0')
load: 'VMMakerGroup'.
And then follow the steps to build the VM:
- http://code.google.com/p/cog/
- http://code.google.com/p/cog/wiki/Guide
-----------
And here ExperimentalBitHandler class comment:
-----------
ExperimentalBitHandler is a small facade for setting and getting the value
of a bit in the Object Header. It requires a special VM which supports the
primitives to set and get the value of such bit. You can get a already
compiled MacOSX VM from: https://gforge.inria.fr/frs/download.php/30042/
CogMTVM-ExperimentalBit.zip.
To know which version of the VM you have to use to compile, check the
dependencies in ConfigurationOfExperimentalBit and also the 'description'
of it. For example, if version 1.0 it depends on 'CogVM' version '3.7'. In
the description of version 1.0 you can also read that the used Git version
of the platform code was 4a65655f0e419248d09a2502ea13b6e787992691 from the
blessed repo.
Basically, there are 3 operations: set the bit to a specific, get the value
of the bit and turn off the bit of all objects. Examples:
'aString' experimentalBit: true.
'astring ' experimentalBit.
Date today experimentalBit: false.
Date today experimentalBit.
ExperimentalBitHandler turnOffExperimentalBitOfAllObjects.
For more details see ExperimentalBitTest.
-------------
Happy Christmats for all the Smalltalk hackers!!!
-- 
Mariano
http://marianopeck.wordpress.com

On Wed, Dec 14, 2011 at 1:24 PM, Mariano Martinez Peck <
marianopeck@gmail.com> wrote:

> Hi guys. As you may notice, I always try to push in the direction of a VM
> where we can have both things: a) a really cooler super fast VM for
> production super critical applications  and b)  the most-flexible-possible
> VM for doing reasearh and experiment.
>
> Now I was thinking the following:  we have one free bit in the
> ObjectHeader. Let's say you are experimenting with something and you would
> like to tag objects, such as, "traversed", "processes", "isProxy", etc. To
> do that small experiment you need to modify the VM, adapt the bit, code the
> primitives, build the VM, put the smalltalk side part etc etc. So I was
> thinking why not providing such small functionality out of the box?  the
> idea would be not to give semantics to the bit since each user will do
> that. So we just provide the VM with 2 primtives, one to get the value
> (#getBitValue) and one to set it (#setBitTo:). Choose the names you want.
>
> Then we do not integrate nothing in our images that use such bit, there
> won't be colisions. Then each guy who wants to experiments with that, can
> use the primitives and do what he wants.
>
> Some people is doing something with its bit: Jean Batiptse is doing XXX, I
> am doing YYY, etc. Either in his work or mine, there are much more changes
> that just that bit, so in anyway, I will end up needing my own VM.
>
> Finally, I could help in providing the code if it is needed.
>
> So, what do you think?
>
> --
> Mariano
> http://marianopeck.wordpress.com
>
>

-- 
Mariano
http://marianopeck.wordpress.com