To: squeak@cs.uiuc.edu, sugar@ccc.uba.ar cc:
From: Juan Manuel Vuletich/Argentina/Contr/IBM @ IBMAR
Hello All - Hola a Todos (This message is repeated below in Spanish, for SUGAR people - En Castellano despues)
Sun has published the specifications for their new second generation Java virtual machine, these are some of its characteristics.
Interesting Aspects
-Handleless. Object references are direct pointers, just like in Squeak. - Accurate, generational, incremental copying garbage collector, with simultaneous mark and compactacion. Like the one Squeak always had. It seems they borrowed the ideas from Squeak! - Object Headers of 2 words (3 in some cases). Squeak is the only Object Environment where 83% (tipically) of the objects have a header with JUST ONE WORD. - Reflective Data represented as Objects. Classes are internally represented as objects.
Being Smalltalk-like more than ever, this new VM could allow us to generate Java bytecodes from a Smalltalk environment. Modifying Squeak object headers (from 1, 2 or 3 words) to use only 2 or 3 words, and surelly several other modifications , it should be possible to run the Squeak environment on a Java VM. This would allow an Internet browser to run Squeak without any plugin.
Not so interesting aspects.
- Enhanced thread management. - Enhanced C interfase - JIT compiler just for havily used code fragments. - Method Inlining.
Perharps, some of this is of interest to those working on optimizing Squeak interpreter.
Now in Spanish...
Sun publico la especificacion de la nueva maquina virtual de segunda generacion para Java en http://java.sun.com/products/hotspot/whitepaper.html, con las siguientes caracteristicas:
Aspectos interesantes
- Handleless. Las referencias a objetos son punteros directos, como en Squeak. - Accurate, generational, incremental copying garbage collector, con mark y compactacion simultanea. Como el que Squeak tuvo siempre. Parece que hubieran tomado la idea de Squeak! - Headers de Objetos de 2 palabras (3 en algunos casos). Squeak es el unico Ambiente de Objetos donde el 83% (tipicamente) de los objetos tiene header de SOLO 1 PALABRA. - Reflective Data represented as Objects. Las clases son (internamente) objetos.
Al parecerse a una maquina virtual Smalltalk mucho mas que antes, deberia ser mas facil la generacion de bytecodes Java en un ambiente Smalltalk. Modificando los headers de objetos de Squeak (de 1, 2 o 3 palabras) para usar unicamente 2 o 3 palabras, y seguramente algunas modificaciones mas, seria posible correr el entorno Squeak sobre una maquina virtual Java. Esto permitiria correr aplicaciones Squeak en un browser de Internet sin necesidad de un plugin.
Aspectos no tan interesantes
- Manejo de sincronizacion de threads mejorado - Interfase a C mejorada. - Compilador JIT solo para las partes de codigo mas usadas. - Method Inlining
Alguna idea quizas sea de interes a los que trabajan en optimizar el interprete de Squeak.
Juan Manuel Vuletich SW Export IGS- IBM Argentina Phone Nbr : 54-1-313-0014 ext. 5207 Tie Line : 840-5207 e-mail: vuletich@ar.ibm.com
Being Smalltalk-like more than ever, this new VM could allow us to generate Java bytecodes from a Smalltalk environment.
Given that it processes exactly the same bytecodes that all the other Java VMs do, there should be no difference at all in whether it will
allow us to generate Java bytecodes from a Smalltalk environment.
It might run them more quickly, or have a smaller memory footprint, but other than that there should be no observable differences in its behavior.
yours,
David Chase
Sun has published the specifications for their new second generation Java virtual machine, these are some of its characteristics.
Interesting Aspects
-Handleless. Object references are direct pointers, just like in Squeak.
Personally, I view this as a bug. Not having an object indirection pointer makes doing "Object become:" highly inefficent. Without a very efficent "become:" it's gets MUCH harder to do transparent proxying, which is real handy for distributing your objects across networks or storage devices. I agree that removing the memory indirection is a performance win. If performance were not an issue, I think an architecture where things are doubly indirect would be cool. You could then control security/protection of arbitrary sets of objects. For Smalltalk to be a full OS, I think this protection would be appropriate. Squeak is not really targeted as a OS replacement though.
- Object Headers of 2 words (3 in some cases). Squeak is the only Object
Environment where 83% (tipically) of the objects have a header with JUST ONE WORD.
This really confuses me. It seems like the reason for using direct object pointers is to eliminate the performance hit from the indirection, so instead you have to mask the header and do table indirections, is this really better? Memory is REALLY cheap now. I can remember when I first heard about Self requiring a 64 meg SparcStation, and though only lunatic fringe researches had that much memory. My 2 main Intel boxes now have 128 and 256 meg of RAM, even my laptop has 40 meg.
Being Smalltalk-like more than ever, this new VM could allow us to generate Java bytecodes from a Smalltalk environment. Modifying Squeak object headers (from 1, 2 or 3 words) to use only 2 or 3 words, and surelly several other modifications , it should be possible to run the Squeak environment on a Java VM. This would allow an Internet browser to run Squeak without any plugin.
A BIG difference between Smalltalk and Java execution environments is the handling of context's. In Java, contexts allways have stack like lifetimes. In Smalltalk, contexts need to be garbage collectable with arbitrary lifetimes. The Java VM architecture is not prepared to cope with this (at least in the past). A significant area of Smalltalk VM development is efficent implementaion of contexts.
- JIT compiler just for havily used code fragments.
- Method Inlining.
Isn't the Java HotSpot technology the evolution of the Self compiler/run-time. My understanding is some of the Self developers formed a company called Anamorphic Systems, which produced a Java/Smalltalk product. Sun then purchased Anamorphic to produce the HotSpot technology. Can anybody confirm or debunk this is how things happened? I'm not sure where I heard this.
It's real painful to watch the Java community relearn many of the same things the Smalltalk community learned MANY years ago. It's really disturbing to think the world has turned into a giant channel of reruns, and somebody misplaced the remote.
A few months back, I went to a demo at Parc of the Xerox Star (I first saw the Star in '81 at NCC). It was real interesting to be reminded that hardware has improved a few orders of magnitude in the last 17 years, but software mabey hasn't improved very much. So what can we do to get back on track for the next decade or two? In 20 years will software be 40 years behind hardware? Or will software be dramatically better than it is now.
Jan Bottorff, President Paradigm Matrix, Inc.
___________________________________________________________________ Paradigm Matrix Inc., San Ramon California "video products and development services for Win32 platforms" Internet: Jan Bottorff janb@pmatrix.com WWW http://www.pmatrix.com Phone: voice (925) 803-9318 fax (925) 803-9397 PGP: public key http://www-swiss.ai.mit.edu/~bal/pks-toplev.html fingerprint 52 CB FF 60 91 25 F9 44 6F 87 23 C9 AB 5D 05 F6 ___________________________________________________________________
squeak-dev@lists.squeakfoundation.org
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David Chase -
Jan Bottorff -
vuletich＠ar.ibm.com