here - Stefan-Marr.de

4.4. RoarVM
Used Software and Libraries Squeak and Pharo were used as development
platforms for specifying the operational semantics of the OMOP using Awe-
SOM and to develop the AST-transformation-based prototype (cf. Sec. 7.1).
While Smalltalk typically uses a bytecode-based representation of the compiled
code, transforming it is low-level and error-prone. To avoid the associated
complexity, the first prototype implementation of the OMOP uses code
transformations based on the AST (abstract syntax tree) instead. The main
benefit is that the AST will be used to generate bytecode that corresponds to
the expectations of the whole Smalltalk toolchain. Using direct bytecode transformation
can result in perhaps more optimal bytecode, however, the used
tools, i. e., the debugger and decompiler, accept only a subset of the legal bytecode
sequences, rendering some correct bytecode sequences non-debuggable.
The AST transformations uses the Refactoring Engine, 4 which generates ASTs
from Smalltalk code and provides a transformation framework implementing
the classic visitor pattern. With these tools it became possible to implement
AST transformations and produce bytecode that was executable and debuggable.
4.4. RoarVM
The RoarVM is a Squeak and Pharo-compatible Smalltalk VM designed and
initially implemented by Ungar and Adams [2009]. It is a platform for experimenting
with parallel programming on the Tilera TILE64 manycore processor
[Wentzlaff et al., 2007]. Building on top of the work of Ungar and Adams,
we ported it to commodity multicore systems. It enables the parallel execution
of Smalltalk code in a shared memory environment. Thus, Smalltalk processes,
i. e., threads, of a given image can be scheduled and executed simultaneously
depending on the available hardware parallelism.
Rationale for Choosing the RoarVM The RoarVM was chosen to experiment
with VM implementations for several reasons. On the one hand, the
complexity of the RoarVM is significantly lower than that of the CogVM, facilitating
experiments with different implementation approaches. Furthermore,
the RoarVM has a parallel execution model, which preserves the opportunity
to investigate support for parallel programming as part of future work (cf.
Sec. 9.5.1).
4 Refactoring Engine, Don Roberts, John Brant, Lukas Renggli, access date: 17 July 2012
http://www.squeaksource.com/rb.html
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