Hi Markus,
if I understand correctly some of the possibilities:
- I can use RBParseTreeSearcher / RBParseTreeRewriter on the twin AST.
(any example how to install / invalidate the twin AST after an effective
RBParseTreeRewriter operation?)
- Any change to the Twin AST is reflected in the method bytecode (as
long as one does invalidate).
This would mean being able to put tracing code with RB patterns, no? And
without having to do a recompilation of the traced method?
Thierry
Le 27/02/2015 00:07, Marcus Denker a écrit :
Hi,
In 40516 there is now a strange, but rather powerful mechanism for
CompiledMethod: the Twin.
What does that do?
you can call on a method #createTwin
(ReflectivityExamples>>#exampleMethod) createTwin.
after this, the CompiledMethod has a high-level representation (the AST)
attached that itself references the CompiledMethod
(they form a twin).
(ReflectivityExamples>>#exampleMethod) reflectiveMethod
The fun thing is now that one can install either in the class. Call #invalidate
to make sure the reflective method is installed.
ReflectiveMethod implements #run:with:in: which calls a compilation hook (too
re-create from the AST) and then installs that in the
method dict and then executes the method:
(ReflectivityExamples>>#exampleMethod) createTwin.
(ReflectivityExamples>>#exampleMethod) invalidate.
self assert: (ReflectivityExamples>>#exampleMethod) class =
ReflectiveMethod.
self assert: ReflectivityExamples new exampleMethod = 5.
self assert: (ReflectivityExamples>>#exampleMethod) class =
CompiledMethod.
Which means that this gives us an in-image, on-demand JIT compiler
AST->Bytecode. In 50 lines of code.
e.g. try on Morph:
Morph methods do: #createTwin.
Morph methods do: #invalidate.
Counting which twin is installed shows us the working set of Morph:
(Morph methods select: [ :each | each class = CompiledMethod ]) size
some 330 method out of nearly 900….
So what can one do with this? In essence this turns the AST into a reflective
representation for Methods
(if you care to set up twin creation + invalidation correctly).
What will this allow us to do? stay tuned...
Marcus
