[Pharo-dev] The evil twin in 40516
marcus.denker at inria.fr
Thu Feb 26 18:07:43 EST 2015
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
after this, the CompiledMethod has a high-level representation (the AST) attached that itself references the CompiledMethod
(they form a twin).
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:
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...
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