2007-03-22

Prunes. Thursdays. Fortress. Locks.

I'm going to try and get a bit more regular with my blogging. Like every Thursday.

This week, I've got my hands on an iRex Iliad from work so I can read the 400 odd page Fortress language specification (1.0 beta) without killing a small tree.

I like Fortress' traits system, it seems to have enough information for the sort of semantic compiler optimisations and automatic parallelism I'm interested in. Although the language doesn't expose these, it's very similar to some of the sorts of thing I was trying to do at BAE with code generation from a maths model, which led me to start playing with kin. Though kin is relational rather than functional. The reference interpreter isn't a high performance system; if I get some time and the kin interpreter gets anywhere, I may use Fortress as an input language, though I do want to do something more with the relational aspect. I like that its definition of an integer is based on rings and fields rather than bit-string operations. My fiancée is in Romania from May to September, so, instead of just pining away, I may actually stop talking and do something on kin rather than a sequence of 400 line micro-benchmarks.

Both for work and kin I've been trying to get up to speed with these guy's work; the publish-subscribe idiom is used heavily within the virtual machine for the system I'm creating at work, and it seems to spend an inordinate proportion of its time waiting for locks on the properties it's published (I'm still getting to grips with interpreting VTune's output for multi-threaded apps).

kin related I'm trying to think of a nice way of packing R32 and R64 vectors so you can both look up type information and operate on them using SSE. For objects with a reference to their type, if each type is aligned to a cache line, it gives more state bits in the word - 4 rather than 2 for a 32bit aligned pointer, which may be useful. For a primitive field in an object, the field type can be associated with the object's value rather than the field's value, as it can't be aliases, so all code which accesses it has to go through the object's traits first. The cases I want to optimise, such as Array[/ (R32)^4, (ZZ32,ZZ32) /] (a 2D array of 4D 32 bit vectors, which has a very efficient contiguous representation) I imagine would also have access to the type of the array and functions would operate primarily on the array. But mapping a magnitude function onto the Array would need to operate on the type of the element, and I was imagining a fully dynamic dispatch (which then solidifies and inlines the commonest branches). Maybe pushing the type onto the function argument stack would work in those cases, rather than making every value carry its type around. In that case, the array member case and the object field or method local variable cases are all the same - the context you got the value from can give the type of the value, which is either the global ref to the type of a primitive, or the reference to the metaclass of a reference type. That should work for both Fortress and ECMAScript type objects constructed from traits. My current model for running ECMAScript is that each time you set a field on an ECMAScript object to a value of a different type to the type you create a new reference type trait object to describe it; these anonymous traits are reference counted in addition to any memory management so may modify rather than copy previous traits if they are only used by the one object; not original but amenable to having a common runtime for all the sorts of languages I tend to use - hpc, dynamic UI, and relational logic.


TME

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