Osvaldo Pinali Doederlein
opinali at gmail.com
Wed Dec 16 03:21:53 PST 2009
Em 15/12/2009 17:20, Neal Gafter escreveu:
> On Tue, Dec 15, 2009 at 10:03 AM, Osvaldo Doederlein
> <opinali at gmail.com <mailto:opinali at gmail.com>> wrote:
> I wish closures to be as lightweight as possible. This means:
> a) The classes that closures are translated to, should be as small
> and fast to load as possible. These classes could benefit from
> JSR-292's anonymous classes, so each synthetic closure class
> doesn't load unnecessary metadata.
> My understanding is that most of the cost comes from the methods, not
> the class. In any case, loading is a one-time thing. SE 7 will
> improve that with a new format for use instead of jar files.
> The 292 EDR doesn't describe anonymous classes. Do you mean method
> handles? It isn't clear that code generated to 292's method handles
> would actually be faster, but without a proposal on how to do it all
> we can do is guess. I strongly encourage you to suggest a form for
> the specification and implementation that would do that.
I really meant anonymous classes, I just assumed this would be in the
scope of 292 because the original motivation was support for
dynamic-typed languages (long time since I've checked the EDR, not
following 292's list...). I realize that the space & loading costs are
small; but then, the same holds for the helper classes generated by many
dynamic langs. Of course the latter tend to produce a much higher number
of such classes; but then, I (somewhat optimistically) envision a future
with next-generation frameworks and DSLs abusing closures... if I ever
have five closures per method and fifty per class, even if that's just
in niche usages, any savings are significant, even with a better
> Lightweight closures are very important for any usage that
> involves abundant, fine-grained closures. One of my old pet peeves
> with Java inner classes is that they're so bloated; closures (as
> powerful as BGGA or CfJ 0.6a+b) will be even more bloated.
> I'm not sure in what sense you see those specifications as requiring
> weight in the implementation. Inner classes are certainly bloated in
> source, and have some start-up-time impact, but the objects themselves
> are small and fast to create and invoke.
I didn't see any impediment to the desired optimizations; I was just
worried that it could exist somewhere I didn't notice. But your feedback
clears these worries.
> It isn't clear how to use jsr292's method handles to specify and
> implement a language construct compatible with the strawman, or what
> the overhead of such a solution would be. I think such a research
> project would be a very worthy undertaking, though I'm afraid I can't
> allocate my own time to the task. If it is to be done in time for SE
> 7 (specified, implemented, and integrated by the beginning of June),
> then whoever wants to make it happen (is that you, Osvaldo?) should
> probably start immediately. I will be happy to provide as much
> feeedback as my time allows.
I didn't took the time to consider MethodHandles, that was not among my
suggestions. MHIs and closures are both special interfaces, so that's
likely another item in the wish-list of optimizations that I hope
somebody, sometime, will do - I'm not able to provide a significant
contribution for this, certainly not in the current JDK7 schedule.
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