On 25 Ago, 20:21, Nick Zbinden <nick...@gmail.com> wrote: > @Aaron: Could you go into why this is the case? What does jruby do > that it needs it so much and clojure does not. > > @Tal Liron: You seem to differ in your opinion with Aaron (pretty sure > you would not be investing your time otherwise). What exactlly are you > attempting to speed up and how does invokedynamic help?
I'm neither of them, nor I am a Clojure hacker, but still I think I can contribute something to the discussion. invokedynamic is basically a hook in the JVM's linking system; it allows language implementers to resolve method calls respecting the semantics of their language, but letting the JVM know about it so it can optimize those method calls. invokedynamic is not just that - it has advanced features like the ability to invalidate call sites (thus forcing the JVM to redo the linking) or to emit guarded calls, in order to specialize "fast paths" (e.g. primitive arithmetic) while providing a slow fallback path (e.g. generic arithmetic). It mostly benefits dynamic object-oriented languages - Ruby, Python, Smalltalk etc. - because all their method calls can get promoted to "native" JVM method calls instead of being implemented in user code. In dynamic functional languages like Lisp dialects, method resolution is not a problem - there's a single method, apply (simplifying things a bit). invokedynamic can help with *class* resolution instead: now in Clojure or Common Lisp every function call which is not inlined must pass through the symbol (or Var in Clojure) - e.g. functionNameSymbol.getFunction().apply(...). This is hard to optimize because the actual class implementing the function is not known to the JVM. With indy that pattern can become simply: invokedynamic "functionName" args - and the Lisp system can resolve the function only once (at least until it is redefined). I.e. the JVM will translate that instruction to: invoke TheClassImplementingTheFunction.apply(theFunctionInstance, ...args). This should make function calls more optimized. Advanced uses of invokedynamic - while complex - can implement things like runtime type-based optimizations as well; but I don't know if that's worth the effort for Lisps. And perhaps there are other or alternative uses of invokedynamic that I haven't considered, please share your ideas! Peace, Alessio -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
