On 05/16/2011 09:52 AM, John Rose wrote: > On May 15, 2011, at 5:36 PM, Charles Oliver Nutter wrote: > >> Can I get a rough guesstimate from the JVM guys how much more overhead >> is involved in accessing a never-changed MutableCallSite versus a >> ConstantCallSite? I have a few places where I want to use >> invokedynamic to lazily initialize some literals. They'll never change >> after the initial construction, but I can't create them in the >> bootstrap because I need the state they pass in (e.g. the >> org.jruby.Ruby instance they're associated with). I'd like to bind a >> constant method handle into the site after the first call and never >> change it again. > At this point, the overhead is nil, because we don't special-case CCS yet. > :-( > > When we do a pass of performance tuning, we'll fix that, and then the > overhead (MCS/CCS) is likely to be a memory reference or two, plus a branch. > > If you are building bytecodes which are specific to a particular > org.jruby.Ruby instance, see if you can put a backpointer to the instance > onto the Class containing the bytecodes, using ClassValue or a static field > or a similar mechanism. Then you can access the Ruby instance in the BSM, > and use a CCS. You are trying to do something pretty normal here, and I'm an > intrigued that it is so hard to get the right info in the BSM; it shouldn't > be.
You need a kind of serialization (using bootstrap arguments) or to store the value somewhere to get it after in the BSM, note that this pattern creates a memory leak, I think the only way to avoid it is to have a special Class.define (a la AnonymousClassLoader) that takes a class with placeholders and the corresponding runtime values > -- John Rémi _______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
