On Jan 6, 2011, at 1:12 AM, Helmut Eller wrote: > * John Rose [2011-01-06 02:37] writes: > >> "Live constants" are definitely one of the use cases that >> invokedynamic is designed for. > > Are/will there be any means to link invokedynamic call sites eagerly > instead of the lazy linking scheme? > > E.g. in Lisp there is this form > > (load-time-value <exp> t) > > that is essentially a constant but <exp> must be evaluated at load time > and not later (as would be done with lazy linking).
This is an unusual pattern for the JVM, but it can be done with invokedynamic by pre-executing the constant-load instruction, as follows: 1. Translate the LTV form into an invokedynamic instruction. 2. Emit the invokedynamic instruction into a private static helper method. 3. Call the helper method from two places: The intended use point, and the <clinit> method. That way, class loading executes <clinit>, which then "warms up" (links) the invokedynamic instruction. If you have many LTV forms in a compilation unit, this leads to many small helper methods, which may be inconvenient. If that is the case, consider a more complex scheme where all LTV forms in a compilation unit are collected, and their evaluation results collected into a private static final object array. Then, individual lazy-linked invokedynamic instructions can pick from the array.. With such a population of similar invokedynamic instructions, it can help (as Mark discovered) to share a common BSM and use the name field to send in a single simple parameter. The most direct way to specify a parameter to a BSM for a single invokedynamic instruction is to specify a static argument in the BootstrapMethods attribute. This is a relatively new feature: http://cr.openjdk.java.net/~jrose/pres/indy-javadoc-mlvm/java/dyn/package-summary.html#args If the parameter is a name-string or if you don't mind decoding strings, you can also specify it as the name of the relevant NameAndType. -- John _______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
