hg: mlvm/mlvm/jdk: meth: add @Hidden annotations

[John Rose]

On Jul 11, 2012, at 2:29 AM, Rémi Forax wrote:

> just a question, even if it's not a big deal if one is able to generate 
> bytecode,
> why Hidden is not a top level type of java.lang.invoke ?

Good question.  The answer is that hiding of stack frames is limited to hiding method handle implementation details.  Specifically, the frames that are to be hidden are those which are not specified by the JSR 292 modifications to the JVMS.

For example, if you have z=filterReturnValue(::x,::y), and some method m does z.invoke(), the visible stack frames will be m calling x and m calling y.  Internally there will be a continuation during the call to x which waits to apply y.  This must be some sort of activation frame, but the JVMS requires it to be hidden.  In JDK 7 it was a ricochet frame (hand assembly code) and in JDK 8 it will be a lambda form activation (bytecode).  Both must be suppressed in backtraces.

A general Lisp-machine-style convention for redacting back traces would be interesting, but it would also require a new JSR.

On the other hand, Hidden could be top-level.  It's a matter of coding taste.  Binding it to LF makes it more clear that it has a specific use.

— John

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