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David,

Here's the problem I'd like to see solved: enable a
library to hold an indirect reference to a Class without preventing
that Class's loader from being reclaimed. The reclamation should happen
automatically when the loader is not otherwise strongly referenced.


You added a further requirement: the class-local value should not
prevent the library's loader from being reclaimed. For example, if code
loaded in a child class loader stores a value (which strongly
references a Class in the child loader) in a Class from the parent
loader, the class-local value in the parent-loaded Class should not
prevent the child loader from being reclaimed.


Your solution is to explicitly clear the class-local value (for
every class regardless of its loader), but doesn't that fail to solve
the original problem? If you're going to explicitly clear anyway, why
do you need this mechanism in the first place?


When I started this thread, I was content with solving the simpler
case: a library loaded in the parent class loader associating data with
classes loaded in a child loader. This is solvable at the library level
and doesn't require explicit clearing. If I want a library loaded in
the child class loader to store information about classes from the
parent loader, I can just keep strong references to the Class objects
because I know that the child loader will be reclaimed before the
parent loader.


Your problem can't be solved at the library level (without explicit clearing, which defeats the purpose of this construct). Ephemerons are the only viable solution that I know of.

Bob