I have discovered that DRLVM appears to clear the referent field of a
PhantomReference before calling its enqueue() method (this can be shown
quite easily by printing the referent field in Reference.enqueue()).
This behaviour appears to differ from the RI, on which a non-null
referent can be got hold of via reflection [1]. The spec for
PhantomReference says:
"Unlike soft and weak references, phantom references are not
automatically cleared by the garbage collector as they are enqueued. An
object that is reachable via phantom references will remain so until all
such references are cleared or themselves become unreachable."
This reads to me that soft and weak references clear their referent
field before being enqueued, but phantom references should only make the
referent eligible for gc once the referent is no longer phantomly
reachable (or reachable at all). If this is the case, it would seem that
DRLVM's current behaviour does not match the spec.
Any comments/thoughts?
Regards,
Oliver
[1] An example of this kind of use/abuse of PhantomReference can be
found at:
http://www.roseindia.net/javatutorials/references.shtml
--
Oliver Deakin
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