Are weak references cleared with soft ones?

Question

Suppose a program holds both weak and soft references to an object X. Suppose the virtual machine clears all the soft references at once, making X weakly reachable. Is the virtual machine guaranteed to clear all the weak references next before normal execution resumes?
I ask because I am setting up an automatic interning system for immutable objects of a certain class that will guarantee that at most one object of a given value is reachable by the rest of the program at one time but will allow objects to be garbage collected if necessary. I need to decide what reference object(s) to keep to each interned object. If I keep only a weak reference, objects will be discarded at the whim of the virtual machine; I would prefer to keep them around longer so they don't have to be recreated so many times. If I keep only a soft reference, I am concerned that another part of the program might keep a weak reference. If the answer to my question above is "no", the soft reference could be cleared and the interning system could create a second object with the same value while the first is still accessible via the weak reference. It seems safest to keep both a soft reference and a weak reference and only recreate the object if the weak reference has been cleared.

Answer 1

Softs hang around until memory needs dictate theygo.
In my experience (Apple's 1.4 VM) this appears to be
as soon as GC is run, making them effectively
useless. Maybe VMs have improved.Not in my experience (Sun 1.4 VM). Soft references hang around forever. I had to stuff my class with bloat to make the instance larger, then change the VM heap size to get it to start collecting my soft references. Whereas the weak references are dumped ASAP. Inside scoop has it that finalizers will delay object collection a bit so be careful of that.
Also the only guarantee is that soft is cleared before weak when they refer to the same object. in my experience weak references go quickly. Like at the first GC when they are weak. You can not depend on any timing with respect to when the weak will be cleared. I don't think the spec even guarantees that soft will be enqueued before weak. Im not sure on that point.