Patch to fix Reference/natReference.

Thu Aug 21 18:59:00 GMT 2003

Tom Tromey wrote:
>David> If Reference.clear() is called and then the Reference is finalized
>David> before its referent, a dangling pointer is created in the object_list
>David> structure in natReference.cc. This happens because the 'copy' field
>David> of the Reference is cleared and that is what is used to find the slot
>David> in the object_list table.
>>Could you try the appended patch instead?
>We think that your patch will cause incorrect Reference semantics, so we 
did not try it.
There would be a race condition as follows:
1) GC decides that referent is collectable and puts it on the finalizer 
queue.
2) User program calles Reference.get() and obtains a valid hard 
reference to referent.
3) GC runs finalizer, causing the Reference to be cleared and put on the 
ReferenceQueue.
Step 3 should never have happened because there is a valid hard 
reference to the referent.
Disappearing links are cleared with the "World Stopped", so there is no 
race if they are used.
David.