[Gc] Trouble with disappearing links

I’m using disappearing links for the first time (I may not know what I’m doing) and they seem to be keeping the object that they are pointing to alive.
I don’t know why the disappearing link is not disappearing and appears to keep the object it points to alive.
Should I not be allocating the memory that contains the disappearing link within the Boehm managed memory?

Pseudo code:
1) I’m implementing a weak key hash table
2) I allocate two parallel arrays (key array/value array) using GC_MALLOC.
3) I write a key and value into each corresponding array.
4) I call GC_register_disappearing_link(&key[0]).  This should make the key entry at index 0 a disappearing link.
5) Then I destroy all references to the key other than what are in the array.
6) The key object stays alive until I reset the key[0] entry - then it gets finalized.


Here is a transcript of the Common Lisp session:

> (setq ht (make-weak-key-hash-table))
(setq ht (make-weak-key-hash-table))

#<CORE:WEAK-KEY-HASH-TABLE @0x11464c1d8) > 
> (low-level-describe ht)
(low-level-describe ht)
WeakKeyHashTable   size: 16
   keys memory range:  0x1142e0c00  - 0x1142e0d00 
   0  key.px@0x1142e0c00  unbound
   1  key.px@0x1142e0c10  unbound
   2  key.px@0x1142e0c20  unbound
   3  key.px@0x1142e0c30  unbound
   4  key.px@0x1142e0c40  unbound
   5  key.px@0x1142e0c50  unbound
   6  key.px@0x1142e0c60  unbound
   7  key.px@0x1142e0c70  unbound
   8  key.px@0x1142e0c80  unbound
   9  key.px@0x1142e0c90  unbound
   10  key.px@0x1142e0ca0  unbound
   11  key.px@0x1142e0cb0  unbound
   12  key.px@0x1142e0cc0  unbound
   13  key.px@0x1142e0cd0  unbound
   14  key.px@0x1142e0ce0  unbound
   15  key.px@0x1142e0cf0  unbound

> (setq key (cons 1 2))
(setq key (cons 1 2))

(1 . 2)
> (weak-hash-table-put ht 0 key 9999)
(weak-hash-table-put ht 0 key 9999)
../../src/gctools/gcalloc.h:969  Registered disappearing link 0x1142e0c00  obj 0x1120c5700  return val = 0

> (low-level-describe ht)
(low-level-describe ht)
WeakKeyHashTable   size: 16
   keys memory range:  0x1142e0c00  - 0x1142e0d00 
   0  key.px@0x1142e0c00  (1 . 2)@0x1120c5700   -->   9999
   1  key.px@0x1142e0c10  unbound
   2  key.px@0x1142e0c20  unbound
   3  key.px@0x1142e0c30  unbound
   4  key.px@0x1142e0c40  unbound
   5  key.px@0x1142e0c50  unbound
   6  key.px@0x1142e0c60  unbound
   7  key.px@0x1142e0c70  unbound
   8  key.px@0x1142e0c80  unbound
   9  key.px@0x1142e0c90  unbound
   10  key.px@0x1142e0ca0  unbound
   11  key.px@0x1142e0cb0  unbound
   12  key.px@0x1142e0cc0  unbound
   13  key.px@0x1142e0cd0  unbound
   14  key.px@0x1142e0ce0  unbound
   15  key.px@0x1142e0cf0  unbound

> (setq key nil)    ;;;   Here I wipe out the only non-disappearing reference to the key
(setq key nil)    ;;;   Here I wipe out the only non-disappearing reference to the key

NIL
> (gctools:garbage-collect)  ;; I force garbage collections - the key object is not collected although I think it should be
(gctools:garbage-collect)

> (gctools:garbage-collect)
(gctools:garbage-collect)

> (gctools:garbage-collect)
(gctools:garbage-collect)

> (gctools:garbage-collect)
(gctools:garbage-collect)

> ;; No finalization messages have been printed
;; No finalization message

> (low-level-describe ht)  ;; Here we see the key object is still alive
(low-level-describe ht)
WeakKeyHashTable   size: 16
   keys memory range:  0x1142e0c00  - 0x1142e0d00 
   0  key.px@0x1142e0c00  (1 . 2)@0x1120c5700   -->   9999
   1  key.px@0x1142e0c10  unbound
   2  key.px@0x1142e0c20  unbound
   3  key.px@0x1142e0c30  unbound
   4  key.px@0x1142e0c40  unbound
   5  key.px@0x1142e0c50  unbound
   6  key.px@0x1142e0c60  unbound
   7  key.px@0x1142e0c70  unbound
   8  key.px@0x1142e0c80  unbound
   9  key.px@0x1142e0c90  unbound
   10  key.px@0x1142e0ca0  unbound
   11  key.px@0x1142e0cb0  unbound
   12  key.px@0x1142e0cc0  unbound
   13  key.px@0x1142e0cd0  unbound
   14  key.px@0x1142e0ce0  unbound
   15  key.px@0x1142e0cf0  unbound

> ;; Key is still there
;; Key is still there


> (weak-hash-table-put ht 0 nil 9999)
(weak-hash-table-put ht 0 nil 9999)
../../src/gctools/gcalloc.h:969  Registered disappearing link 0x1142e0c00  obj 0x9  return val = 1

> (gctools:garbage-collect)   ;; Now the object will be collected and a finalization function called
(gctools:garbage-collect)
../../src/gctools/gcalloc.h:894 Boehm finalized weak linked address 0x1120c5700 at 0x1142e0c00

> (low-level-describe ht)
(low-level-describe ht)
WeakKeyHashTable   size: 16
   keys memory range:  0x1142e0c00  - 0x1142e0d00 
   0  key.px@0x1142e0c00  nil
   1  key.px@0x1142e0c10  unbound
   2  key.px@0x1142e0c20  unbound
   3  key.px@0x1142e0c30  unbound
   4  key.px@0x1142e0c40  unbound
   5  key.px@0x1142e0c50  unbound
   6  key.px@0x1142e0c60  unbound
   7  key.px@0x1142e0c70  unbound
   8  key.px@0x1142e0c80  unbound
   9  key.px@0x1142e0c90  unbound
   10  key.px@0x1142e0ca0  unbound
   11  key.px@0x1142e0cb0  unbound
   12  key.px@0x1142e0cc0  unbound
   13  key.px@0x1142e0cd0  unbound
   14  key.px@0x1142e0ce0  unbound
   15  key.px@0x1142e0cf0  unbound

>

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