Re: [PATCH] Marking weak alist vectors, #2

[Han-Wen Nienhuys]

Ludovic Courtès wrote:
> Hi,
>
> Below is an improved version of the patch I originally sent.  The goal
> of the original patch (and associated test case) was to ensure that an
> object associated to a weak key (resp. a weak value) is GC'd _after_
> that key (resp. value).
>
> However, as Han-Wen pointed out earlier in this thread, with the
> original patch, cyclical structures within a weak-key (or weak-value)
> alist vectors would never become unmarked.  By "cyclical structure", I
> mean something like:
>
>   key A is associated to B
>   key B is associated to C
>
> Here (assuming a weakly-keyed alist vector), object B is used both as a
> key and a value, resulting in a "cyclical structure".

No, this is not cyclic. The problem is a situation where key A is 
associated to key A, eg.

  (define x (cons 1 2))
  (set-cdr! x s)
  (weak-key-hash-table-set! table s x)

x points back to s, and s is a key in the table.

(I haven't looked at how your patch deals with this, just clarifying 
your text)

--
 Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen