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From: Alexandre Pilkiewicz <alexandre.pilkiewicz@polytechnique.org>
To: caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Questions on replacing finalizers and =?iso-8859-1?q?memory=09footprints?=
Date: Sat, 8 Dec 2007 10:57:54 +0100
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X-Spam: no; 0.00; finalizers:01 footprints:01 filliatre:01 hashtable:01 hash:01 hash:01 hashtbl:01 node:01 memq:01 node:01 garbage:01 caml-list:01 termination:01 int:01 append:02 

Le Friday 07 December 2007 22:01:23 forum@x9c.fr, vous avez =E9crit=A0:
> Le 7 d=E9c. 07 =E0 20:54, Jean-Christophe Filli=E2tre a =E9crit :
> My mistake, I did not take into account the fact that if a block is
> moved by the
> garbage collector, its reference is updated in the hashtable *too*.
> Hence the termination guarantee.

I think the problem is with the hash function :

	let hash o =3D Hashtbl.hash (magic o : int)

If you put an object in the hash table, it is stored under a key that depen=
ds=20
on it's address a1. Once it's moved by the GC to the address a2, its=20
reference is changed to a2, but not its key which is still the hash of a1. =
So=20
when you check after that if your object is allready in the hash table, you=
=20
look under the key hash(a2) if it's allready there, but it's not ! And if y=
ou=20
are very unlucky (and have very few memory), it might append several time.

One solution could be to store the objects in a normal list and to look at =
the=20
entire list every time. It would be *much* slower on huge structures, but=20
probably more "correct" (so if used only for debug purpose, why not..)

let node_list =3D ref []

let in_list o =3D List.memq o !node_list

let add_in_list o =3D node_list :=3D o::!node_list

let reset_list () =3D node_list :=3D []

=2D-=20
Alexandre Pilkiewicz