- From: Henrik Frystyk Nielsen <frystyk@w3.org>
- Date: Wed, 26 Jun 1996 09:05:51 -0400
- To: brian@quiotix.com (Brian Goetz), www-lib-bugs@w3.org
Brian Goetz writes:
> In HTNet.c, in HTNetCall_deleteAll, you use the following logic to delete
> all elements of a list:
>
> while ((pres = (NetCall *) HTList_nextObject(cur))) {
> HTList_removeObject(list, (void *) pres);
> HT_FREE(pres);
> }
>
> Unfortunately, this involves cur now pointing to an element that has been
> freed. This works, accidentally, in most non-threaded environments, but
> it's a very dangerous coding practice. (I think this derives from the
> somewhat non-obvious way in which the HTList_nextObject macro works.)
>
> This logic is used in other places in the library, too. Possible solutions:
> - place the code "cur = list" after the HT_FREE in this loop (not the best
> solution, IMHO)
> - Don't remove the object inside the loop; just free all the objects, and then
> free the list (also has some undesirable behavior in threaded environments)
> - Use a thread-safe "enumerate" macro, which might allow for the enumerated
> objects to be deleted.
> - lots of others.
Yes - you are right - this is a dangerous thing. What I have tried to enfore is to
not remove the list until after the objects have been cleared. Then the cur pointer
are always valid.
BTW: What kind of threaded environment are you using?
I am very interestded in hearing about your experiences!
Thanks!
Henrik Frystyk
Received on Wednesday, 26 June 1996 09:05:53 UTC