betz (04/06/83)
Patch for XLISP Version 1.0
It turns out that there is a fairly serious problem with the
version of 'xlobj.c' that I sent out with the most recent
xlisp distribution. The problem occurs when a new object is
being allocated. The routine that allocates the list of
instance variable values for the new object fails to
register the pointer to the list it is constructing. This
means that if garbage collection is initiated during the
process of building the new list, it is possible that the
garbage collector could collect the part of the list that
has already been built. In order to solve this problem, the
following routine should be inserted into the distribution
copy of 'xlobj.c' replacing the routine with the same name.
/* makelist - make a list of nodes */
static struct node *makelist(cnt)
int cnt;
{
struct node *oldstk,list,*lnew;
/* create a new stack frame */
oldstk = xlsave(&list,NULL);
/* make the list */
for (; cnt > 0; cnt--) {
lnew = newnode(LIST);
lnew->n_listnext = list.n_ptr;
list.n_ptr = lnew;
}
/* restore the previous stack frame */
xlstack = oldstk;
/* return the list */
return (list.n_ptr);
}
After replacing the 'makelist' routine, 'xlobj.c' should be
recompiled and xlisp should be relinked.
Sorry about that!
David Betz