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fix subtle and bad scm_internal_hash_fold bug for weak tables

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* libguile/hashtab.c (scm_internal_hash_fold): Don't try to unlink
  deleted weak pairs.  Our previous code was buggy (`prev' should have
  only been updated in the case of a successful traversal), but more
  than that, we're not in the alloc lock.

  Thanks very much to Michael Wells for the report, and the debugging!
This commit is contained in:
Andy Wingo 2011-05-30 11:33:10 +02:00
parent dfb572a7bf
commit 2187975e39
1 changed files with 10 additions and 30 deletions
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36
libguile/hashtab.c
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@ -1377,39 +1377,19 @@ scm_internal_hash_fold (scm_t_hash_fold_fn fn, void *closure,
n = SCM_SIMPLE_VECTOR_LENGTH (buckets);
for (i = 0; i < n; ++i)
{
SCM prev, ls;
SCM ls, handle;
for (prev = SCM_BOOL_F, ls = SCM_SIMPLE_VECTOR_REF (buckets, i);
!scm_is_null (ls);
prev = ls, ls = SCM_CDR (ls))
for (ls = SCM_SIMPLE_VECTOR_REF (buckets, i); !scm_is_null (ls);
ls = SCM_CDR (ls))
{
SCM handle;
if (!scm_is_pair (ls))
SCM_WRONG_TYPE_ARG (SCM_ARG3, buckets);
handle = SCM_CAR (ls);
if (!scm_is_pair (handle))
SCM_WRONG_TYPE_ARG (SCM_ARG3, buckets);
if (SCM_HASHTABLE_WEAK_P (table))
{
if (SCM_WEAK_PAIR_DELETED_P (handle))
{
/* We hit a weak pair whose car/cdr has become
unreachable: unlink it from the bucket. */
if (scm_is_true (prev))
SCM_SETCDR (prev, SCM_CDR (ls));
else
SCM_SIMPLE_VECTOR_SET (buckets, i, SCM_CDR (ls));
/* Update the item count. */
SCM_HASHTABLE_DECREMENT (table);
if (SCM_HASHTABLE_WEAK_P (table) && SCM_WEAK_PAIR_DELETED_P (handle))
/* Don't try to unlink this weak pair, as we're not within
the allocation lock. Instead rely on
vacuum_weak_hash_table to do its job. */
continue;
}
}
else
result = fn (closure, SCM_CAR (handle), SCM_CDR (handle), result);
}
}