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GC dead links in weak hash tables before a possible rehash

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* libguile/hashtab.c (vacuum_weak_hash_table): New helper, goes through
  the entirety of a weak hash table, vacuuming dead entries.
  (scm_hash_fn_create_handle_x): If when adding to a weak hash table, we
  would trigger a rehash, vacuum the table first.  The weak_bucket_assoc
  would have only caught dead entries within one bucket.

  Without this patch, the following code leaks:

  (let lp ()
    (call-with-output-string
      (lambda (port)
        (display "foo" port)))
    (lp))
This commit is contained in:
Andy Wingo 2011-02-23 11:59:38 +01:00
parent 85bdb6ac9c
commit 40d2a0076a
1 changed files with 29 additions and 5 deletions
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34
libguile/hashtab.c
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@ -120,6 +120,26 @@ scm_fixup_weak_alist (SCM alist, size_t *removed_items)
return result;
}
static void
vacuum_weak_hash_table (SCM table)
{
SCM buckets = SCM_HASHTABLE_VECTOR (table);
unsigned long k = SCM_SIMPLE_VECTOR_LENGTH (buckets);
size_t len = SCM_HASHTABLE_N_ITEMS (table);
while (k--)
{
size_t removed;
SCM alist = SCM_SIMPLE_VECTOR_REF (buckets, k);
alist = scm_fixup_weak_alist (alist, &removed);
assert (removed <= len);
len -= removed;
SCM_SIMPLE_VECTOR_SET (buckets, k, alist);
}
SCM_SET_HASHTABLE_N_ITEMS (table, len);
}
/* Packed arguments for `do_weak_bucket_fixup'. */
struct t_fixup_args
@ -651,12 +671,16 @@ scm_hash_fn_create_handle_x (SCM table, SCM obj, SCM init,
}
SCM_SETCDR (new_bucket, SCM_SIMPLE_VECTOR_REF (buckets, k));
SCM_SIMPLE_VECTOR_SET (buckets, k, new_bucket);
/* Update element count and maybe rehash the table. The
table might have too few entries here since weak hash
tables used with the hashx_* functions can not be
rehashed after GC.
*/
SCM_HASHTABLE_INCREMENT (table);
/* Maybe rehash the table. If it's a weak table, pump all of the
buckets first to remove stale links. If the weak table is of
the kind that gets lots of insertions of short-lived values, we
might never need to actually rehash. */
if (SCM_HASHTABLE_WEAK_P (table)
&& SCM_HASHTABLE_N_ITEMS (table) > SCM_HASHTABLE_UPPER (table))
vacuum_weak_hash_table (table);
if (SCM_HASHTABLE_N_ITEMS (table) < SCM_HASHTABLE_LOWER (table)
|| SCM_HASHTABLE_N_ITEMS (table) > SCM_HASHTABLE_UPPER (table))
scm_i_rehash (table, hash_fn, closure, FUNC_NAME);