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-rw-r--r--libguile/hashtab.c322
1 files changed, 208 insertions, 114 deletions
diff --git a/libguile/hashtab.c b/libguile/hashtab.c
index 2fe09196c..633d26261 100644
--- a/libguile/hashtab.c
+++ b/libguile/hashtab.c
@@ -30,6 +30,8 @@
#include "libguile/validate.h"
#include "libguile/hashtab.h"
+
+
/* NOTES
@@ -78,8 +80,99 @@ static unsigned long hashtable_size[] = {
static char *s_hashtable = "hashtable";
-SCM weak_hashtables = SCM_EOL;
+
+/* Helper functions and macros to deal with weak pairs.
+
+ Weak pairs need to be accessed very carefully since their components can
+ be nullified by the GC when the object they refer to becomes unreachable.
+ Hence the macros and functions below that detect such weak pairs within
+ buckets and remove them. */
+
+
+/* Return a ``usable'' version of ALIST, an alist of weak pairs. By
+ ``usable'', we mean that it contains only valid Scheme objects. On
+ return, REMOVE_ITEMS is set to the number of pairs that have been
+ deleted. */
+static SCM
+scm_fixup_weak_alist (SCM alist, size_t *removed_items)
+{
+ SCM result;
+ SCM prev = SCM_EOL;
+
+ *removed_items = 0;
+ for (result = alist;
+ scm_is_pair (alist);
+ prev = alist, alist = SCM_CDR (alist))
+ {
+ SCM pair = SCM_CAR (alist);
+
+ if (scm_is_pair (pair))
+ {
+ if (SCM_WEAK_PAIR_DELETED_P (pair))
+ {
+ /* Remove from ALIST weak pair PAIR whose car/cdr has been
+ nullified by the GC. */
+ if (prev == SCM_EOL)
+ result = SCM_CDR (alist);
+ else
+ SCM_SETCDR (prev, SCM_CDR (alist));
+
+ (*removed_items)++;
+ continue;
+ }
+ }
+ }
+
+ return result;
+}
+
+
+/* Helper macros. */
+
+/* Return true if OBJ is either a weak hash table or a weak alist vector (as
+ defined in `weaks.[ch]').
+ FIXME: We should eventually keep only weah hash tables. Actually, the
+ procs in `weaks.c' already no longer return vectors. */
+/* XXX: We assume that if OBJ is a vector, then it's a _weak_ alist vector. */
+#define IS_WEAK_THING(_obj) \
+ ((SCM_HASHTABLE_P (table) && (SCM_HASHTABLE_WEAK_P (table))) \
+ || (SCM_I_IS_VECTOR (table)))
+
+
+
+/* Fixup BUCKET, an alist part of weak hash table OBJ. BUCKETS is the full
+ bucket vector for OBJ and IDX is the index of BUCKET within this
+ vector. See also `scm_internal_hash_fold ()'. */
+#define START_WEAK_BUCKET_FIXUP(_obj, _buckets, _idx, _bucket, _hashfn) \
+do \
+ { \
+ size_t _removed; \
+ \
+ /* Disable the GC so that BUCKET remains valid until ASSOC_FN has \
+ returned. */ \
+ /* FIXME: We could maybe trigger a rehash here depending on whether \
+ `scm_fixup_weak_alist ()' noticed some change. */ \
+ GC_disable (); \
+ (_bucket) = scm_fixup_weak_alist ((_bucket), &_removed); \
+ SCM_SIMPLE_VECTOR_SET ((_buckets), (_idx), (_bucket)); \
+ \
+ if ((_removed) && (SCM_HASHTABLE_P (_obj))) \
+ { \
+ SCM_SET_HASHTABLE_N_ITEMS ((_obj), \
+ SCM_HASHTABLE_N_ITEMS (_obj) - _removed); \
+ scm_i_rehash ((_obj), (_hashfn), \
+ NULL, "START_WEAK_BUCKET_FIXUP"); \
+ } \
+ } \
+while (0)
+
+/* Terminate a weak bucket fixup phase. */
+#define END_WEAK_BUCKET_FIXUP(_obj, _buckets, _idx, _bucket, _hashfn) \
+ do { GC_enable (); } while (0)
+
+
+
static SCM
make_hash_table (int flags, unsigned long k, const char *func_name)
{
@@ -89,24 +182,22 @@ make_hash_table (int flags, unsigned long k, const char *func_name)
while (i < HASHTABLE_SIZE_N && n > hashtable_size[i])
++i;
n = hashtable_size[i];
- if (flags)
- vector = scm_i_allocate_weak_vector (flags, scm_from_int (n), SCM_EOL);
- else
- vector = scm_c_make_vector (n, SCM_EOL);
- t = scm_gc_malloc (sizeof (*t), s_hashtable);
+
+ /* In both cases, i.e., regardless of whether we are creating a weak hash
+ table, we return a non-weak vector. This is because the vector itself
+ is not weak in the case of a weak hash table: the alist pairs are. */
+ vector = scm_c_make_vector (n, SCM_EOL);
+
+ t = scm_gc_malloc_pointerless (sizeof (*t), s_hashtable);
t->min_size_index = t->size_index = i;
t->n_items = 0;
t->lower = 0;
t->upper = 9 * n / 10;
t->flags = flags;
t->hash_fn = NULL;
- if (flags)
- {
- SCM_NEWSMOB3 (table, scm_tc16_hashtable, vector, t, weak_hashtables);
- weak_hashtables = table;
- }
- else
- SCM_NEWSMOB3 (table, scm_tc16_hashtable, vector, t, SCM_EOL);
+
+ SCM_NEWSMOB2 (table, scm_tc16_hashtable, vector, t);
+
return table;
}
@@ -153,13 +244,8 @@ scm_i_rehash (SCM table,
SCM_HASHTABLE (table)->lower = new_size / 4;
SCM_HASHTABLE (table)->upper = 9 * new_size / 10;
buckets = SCM_HASHTABLE_VECTOR (table);
-
- if (SCM_HASHTABLE_WEAK_P (table))
- new_buckets = scm_i_allocate_weak_vector (SCM_HASHTABLE_FLAGS (table),
- scm_from_ulong (new_size),
- SCM_EOL);
- else
- new_buckets = scm_c_make_vector (new_size, SCM_EOL);
+
+ new_buckets = scm_c_make_vector (new_size, SCM_EOL);
/* When this is a weak hashtable, running the GC might change it.
We need to cope with this while rehashing its elements. We do
@@ -182,9 +268,15 @@ scm_i_rehash (SCM table,
while (scm_is_pair (ls))
{
unsigned long h;
+
cell = ls;
handle = SCM_CAR (cell);
ls = SCM_CDR (ls);
+
+ if (SCM_WEAK_PAIR_DELETED_P (handle))
+ /* HANDLE is a nullified weak pair: skip it. */
+ continue;
+
h = hash_fn (SCM_CAR (handle), new_size, closure);
if (h >= new_size)
scm_out_of_range (func_name, scm_from_ulong (h));
@@ -215,81 +307,6 @@ hashtable_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
return 1;
}
-#define UNMARKED_CELL_P(x) (SCM_NIMP(x) && !SCM_GC_MARK_P (x))
-
-/* keep track of hash tables that need to shrink after scan */
-static SCM to_rehash = SCM_EOL;
-
-/* scan hash tables and update hash tables item count */
-void
-scm_i_scan_weak_hashtables ()
-{
- SCM *next = &weak_hashtables;
- SCM h = *next;
- while (!scm_is_null (h))
- {
- if (!SCM_GC_MARK_P (h))
- *next = h = SCM_HASHTABLE_NEXT (h);
- else
- {
- SCM vec = SCM_HASHTABLE_VECTOR (h);
- size_t delta = SCM_I_WVECT_DELTA (vec);
- SCM_I_SET_WVECT_DELTA (vec, 0);
- SCM_SET_HASHTABLE_N_ITEMS (h, SCM_HASHTABLE_N_ITEMS (h) - delta);
-
- if (SCM_HASHTABLE_N_ITEMS (h) < SCM_HASHTABLE_LOWER (h))
- {
- SCM tmp = SCM_HASHTABLE_NEXT (h);
- /* temporarily move table from weak_hashtables to to_rehash */
- SCM_SET_HASHTABLE_NEXT (h, to_rehash);
- to_rehash = h;
- *next = h = tmp;
- }
- else
- {
- next = SCM_HASHTABLE_NEXTLOC (h);
- h = SCM_HASHTABLE_NEXT (h);
- }
- }
- }
-}
-
-static void *
-rehash_after_gc (void *dummy1 SCM_UNUSED,
- void *dummy2 SCM_UNUSED,
- void *dummy3 SCM_UNUSED)
-{
- if (!scm_is_null (to_rehash))
- {
- SCM first = to_rehash, last, h;
- /* important to clear to_rehash here so that we don't get stuck
- in an infinite loop if scm_i_rehash causes GC */
- to_rehash = SCM_EOL;
- h = first;
- do
- {
- /* Rehash only when we have a hash_fn.
- */
- if (SCM_HASHTABLE (h)->hash_fn)
- scm_i_rehash (h, SCM_HASHTABLE (h)->hash_fn, NULL,
- "rehash_after_gc");
- last = h;
- h = SCM_HASHTABLE_NEXT (h);
- } while (!scm_is_null (h));
- /* move tables back to weak_hashtables */
- SCM_SET_HASHTABLE_NEXT (last, weak_hashtables);
- weak_hashtables = first;
- }
- return 0;
-}
-
-static size_t
-hashtable_free (SCM obj)
-{
- scm_gc_free (SCM_HASHTABLE (obj), sizeof (scm_t_hashtable), s_hashtable);
- return 0;
-}
-
SCM
scm_c_make_hash_table (unsigned long k)
@@ -413,19 +430,34 @@ SCM
scm_hash_fn_get_handle (SCM table, SCM obj, unsigned long (*hash_fn)(), SCM (*assoc_fn)(), void * closure)
#define FUNC_NAME "scm_hash_fn_get_handle"
{
+ int weak = 0;
unsigned long k;
- SCM h;
+ SCM buckets, alist, h;
if (SCM_HASHTABLE_P (table))
- table = SCM_HASHTABLE_VECTOR (table);
+ buckets = SCM_HASHTABLE_VECTOR (table);
else
- SCM_VALIDATE_VECTOR (1, table);
- if (SCM_SIMPLE_VECTOR_LENGTH (table) == 0)
+ {
+ SCM_VALIDATE_VECTOR (1, table);
+ buckets = table;
+ }
+
+ if (SCM_SIMPLE_VECTOR_LENGTH (buckets) == 0)
return SCM_BOOL_F;
- k = hash_fn (obj, SCM_SIMPLE_VECTOR_LENGTH (table), closure);
- if (k >= SCM_SIMPLE_VECTOR_LENGTH (table))
+ k = hash_fn (obj, SCM_SIMPLE_VECTOR_LENGTH (buckets), closure);
+ if (k >= SCM_SIMPLE_VECTOR_LENGTH (buckets))
scm_out_of_range ("hash_fn_get_handle", scm_from_ulong (k));
- h = assoc_fn (obj, SCM_SIMPLE_VECTOR_REF (table, k), closure);
+
+ weak = IS_WEAK_THING (table);
+ alist = SCM_SIMPLE_VECTOR_REF (buckets, k);
+
+ if (weak)
+ START_WEAK_BUCKET_FIXUP (table, buckets, k, alist, hash_fn);
+
+ h = assoc_fn (obj, alist, closure);
+ if (weak)
+ END_WEAK_BUCKET_FIXUP (table, buckets, k, alist, hash_fn);
+
return h;
}
#undef FUNC_NAME
@@ -436,8 +468,9 @@ scm_hash_fn_create_handle_x (SCM table, SCM obj, SCM init, unsigned long (*hash_
SCM (*assoc_fn)(), void * closure)
#define FUNC_NAME "scm_hash_fn_create_handle_x"
{
+ int weak = 0;
unsigned long k;
- SCM buckets, it;
+ SCM buckets, alist, it;
if (SCM_HASHTABLE_P (table))
buckets = SCM_HASHTABLE_VECTOR (table);
@@ -453,7 +486,16 @@ scm_hash_fn_create_handle_x (SCM table, SCM obj, SCM init, unsigned long (*hash_
k = hash_fn (obj, SCM_SIMPLE_VECTOR_LENGTH (buckets), closure);
if (k >= SCM_SIMPLE_VECTOR_LENGTH (buckets))
scm_out_of_range ("hash_fn_create_handle_x", scm_from_ulong (k));
- it = assoc_fn (obj, SCM_SIMPLE_VECTOR_REF (buckets, k), closure);
+
+ weak = IS_WEAK_THING (table);
+ alist = SCM_SIMPLE_VECTOR_REF (buckets, k);
+ if (weak)
+ START_WEAK_BUCKET_FIXUP (table, buckets, k, alist, hash_fn);
+
+ it = assoc_fn (obj, alist, closure);
+ if (weak)
+ END_WEAK_BUCKET_FIXUP (table, buckets, k, alist, hash_fn);
+
if (scm_is_true (it))
return it;
else
@@ -464,7 +506,25 @@ scm_hash_fn_create_handle_x (SCM table, SCM obj, SCM init, unsigned long (*hash_
again since the hashtable might have been rehashed. This
necessitates a new hash value as well.
*/
- SCM new_bucket = scm_acons (obj, init, SCM_EOL);
+ SCM handle, new_bucket;
+
+ if ((SCM_HASHTABLE_P (table)) && (SCM_HASHTABLE_WEAK_P (table)))
+ {
+ /* FIXME: We don't support weak alist vectors. */
+ /* Use a weak cell. */
+ if (SCM_HASHTABLE_DOUBLY_WEAK_P (table))
+ handle = scm_doubly_weak_pair (obj, init);
+ else if (SCM_HASHTABLE_WEAK_KEY_P (table))
+ handle = scm_weak_car_pair (obj, init);
+ else
+ handle = scm_weak_cdr_pair (obj, init);
+ }
+ else
+ /* Use a regular, non-weak cell. */
+ handle = scm_cons (obj, init);
+
+ new_bucket = scm_cons (handle, SCM_EOL);
+
if (!scm_is_eq (table, buckets)
&& !scm_is_eq (SCM_HASHTABLE_VECTOR (table), buckets))
{
@@ -519,14 +579,15 @@ scm_hash_fn_set_x (SCM table, SCM obj, SCM val, unsigned long (*hash_fn)(),
}
-SCM
+SCM
scm_hash_fn_remove_x (SCM table, SCM obj,
unsigned long (*hash_fn)(),
SCM (*assoc_fn)(),
void *closure)
{
+ int weak = 0;
unsigned long k;
- SCM buckets, h;
+ SCM buckets, alist, h;
if (SCM_HASHTABLE_P (table))
buckets = SCM_HASHTABLE_VECTOR (table);
@@ -542,7 +603,16 @@ scm_hash_fn_remove_x (SCM table, SCM obj,
k = hash_fn (obj, SCM_SIMPLE_VECTOR_LENGTH (buckets), closure);
if (k >= SCM_SIMPLE_VECTOR_LENGTH (buckets))
scm_out_of_range ("hash_fn_remove_x", scm_from_ulong (k));
- h = assoc_fn (obj, SCM_SIMPLE_VECTOR_REF (buckets, k), closure);
+
+ weak = IS_WEAK_THING (table);
+ alist = SCM_SIMPLE_VECTOR_REF (buckets, k);
+ if (weak)
+ START_WEAK_BUCKET_FIXUP (table, buckets, k, alist, hash_fn);
+
+ h = assoc_fn (obj, alist, closure);
+ if (weak)
+ END_WEAK_BUCKET_FIXUP (table, buckets, k, alist, hash_fn);
+
if (scm_is_true (h))
{
SCM_SIMPLE_VECTOR_SET
@@ -917,21 +987,47 @@ scm_internal_hash_fold (SCM (*fn) (), void *closure, SCM init, SCM table)
if (SCM_HASHTABLE_P (table))
buckets = SCM_HASHTABLE_VECTOR (table);
else
+ /* Weak alist vector. */
buckets = table;
n = SCM_SIMPLE_VECTOR_LENGTH (buckets);
for (i = 0; i < n; ++i)
{
- SCM ls = SCM_SIMPLE_VECTOR_REF (buckets, i), handle;
- while (!scm_is_null (ls))
+ SCM prev, ls;
+
+ for (prev = SCM_BOOL_F, ls = SCM_SIMPLE_VECTOR_REF (buckets, i);
+ !scm_is_null (ls);
+ prev = ls, ls = SCM_CDR (ls))
{
+ SCM handle;
+
if (!scm_is_pair (ls))
scm_wrong_type_arg (s_scm_hash_fold, SCM_ARG3, buckets);
+
handle = SCM_CAR (ls);
if (!scm_is_pair (handle))
scm_wrong_type_arg (s_scm_hash_fold, SCM_ARG3, buckets);
+
+ if (IS_WEAK_THING (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 (prev != SCM_BOOL_F)
+ SCM_SETCDR (prev, SCM_CDR (ls));
+ else
+ SCM_SIMPLE_VECTOR_SET (buckets, i, SCM_CDR (ls));
+
+ if (SCM_HASHTABLE_P (table))
+ /* Update the item count. */
+ SCM_HASHTABLE_DECREMENT (table);
+
+ continue;
+ }
+ }
+
result = fn (closure, SCM_CAR (handle), SCM_CDR (handle), result);
- ls = SCM_CDR (ls);
}
}
@@ -1066,11 +1162,9 @@ SCM_DEFINE (scm_hash_map_to_list, "hash-map->list", 2, 0, 0,
void
scm_hashtab_prehistory ()
{
+ /* Initialize the hashtab SMOB type. */
scm_tc16_hashtable = scm_make_smob_type (s_hashtable, 0);
- scm_set_smob_mark (scm_tc16_hashtable, scm_markcdr);
scm_set_smob_print (scm_tc16_hashtable, hashtable_print);
- scm_set_smob_free (scm_tc16_hashtable, hashtable_free);
- scm_c_hook_add (&scm_after_gc_c_hook, rehash_after_gc, 0, 0);
}
void