return;
}
+static
+int _cds_lfht_replace(struct cds_lfht *ht, unsigned long size,
+ struct cds_lfht_node *old_node,
+ struct cds_lfht_node *ret_next,
+ struct cds_lfht_node *new_node)
+{
+ struct cds_lfht_node *dummy, *old_next;
+ struct _cds_lfht_node *lookup;
+ int flagged = 0;
+ unsigned long hash, index, order;
+
+ if (!old_node) /* Return -ENOENT if asked to replace NULL node */
+ goto end;
+
+ assert(!is_removed(old_node));
+ assert(!is_dummy(old_node));
+ assert(!is_removed(new_node));
+ assert(!is_dummy(new_node));
+ assert(new_node != old_node);
+ do {
+ /* Insert after node to be replaced */
+ old_next = ret_next;
+ if (is_removed(old_next)) {
+ /*
+ * Too late, the old node has been removed under us
+ * between lookup and replace. Fail.
+ */
+ goto end;
+ }
+ assert(!is_dummy(old_next));
+ assert(new_node != clear_flag(old_next));
+ new_node->p.next = clear_flag(old_next);
+ /*
+ * Here is the whole trick for lock-free replace: we add
+ * the replacement node _after_ the node we want to
+ * replace by atomically setting its next pointer at the
+ * same time we set its removal flag. Given that
+ * the lookups/get next use an iterator aware of the
+ * next pointer, they will either skip the old node due
+ * to the removal flag and see the new node, or use
+ * the old node, but will not see the new one.
+ */
+ ret_next = uatomic_cmpxchg(&old_node->p.next,
+ old_next, flag_removed(new_node));
+ } while (ret_next != old_next);
+
+ /* We performed the replacement. */
+ flagged = 1;
+
+ /*
+ * Ensure that the old node is not visible to readers anymore:
+ * lookup for the node, and remove it (along with any other
+ * logically removed node) if found.
+ */
+ hash = bit_reverse_ulong(old_node->p.reverse_hash);
+ assert(size > 0);
+ index = hash & (size - 1);
+ order = get_count_order_ulong(index + 1);
+ lookup = &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
+ dummy = (struct cds_lfht_node *) lookup;
+ _cds_lfht_gc_bucket(dummy, new_node);
+end:
+ /*
+ * Only the flagging action indicated that we (and no other)
+ * replaced the node from the hash table.
+ */
+ if (flagged) {
+ assert(is_removed(rcu_dereference(old_node->p.next)));
+ return 0;
+ } else {
+ return -ENOENT;
+ }
+}
+
static
struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
unsigned long size,
}
replace:
- /* Insert after node to be replaced */
- iter_prev = clear_flag(iter);
- iter = next;
- assert(node != clear_flag(iter));
- assert(!is_removed(iter_prev));
- assert(!is_removed(iter));
- assert(iter_prev != node);
- assert(!dummy);
- node->p.next = clear_flag(iter);
- if (is_dummy(iter))
- new_node = flag_dummy(node);
- else
- new_node = node;
- /*
- * Here is the whole trick for lock-free replace: we add
- * the replacement node _after_ the node we want to
- * replace by atomically setting its next pointer at the
- * same time we set its removal flag. Given that
- * the lookups/get next use an iterator aware of the
- * next pointer, they will either skip the old node due
- * to the removal flag and see the new node, or use
- * the old node, but will not see the new one.
- */
- new_node = flag_removed(new_node);
- if (uatomic_cmpxchg(&iter_prev->p.next,
- iter, new_node) != iter) {
- continue; /* retry */
+
+ if (!_cds_lfht_replace(ht, size, clear_flag(iter), next,
+ node)) {
+ return_node = clear_flag(iter);
+ goto end; /* gc already done */
} else {
- return_node = iter_prev;
- goto gc_end;
+ continue; /* retry */
}
gc_node:
lookup = &ht->t.tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
dummy_node = (struct cds_lfht_node *) lookup;
_cds_lfht_gc_bucket(dummy_node, node);
+end:
return return_node;
}
int flagged = 0;
unsigned long hash, index, order;
+ if (!node) /* Return -ENOENT if asked to delete NULL node */
+ goto end;
+
/* logically delete the node */
assert(!is_dummy(node));
assert(!is_removed(node));
if (flagged) {
assert(is_removed(rcu_dereference(node->p.next)));
return 0;
- } else
+ } else {
return -ENOENT;
+ }
}
static
return ret;
}
-struct cds_lfht_node *cds_lfht_replace(struct cds_lfht *ht,
+struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht,
struct cds_lfht_node *node)
{
unsigned long hash, size;
return ret;
}
-int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node)
+int cds_lfht_replace(struct cds_lfht *ht, struct cds_lfht_iter *old_iter,
+ struct cds_lfht_node *new_node)
+{
+ unsigned long size;
+
+ size = rcu_dereference(ht->t.size);
+ return _cds_lfht_replace(ht, size, old_iter->node, old_iter->next,
+ new_node);
+}
+
+int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_iter *iter)
{
unsigned long size;
int ret;
size = rcu_dereference(ht->t.size);
- ret = _cds_lfht_del(ht, size, node, 0);
+ ret = _cds_lfht_del(ht, size, iter->node, 0);
if (!ret)
ht_count_del(ht, size);
return ret;
* The semantic of this function is that if only this function is used
* to add keys into the table, no duplicated keys should ever be
* observable in the table. The same guarantee apply for combination of
- * add_unique and replace (see below).
+ * add_unique and add_replace (see below).
*/
struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
struct cds_lfht_node *node);
/*
- * cds_lfht_replace - replace a node within hash table.
+ * cds_lfht_add_replace - replace or add a node within hash table.
*
* Return the node replaced upon success. If no node matching the key
* was present, return NULL, which also means the operation succeeded.
* freeing the memory reserved for the returned node.
*
* The semantic of replacement vs lookups is the following: if lookups
- * are performed between a key insertion and its removal, we guarantee
- * that the lookups will always find the key if it is replaced
- * concurrently with the lookups.
+ * are performed between a key unique insertion and its removal, we
+ * guarantee that the lookups and get next will always find exactly one
+ * instance of the key if it is replaced concurrently with the lookups.
*
* Providing this semantic allows us to ensure that replacement-only
* schemes will never generate duplicated keys. It also allows us to
- * guarantee that a combination of replacement and add_unique updates
+ * guarantee that a combination of add_replace and add_unique updates
* will never generate duplicated keys.
*/
-struct cds_lfht_node *cds_lfht_replace(struct cds_lfht *ht,
+struct cds_lfht_node *cds_lfht_add_replace(struct cds_lfht *ht,
struct cds_lfht_node *node);
/*
- * cds_lfht_del - remove node from hash table.
+ * cds_lfht_replace - replace a node pointer to by iter within hash table.
*
- * Return 0 if the node is successfully removed.
- * Node can be looked up with cds_lfht_lookup. RCU read-side lock must
- * be held between lookup and removal.
+ * Return 0 if replacement is successful, negative value otherwise.
+ * Replacing a NULL old node or an already removed node will fail with a
+ * negative value.
+ * Old node can be looked up with cds_lfht_lookup and cds_lfht_next.
+ * RCU read-side lock must be held between lookup and replacement.
+ * Call with rcu_read_lock held.
+ * After successful replacement, a grace period must be waited for before
+ * freeing the memory reserved for the old node (which can be accessed
+ * with cds_lfht_iter_get_node).
+ *
+ * The semantic of replacement vs lookups is the following: if lookups
+ * are performed between a key unique insertion and its removal, we
+ * guarantee that the lookups and get next will always find exactly one
+ * instance of the key if it is replaced concurrently with the lookups.
+ *
+ * Providing this semantic allows us to ensure that replacement-only
+ * schemes will never generate duplicated keys. It also allows us to
+ * guarantee that a combination of add_replace and add_unique updates
+ * will never generate duplicated keys.
+ */
+int cds_lfht_replace(struct cds_lfht *ht, struct cds_lfht_iter *old_iter,
+ struct cds_lfht_node *new_node);
+
+/*
+ * cds_lfht_del - remove node pointed to by iterator from hash table.
+ *
+ * Return 0 if the node is successfully removed, negative value
+ * otherwise.
+ * Replacing a NULL node or an already removed node will fail with a
+ * negative value.
+ * Node can be looked up with cds_lfht_lookup and cds_lfht_next.
+ * cds_lfht_iter_get_node.
+ * RCU read-side lock must be held between lookup and removal.
* Call with rcu_read_lock held.
* After successful removal, a grace period must be waited for before
- * freeing the memory reserved for node.
+ * freeing the memory reserved for old node (which can be accessed with
+ * cds_lfht_iter_get_node).
*/
-int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node);
+int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_iter *iter);
/*
* cds_lfht_resize - Force a hash table resize
projects / urcu.git / commitdiff
