rculfhash: remove now unneeded gc flag (combine with removed)

[urcu.git] / urcu / rculfhash.h

diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h
index c1c9ddcf2a28d662668bf0ac465e658417730828..7afd6244a97df896cc54af017e8f217edda926a5 100644 (file)
--- a/urcu/rculfhash.h
+++ b/urcu/rculfhash.h
@@ -40,7 +40,7 @@ extern "C" {
 struct _cds_lfht_node {
        struct cds_lfht_node *next;     /* ptr | DUMMY_FLAG | REMOVED_FLAG */
        unsigned long reverse_hash;
-};
+} __attribute__((aligned(8)));
 
 struct cds_lfht_node {
        /* cache-hot for iteration */
@@ -51,6 +51,16 @@ struct cds_lfht_node {
        struct rcu_head head;
 };
 
+struct cds_lfht_iter {
+       struct cds_lfht_node *node, *next;
+};
+
+static inline
+struct cds_lfht_node *cds_lfht_iter_get_node(struct cds_lfht_iter *iter)
+{
+       return iter->node;
+}
+
 struct cds_lfht;
 
 /*
@@ -155,31 +165,36 @@ int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr);
  * Call with rcu_read_lock held.
  */
 void cds_lfht_count_nodes(struct cds_lfht *ht,
-                       unsigned long *count,
-                       unsigned long *removed);
+               unsigned long *count,
+               unsigned long *removed);
 
 /*
  * cds_lfht_lookup - lookup a node by key.
  *
- * Return NULL if not found.
+ * Output in "*iter". *iter->node set to NULL if not found.
  * Call with rcu_read_lock held.
  */
-struct cds_lfht_node *cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len);
+void cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len,
+               struct cds_lfht_iter *iter);
 
 /*
  * cds_lfht_next - get the next item with same key (after a lookup).
  *
- * Return NULL if no following node exists with same key.
- * RCU read-side lock must be held across cds_lfht_lookup and cds_lfht_next calls, and also
- * between cds_lfht_next calls using the node returned by a previous
- * cds_lfht_next.  Call with rcu_read_lock held.
+ * Uses an iterator initialized by a lookup.
+ * Sets *iter-node to the following node with same key.
+ * Sets *iter->node to NULL if no following node exists with same key.
+ * RCU read-side lock must be held across cds_lfht_lookup and
+ * cds_lfht_next calls, and also between cds_lfht_next calls using the
+ * node returned by a previous cds_lfht_next.
+ * Call with rcu_read_lock held.
  */
-struct cds_lfht_node *cds_lfht_next(struct cds_lfht *ht, struct cds_lfht_node *node);
+void cds_lfht_next(struct cds_lfht *ht, struct cds_lfht_iter *iter);
 
 /*
  * cds_lfht_add - add a node to the hash table.
  *
  * Call with rcu_read_lock held.
+ * This function supports adding redundant keys into the table.
  */
 void cds_lfht_add(struct cds_lfht *ht, struct cds_lfht_node *node);
 
@@ -191,15 +206,47 @@ void cds_lfht_add(struct cds_lfht *ht, struct cds_lfht_node *node);
  * cds_lfht_add_unique fails, the node passed as parameter should be
  * freed by the caller.
  * Call with rcu_read_lock held.
+ *
+ * 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).
+ */
+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.
+ *
+ * Return the node replaced upon success. If no node matching the key
+ * was present, return NULL, which also means the operation succeeded.
+ * This replacement operation should never fail.
+ * Call with rcu_read_lock held.
+ * After successful replacement, a grace period must be waited for before
+ * 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.
+ *
+ * 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
+ * will never generate duplicated keys.
  */
-struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht, struct cds_lfht_node *node);
+struct cds_lfht_node *cds_lfht_replace(struct cds_lfht *ht,
+               struct cds_lfht_node *node);
 
 /*
  * cds_lfht_del - remove node from 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.
  * Call with rcu_read_lock held.
+ * After successful removal, a grace period must be waited for before
+ * freeing the memory reserved for node.
  */
 int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node);