rculfhash: spawn only number of threads required for resize

[urcu.git] / urcu / rculfhash.h

diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h
index 8f501ea29b7b1e549c9b2d87f9ecf2e769251af0..4f7cc526f9ddc93528276c3e5740dab9c6f54f9f 100644 (file)
--- a/urcu/rculfhash.h
+++ b/urcu/rculfhash.h
@@ -21,6 +21,8 @@
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * Include this file _after_ including your URCU flavor.
  */
 
 #include <stdint.h>
@@ -80,12 +82,9 @@ enum {
 };
 
 /*
- * cds_lfht_new - allocate a hash table.
- *
- * init_size must be power of two.
- * Return NULL on error.
+ * _cds_lfht_new - API used by cds_lfht_new wrapper. Do not use directly.
  */
-struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
+struct cds_lfht *_cds_lfht_new(cds_lfht_hash_fct hash_fct,
                        cds_lfht_compare_fct compare_fct,
                        unsigned long hash_seed,
                        unsigned long init_size,
@@ -94,14 +93,61 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
                                void (*func)(struct rcu_head *head)),
                        void (*cds_lfht_synchronize_rcu)(void),
                        void (*cds_lfht_rcu_read_lock)(void),
-                       void (*cds_lfht_rcu_read_unlock)(void));
+                       void (*cds_lfht_rcu_read_unlock)(void),
+                       void (*cds_lfht_rcu_thread_offline)(void),
+                       void (*cds_lfht_rcu_thread_online)(void),
+                       void (*cds_lfht_rcu_register_thread)(void),
+                       void (*cds_lfht_rcu_unregister_thread)(void),
+                       pthread_attr_t *attr);
+
+/*
+ * cds_lfht_new - allocate a hash table.
+ * @hash_fct: the hashing function.
+ * @compare_fct: the key comparison function.
+ * @hash_seed: the seed for hash function.
+ * @init_size: number of nodes to allocate initially. Must be power of two.
+ * @flags: hash table creation flags (can be combined with bitwise or: '|').
+ *           0: no flags.
+ *           CDS_LFHT_AUTO_RESIZE: automatically resize hash table.
+ * @attr: optional resize worker thread attributes. NULL for default.
+ *
+ * Return NULL on error.
+ * Note: the RCU flavor must be already included before the hash table header.
+ *
+ * The programmer is responsible for ensuring that resize operation has a
+ * priority equal to hash table updater threads. It should be performed by
+ * specifying the appropriate priority in the pthread "attr" argument, and,
+ * for CDS_LFHT_AUTO_RESIZE, by ensuring that call_rcu worker threads also have
+ * this priority level. Having lower priority for call_rcu and resize threads
+ * does not pose any correctness issue, but the resize operations could be
+ * starved by updates, thus leading to long hash table bucket chains.
+ */
+static inline
+struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
+                       cds_lfht_compare_fct compare_fct,
+                       unsigned long hash_seed,
+                       unsigned long init_size,
+                       int flags,
+                       pthread_attr_t *attr)
+{
+       return _cds_lfht_new(hash_fct, compare_fct, hash_seed,
+                       init_size, flags,
+                       call_rcu, synchronize_rcu, rcu_read_lock,
+                       rcu_read_unlock, rcu_thread_offline,
+                       rcu_thread_online, rcu_register_thread,
+                       rcu_unregister_thread, attr);
+}
 
 /*
  * cds_lfht_destroy - destroy a hash table.
+ * @ht: the hash table to destroy.
+ * @attr: (output) resize worker thread attributes, as received by cds_lfht_new.
+ *        The caller will typically want to free this pointer if dynamically
+ *        allocated.
  *
  * Return 0 on success, negative error value on error.
  */
-int cds_lfht_destroy(struct cds_lfht *ht);
+int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr);
 
 /*
  * cds_lfht_count_nodes - count the number of nodes in the hash table.