Comment list behavior wrt lock-freedom

[urcu.git] / rculfhash.c

diff --git a/rculfhash.c b/rculfhash.c
index 497a9eacdebd764771d1e6e2e88a95c019f83724..4abf27a9a5dd5e9f56f97d669de88e58705e741d 100644 (file)
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -46,7 +46,8 @@
 #define dbg_printf(args...)
 #endif
 
-#define BUCKET_SIZE_RESIZE_THRESHOLD   4
+#define CHAIN_LEN_TARGET               4
+#define CHAIN_LEN_RESIZE_THRESHOLD     16
 
 #ifndef max
 #define max(a, b)      ((a) > (b) ? (a) : (b))
@@ -165,8 +166,9 @@ static
 void check_resize(struct rcu_ht *ht, struct rcu_table *t,
                  uint32_t chain_len)
 {
-       if (chain_len >= BUCKET_SIZE_RESIZE_THRESHOLD)
-               ht_resize_lazy(ht, t, log2_u32(chain_len));
+       if (chain_len >= CHAIN_LEN_RESIZE_THRESHOLD)
+               ht_resize_lazy(ht, t,
+                       log2_u32(chain_len - CHAIN_LEN_TARGET));
 }
 
 static
@@ -218,12 +220,15 @@ void _ht_add(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node)
                        iter = clear_flag(rcu_dereference(iter_prev->next));
                        if (unlikely(!iter))
                                break;
-                       if (iter->reverse_hash < node->reverse_hash)
+                       if (iter->reverse_hash > node->reverse_hash)
                                break;
                        iter_prev = iter;
                        check_resize(ht, t, ++chain_len);
                }
-               /* add in iter_prev->next */
+               /*
+                * add in iter_prev->next: TODO: check for helping
+                * delete, for lock-freedom...
+                */
                if (is_removed(iter))
                        continue;
                assert(node != iter);
@@ -253,7 +258,7 @@ retry:
                iter = clear_flag(rcu_dereference(iter_prev->next));
                if (unlikely(!iter))
                        break;
-               if (iter->reverse_hash < node->reverse_hash)
+               if (unlikely(iter->reverse_hash > node->reverse_hash))
                        break;
                if (iter == node) {
                        found = 1;
@@ -284,9 +289,13 @@ retry:
                flagged = 1;
        }
        /*
-        * Remove the element from the list. Retry if there has been a
-        * concurrent add (there cannot be a concurrent delete, because
-        * we won the deletion flag cmpxchg).
+        * Remove the element from the list.
+        * Retry if there has been a concurrent add before us.
+        * Retry if the prev node has been deleted.
+        * There cannot be a concurrent delete for our position, because
+        * we won the deletion flag cmpxchg.
+        * If there is a concurrent add after us, our deletion flag
+        * makes it busy-loop (FIXME: not lock-free).
         */
        if (uatomic_cmpxchg(&iter_prev->next, iter, clear_flag(next)) != iter)
                goto retry;
@@ -353,12 +362,12 @@ struct rcu_ht_node *ht_lookup(struct rcu_ht *ht, void *key, size_t key_len)
        for (;;) {
                if (unlikely(!node))
                        break;
-               if (node->reverse_hash > reverse_hash) {
+               if (unlikely(node->reverse_hash > reverse_hash)) {
                        node = NULL;
                        break;
                }
                if (!ht->compare_fct(node->key, node->key_len, key, key_len)) {
-                       if (is_removed(rcu_dereference(node->next)))
+                       if (unlikely(is_removed(rcu_dereference(node->next))))
                                node = NULL;
                        break;
                }