X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=rculfhash.c;h=44a589b03361a33c7625d1b336f05da77d6b1bca;hb=f6fdd688eb73510a5192a4560c34d7e8caac77aa;hp=193857647439ef9cc3cfbc222184cab4c32c3360;hpb=4c3a0329b746828a7d686977dec0575a63db5c8b;p=urcu.git

diff --git a/rculfhash.c b/rculfhash.c
index 1938576..44a589b 100644
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -120,11 +120,11 @@
  * order              bits       reverse
  * 0               0  000        000
  *                 |
- * 1               |  1  001        100             <-
- *                 |  |                              |
- * 2               |  |  2  010        010           |
- *                 |  |  |  3  011        110    <-  |
- *                 |  |  |  |                     |  |
+ * 1               |  1  001        100       <-    <-
+ *                 |  |                        |     |
+ * 2               |  |  2  010        010     |     |
+ *                 |  |  |  3  011        110  | <-  |
+ *                 |  |  |  |                  |  |  |
  * 3               -> |  |  |  4  100        001  |  |
  *                    -> |  |     5  101        101  |
  *                       -> |        6  110        011
@@ -166,6 +166,16 @@
 #define CHAIN_LEN_TARGET		1
 #define CHAIN_LEN_RESIZE_THRESHOLD	3
 
+/*
+ * Define the minimum table size. Protects against hash table resize overload
+ * when too many entries are added quickly before the resize can complete.
+ * This is especially the case if the table could be shrinked to a size of 1.
+ * TODO: we might want to make the add/remove operations help the resize to
+ * add or remove dummy nodes when a resize is ongoing to ensure upper-bound on
+ * chain length.
+ */
+#define MIN_TABLE_SIZE			128
+
 #ifndef max
 #define max(a, b)	((a) > (b) ? (a) : (b))
 #endif
@@ -699,7 +709,7 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht, struct rcu_table *t,
 		 */
 		index = hash & (t->size - 1);
 		order = get_count_order_ulong(index + 1);
-		lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
+		lookup = &t->tbl[order]->nodes[index & ((!order ? 0 : (1UL << (order - 1))) - 1)];
 		iter_prev = (struct cds_lfht_node *) lookup;
 		/* We can always skip the dummy node initially */
 		iter = rcu_dereference(iter_prev->p.next);
@@ -755,7 +765,7 @@ gc_end:
 	/* Garbage collect logically removed nodes in the bucket */
 	index = hash & (t->size - 1);
 	order = get_count_order_ulong(index + 1);
-	lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
+	lookup = &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);
 	return node;
@@ -799,7 +809,7 @@ int _cds_lfht_remove(struct cds_lfht *ht, struct rcu_table *t,
 	assert(t->size > 0);
 	index = hash & (t->size - 1);
 	order = get_count_order_ulong(index + 1);
-	lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
+	lookup = &t->tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1)) - 1))];
 	dummy = (struct cds_lfht_node *) lookup;
 	_cds_lfht_gc_bucket(dummy, node);
 end:
@@ -917,7 +927,7 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
 	ht->percpu_count = alloc_per_cpu_items_count();
 	/* this mutex should not nest in read-side C.S. */
 	pthread_mutex_init(&ht->resize_mutex, NULL);
-	order = get_count_order_ulong(max(init_size, 1)) + 1;
+	order = get_count_order_ulong(max(init_size, MIN_TABLE_SIZE)) + 1;
 	ht->t = calloc(1, sizeof(struct cds_lfht)
 		       + (order * sizeof(struct rcu_level *)));
 	ht->t->size = 0;
@@ -940,9 +950,9 @@ struct cds_lfht_node *cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key
 	t = rcu_dereference(ht->t);
 	index = hash & (t->size - 1);
 	order = get_count_order_ulong(index + 1);
-	lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
+	lookup = &t->tbl[order]->nodes[index & (!order ? 0 : ((1UL << (order - 1))) - 1)];
 	dbg_printf("lookup hash %lu index %lu order %lu aridx %lu\n",
-		   hash, index, order, index & ((1UL << (order - 1)) - 1));
+		   hash, index, order, index & (!order ? 0 : ((1UL << (order - 1)) - 1)));
 	node = (struct cds_lfht_node *) lookup;
 	for (;;) {
 		if (unlikely(!node))
@@ -1154,7 +1164,7 @@ void _do_cds_lfht_shrink(struct cds_lfht *ht, struct rcu_table *old_t,
 	unsigned long old_order, new_order;
 	struct rcu_table *new_t;
 
-	new_size = max(new_size, 1);
+	new_size = max(new_size, MIN_TABLE_SIZE);
 	old_order = get_count_order_ulong(old_size) + 1;
 	new_order = get_count_order_ulong(new_size) + 1;
 	printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n",
@@ -1214,7 +1224,7 @@ static
 unsigned long resize_target_update_count(struct rcu_table *t,
 				   unsigned long count)
 {
-	count = max(count, 1);
+	count = max(count, MIN_TABLE_SIZE);
 	return uatomic_set(&t->resize_target, count);
 }