#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 the minimum table size.
*/
#define MIN_TABLE_SIZE 128
struct cds_lfht *ht;
};
+static
+struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
+ unsigned long size,
+ struct cds_lfht_node *node,
+ int unique, int dummy);
+
/*
* Algorithm to reverse bits in a word by lookup table, extended to
* 64-bit words.
* Remove all logically deleted nodes from a bucket up to a certain node key.
*/
static
-void _cds_lfht_gc_bucket(struct cds_lfht_node *dummy, struct cds_lfht_node *node)
+int _cds_lfht_gc_bucket(struct cds_lfht_node *dummy, struct cds_lfht_node *node)
{
struct cds_lfht_node *iter_prev, *iter, *next, *new_next;
iter_prev = dummy;
/* We can always skip the dummy node initially */
iter = rcu_dereference(iter_prev->p.next);
+ if (unlikely(iter == NULL)) {
+ /*
+ * We are executing concurrently with a hash table
+ * expand, so we see a dummy node with NULL next value.
+ * Help expand by linking this node into the list and
+ * retry.
+ */
+ return 1;
+ }
assert(iter_prev->p.reverse_hash <= node->p.reverse_hash);
/*
* We should never be called with dummy (start of chain)
assert(dummy != node);
for (;;) {
if (unlikely(!clear_flag(iter)))
- return;
+ return 0;
if (likely(clear_flag(iter)->p.reverse_hash > node->p.reverse_hash))
- return;
+ return 0;
next = rcu_dereference(clear_flag(iter)->p.next);
if (likely(is_removed(next)))
break;
new_next = clear_flag(next);
(void) uatomic_cmpxchg(&iter_prev->p.next, iter, new_next);
}
+ return 0;
}
static
iter_prev = (struct cds_lfht_node *) lookup;
/* We can always skip the dummy node initially */
iter = rcu_dereference(iter_prev->p.next);
+ if (unlikely(iter == NULL)) {
+ /*
+ * We are executing concurrently with a hash table
+ * expand, so we see a dummy node with NULL next value.
+ * Help expand by linking this node into the list and
+ * retry.
+ */
+ (void) _cds_lfht_add(ht, size >> 1, iter_prev, 0, 1);
+ continue; /* retry */
+ }
assert(iter_prev->p.reverse_hash <= node->p.reverse_hash);
for (;;) {
+ /*
+ * When adding a dummy node, we allow concurrent
+ * add/removal to help. If we find the dummy node in
+ * place, skip its insertion.
+ */
+ if (unlikely(dummy && clear_flag(iter) == node))
+ return node;
if (unlikely(!clear_flag(iter)))
goto insert;
if (likely(clear_flag(iter)->p.reverse_hash > node->p.reverse_hash))
order = get_count_order_ulong(index + 1);
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);
+ if (_cds_lfht_gc_bucket(dummy_node, node)) {
+ /* Help expand */
+ (void) _cds_lfht_add(ht, size >> 1, dummy_node, 0, 1);
+ goto gc_end; /* retry */
+ }
return node;
}
* the node, and remove it (along with any other logically removed node)
* if found.
*/
+gc_retry:
hash = bit_reverse_ulong(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, node);
+ if (_cds_lfht_gc_bucket(dummy, node)) {
+ /* Help expand */
+ (void) _cds_lfht_add(ht, size >> 1, dummy, 0, 1);
+ goto gc_retry; /* retry */
+ }
end:
/*
* Only the flagging action indicated that we (and no other)
len = !i ? 1 : 1UL << (i - 1);
dbg_printf("init order %lu len: %lu\n", i, len);
+
+ /* Stop expand if the resize target changes under us */
+ if (CMM_LOAD_SHARED(ht->t.resize_target) < (!i ? 1 : (1UL << i)))
+ break;
+
ht->t.tbl[i] = calloc(1, sizeof(struct rcu_level)
+ (len * sizeof(struct _cds_lfht_node)));
/* Set all dummy nodes reverse hash values for a level */
init_table_hash(ht, i, len);
+ /*
+ * Update table size. At this point, concurrent add/remove see
+ * dummy nodes with correctly initialized reverse hash value,
+ * but with NULL next pointers. If they do, they can help us
+ * link the dummy nodes into the list and retry.
+ */
+ cmm_smp_wmb(); /* populate data before RCU size */
+ CMM_STORE_SHARED(ht->t.size, !i ? 1 : (1UL << i));
+
/*
* Link all dummy nodes into the table. Concurrent
* add/remove are helping us.
*/
init_table_link(ht, i, len);
- /*
- * Update table size (after init for now, because no
- * concurrent updater help (TODO)).
- */
- cmm_smp_wmb(); /* populate data before RCU size */
- CMM_STORE_SHARED(ht->t.size, !i ? 1 : (1UL << i));
dbg_printf("init new size: %lu\n", !i ? 1 : (1UL << i));
if (CMM_LOAD_SHARED(ht->in_progress_destroy))
break;
first_order, first_order + len_order);
end_order = first_order + len_order;
assert(first_order > 0);
- assert(ht->t.size == (1UL << (first_order - 1)));
for (i = end_order - 1; i >= first_order; i--) {
unsigned long len;
len = !i ? 1 : 1UL << (i - 1);
dbg_printf("fini order %lu len: %lu\n", i, len);
+ /* Stop shrink if the resize target changes under us */
+ if (CMM_LOAD_SHARED(ht->t.resize_target) > (1UL << (i - 1)))
+ break;
+
+ cmm_smp_wmb(); /* populate data before RCU size */
+ CMM_STORE_SHARED(ht->t.size, 1UL << (i - 1));
+
+ /*
+ * We need to wait for all add operations to reach Q.S. (and
+ * thus use the new table for lookups) before we can start
+ * releasing the old dummy nodes. Otherwise their lookup will
+ * return a logically removed node as insert position.
+ */
+ ht->cds_lfht_synchronize_rcu();
+
/*
* Set "removed" flag in dummy nodes about to be removed.
* Unlink all now-logically-removed dummy node pointers.
ht->flags = flags;
ht->cds_lfht_rcu_thread_offline();
pthread_mutex_lock(&ht->resize_mutex);
+ ht->t.resize_target = 1UL << (order - 1);
init_table(ht, 0, order);
pthread_mutex_unlock(&ht->resize_mutex);
ht->cds_lfht_rcu_thread_online();
old_size, old_order, new_size, new_order);
assert(new_size < old_size);
- cmm_smp_wmb(); /* populate data before RCU size */
- CMM_STORE_SHARED(ht->t.size, new_size);
-
- /*
- * We need to wait for all add operations to reach Q.S. (and
- * thus use the new table for lookups) before we can start
- * releasing the old dummy nodes. Otherwise their lookup will
- * return a logically removed node as insert position.
- */
- ht->cds_lfht_synchronize_rcu();
-
/* Remove and unlink all dummy nodes to remove. */
fini_table(ht, new_order, old_order - new_order);
}
ht->t.resize_initiated = 0;
/* write resize_initiated before read resize_target */
cmm_smp_mb();
- } while (new_size != CMM_LOAD_SHARED(ht->t.resize_target));
+ } while (ht->t.size != CMM_LOAD_SHARED(ht->t.resize_target));
}
static
projects / urcu.git / blobdiff