/*
* rculfhash.c
*
- * Userspace RCU library - Lock-Free Expandable RCU Hash Table
+ * Userspace RCU library - Lock-Free Resizable RCU Hash Table
*
* Copyright 2010-2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*
* symposium on Parallel algorithms and architectures, ACM Press,
* (2002), 73-82.
*
- * Some specificities of this Lock-Free Expandable RCU Hash Table
+ * Some specificities of this Lock-Free Resizable RCU Hash Table
* implementation:
*
* - RCU read-side critical section allows readers to perform hash
* - An index of dummy nodes is kept. These dummy nodes are the hash
* table "buckets", and they are also chained together in the
* split-ordered list, which allows recursive expansion.
- * - The resize operation only allows expanding the hash table.
- * It is triggered either through an API call or automatically by
- * detecting long chains in the add operation.
+ * - The resize operation for small tables only allows expanding the hash table.
+ * It is triggered automatically by detecting long chains in the add
+ * operation.
+ * - The resize operation for larger tables (and available through an
+ * API) allows both expanding and shrinking the hash table.
+ * - Per-CPU Split-counters are used to keep track of the number of
+ * nodes within the hash table for automatic resize triggering.
* - Resize operation initiated by long chain detection is executed by a
* call_rcu thread, which keeps lock-freedom of add and remove.
* - Resize operations are protected by a mutex.
* - The per-order dummy node tables contain a compact version of the
* hash table nodes. These tables are invariant after they are
* populated into the hash table.
+ *
+ * A bit of ascii art explanation:
+ *
+ * Order index is the off-by-one compare to the actual power of 2 because
+ * we use index 0 to deal with the 0 special-case.
+ *
+ * This shows the nodes for a small table ordered by reversed bits:
+ *
+ * bits reverse
+ * 0 000 000
+ * 4 100 001
+ * 2 010 010
+ * 6 110 011
+ * 1 001 100
+ * 5 101 101
+ * 3 011 110
+ * 7 111 111
+ *
+ * This shows the nodes in order of non-reversed bits, linked by
+ * reversed-bit order.
+ *
+ * order bits reverse
+ * 0 0 000 000
+ * |
+ * 1 | 1 001 100 <-
+ * | | |
+ * 2 | | 2 010 010 |
+ * | | | 3 011 110 <- |
+ * | | | | | |
+ * 3 -> | | | 4 100 001 | |
+ * -> | | 5 101 101 |
+ * -> | 6 110 011
+ * -> 7 111 111
*/
#define _LGPL_SOURCE
unsigned long add, remove;
} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
+struct rcu_level {
+ struct rcu_head head;
+ struct _cds_lfht_node nodes[0];
+};
+
struct rcu_table {
unsigned long size; /* always a power of 2 */
unsigned long resize_target;
int resize_initiated;
struct rcu_head head;
- struct _cds_lfht_node *tbl[0];
+ struct rcu_level *tbl[0];
};
struct cds_lfht {
unsigned int in_progress_resize, in_progress_destroy;
void (*cds_lfht_call_rcu)(struct rcu_head *head,
void (*func)(struct rcu_head *head));
+ void (*cds_lfht_synchronize_rcu)(void);
unsigned long count; /* global approximate item count */
struct ht_items_count *percpu_count; /* per-cpu item count */
};
return v;
}
+static
+void cds_lfht_free_table_cb(struct rcu_head *head)
+{
+ struct rcu_table *t =
+ caa_container_of(head, struct rcu_table, head);
+ free(t);
+}
+
+static
+void cds_lfht_free_level(struct rcu_head *head)
+{
+ struct rcu_level *l =
+ caa_container_of(head, struct rcu_level, head);
+ free(l);
+}
+
/*
* Remove all logically deleted nodes from a bucket up to a certain node key.
*/
*/
index = hash & (t->size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)];
+ lookup = &t->tbl[order]->nodes[index & ((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);
/* Garbage collect logically removed nodes in the bucket */
index = hash & (t->size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)];
+ lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
dummy_node = (struct cds_lfht_node *) lookup;
_cds_lfht_gc_bucket(dummy_node, node);
return node;
static
int _cds_lfht_remove(struct cds_lfht *ht, struct rcu_table *t,
- struct cds_lfht_node *node)
+ struct cds_lfht_node *node, int dummy_removal)
{
struct cds_lfht_node *dummy, *next, *old;
struct _cds_lfht_node *lookup;
next = old;
if (unlikely(is_removed(next)))
goto end;
- assert(!is_dummy(next));
+ if (dummy_removal)
+ assert(is_dummy(next));
+ else
+ assert(!is_dummy(next));
old = uatomic_cmpxchg(&node->p.next, next,
flag_removed(next));
} while (old != next);
/* We performed the (logical) deletion. */
flagged = 1;
+ if (dummy_removal)
+ node = clear_flag(node);
+
/*
* Ensure that the node is not visible to readers anymore: lookup for
* the node, and remove it (along with any other logically removed node)
* if found.
*/
hash = bit_reverse_ulong(node->p.reverse_hash);
- index = hash & (t->size - 1);
+ /*
+ * When removing a dummy node, we need to consider the lower
+ * order table, so we don't end up looking up the dummy nodes we
+ * are currently removing.
+ */
+
+ if (dummy_removal)
+ index = hash & ((t->size >> 1) - 1);
+ else
+ index = hash & (t->size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)];
+ lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
dummy = (struct cds_lfht_node *) lookup;
_cds_lfht_gc_bucket(dummy, node);
end:
len = !i ? 1 : 1UL << (i - 1);
dbg_printf("init order %lu len: %lu\n", i, len);
- t->tbl[i] = calloc(len, sizeof(struct _cds_lfht_node));
+ t->tbl[i] = calloc(1, sizeof(struct rcu_level)
+ + (len * sizeof(struct _cds_lfht_node)));
for (j = 0; j < len; j++) {
+ struct cds_lfht_node *new_node =
+ (struct cds_lfht_node *) &t->tbl[i]->nodes[j];
+
dbg_printf("init entry: i %lu j %lu hash %lu\n",
i, j, !i ? 0 : (1UL << (i - 1)) + j);
- struct cds_lfht_node *new_node =
- (struct cds_lfht_node *) &t->tbl[i][j];
new_node->p.reverse_hash =
bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j);
(void) _cds_lfht_add(ht, t, new_node, 0, 1);
t->resize_initiated = 0;
}
+static
+void fini_table(struct cds_lfht *ht, struct rcu_table *t,
+ unsigned long first_order, unsigned long len_order)
+{
+ long i, end_order;
+
+ dbg_printf("fini table: first_order %lu end_order %lu\n",
+ first_order, first_order + len_order);
+ end_order = first_order + len_order;
+ assert(first_order > 0);
+ assert(t->size == (1UL << (end_order - 1)));
+ for (i = end_order - 1; i >= first_order; i--) {
+ unsigned long j, len;
+
+ len = !i ? 1 : 1UL << (i - 1);
+ dbg_printf("fini order %lu len: %lu\n", i, len);
+ /* Unlink */
+ for (j = 0; j < len; j++) {
+ struct cds_lfht_node *new_node =
+ (struct cds_lfht_node *) &t->tbl[i]->nodes[j];
+
+ dbg_printf("fini entry: i %lu j %lu hash %lu\n",
+ i, j, !i ? 0 : (1UL << (i - 1)) + j);
+ new_node->p.reverse_hash =
+ bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j);
+ (void) _cds_lfht_remove(ht, t, new_node, 1);
+ if (CMM_LOAD_SHARED(ht->in_progress_destroy))
+ break;
+ }
+ ht->cds_lfht_call_rcu(&t->tbl[i]->head, cds_lfht_free_level);
+ /* Update table size */
+ t->size = (i == 1) ? 0 : 1UL << (i - 2);
+ dbg_printf("fini new size: %lu\n", t->size);
+ if (CMM_LOAD_SHARED(ht->in_progress_destroy))
+ break;
+ }
+ t->resize_target = t->size;
+ t->resize_initiated = 0;
+}
+
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,
void (*cds_lfht_call_rcu)(struct rcu_head *head,
- void (*func)(struct rcu_head *head)))
+ void (*func)(struct rcu_head *head)),
+ void (*cds_lfht_synchronize_rcu)(void))
{
struct cds_lfht *ht;
unsigned long order;
ht->compare_fct = compare_fct;
ht->hash_seed = hash_seed;
ht->cds_lfht_call_rcu = cds_lfht_call_rcu;
+ ht->cds_lfht_synchronize_rcu = cds_lfht_synchronize_rcu;
ht->in_progress_resize = 0;
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;
ht->t = calloc(1, sizeof(struct cds_lfht)
- + (order * sizeof(struct _cds_lfht_node *)));
+ + (order * sizeof(struct rcu_level *)));
ht->t->size = 0;
pthread_mutex_lock(&ht->resize_mutex);
init_table(ht, ht->t, 0, order);
t = rcu_dereference(ht->t);
index = hash & (t->size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)];
+ lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
dbg_printf("lookup hash %lu index %lu order %lu aridx %lu\n",
hash, index, order, index & ((1UL << (order - 1)) - 1));
node = (struct cds_lfht_node *) lookup;
int ret;
t = rcu_dereference(ht->t);
- ret = _cds_lfht_remove(ht, t, node);
+ ret = _cds_lfht_remove(ht, t, node, 0);
if (!ret)
ht_count_remove(ht, t);
return ret;
t = ht->t;
/* Check that the table is empty */
- lookup = &t->tbl[0][0];
+ lookup = &t->tbl[0]->nodes[0];
node = (struct cds_lfht_node *) lookup;
do {
node = clear_flag(node)->p.next;
for (i = 0; i < len; i++) {
dbg_printf("delete order %lu i %lu hash %lu\n",
order, i,
- bit_reverse_ulong(t->tbl[order][i].reverse_hash));
- assert(is_dummy(t->tbl[order][i].next));
+ bit_reverse_ulong(t->tbl[order]->nodes[i].reverse_hash));
+ assert(is_dummy(t->tbl[order]->nodes[i].next));
}
free(t->tbl[order]);
}
t = rcu_dereference(ht->t);
/* Count non-dummy nodes in the table */
- lookup = &t->tbl[0][0];
+ lookup = &t->tbl[0]->nodes[0];
node = (struct cds_lfht_node *) lookup;
do {
next = rcu_dereference(node->p.next);
dbg_printf("number of dummy nodes: %lu\n", nr_dummy);
}
+/* called with resize mutex held */
static
-void cds_lfht_free_table_cb(struct rcu_head *head)
+void _do_cds_lfht_grow(struct cds_lfht *ht, struct rcu_table *old_t,
+ unsigned long old_size, unsigned long new_size)
{
- struct rcu_table *t =
- caa_container_of(head, struct rcu_table, head);
- free(t);
+ unsigned long old_order, new_order;
+ struct rcu_table *new_t;
+
+ 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",
+ old_size, old_order, new_size, new_order);
+ new_t = malloc(sizeof(struct cds_lfht)
+ + (new_order * sizeof(struct rcu_level *)));
+ assert(new_size > old_size);
+ memcpy(&new_t->tbl, &old_t->tbl,
+ old_order * sizeof(struct rcu_level *));
+ init_table(ht, new_t, old_order, new_order - old_order);
+ /* Changing table and size atomically wrt lookups */
+ rcu_assign_pointer(ht->t, new_t);
+ ht->cds_lfht_call_rcu(&old_t->head, cds_lfht_free_table_cb);
}
/* called with resize mutex held */
static
-void _do_cds_lfht_resize(struct cds_lfht *ht)
+void _do_cds_lfht_shrink(struct cds_lfht *ht, struct rcu_table *old_t,
+ unsigned long old_size, unsigned long new_size)
{
- unsigned long new_size, old_size, old_order, new_order;
- struct rcu_table *new_t, *old_t;
+ unsigned long old_order, new_order;
+ struct rcu_table *new_t;
- old_t = ht->t;
- old_size = old_t->size;
+ new_size = max(new_size, 1);
old_order = get_count_order_ulong(old_size) + 1;
-
- new_size = CMM_LOAD_SHARED(old_t->resize_target);
- if (old_size == new_size)
- return;
new_order = get_count_order_ulong(new_size) + 1;
printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n",
old_size, old_order, new_size, new_order);
new_t = malloc(sizeof(struct cds_lfht)
- + (new_order * sizeof(struct _cds_lfht_node *)));
- assert(new_size > old_size);
+ + (new_order * sizeof(struct rcu_level *)));
+ assert(new_size < old_size);
memcpy(&new_t->tbl, &old_t->tbl,
- old_order * sizeof(struct _cds_lfht_node *));
- init_table(ht, new_t, old_order, new_order - old_order);
+ new_order * sizeof(struct rcu_level *));
+ new_t->size = !new_order ? 1 : (1UL << (new_order - 1));
+ new_t->resize_target = new_t->size;
+ new_t->resize_initiated = 0;
+
/* Changing table and size atomically wrt lookups */
rcu_assign_pointer(ht->t, new_t);
+
+ /*
+ * We need to wait for all reader threads to reach Q.S. (and
+ * thus use the new table for lookups) before we can start
+ * releasing the old dummy nodes.
+ */
+ ht->cds_lfht_synchronize_rcu();
+
+ /* Unlink and remove all now-unused dummy node pointers. */
+ fini_table(ht, old_t, new_order, old_order - new_order);
ht->cds_lfht_call_rcu(&old_t->head, cds_lfht_free_table_cb);
}
+
+/* called with resize mutex held */
+static
+void _do_cds_lfht_resize(struct cds_lfht *ht)
+{
+ unsigned long new_size, old_size;
+ struct rcu_table *old_t;
+
+ old_t = ht->t;
+ old_size = old_t->size;
+ new_size = CMM_LOAD_SHARED(old_t->resize_target);
+ if (old_size < new_size)
+ _do_cds_lfht_grow(ht, old_t, old_size, new_size);
+ else if (old_size > new_size)
+ _do_cds_lfht_shrink(ht, old_t, old_size, new_size);
+ else
+ CMM_STORE_SHARED(old_t->resize_initiated, 0);
+}
+
static
unsigned long resize_target_update(struct rcu_table *t,
int growth_order)
t->size << growth_order);
}
-void cds_lfht_resize(struct cds_lfht *ht, int growth)
+static
+unsigned long resize_target_update_count(struct rcu_table *t,
+ unsigned long count)
+{
+ count = max(count, 1);
+ return uatomic_set(&t->resize_target, count);
+}
+
+void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size)
{
struct rcu_table *t = rcu_dereference(ht->t);
unsigned long target_size;
- if (growth < 0) {
- /*
- * Silently refuse to shrink hash table. (not supported)
- */
- dbg_printf("shrinking hash table not supported.\n");
- return;
- }
-
- target_size = resize_target_update(t, growth);
- if (t->size < target_size) {
- CMM_STORE_SHARED(t->resize_initiated, 1);
- pthread_mutex_lock(&ht->resize_mutex);
- _do_cds_lfht_resize(ht);
- pthread_mutex_unlock(&ht->resize_mutex);
- }
+ target_size = resize_target_update_count(t, new_size);
+ CMM_STORE_SHARED(t->resize_initiated, 1);
+ pthread_mutex_lock(&ht->resize_mutex);
+ _do_cds_lfht_resize(ht);
+ pthread_mutex_unlock(&ht->resize_mutex);
}
static
#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
-static
-unsigned long resize_target_update_count(struct rcu_table *t,
- unsigned long count)
-{
- return uatomic_set(&t->resize_target, count);
-}
-
static
void cds_lfht_resize_lazy_count(struct cds_lfht *ht, struct rcu_table *t,
unsigned long count)
unsigned long target_size;
target_size = resize_target_update_count(t, count);
- if (!CMM_LOAD_SHARED(t->resize_initiated) && t->size < target_size) {
+ if (!CMM_LOAD_SHARED(t->resize_initiated)) {
uatomic_inc(&ht->in_progress_resize);
cmm_smp_mb(); /* increment resize count before calling it */
work = malloc(sizeof(*work));
projects / urcu.git / commitdiff
