/*
* 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
#define dbg_printf(fmt, args...)
#endif
-#define CHAIN_LEN_TARGET 4
-#define CHAIN_LEN_RESIZE_THRESHOLD 8
-
-/* Commit counter changes to global counter each 1024 steps */
+/*
+ * Per-CPU split-counters lazily update the global counter each 1024
+ * addition/removal. It automatically keeps track of resize required.
+ * We use the bucket length as indicator for need to expand for small
+ * tables and machines lacking per-cpu data suppport.
+ */
#define COUNT_COMMIT_ORDER 10
+#define CHAIN_LEN_TARGET 1
+#define CHAIN_LEN_RESIZE_THRESHOLD 3
+
+/*
+ * Define the minimum table size.
+ */
+#define MIN_TABLE_SIZE 1
+
+#if (CAA_BITS_PER_LONG == 32)
+#define MAX_TABLE_ORDER 32
+#else
+#define MAX_TABLE_ORDER 64
+#endif
+
+/*
+ * Minimum number of dummy nodes to touch per thread to parallelize grow/shrink.
+ */
+#define MIN_PARTITION_PER_THREAD_ORDER 12
+#define MIN_PARTITION_PER_THREAD (1UL << MIN_PARTITION_PER_THREAD_ORDER)
+
+#ifndef min
+#define min(a, b) ((a) < (b) ? (a) : (b))
+#endif
#ifndef max
#define max(a, b) ((a) > (b) ? (a) : (b))
/*
* The removed flag needs to be updated atomically with the pointer.
+ * It indicates that no node must attach to the node scheduled for
+ * removal, and that node garbage collection must be performed.
* The dummy flag does not require to be updated atomically with the
* pointer, but it is added as a pointer low bit flag to save space.
*/
#define DUMMY_FLAG (1UL << 1)
#define FLAGS_MASK ((1UL << 2) - 1)
+/* Value of the end pointer. Should not interact with flags. */
+#define END_VALUE NULL
+
struct ht_items_count {
- unsigned long add, remove;
+ unsigned long add, del;
} __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 size; /* always a power of 2, shared (RCU) */
unsigned long resize_target;
int resize_initiated;
- struct rcu_head head;
- struct _cds_lfht_node *tbl[0];
+ struct rcu_level *tbl[MAX_TABLE_ORDER];
};
struct cds_lfht {
- struct rcu_table *t; /* shared */
+ struct rcu_table t;
cds_lfht_hash_fct hash_fct;
cds_lfht_compare_fct compare_fct;
unsigned long hash_seed;
+ int flags;
+ /*
+ * We need to put the work threads offline (QSBR) when taking this
+ * mutex, because we use synchronize_rcu within this mutex critical
+ * section, which waits on read-side critical sections, and could
+ * therefore cause grace-period deadlock if we hold off RCU G.P.
+ * completion.
+ */
pthread_mutex_t resize_mutex; /* resize mutex: add/del mutex */
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);
+ void (*cds_lfht_rcu_read_lock)(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 *resize_attr; /* Resize threads attributes */
unsigned long count; /* global approximate item count */
struct ht_items_count *percpu_count; /* per-cpu item count */
};
struct cds_lfht *ht;
};
+struct partition_resize_work {
+ struct rcu_head head;
+ struct cds_lfht *ht;
+ unsigned long i, start, len;
+ void (*fct)(struct cds_lfht *ht, unsigned long i,
+ unsigned long start, unsigned long len);
+};
+
+enum add_mode {
+ ADD_DEFAULT = 0,
+ ADD_UNIQUE = 1,
+ ADD_REPLACE = 2,
+};
+
+static
+struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
+ unsigned long size,
+ struct cds_lfht_node *node,
+ enum add_mode mode, int dummy);
+
/*
* Algorithm to reverse bits in a word by lookup table, extended to
* 64-bit words.
return order;
}
-static
-void cds_lfht_resize_lazy(struct cds_lfht *ht, struct rcu_table *t, int growth);
+#ifdef POISON_FREE
+#define poison_free(ptr) \
+ do { \
+ memset(ptr, 0x42, sizeof(*(ptr))); \
+ free(ptr); \
+ } while (0)
+#else
+#define poison_free(ptr) free(ptr)
+#endif
static
-void cds_lfht_resize_lazy_count(struct cds_lfht *ht, struct rcu_table *t,
- unsigned long count);
+void cds_lfht_resize_lazy(struct cds_lfht *ht, unsigned long size, int growth);
/*
* If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
* In the unfortunate event the number of CPUs reported would be
* inaccurate, we use modulo arithmetic on the number of CPUs we got.
*/
-
#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
+static
+void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
+ unsigned long count);
+
static long nr_cpus_mask = -1;
static
static
void free_per_cpu_items_count(struct ht_items_count *count)
{
- free(count);
+ poison_free(count);
}
static
}
static
-void ht_count_add(struct cds_lfht *ht, struct rcu_table *t)
+void ht_count_add(struct cds_lfht *ht, unsigned long size)
{
unsigned long percpu_count;
int cpu;
1UL << COUNT_COMMIT_ORDER);
/* If power of 2 */
if (!(count & (count - 1))) {
- dbg_printf("add global %lu\n", count);
- cds_lfht_resize_lazy_count(ht, t, count);
+ if ((count >> CHAIN_LEN_RESIZE_THRESHOLD) < size)
+ return;
+ dbg_printf("add set global %lu\n", count);
+ cds_lfht_resize_lazy_count(ht, size,
+ count >> (CHAIN_LEN_TARGET - 1));
}
}
}
static
-void ht_count_remove(struct cds_lfht *ht, struct rcu_table *t)
+void ht_count_del(struct cds_lfht *ht, unsigned long size)
{
unsigned long percpu_count;
int cpu;
cpu = ht_get_cpu();
if (unlikely(cpu < 0))
return;
- percpu_count = uatomic_add_return(&ht->percpu_count[cpu].remove, -1);
+ percpu_count = uatomic_add_return(&ht->percpu_count[cpu].del, -1);
if (unlikely(!(percpu_count & ((1UL << COUNT_COMMIT_ORDER) - 1)))) {
unsigned long count;
- dbg_printf("remove percpu %lu\n", percpu_count);
+ dbg_printf("del percpu %lu\n", percpu_count);
count = uatomic_add_return(&ht->count,
-(1UL << COUNT_COMMIT_ORDER));
/* If power of 2 */
if (!(count & (count - 1))) {
- dbg_printf("remove global %lu\n", count);
- cds_lfht_resize_lazy_count(ht, t, count);
+ if ((count >> CHAIN_LEN_RESIZE_THRESHOLD) >= size)
+ return;
+ dbg_printf("del set global %lu\n", count);
+ cds_lfht_resize_lazy_count(ht, size,
+ count >> (CHAIN_LEN_TARGET - 1));
}
}
}
}
static
-void ht_count_add(struct cds_lfht *ht)
+void ht_count_add(struct cds_lfht *ht, unsigned long size)
{
}
static
-void ht_count_remove(struct cds_lfht *ht)
+void ht_count_del(struct cds_lfht *ht, unsigned long size)
{
}
static
-void check_resize(struct cds_lfht *ht, struct rcu_table *t,
- uint32_t chain_len)
+void check_resize(struct cds_lfht *ht, unsigned long size, uint32_t chain_len)
{
- return; //TEST
+ unsigned long count;
+
+ if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
+ return;
+ count = uatomic_read(&ht->count);
+ /*
+ * Use bucket-local length for small table expand and for
+ * environments lacking per-cpu data support.
+ */
+ if (count >= (1UL << COUNT_COMMIT_ORDER))
+ return;
if (chain_len > 100)
dbg_printf("WARNING: large chain length: %u.\n",
chain_len);
if (chain_len >= CHAIN_LEN_RESIZE_THRESHOLD)
- cds_lfht_resize_lazy(ht, t,
+ cds_lfht_resize_lazy(ht, size,
get_count_order_u32(chain_len - (CHAIN_LEN_TARGET - 1)));
}
{
return (struct cds_lfht_node *) (((unsigned long) node) | DUMMY_FLAG);
}
-
+
+static
+struct cds_lfht_node *get_end(void)
+{
+ return (struct cds_lfht_node *) END_VALUE;
+}
+
+static
+int is_end(struct cds_lfht_node *node)
+{
+ return clear_flag(node) == (struct cds_lfht_node *) END_VALUE;
+}
+
static
unsigned long _uatomic_max(unsigned long *ptr, unsigned long v)
{
return v;
}
+static
+void cds_lfht_free_level(struct rcu_head *head)
+{
+ struct rcu_level *l =
+ caa_container_of(head, struct rcu_level, head);
+ poison_free(l);
+}
+
/*
* Remove all logically deleted nodes from a bucket up to a certain node key.
*/
{
struct cds_lfht_node *iter_prev, *iter, *next, *new_next;
+ assert(!is_dummy(dummy));
+ assert(!is_removed(dummy));
+ assert(!is_dummy(node));
+ assert(!is_removed(node));
for (;;) {
iter_prev = dummy;
/* We can always skip the dummy node initially */
iter = rcu_dereference(iter_prev->p.next);
assert(iter_prev->p.reverse_hash <= node->p.reverse_hash);
+ /*
+ * We should never be called with dummy (start of chain)
+ * and logically removed node (end of path compression
+ * marker) being the actual same node. This would be a
+ * bug in the algorithm implementation.
+ */
+ assert(dummy != node);
for (;;) {
- if (unlikely(!clear_flag(iter)))
+ if (unlikely(is_end(iter)))
return;
if (likely(clear_flag(iter)->p.reverse_hash > node->p.reverse_hash))
return;
new_next = flag_dummy(clear_flag(next));
else
new_next = clear_flag(next);
+ if (is_removed(iter))
+ new_next = flag_removed(new_next);
(void) uatomic_cmpxchg(&iter_prev->p.next, iter, new_next);
}
+ return;
}
static
-struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht, struct rcu_table *t,
- struct cds_lfht_node *node, int unique, int dummy)
+struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
+ unsigned long size,
+ struct cds_lfht_node *node,
+ enum add_mode mode, int dummy)
{
struct cds_lfht_node *iter_prev, *iter, *next, *new_node, *new_next,
- *dummy_node;
+ *dummy_node, *return_node;
struct _cds_lfht_node *lookup;
unsigned long hash, index, order;
- if (!t->size) {
+ assert(!is_dummy(node));
+ assert(!is_removed(node));
+ if (!size) {
assert(dummy);
- node->p.next = flag_dummy(NULL);
+ node->p.next = flag_dummy(get_end());
return node; /* Initial first add (head) */
}
hash = bit_reverse_ulong(node->p.reverse_hash);
* iter_prev points to the non-removed node prior to the
* insert location.
*/
- index = hash & (t->size - 1);
+ index = hash & (size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)];
+ lookup = &ht->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);
assert(iter_prev->p.reverse_hash <= node->p.reverse_hash);
for (;;) {
- if (unlikely(!clear_flag(iter)))
+ if (unlikely(is_end(iter)))
goto insert;
if (likely(clear_flag(iter)->p.reverse_hash > node->p.reverse_hash))
goto insert;
next = rcu_dereference(clear_flag(iter)->p.next);
if (unlikely(is_removed(next)))
goto gc_node;
- if (unique
+ if ((mode == ADD_UNIQUE || mode == ADD_REPLACE)
&& !is_dummy(next)
&& !ht->compare_fct(node->key, node->key_len,
clear_flag(iter)->key,
- clear_flag(iter)->key_len))
- return clear_flag(iter);
+ clear_flag(iter)->key_len)) {
+ if (mode == ADD_UNIQUE)
+ return clear_flag(iter);
+ else /* mode == ADD_REPLACE */
+ goto replace;
+ }
/* Only account for identical reverse hash once */
if (iter_prev->p.reverse_hash != clear_flag(iter)->p.reverse_hash
&& !is_dummy(next))
- check_resize(ht, t, ++chain_len);
+ check_resize(ht, size, ++chain_len);
iter_prev = clear_flag(iter);
iter = next;
}
+
insert:
assert(node != clear_flag(iter));
assert(!is_removed(iter_prev));
+ assert(!is_removed(iter));
assert(iter_prev != node);
if (!dummy)
node->p.next = clear_flag(iter);
else
new_node = node;
if (uatomic_cmpxchg(&iter_prev->p.next, iter,
- new_node) != iter)
+ new_node) != iter) {
continue; /* retry */
+ } else {
+ if (mode == ADD_REPLACE)
+ return_node = NULL;
+ else /* ADD_DEFAULT and ADD_UNIQUE */
+ return_node = node;
+ goto gc_end;
+ }
+
+ replace:
+ /* Insert after node to be replaced */
+ iter_prev = clear_flag(iter);
+ iter = next;
+ assert(node != clear_flag(iter));
+ assert(!is_removed(iter_prev));
+ assert(!is_removed(iter));
+ assert(iter_prev != node);
+ assert(!dummy);
+ node->p.next = clear_flag(iter);
+ if (is_dummy(iter))
+ new_node = flag_dummy(node);
else
+ new_node = node;
+ /*
+ * Here is the whole trick for lock-free replace: we add
+ * the replacement node _after_ the node we want to
+ * replace by atomically setting its next pointer at the
+ * same time we set its removal flag. Given that
+ * the lookups/get next use an iterator aware of the
+ * next pointer, they will either skip the old node due
+ * to the removal flag and see the new node, or use
+ * the old node, but will not see the new one.
+ */
+ new_node = flag_removed(new_node);
+ if (uatomic_cmpxchg(&iter_prev->p.next,
+ iter, new_node) != iter) {
+ continue; /* retry */
+ } else {
+ return_node = iter_prev;
goto gc_end;
+ }
+
gc_node:
assert(!is_removed(iter));
if (is_dummy(iter))
}
gc_end:
/* Garbage collect logically removed nodes in the bucket */
- index = hash & (t->size - 1);
+ index = hash & (size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 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);
- return node;
+ return return_node;
}
static
-int _cds_lfht_remove(struct cds_lfht *ht, struct rcu_table *t,
- struct cds_lfht_node *node)
+int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
+ struct cds_lfht_node *node,
+ int dummy_removal)
{
struct cds_lfht_node *dummy, *next, *old;
struct _cds_lfht_node *lookup;
unsigned long hash, index, order;
/* logically delete the node */
+ assert(!is_dummy(node));
+ assert(!is_removed(node));
old = rcu_dereference(node->p.next);
do {
+ struct cds_lfht_node *new_next;
+
next = old;
if (unlikely(is_removed(next)))
goto end;
- assert(!is_dummy(next));
- old = uatomic_cmpxchg(&node->p.next, next,
- flag_removed(next));
+ if (dummy_removal)
+ assert(is_dummy(next));
+ else
+ assert(!is_dummy(next));
+ new_next = flag_removed(next);
+ old = uatomic_cmpxchg(&node->p.next, next, new_next);
} while (old != next);
/* We performed the (logical) deletion. */
* if found.
*/
hash = bit_reverse_ulong(node->p.reverse_hash);
- index = hash & (t->size - 1);
+ assert(size > 0);
+ index = hash & (size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 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);
end:
}
static
-void init_table(struct cds_lfht *ht, struct rcu_table *t,
+void *partition_resize_thread(void *arg)
+{
+ struct partition_resize_work *work = arg;
+
+ work->ht->cds_lfht_rcu_register_thread();
+ work->fct(work->ht, work->i, work->start, work->len);
+ work->ht->cds_lfht_rcu_unregister_thread();
+ return NULL;
+}
+
+static
+void partition_resize_helper(struct cds_lfht *ht, unsigned long i,
+ unsigned long len,
+ void (*fct)(struct cds_lfht *ht, unsigned long i,
+ unsigned long start, unsigned long len))
+{
+ unsigned long partition_len;
+ struct partition_resize_work *work;
+ int thread, ret;
+ unsigned long nr_threads;
+ pthread_t *thread_id;
+
+ /*
+ * Note: nr_cpus_mask + 1 is always power of 2.
+ * We spawn just the number of threads we need to satisfy the minimum
+ * partition size, up to the number of CPUs in the system.
+ */
+ nr_threads = min(nr_cpus_mask + 1,
+ len >> MIN_PARTITION_PER_THREAD_ORDER);
+ partition_len = len >> get_count_order_ulong(nr_threads);
+ work = calloc(nr_threads, sizeof(*work));
+ thread_id = calloc(nr_threads, sizeof(*thread_id));
+ assert(work);
+ for (thread = 0; thread < nr_threads; thread++) {
+ work[thread].ht = ht;
+ work[thread].i = i;
+ work[thread].len = partition_len;
+ work[thread].start = thread * partition_len;
+ work[thread].fct = fct;
+ ret = pthread_create(&thread_id[thread], ht->resize_attr,
+ partition_resize_thread, &work[thread]);
+ assert(!ret);
+ }
+ for (thread = 0; thread < nr_threads; thread++) {
+ ret = pthread_join(thread_id[thread], NULL);
+ assert(!ret);
+ }
+ free(work);
+ free(thread_id);
+}
+
+/*
+ * Holding RCU read lock to protect _cds_lfht_add against memory
+ * reclaim that could be performed by other call_rcu worker threads (ABA
+ * problem).
+ *
+ * When we reach a certain length, we can split this population phase over
+ * many worker threads, based on the number of CPUs available in the system.
+ * This should therefore take care of not having the expand lagging behind too
+ * many concurrent insertion threads by using the scheduler's ability to
+ * schedule dummy node population fairly with insertions.
+ */
+static
+void init_table_populate_partition(struct cds_lfht *ht, unsigned long i,
+ unsigned long start, unsigned long len)
+{
+ unsigned long j;
+
+ ht->cds_lfht_rcu_read_lock();
+ for (j = start; j < start + len; j++) {
+ struct cds_lfht_node *new_node =
+ (struct cds_lfht_node *) &ht->t.tbl[i]->nodes[j];
+
+ dbg_printf("init populate: 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_add(ht, !i ? 0 : (1UL << (i - 1)),
+ new_node, ADD_DEFAULT, 1);
+ if (CMM_LOAD_SHARED(ht->in_progress_destroy))
+ break;
+ }
+ ht->cds_lfht_rcu_read_unlock();
+}
+
+static
+void init_table_populate(struct cds_lfht *ht, unsigned long i,
+ unsigned long len)
+{
+ assert(nr_cpus_mask != -1);
+ if (nr_cpus_mask < 0 || len < 2 * MIN_PARTITION_PER_THREAD) {
+ ht->cds_lfht_rcu_thread_online();
+ init_table_populate_partition(ht, i, 0, len);
+ ht->cds_lfht_rcu_thread_offline();
+ return;
+ }
+ partition_resize_helper(ht, i, len, init_table_populate_partition);
+}
+
+static
+void init_table(struct cds_lfht *ht,
unsigned long first_order, unsigned long len_order)
{
unsigned long i, end_order;
dbg_printf("init table: first_order %lu end_order %lu\n",
first_order, first_order + len_order);
end_order = first_order + len_order;
- t->size = !first_order ? 0 : (1UL << (first_order - 1));
for (i = first_order; i < end_order; i++) {
- unsigned long j, len;
+ unsigned long len;
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));
- for (j = 0; j < len; 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);
- if (CMM_LOAD_SHARED(ht->in_progress_destroy))
- break;
- }
- /* Update table size */
- t->size = !i ? 1 : (1UL << i);
- dbg_printf("init new size: %lu\n", t->size);
+
+ /* 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)));
+ assert(ht->t.tbl[i]);
+
+ /*
+ * Set all dummy nodes reverse hash values for a level and
+ * link all dummy nodes into the table.
+ */
+ init_table_populate(ht, i, len);
+
+ /*
+ * Update table size.
+ */
+ 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;
+ }
+}
+
+/*
+ * Holding RCU read lock to protect _cds_lfht_remove against memory
+ * reclaim that could be performed by other call_rcu worker threads (ABA
+ * problem).
+ * For a single level, we logically remove and garbage collect each node.
+ *
+ * As a design choice, we perform logical removal and garbage collection on a
+ * node-per-node basis to simplify this algorithm. We also assume keeping good
+ * cache locality of the operation would overweight possible performance gain
+ * that could be achieved by batching garbage collection for multiple levels.
+ * However, this would have to be justified by benchmarks.
+ *
+ * Concurrent removal and add operations are helping us perform garbage
+ * collection of logically removed nodes. We guarantee that all logically
+ * removed nodes have been garbage-collected (unlinked) before call_rcu is
+ * invoked to free a hole level of dummy nodes (after a grace period).
+ *
+ * Logical removal and garbage collection can therefore be done in batch or on a
+ * node-per-node basis, as long as the guarantee above holds.
+ *
+ * When we reach a certain length, we can split this removal over many worker
+ * threads, based on the number of CPUs available in the system. This should
+ * take care of not letting resize process lag behind too many concurrent
+ * updater threads actively inserting into the hash table.
+ */
+static
+void remove_table_partition(struct cds_lfht *ht, unsigned long i,
+ unsigned long start, unsigned long len)
+{
+ unsigned long j;
+
+ ht->cds_lfht_rcu_read_lock();
+ for (j = start; j < start + len; j++) {
+ struct cds_lfht_node *fini_node =
+ (struct cds_lfht_node *) &ht->t.tbl[i]->nodes[j];
+
+ dbg_printf("remove entry: i %lu j %lu hash %lu\n",
+ i, j, !i ? 0 : (1UL << (i - 1)) + j);
+ fini_node->p.reverse_hash =
+ bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j);
+ (void) _cds_lfht_del(ht, !i ? 0 : (1UL << (i - 1)),
+ fini_node, 1);
if (CMM_LOAD_SHARED(ht->in_progress_destroy))
break;
}
- t->resize_target = t->size;
- t->resize_initiated = 0;
+ ht->cds_lfht_rcu_read_unlock();
}
-struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct,
+static
+void remove_table(struct cds_lfht *ht, unsigned long i, unsigned long len)
+{
+
+ assert(nr_cpus_mask != -1);
+ if (nr_cpus_mask < 0 || len < 2 * MIN_PARTITION_PER_THREAD) {
+ ht->cds_lfht_rcu_thread_online();
+ remove_table_partition(ht, i, 0, len);
+ ht->cds_lfht_rcu_thread_offline();
+ return;
+ }
+ partition_resize_helper(ht, i, len, remove_table_partition);
+}
+
+static
+void fini_table(struct cds_lfht *ht,
+ 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);
+ 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.
+ * Concurrent add/remove operation are helping us doing
+ * the gc.
+ */
+ remove_table(ht, i, len);
+
+ ht->cds_lfht_call_rcu(&ht->t.tbl[i]->head, cds_lfht_free_level);
+
+ dbg_printf("fini new size: %lu\n", 1UL << i);
+ if (CMM_LOAD_SHARED(ht->in_progress_destroy))
+ break;
+ }
+}
+
+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,
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),
+ void (*cds_lfht_rcu_read_lock)(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)
{
struct cds_lfht *ht;
unsigned long order;
if (init_size && (init_size & (init_size - 1)))
return NULL;
ht = calloc(1, sizeof(struct cds_lfht));
+ assert(ht);
ht->hash_fct = hash_fct;
ht->compare_fct = compare_fct;
ht->hash_seed = hash_seed;
ht->cds_lfht_call_rcu = cds_lfht_call_rcu;
- ht->in_progress_resize = 0;
+ ht->cds_lfht_synchronize_rcu = cds_lfht_synchronize_rcu;
+ ht->cds_lfht_rcu_read_lock = cds_lfht_rcu_read_lock;
+ ht->cds_lfht_rcu_read_unlock = cds_lfht_rcu_read_unlock;
+ ht->cds_lfht_rcu_thread_offline = cds_lfht_rcu_thread_offline;
+ ht->cds_lfht_rcu_thread_online = cds_lfht_rcu_thread_online;
+ ht->cds_lfht_rcu_register_thread = cds_lfht_rcu_register_thread;
+ ht->cds_lfht_rcu_unregister_thread = cds_lfht_rcu_unregister_thread;
+ ht->resize_attr = attr;
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 *)));
- ht->t->size = 0;
+ order = get_count_order_ulong(max(init_size, MIN_TABLE_SIZE)) + 1;
+ ht->flags = flags;
+ ht->cds_lfht_rcu_thread_offline();
pthread_mutex_lock(&ht->resize_mutex);
- init_table(ht, ht->t, 0, order);
+ ht->t.resize_target = 1UL << (order - 1);
+ init_table(ht, 0, order);
pthread_mutex_unlock(&ht->resize_mutex);
+ ht->cds_lfht_rcu_thread_online();
return ht;
}
-struct cds_lfht_node *cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len)
+void cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key_len,
+ struct cds_lfht_iter *iter)
{
- struct rcu_table *t;
- struct cds_lfht_node *node, *next;
+ struct cds_lfht_node *node, *next, *dummy_node;
struct _cds_lfht_node *lookup;
- unsigned long hash, reverse_hash, index, order;
+ unsigned long hash, reverse_hash, index, order, size;
hash = ht->hash_fct(key, key_len, ht->hash_seed);
reverse_hash = bit_reverse_ulong(hash);
- t = rcu_dereference(ht->t);
- index = hash & (t->size - 1);
+ size = rcu_dereference(ht->t.size);
+ index = hash & (size - 1);
order = get_count_order_ulong(index + 1);
- lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)];
+ lookup = &ht->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));
- node = (struct cds_lfht_node *) lookup;
+ hash, index, order, index & (!order ? 0 : ((1UL << (order - 1)) - 1)));
+ dummy_node = (struct cds_lfht_node *) lookup;
+ /* We can always skip the dummy node initially */
+ node = rcu_dereference(dummy_node->p.next);
+ node = clear_flag(node);
for (;;) {
- if (unlikely(!node))
+ if (unlikely(is_end(node))) {
+ node = NULL;
break;
+ }
if (unlikely(node->p.reverse_hash > reverse_hash)) {
node = NULL;
break;
node = clear_flag(next);
}
assert(!node || !is_dummy(rcu_dereference(node->p.next)));
- return node;
+ iter->node = node;
+ iter->next = next;
}
-struct cds_lfht_node *cds_lfht_next(struct cds_lfht *ht,
- struct cds_lfht_node *node)
+void cds_lfht_next(struct cds_lfht *ht, struct cds_lfht_iter *iter)
{
- struct cds_lfht_node *next;
+ struct cds_lfht_node *node, *next;
unsigned long reverse_hash;
void *key;
size_t key_len;
+ node = iter->node;
reverse_hash = node->p.reverse_hash;
key = node->key;
key_len = node->key_len;
- next = rcu_dereference(node->p.next);
+ next = iter->next;
node = clear_flag(next);
for (;;) {
- if (unlikely(!node))
+ if (unlikely(is_end(node))) {
+ node = NULL;
break;
+ }
if (unlikely(node->p.reverse_hash > reverse_hash)) {
node = NULL;
break;
node = clear_flag(next);
}
assert(!node || !is_dummy(rcu_dereference(node->p.next)));
- return node;
+ iter->node = node;
+ iter->next = next;
}
void cds_lfht_add(struct cds_lfht *ht, struct cds_lfht_node *node)
{
- struct rcu_table *t;
- unsigned long hash;
+ unsigned long hash, size;
hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
- t = rcu_dereference(ht->t);
- (void) _cds_lfht_add(ht, t, node, 0, 0);
- ht_count_add(ht, t);
+ size = rcu_dereference(ht->t.size);
+ (void) _cds_lfht_add(ht, size, node, ADD_DEFAULT, 0);
+ ht_count_add(ht, size);
}
struct cds_lfht_node *cds_lfht_add_unique(struct cds_lfht *ht,
- struct cds_lfht_node *node)
+ struct cds_lfht_node *node)
{
- struct rcu_table *t;
- unsigned long hash;
+ unsigned long hash, size;
struct cds_lfht_node *ret;
hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
- t = rcu_dereference(ht->t);
- ret = _cds_lfht_add(ht, t, node, 1, 0);
- if (ret != node)
- ht_count_add(ht, t);
+ size = rcu_dereference(ht->t.size);
+ ret = _cds_lfht_add(ht, size, node, ADD_UNIQUE, 0);
+ if (ret == node)
+ ht_count_add(ht, size);
return ret;
}
-int cds_lfht_remove(struct cds_lfht *ht, struct cds_lfht_node *node)
+struct cds_lfht_node *cds_lfht_replace(struct cds_lfht *ht,
+ struct cds_lfht_node *node)
{
- struct rcu_table *t;
+ unsigned long hash, size;
+ struct cds_lfht_node *ret;
+
+ hash = ht->hash_fct(node->key, node->key_len, ht->hash_seed);
+ node->p.reverse_hash = bit_reverse_ulong((unsigned long) hash);
+
+ size = rcu_dereference(ht->t.size);
+ ret = _cds_lfht_add(ht, size, node, ADD_REPLACE, 0);
+ if (ret == NULL)
+ ht_count_add(ht, size);
+ return ret;
+}
+
+int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node)
+{
+ unsigned long size;
int ret;
- t = rcu_dereference(ht->t);
- ret = _cds_lfht_remove(ht, t, node);
+ size = rcu_dereference(ht->t.size);
+ ret = _cds_lfht_del(ht, size, node, 0);
if (!ret)
- ht_count_remove(ht, t);
+ ht_count_del(ht, size);
return ret;
}
static
int cds_lfht_delete_dummy(struct cds_lfht *ht)
{
- struct rcu_table *t;
struct cds_lfht_node *node;
struct _cds_lfht_node *lookup;
- unsigned long order, i;
+ unsigned long order, i, size;
- t = ht->t;
/* Check that the table is empty */
- lookup = &t->tbl[0][0];
+ lookup = &ht->t.tbl[0]->nodes[0];
node = (struct cds_lfht_node *) lookup;
do {
node = clear_flag(node)->p.next;
if (!is_dummy(node))
return -EPERM;
assert(!is_removed(node));
- } while (clear_flag(node));
+ } while (!is_end(node));
+ /*
+ * size accessed without rcu_dereference because hash table is
+ * being destroyed.
+ */
+ size = ht->t.size;
/* Internal sanity check: all nodes left should be dummy */
- for (order = 0; order < get_count_order_ulong(t->size) + 1; order++) {
+ for (order = 0; order < get_count_order_ulong(size) + 1; order++) {
unsigned long len;
len = !order ? 1 : 1UL << (order - 1);
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(ht->t.tbl[order]->nodes[i].reverse_hash));
+ assert(is_dummy(ht->t.tbl[order]->nodes[i].next));
}
- free(t->tbl[order]);
+ poison_free(ht->t.tbl[order]);
}
return 0;
}
* Should only be called when no more concurrent readers nor writers can
* possibly access the table.
*/
-int cds_lfht_destroy(struct cds_lfht *ht)
+int cds_lfht_destroy(struct cds_lfht *ht, pthread_attr_t **attr)
{
int ret;
ret = cds_lfht_delete_dummy(ht);
if (ret)
return ret;
- free(ht->t);
free_per_cpu_items_count(ht->percpu_count);
- free(ht);
+ if (attr)
+ *attr = ht->resize_attr;
+ poison_free(ht);
return ret;
}
unsigned long *count,
unsigned long *removed)
{
- struct rcu_table *t;
struct cds_lfht_node *node, *next;
struct _cds_lfht_node *lookup;
unsigned long nr_dummy = 0;
*count = 0;
*removed = 0;
- t = rcu_dereference(ht->t);
/* Count non-dummy nodes in the table */
- lookup = &t->tbl[0][0];
+ lookup = &ht->t.tbl[0]->nodes[0];
node = (struct cds_lfht_node *) lookup;
do {
next = rcu_dereference(node->p.next);
else
(nr_dummy)++;
node = clear_flag(next);
- } while (node);
+ } while (!is_end(node));
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,
+ 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;
+
+ 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);
+ assert(new_size > old_size);
+ init_table(ht, old_order, new_order - old_order);
}
/* called with resize mutex held */
static
-void _do_cds_lfht_resize(struct cds_lfht *ht)
+void _do_cds_lfht_shrink(struct cds_lfht *ht,
+ 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;
- old_t = ht->t;
- old_size = old_t->size;
+ new_size = max(new_size, MIN_TABLE_SIZE);
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);
- 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);
- /* 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);
+ assert(new_size < old_size);
+
+ /* Remove and unlink all dummy nodes to remove. */
+ fini_table(ht, new_order, old_order - new_order);
+}
+
+
+/* called with resize mutex held */
+static
+void _do_cds_lfht_resize(struct cds_lfht *ht)
+{
+ unsigned long new_size, old_size;
+
+ /*
+ * Resize table, re-do if the target size has changed under us.
+ */
+ do {
+ ht->t.resize_initiated = 1;
+ old_size = ht->t.size;
+ new_size = CMM_LOAD_SHARED(ht->t.resize_target);
+ if (old_size < new_size)
+ _do_cds_lfht_grow(ht, old_size, new_size);
+ else if (old_size > new_size)
+ _do_cds_lfht_shrink(ht, old_size, new_size);
+ ht->t.resize_initiated = 0;
+ /* write resize_initiated before read resize_target */
+ cmm_smp_mb();
+ } while (ht->t.size != CMM_LOAD_SHARED(ht->t.resize_target));
}
static
-unsigned long resize_target_update(struct rcu_table *t,
+unsigned long resize_target_update(struct cds_lfht *ht, unsigned long size,
int growth_order)
{
- return _uatomic_max(&t->resize_target,
- t->size << growth_order);
+ return _uatomic_max(&ht->t.resize_target,
+ size << growth_order);
}
static
-unsigned long resize_target_update_count(struct rcu_table *t,
- unsigned long count)
+void resize_target_update_count(struct cds_lfht *ht,
+ unsigned long count)
{
- return _uatomic_max(&t->resize_target, count);
+ count = max(count, MIN_TABLE_SIZE);
+ uatomic_set(&ht->t.resize_target, count);
}
-void cds_lfht_resize(struct cds_lfht *ht, int growth)
+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);
- }
+ resize_target_update_count(ht, new_size);
+ CMM_STORE_SHARED(ht->t.resize_initiated, 1);
+ ht->cds_lfht_rcu_thread_offline();
+ pthread_mutex_lock(&ht->resize_mutex);
+ _do_cds_lfht_resize(ht);
+ pthread_mutex_unlock(&ht->resize_mutex);
+ ht->cds_lfht_rcu_thread_online();
}
static
caa_container_of(head, struct rcu_resize_work, head);
struct cds_lfht *ht = work->ht;
+ ht->cds_lfht_rcu_thread_offline();
pthread_mutex_lock(&ht->resize_mutex);
_do_cds_lfht_resize(ht);
pthread_mutex_unlock(&ht->resize_mutex);
- free(work);
+ ht->cds_lfht_rcu_thread_online();
+ poison_free(work);
cmm_smp_mb(); /* finish resize before decrement */
uatomic_dec(&ht->in_progress_resize);
}
static
-void cds_lfht_resize_lazy(struct cds_lfht *ht, struct rcu_table *t, int growth)
+void cds_lfht_resize_lazy(struct cds_lfht *ht, unsigned long size, int growth)
{
struct rcu_resize_work *work;
unsigned long target_size;
- target_size = resize_target_update(t, growth);
- if (!CMM_LOAD_SHARED(t->resize_initiated) && t->size < target_size) {
+ target_size = resize_target_update(ht, size, growth);
+ /* Store resize_target before read resize_initiated */
+ cmm_smp_mb();
+ if (!CMM_LOAD_SHARED(ht->t.resize_initiated) && size < target_size) {
uatomic_inc(&ht->in_progress_resize);
cmm_smp_mb(); /* increment resize count before calling it */
work = malloc(sizeof(*work));
work->ht = ht;
ht->cds_lfht_call_rcu(&work->head, do_resize_cb);
- CMM_STORE_SHARED(t->resize_initiated, 1);
+ CMM_STORE_SHARED(ht->t.resize_initiated, 1);
}
}
+#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
+
static
-void cds_lfht_resize_lazy_count(struct cds_lfht *ht, struct rcu_table *t,
+void cds_lfht_resize_lazy_count(struct cds_lfht *ht, unsigned long size,
unsigned long count)
{
struct rcu_resize_work *work;
- unsigned long target_size;
- target_size = resize_target_update_count(t, count);
- if (!CMM_LOAD_SHARED(t->resize_initiated) && t->size < target_size) {
+ if (!(ht->flags & CDS_LFHT_AUTO_RESIZE))
+ return;
+ resize_target_update_count(ht, count);
+ /* Store resize_target before read resize_initiated */
+ cmm_smp_mb();
+ if (!CMM_LOAD_SHARED(ht->t.resize_initiated)) {
uatomic_inc(&ht->in_progress_resize);
cmm_smp_mb(); /* increment resize count before calling it */
work = malloc(sizeof(*work));
work->ht = ht;
ht->cds_lfht_call_rcu(&work->head, do_resize_cb);
- CMM_STORE_SHARED(t->resize_initiated, 1);
+ CMM_STORE_SHARED(ht->t.resize_initiated, 1);
}
}
+
+#endif
projects / urcu.git / blobdiff