#include <arch_atomic.h>
#include <compiler.h>
#include <urcu/jhash.h>
+#include <stdio.h>
+#include <pthread.h>
#include <urcu-ht.h>
+/*
+ * Maximum number of hash table buckets: 256M on 64-bit.
+ * Should take about 512MB max if we assume 1 node per 4 buckets.
+ */
+#define MAX_HT_BUCKETS ((256 << 10) / sizeof(void *))
+
+/* node flags */
+#define NODE_STOLEN (1 << 0)
+
struct rcu_ht_node;
struct rcu_ht_node {
struct rcu_ht_node *next;
void *key;
void *data;
- int stolen;
+ unsigned int flags;
+};
+
+struct rcu_table {
+ unsigned long size;
+ struct rcu_ht_node *tbl[0];
};
struct rcu_ht {
- struct rcu_ht_node **tbl;
+ struct rcu_table *t; /* shared */
ht_hash_fct hash_fct;
void (*free_fct)(void *data); /* fct to free data */
uint32_t keylen;
uint32_t hashseed;
- struct ht_size {
- unsigned long add;
- unsigned long lookup;
- } size;
+ pthread_mutex_t resize_mutex; /* resize mutex: add/del mutex */
+ int resize_ongoing; /* fast-path resize check */
};
struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data),
ht = calloc(1, sizeof(struct rcu_ht));
ht->hash_fct = hash_fct;
ht->free_fct = free_fct;
- ht->size.add = init_size;
- ht->size.lookup = init_size;
ht->keylen = keylen;
ht->hashseed = hashseed;
- ht->tbl = calloc(init_size, sizeof(struct rcu_ht_node *));
+ /* this mutex should not nest in read-side C.S. */
+ pthread_mutex_init(&ht->resize_mutex, NULL);
+ ht->resize_ongoing = 0; /* shared */
+ ht->t = calloc(1, sizeof(struct rcu_table)
+ + (init_size * sizeof(struct rcu_ht_node *)));
+ ht->t->size = init_size;
return ht;
}
void *ht_lookup(struct rcu_ht *ht, void *key)
{
+ struct rcu_table *t;
unsigned long hash;
struct rcu_ht_node *node;
void *ret;
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size.lookup;
-
rcu_read_lock();
- node = rcu_dereference(ht->tbl[hash]);
+ t = rcu_dereference(ht->t);
+ smp_read_barrier_depends(); /* read t before size and table */
+ hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % t->size;
+ smp_read_barrier_depends(); /* read size before links */
+ node = rcu_dereference(t->tbl[hash]);
for (;;) {
if (likely(!node)) {
ret = NULL;
int ht_add(struct rcu_ht *ht, void *key, void *data)
{
struct rcu_ht_node *node, *old_head, *new_head;
+ struct rcu_table *t;
unsigned long hash;
int ret = 0;
new_head = calloc(1, sizeof(struct rcu_ht_node));
new_head->key = key;
new_head->data = data;
- new_head->stolen = 0;
+ new_head->flags = 0;
/* here comes the fun and tricky part.
* Add at the beginning with a cmpxchg.
* Hold a read lock between the moment the first element is read
retry:
rcu_read_lock();
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size.add;
+ if (unlikely(LOAD_SHARED(ht->resize_ongoing))) {
+ rcu_read_unlock();
+ /*
+ * Wait for resize to complete before continuing.
+ */
+ ret = pthread_mutex_lock(&ht->resize_mutex);
+ assert(!ret);
+ ret = pthread_mutex_unlock(&ht->resize_mutex);
+ assert(!ret);
+ goto retry;
+ }
+
+ t = rcu_dereference(ht->t);
+ /* no read barrier needed, because no concurrency with resize */
+ hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % t->size;
- old_head = node = rcu_dereference(ht->tbl[hash]);
+ old_head = node = rcu_dereference(t->tbl[hash]);
for (;;) {
if (likely(!node)) {
break;
node = rcu_dereference(node->next);
}
new_head->next = old_head;
- if (rcu_cmpxchg_pointer(&ht->tbl[hash], old_head, new_head) != old_head)
+ if (rcu_cmpxchg_pointer(&t->tbl[hash], old_head, new_head) != old_head)
goto restart;
end:
rcu_read_unlock();
-
return ret;
/* restart loop, release and re-take the read lock to be kind to GP */
void *ht_steal(struct rcu_ht *ht, void *key)
{
struct rcu_ht_node **prev, *node, *del_node = NULL;
+ struct rcu_table *t;
unsigned long hash;
void *data;
+ int ret;
retry:
rcu_read_lock();
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size.lookup;
+ if (unlikely(LOAD_SHARED(ht->resize_ongoing))) {
+ rcu_read_unlock();
+ /*
+ * Wait for resize to complete before continuing.
+ */
+ ret = pthread_mutex_lock(&ht->resize_mutex);
+ assert(!ret);
+ ret = pthread_mutex_unlock(&ht->resize_mutex);
+ assert(!ret);
+ goto retry;
+ }
+
+ t = rcu_dereference(ht->t);
+ /* no read barrier needed, because no concurrency with resize */
+ hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % t->size;
- prev = &ht->tbl[hash];
+ prev = &t->tbl[hash];
node = rcu_dereference(*prev);
for (;;) {
if (likely(!node)) {
node = rcu_dereference(*prev);
}
- /* Another concurrent thread stole it ? If so, let it deal with this. */
- if (cmpxchg(&node->stolen, 0, 1) != 0)
- goto error;
+ if (!del_node) {
+ /*
+ * Another concurrent thread stole it ? If so, let it deal with
+ * this. Assume NODE_STOLEN is the only flag. If this changes,
+ * read flags before cmpxchg.
+ */
+ if (cmpxchg(&node->flags, 0, NODE_STOLEN) != 0)
+ goto error;
+ }
/* Found it ! pointer to object is in "prev" */
if (rcu_cmpxchg_pointer(prev, node, node->next) == node)
{
unsigned long i;
struct rcu_ht_node **prev, *node, *inext;
+ struct rcu_table *t;
int cnt = 0;
+ int ret;
- for (i = 0; i < ht->size.lookup; i++) {
+ /*
+ * Mutual exclusion with resize operations, but leave add/steal execute
+ * concurrently. This is OK because we operate only on the heads.
+ */
+ ret = pthread_mutex_lock(&ht->resize_mutex);
+ assert(!ret);
+
+ t = rcu_dereference(ht->t);
+ /* no read barrier needed, because no concurrency with resize */
+ for (i = 0; i < t->size; i++) {
rcu_read_lock();
- prev = &ht->tbl[i];
+ prev = &t->tbl[i];
/*
* Cut the head. After that, we own the first element.
*/
node = inext;
}
}
+
+ ret = pthread_mutex_unlock(&ht->resize_mutex);
+ assert(!ret);
return cnt;
}
int ret;
ret = ht_delete_all(ht);
- free(ht->tbl);
+ free(ht->t);
free(ht);
return ret;
}
+static void ht_resize_grow(struct rcu_ht *ht)
+{
+ unsigned long i, new_size, old_size;
+ struct rcu_table *new_t, *old_t;
+ struct rcu_ht_node *node, *new_node, *tmp;
+ unsigned long hash;
+
+ old_t = ht->t;
+ old_size = old_t->size;
+
+ if (old_size == MAX_HT_BUCKETS)
+ return;
+
+ new_size = old_size << 1;
+ new_t = calloc(1, sizeof(struct rcu_table)
+ + (new_size * sizeof(struct rcu_ht_node *)));
+ new_t->size = new_size;
+
+ for (i = 0; i < old_size; i++) {
+ /*
+ * Re-hash each entry, insert in new table.
+ * It's important that a reader looking for a key _will_ find it
+ * if it's in the table.
+ * Copy each node. (just the node, not ->data)
+ */
+ node = old_t->tbl[i];
+ while (node) {
+ hash = ht->hash_fct(node->key, ht->keylen, ht->hashseed)
+ % new_size;
+ new_node = malloc(sizeof(struct rcu_ht_node));
+ new_node->key = node->key;
+ new_node->data = node->data;
+ new_node->flags = node->flags;
+ new_node->next = new_t->tbl[hash]; /* link to first */
+ new_t->tbl[hash] = new_node; /* add to head */
+ node = node->next;
+ }
+ }
+
+ /* Changing table and size atomically wrt lookups */
+ rcu_assign_pointer(ht->t, new_t);
+
+ /* Ensure all concurrent lookups use new size and table */
+ synchronize_rcu();
+
+ for (i = 0; i < old_size; i++) {
+ node = old_t->tbl[i];
+ while (node) {
+ tmp = node->next;
+ free(node);
+ node = tmp;
+ }
+ }
+ free(old_t);
+}
+
+static void ht_resize_shrink(struct rcu_ht *ht)
+{
+ unsigned long i, new_size;
+ struct rcu_table *new_t, *old_t;
+ struct rcu_ht_node **prev, *node;
+
+ old_t = ht->t;
+ if (old_t->size == 1)
+ return;
+
+ new_size = old_t->size >> 1;
+
+ for (i = 0; i < new_size; i++) {
+ /* Link end with first entry of i + new_size */
+ prev = &old_t->tbl[i];
+ node = *prev;
+ while (node) {
+ prev = &node->next;
+ node = *prev;
+ }
+ *prev = old_t->tbl[i + new_size];
+ }
+ smp_wmb(); /* write links before changing size */
+ STORE_SHARED(old_t->size, new_size);
+
+ /* Ensure all concurrent lookups use new size */
+ synchronize_rcu();
+
+ new_t = realloc(old_t, sizeof(struct rcu_table)
+ + (new_size * sizeof(struct rcu_ht_node *)));
+ /* shrinking, pointers should not move */
+ assert(new_t == old_t);
+}
+
+/*
+ * growth: >0: *2, <0: /2
+ */
+void ht_resize(struct rcu_ht *ht, int growth)
+{
+ int ret;
+
+ ret = pthread_mutex_lock(&ht->resize_mutex);
+ assert(!ret);
+ STORE_SHARED(ht->resize_ongoing, 1);
+ synchronize_rcu();
+ /* All add/remove are waiting on the mutex. */
+ if (growth > 0)
+ ht_resize_grow(ht);
+ else if (growth < 0)
+ ht_resize_shrink(ht);
+ smp_mb();
+ STORE_SHARED(ht->resize_ongoing, 0);
+ ret = pthread_mutex_unlock(&ht->resize_mutex);
+ assert(!ret);
+}
+
/*
* Expects keys <= than pointer size to be encoded in the pointer itself.
*/
projects / urcu.git / blobdiff