#define _LGPL_SOURCE
#include <stdlib.h>
+#include <errno.h>
+#include <assert.h>
+#include <stdio.h>
+
#include <urcu.h>
+#include <urcu-defer.h>
#include <arch.h>
#include <arch_atomic.h>
-#include <assert.h>
#include <compiler.h>
-#include <urcu-defer.h>
-#include <errno.h>
-#include <urcu-ht.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 *next;
void *key;
void *data;
+ 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 */
- unsigned long size;
uint32_t keylen;
uint32_t hashseed;
pthread_mutex_t resize_mutex; /* resize mutex: add/del mutex */
ht = calloc(1, sizeof(struct rcu_ht));
ht->hash_fct = hash_fct;
ht->free_fct = free_fct;
- ht->size = init_size;
ht->keylen = keylen;
ht->hashseed = hashseed;
/* this mutex should not nest in read-side C.S. */
pthread_mutex_init(&ht->resize_mutex, NULL);
- ht->resize_ongoing = 0;
- ht->tbl = calloc(init_size, sizeof(struct rcu_ht_node *));
+ 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;
- smp_read_barrier_depends(); /* read size before links */
-
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->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();
- if (unlikely(ht->resize_ongoing)) {
+ if (unlikely(LOAD_SHARED(ht->resize_ongoing))) {
rcu_read_unlock();
/*
* Wait for resize to complete before continuing.
goto retry;
}
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size;
+ 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();
/*
* Restart until we successfully remove the entry, or no entry is left
* ((void *)(unsigned long)-ENOENT).
- * Deal with concurrent stealers by verifying that there are no element
- * in the list still pointing to the element stolen. (del_node)
+ * Deal with concurrent stealers by doing an extra verification pass to check
+ * that no element in the list are still pointing to the element stolen.
+ * This could happen if two concurrent steal for consecutive objects are
+ * executed. A pointer to an object being stolen could be saved by the
+ * concurrent stealer for the previous object.
+ * Also, given that in this precise scenario, another stealer can also want to
+ * delete the doubly-referenced object; use a "stolen" flag to let only one
+ * stealer delete the object.
*/
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();
- if (unlikely(ht->resize_ongoing)) {
+ if (unlikely(LOAD_SHARED(ht->resize_ongoing))) {
rcu_read_unlock();
/*
* Wait for resize to complete before continuing.
goto retry;
}
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size;
+ 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)) {
if (del_node) {
goto end;
} else {
- data = (void *)(unsigned long)-ENOENT;
goto error;
}
}
prev = &node->next;
node = rcu_dereference(*prev);
}
+
+ 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)
+ if (rcu_cmpxchg_pointer(prev, node, node->next) == node)
del_node = node;
goto restart;
*/
rcu_read_unlock();
- data = node->data;
- call_rcu(free, node);
+ data = del_node->data;
+ call_rcu(free, del_node);
return data;
error:
+ data = (void *)(unsigned long)-ENOENT;
rcu_read_unlock();
return data;
{
unsigned long i;
struct rcu_ht_node **prev, *node, *inext;
+ struct rcu_table *t;
int cnt = 0;
int ret;
ret = pthread_mutex_lock(&ht->resize_mutex);
assert(!ret);
- for (i = 0; i < ht->size; i++) {
+ 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.
*/
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_ht_node **new_tbl, **old_tbl;
+ struct rcu_table *new_t, *old_t;
struct rcu_ht_node *node, *new_node, *tmp;
unsigned long hash;
- old_size = ht->size;
+ old_t = ht->t;
+ old_size = old_t->size;
- if (old_size == 1)
+ if (old_size == MAX_HT_BUCKETS)
return;
new_size = old_size << 1;
- new_tbl = calloc(new_size, sizeof(struct rcu_ht_node *));
+ 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++) {
/*
* if it's in the table.
* Copy each node. (just the node, not ->data)
*/
- node = ht->tbl[i];
+ 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->next = new_tbl[i]; /* add to head */
- new_tbl[i] = new_node;
+ 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;
}
}
- old_tbl = ht->tbl;
- ht->tbl = new_tbl;
- smp_wmb(); /* write links and table before changing size */
- ht->size = new_size;
+ /* 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_tbl[i];
+ node = old_t->tbl[i];
while (node) {
tmp = node->next;
free(node);
node = tmp;
}
}
- free(old_tbl);
+ free(old_t);
}
static void ht_resize_shrink(struct rcu_ht *ht)
{
unsigned long i, new_size;
- struct rcu_ht_node **new_tbl;
+ struct rcu_table *new_t, *old_t;
struct rcu_ht_node **prev, *node;
- if (ht->size == 1)
+ old_t = ht->t;
+ if (old_t->size == 1)
return;
- new_size = ht->size >> 1;
+ new_size = old_t->size >> 1;
for (i = 0; i < new_size; i++) {
- /* Link end with first entry of 2*i */
- prev = &ht->tbl[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 = ht->tbl[i << 1];
+ *prev = old_t->tbl[i + new_size];
}
smp_wmb(); /* write links before changing size */
- ht->size = new_size;
+ STORE_SHARED(old_t->size, new_size);
/* Ensure all concurrent lookups use new size */
synchronize_rcu();
- new_tbl = realloc(ht->tbl, new_size * sizeof(struct rcu_ht_node *));
+ new_t = realloc(old_t, sizeof(struct rcu_table)
+ + (new_size * sizeof(struct rcu_ht_node *)));
/* shrinking, pointers should not move */
- assert(new_tbl == ht->tbl);
+ assert(new_t == old_t);
}
/*
ret = pthread_mutex_lock(&ht->resize_mutex);
assert(!ret);
- ht->resize_ongoing = 1;
+ STORE_SHARED(ht->resize_ongoing, 1);
synchronize_rcu();
/* All add/remove are waiting on the mutex. */
if (growth > 0)
else if (growth < 0)
ht_resize_shrink(ht);
smp_mb();
- ht->resize_ongoing = 0;
+ STORE_SHARED(ht->resize_ongoing, 0);
ret = pthread_mutex_unlock(&ht->resize_mutex);
assert(!ret);
}
projects / urcu.git / blobdiff