+/*
+ * TODO: keys are currently assumed <= sizeof(void *). Key target never freed.
+ */
+
#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/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;
+ unsigned int flags;
+};
+
+struct rcu_table {
+ unsigned long size;
+ struct rcu_ht_node *tbl[0];
};
struct rcu_ht {
- struct rcu_ht_node *tbl[HASH_SIZE];
+ 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;
+ 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))
+struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*free_fct)(void *data),
+ unsigned long init_size, uint32_t keylen,
+ uint32_t hashseed)
{
struct rcu_ht *ht;
ht = calloc(1, sizeof(struct rcu_ht));
ht->hash_fct = hash_fct;
ht->free_fct = free_fct;
+ 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; /* shared */
+ ht->t = calloc(1, sizeof(struct rcu_table)
+ + (init_size * sizeof(struct rcu_ht_node *)));
+ ht->t->size = init_size;
return ht;
}
-/* delete all elements */
-void ht_delete_all(struct rcu_ht *ht)
-{
- unsigned long i;
- struct rcu_ht_node **prev, *node;
-
- for (i = 0; i < HASH_SIZE; i++) {
- rcu_read_lock();
-
- prev = &ht->tbl[i];
- node = rcu_dereference(*prev);
- /*
- * Cut the head, therefore whole bucket will be unused
- * after GP. (except for concurrent additions)
- */
- rcu_assign_pointer(prev, NULL);
- for (;;) {
- if (likely(!node)) {
- break;
- }
- prev = &node->next;
- if (node->data)
- call_rcu(ht->free_fct, node->data);
- call_rcu(free, node);
- node = rcu_dereference(*prev);
- }
- rcu_read_unlock();
- }
-}
-
-/*
- * Should only be called when no more concurrent readers nor writers can
- * possibly access the table.
- */
-void ht_destroy(struct rcu_ht *ht)
-{
- ht_delete_all(ht);
- free(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);
-
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;
- hash = ht->hash_fct(key);
-
+ 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();
- old_head = node = rcu_dereference(ht->tbl[hash]);
+ 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(t->tbl[hash]);
for (;;) {
if (likely(!node)) {
break;
}
node = rcu_dereference(node->next);
}
- if (rcu_cmpxchg_pointer(&ht->tbl[hash], old_head, new_head) != old_head)
+ new_head->next = 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 */
/*
* Restart until we successfully remove the entry, or no entry is left
* ((void *)(unsigned long)-ENOENT).
+ * 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;
+ struct rcu_ht_node **prev, *node, *del_node = NULL;
+ struct rcu_table *t;
unsigned long hash;
void *data;
-
- hash = ht->hash_fct(key);
+ int ret;
retry:
rcu_read_lock();
- prev = &ht->tbl[hash];
+ 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 = &t->tbl[hash];
node = rcu_dereference(*prev);
for (;;) {
if (likely(!node)) {
- data = (void *)(unsigned long)-ENOENT;
- goto end;
+ if (del_node) {
+ goto end;
+ } else {
+ goto error;
+ }
}
if (node->key == key) {
break;
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)
- goto restart;
+ if (rcu_cmpxchg_pointer(prev, node, node->next) == node)
+ del_node = node;
+ goto restart;
+
end:
+ /*
+ * From that point, we own node. Note that there can still be concurrent
+ * RCU readers using it. We can free it outside of read lock after a GP.
+ */
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;
/* restart loop, release and re-take the read lock to be kind to GP */
void *data;
data = ht_steal(ht, key);
- if (data) {
- if (ht->free_fct && data)
+ if (data && data != (void *)(unsigned long)-ENOENT) {
+ if (ht->free_fct)
call_rcu(ht->free_fct, data);
return 0;
} else {
}
}
-unsigned long stupid_hash(void *key)
+/* Delete all old elements. Allow concurrent writer accesses. */
+int ht_delete_all(struct rcu_ht *ht)
+{
+ unsigned long i;
+ struct rcu_ht_node **prev, *node, *inext;
+ struct rcu_table *t;
+ int cnt = 0;
+ int ret;
+
+ /*
+ * 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 = &t->tbl[i];
+ /*
+ * Cut the head. After that, we own the first element.
+ */
+ node = rcu_xchg_pointer(prev, NULL);
+ if (!node) {
+ rcu_read_unlock();
+ continue;
+ }
+ /*
+ * We manage a list shared with concurrent writers and readers.
+ * Note that a concurrent add may or may not be deleted by us,
+ * depending if it arrives before or after the head is cut.
+ * "node" points to our first node. Remove first elements
+ * iteratively.
+ */
+ for (;;) {
+ inext = NULL;
+ prev = &node->next;
+ if (prev)
+ inext = rcu_xchg_pointer(prev, NULL);
+ /*
+ * "node" is the first element of the list we have cut.
+ * We therefore own it, no concurrent writer may delete
+ * it. There can only be concurrent lookups. Concurrent
+ * add can only be done on a bucket head, but we've cut
+ * it already. inext is also owned by us, because we
+ * have exchanged it for "NULL". It will therefore be
+ * safe to use it after a G.P.
+ */
+ rcu_read_unlock();
+ if (node->data)
+ call_rcu(ht->free_fct, node->data);
+ call_rcu(free, node);
+ cnt++;
+ if (likely(!inext))
+ break;
+ rcu_read_lock();
+ node = inext;
+ }
+ }
+
+ ret = pthread_mutex_unlock(&ht->resize_mutex);
+ assert(!ret);
+ return cnt;
+}
+
+/*
+ * Should only be called when no more concurrent readers nor writers can
+ * possibly access the table.
+ */
+int ht_destroy(struct rcu_ht *ht)
+{
+ int ret;
+
+ ret = ht_delete_all(ht);
+ free(ht->t);
+ free(ht);
+ return ret;
+}
+
+static void ht_resize_grow(struct rcu_ht *ht)
{
- return (unsigned long)key % HASH_SIZE;
+ 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.
+ */
+uint32_t ht_jhash(void *key, uint32_t length, uint32_t initval)
+{
+ uint32_t ret;
+ void *vkey;
+
+ if (length <= sizeof(void *))
+ vkey = &key;
+ else
+ vkey = key;
+ ret = jhash(vkey, length, initval);
+ return ret;
}
projects / urcu.git / blobdiff