#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>
+
+/* 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_ht {
struct rcu_ht_node **tbl;
ht_hash_fct hash_fct;
void (*free_fct)(void *data); /* fct to free data */
+ unsigned long size;
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->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 *));
return ht;
}
struct rcu_ht_node *node;
void *ret;
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size.lookup;
+ 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]);
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();
- hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size.add;
+ if (unlikely(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;
+ }
+
+ hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size;
old_head = node = rcu_dereference(ht->tbl[hash]);
for (;;) {
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 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;
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(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;
+ }
+
+ hash = ht->hash_fct(key, ht->keylen, ht->hashseed) % ht->size;
prev = &ht->tbl[hash];
node = rcu_dereference(*prev);
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;
return data;
error:
+ data = (void *)(unsigned long)-ENOENT;
rcu_read_unlock();
return data;
unsigned long i;
struct rcu_ht_node **prev, *node, *inext;
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);
- for (i = 0; i < ht->size.lookup; i++) {
+ for (i = 0; i < ht->size; i++) {
rcu_read_lock();
prev = &ht->tbl[i];
/*
node = inext;
}
}
+
+ ret = pthread_mutex_unlock(&ht->resize_mutex);
+ assert(!ret);
return cnt;
}
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_ht_node *node, *new_node, *tmp;
+ unsigned long hash;
+
+ old_size = ht->size;
+
+ if (old_size == 1)
+ return;
+
+ new_size = old_size << 1;
+ new_tbl = calloc(new_size, sizeof(struct rcu_ht_node *));
+
+ 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 = ht->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;
+ node = node->next;
+ }
+ }
+
+ old_tbl = ht->tbl;
+ ht->tbl = new_tbl;
+ smp_wmb(); /* write links and table before changing size */
+ ht->size = new_size;
+
+ /* Ensure all concurrent lookups use new size and table */
+ synchronize_rcu();
+
+ for (i = 0; i < old_size; i++) {
+ node = old_tbl[i];
+ while (node) {
+ tmp = node->next;
+ free(node);
+ node = tmp;
+ }
+ }
+ free(old_tbl);
+}
+
+static void ht_resize_shrink(struct rcu_ht *ht)
+{
+ unsigned long i, new_size;
+ struct rcu_ht_node **new_tbl;
+ struct rcu_ht_node **prev, *node;
+
+ if (ht->size == 1)
+ return;
+
+ new_size = ht->size >> 1;
+
+ for (i = 0; i < new_size; i++) {
+ /* Link end with first entry of 2*i */
+ prev = &ht->tbl[i];
+ node = *prev;
+ while (node) {
+ prev = &node->next;
+ node = *prev;
+ }
+ *prev = ht->tbl[i << 1];
+ }
+ smp_wmb(); /* write links before changing size */
+ ht->size = new_size;
+
+ /* Ensure all concurrent lookups use new size */
+ synchronize_rcu();
+
+ new_tbl = realloc(ht->tbl, new_size * sizeof(struct rcu_ht_node *));
+ /* shrinking, pointers should not move */
+ assert(new_tbl == ht->tbl);
+}
+
+/*
+ * 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);
+ 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();
+ 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