X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-ht.c;h=b8777acae895ec8907ffbe6a6ddf1c5b4c37a912;hp=e3fd3137a9273795bb6842b110a47774120ae5ae;hb=1e52eccf3cb657dccb197132f7cb47b683902538;hpb=7ce4eb3848a2d2bdd6a267bfddfc8a36fcd45d66

diff --git a/urcu-ht.c b/urcu-ht.c
index e3fd313..b8777ac 100644
--- a/urcu-ht.c
+++ b/urcu-ht.c
@@ -5,16 +5,28 @@
 
 #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;
 
@@ -22,18 +34,22 @@ 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 */
 	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),
@@ -45,24 +61,30 @@ 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;
@@ -87,12 +109,14 @@ void *ht_lookup(struct rcu_ht *ht, void *key)
 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
@@ -104,9 +128,23 @@ int ht_add(struct rcu_ht *ht, void *key, void *data)
 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;
@@ -118,11 +156,10 @@ retry:
 		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 */
@@ -134,28 +171,49 @@ restart:
 /*
  * 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();
 
-	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)) {
 			if (del_node) {
 				goto end;
 			} else {
-				data = (void *)(unsigned long)-ENOENT;
 				goto error;
 			}
 		}
@@ -165,6 +223,17 @@ retry:
 		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)
 		del_node = node;
@@ -182,6 +251,7 @@ end:
 	return data;
 
 error:
+	data = (void *)(unsigned long)-ENOENT;
 	rcu_read_unlock();
 	return data;
 
@@ -210,11 +280,22 @@ 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);
 
-	for (i = 0; i < ht->size.lookup; 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.
 		 */
@@ -255,6 +336,9 @@ int ht_delete_all(struct rcu_ht *ht)
 			node = inext;
 		}
 	}
+
+	ret = pthread_mutex_unlock(&ht->resize_mutex);
+	assert(!ret);
 	return cnt;
 }
 
@@ -267,11 +351,123 @@ int ht_destroy(struct rcu_ht *ht)
 	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.
  */