X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-ht.c;h=e598e4533e01657c0e13f5b8158dd613a986b399;hp=b4c832699565e29ea791c9c3835fa2d9041d8087;hb=464a1ec99d37c841a028f96482ef106e5b406c6f;hpb=674f7a6983f888438c36f8fba179db1a5349d3e9

diff --git a/urcu-ht.c b/urcu-ht.c
index b4c8326..e598e45 100644
--- a/urcu-ht.c
+++ b/urcu-ht.c
@@ -1,4 +1,8 @@
 
+/*
+ * TODO: keys are currently assumed <= sizeof(void *). Key target never freed.
+ */
+
 #define _LGPL_SOURCE
 #include <stdlib.h>
 #include <urcu.h>
@@ -10,6 +14,8 @@
 #include <errno.h>
 #include <urcu-ht.h>
 #include <urcu/jhash.h>
+#include <stdio.h>
+#include <pthread.h>
 
 struct rcu_ht_node;
 
@@ -23,22 +29,28 @@ struct rcu_ht {
 	struct rcu_ht_node **tbl;
 	ht_hash_fct hash_fct;
 	void (*free_fct)(void *data);	/* fct to free data */
-	struct ht_size {
-		unsigned long add;
-		unsigned long lookup;
-	} size;
+	unsigned long size;
+	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),
-		      unsigned long init_size)
+		      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->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;
 }
@@ -49,10 +61,11 @@ void *ht_lookup(struct rcu_ht *ht, void *key)
 	struct rcu_ht_node *node;
 	void *ret;
 
-	hash = ht->hash_fct(key) % 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]);
+	node = rcu_dereference(ht->tbl[hash]);
 	for (;;) {
 		if (likely(!node)) {
 			ret = NULL;
@@ -83,8 +96,6 @@ int ht_add(struct rcu_ht *ht, void *key, void *data)
 	new_head = calloc(1, sizeof(struct rcu_ht_node));
 	new_head->key = key;
 	new_head->data = data;
-	hash = ht->hash_fct(key) % ht->size.add;
-
 	/* 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
@@ -96,7 +107,21 @@ int ht_add(struct rcu_ht *ht, void *key, void *data)
 retry:
 	rcu_read_lock();
 
-	old_head = node = rcu_dereference(*ht->tbl[hash]);
+	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 (;;) {
 		if (likely(!node)) {
 			break;
@@ -107,11 +132,11 @@ retry:
 		}
 		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(&ht->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 */
@@ -123,24 +148,43 @@ 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)
  */
 void *ht_steal(struct rcu_ht *ht, void *key)
 {
-	struct rcu_ht_node **prev, *node;
+	struct rcu_ht_node **prev, *node, *del_node = NULL;
 	unsigned long hash;
 	void *data;
-
-	hash = ht->hash_fct(key) % ht->size.lookup;
+	int ret;
 
 retry:
 	rcu_read_lock();
 
-	prev = ht->tbl[hash];
+	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);
 	for (;;) {
 		if (likely(!node)) {
-			data = (void *)(unsigned long)-ENOENT;
-			goto end;
+			if (del_node) {
+				goto end;
+			} else {
+				data = (void *)(unsigned long)-ENOENT;
+				goto error;
+			}
 		}
 		if (node->key == key) {
 			break;
@@ -150,13 +194,22 @@ retry:
 	}
 	/* Found it ! pointer to object is in "prev" */
 	if (rcu_cmpxchg_pointer(prev, node, node->next) != node)
-		goto restart;
+		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);
+	return data;
 
+error:
+	rcu_read_unlock();
 	return data;
 
 	/* restart loop, release and re-take the read lock to be kind to GP */
@@ -170,8 +223,8 @@ int ht_delete(struct rcu_ht *ht, void *key)
 	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 {
@@ -180,21 +233,28 @@ int ht_delete(struct rcu_ht *ht, void *key)
 }
 
 /* Delete all old elements. Allow concurrent writer accesses. */
-void ht_delete_all(struct rcu_ht *ht)
+int ht_delete_all(struct rcu_ht *ht)
 {
 	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();
-cut_head:
-		prev = ht->tbl[i];
-		if (prev) {
-			/*
-			 * Cut the head. After that, we own the first element.
-			 */
-			node = rcu_xchg_pointer(prev, NULL);
-		} else {
+		prev = &ht->tbl[i];
+		/*
+		 * Cut the head. After that, we own the first element.
+		 */
+		node = rcu_xchg_pointer(prev, NULL);
+		if (!node) {
 			rcu_read_unlock();
 			continue;
 		}
@@ -206,8 +266,10 @@ cut_head:
 		 * iteratively.
 		 */
 		for (;;) {
+			inext = NULL;
 			prev = &node->next;
-			inext = rcu_xchg_pointer(prev, NULL);
+			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
@@ -221,26 +283,153 @@ cut_head:
 			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.
  */
-void ht_destroy(struct rcu_ht *ht)
+int ht_destroy(struct rcu_ht *ht)
 {
-	ht_delete_all(ht);
+	int ret;
+
+	ret = ht_delete_all(ht);
 	free(ht->tbl);
 	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_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.
+ */
 uint32_t ht_jhash(void *key, uint32_t length, uint32_t initval)
 {
-	return jhash(key, length, initval);
+	uint32_t ret;
+	void *vkey;
+
+	if (length <= sizeof(void *))
+		vkey = &key;
+	else
+		vkey = key;
+	ret = jhash(vkey, length, initval);
+	return ret;
 }