doc/examples: cds_lfht_add_unique

[urcu.git] / doc / examples / rculfhash / cds_lfht_add_unique.c

diff --git a/doc/examples/rculfhash/cds_lfht_add_unique.c b/doc/examples/rculfhash/cds_lfht_add_unique.c
new file mode 100644 (file)
index 0000000..ec594c8
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+++ b/doc/examples/rculfhash/cds_lfht_add_unique.c
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+/*
+ * Copyright (C) 2013  Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program for any
+ * purpose,  provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is
+ * granted, provided the above notices are retained, and a notice that
+ * the code was modified is included with the above copyright notice.
+ *
+ * This example shows how to add unique nodes into a RCU lock-free hash
+ * table. We use a "seqnum" field to show which node is staying in the
+ * hash table. This hash table requires using a RCU scheme.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include <urcu.h>              /* RCU flavor */
+#include <urcu/rculfhash.h>    /* RCU Lock-free hash table */
+#include <urcu/compiler.h>     /* For CAA_ARRAY_SIZE */
+#include "jhash.h"             /* Example hash function */
+
+/*
+ * Nodes populated into the hash table.
+ */
+struct mynode {
+       int value;                      /* Node content */
+       int seqnum;                     /* Our node sequence number */
+       struct cds_lfht_node node;      /* Chaining in hash table */
+};
+
+int match(struct cds_lfht_node *ht_node, const void *_key)
+{
+       struct mynode *node =
+               caa_container_of(ht_node, struct mynode, node);
+       const unsigned int *key = _key;
+
+       return *key == node->value;
+}
+
+int main(int argc, char **argv)
+{
+       int values[] = { -5, 42, 42, 36, 24, }; /* 42 is duplicated */
+       struct cds_lfht *ht;    /* Hash table */
+       unsigned int i;
+       int ret = 0, seqnum = 0;
+       uint32_t seed;
+       struct cds_lfht_iter iter;      /* For iteration on hash table */
+       struct cds_lfht_node *ht_node;
+       struct mynode *node;
+
+       /*
+        * Each thread need using RCU read-side need to be explicitly
+        * registered.
+        */
+       rcu_register_thread();
+
+       /* Use time as seed for hash table hashing. */
+       seed = (uint32_t) time(NULL);
+
+       /*
+        * Allocate hash table.
+        */
+       ht = cds_lfht_new(1, 1, 0,
+               CDS_LFHT_AUTO_RESIZE | CDS_LFHT_ACCOUNTING,
+               NULL);
+       if (!ht) {
+               printf("Error allocating hash table\n");
+               ret = -1;
+               goto end;
+       }
+
+       /*
+        * Add nodes to hash table.
+        */
+       for (i = 0; i < CAA_ARRAY_SIZE(values); i++) {
+               unsigned long hash;
+               int value;
+
+               node = malloc(sizeof(*node));
+               if (!node) {
+                       ret = -1;
+                       goto end;
+               }
+
+               cds_lfht_node_init(&node->node);
+               value = values[i];
+               node->value = value;
+               node->seqnum = seqnum++;
+               hash = jhash(&value, sizeof(value), seed);
+
+               /*
+                * cds_lfht_add() needs to be called from RCU read-side
+                * critical section.
+                */
+               rcu_read_lock();
+               ht_node = cds_lfht_add_unique(ht, hash, match, &value,
+                       &node->node);
+               /*
+                * cds_lfht_add_unique() returns the added node if not
+                * already present, else returns the node matching the
+                * key.
+                */
+               if (ht_node != &node->node) {
+                       /*
+                        * We found a match. Therefore, to ensure we
+                        * don't add duplicates, cds_lfht_add_unique()
+                        * acted as a RCU lookup, returning the found
+                        * match. It did not add the new node to the
+                        * hash table, so we can free it on the spot.
+                        */
+                       printf("Not adding duplicate key: %d, seqnum: %d\n",
+                               node->value, node->seqnum);
+                       free(node);
+               } else {
+                       printf("Add key: %d, seqnum: %d\n",
+                               node->value, node->seqnum);
+               }
+               rcu_read_unlock();
+       }
+
+       /*
+        * Iterate over each hash table node. Those will appear in
+        * random order, depending on the hash seed. Iteration needs to
+        * be performed within RCU read-side critical section.
+        */
+       printf("hash table content (random order):");
+       rcu_read_lock();
+       cds_lfht_for_each_entry(ht, &iter, node, node) {
+               printf(" (key: %d, seqnum: %d)",
+                       node->value, node->seqnum);
+       }
+       rcu_read_unlock();
+       printf("\n");
+
+end:
+       rcu_unregister_thread();
+       return ret;
+}