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* Copyright 2011 LiveProfile
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#ifndef HASH_RING_H
#define HASH_RING_H
#include <stdint.h>
#define HASH_RING_OK 0
#define HASH_RING_ERR 1
typedef struct ll_t {
void *data;
struct ll_t *next;
} ll_t;
typedef uint8_t HASH_FUNCTION;
* All nodes in the ring must have a unique name.
* The 'name' bytes below are hashed to place the node in the ring.
* The name is typically human readable and should be consistent on all clients using
* the hash ring.
typedef struct hash_ring_node_t {
uint8_t *name;
uint32_t nameLen;
} hash_ring_node_t;
* Nodes have many items, each item has a number derived from the node's name.
typedef struct hash_ring_item_t {
hash_ring_node_t *node;
/* number is dervied from a hash of the node's key */
uint64_t number;
} hash_ring_item_t;
* This structure contains an array with the ring's items, as well as
* a list of nodes. A node appears in the ring numReplicas times.
typedef struct hash_ring_t {
uint32_t numReplicas;
/* List of nodes in the ring */
ll_t *nodes;
/* The number of nodes in the ring */
uint32_t numNodes;
* Array of items in the ring
* This array is sorted ascending
hash_ring_item_t **items;
/* The number of items in the ring */
uint32_t numItems;
/* The hash function to use for this ring */
} hash_ring_t;
* Creates a new hash ring.
* The numReplicas parameter must be specified. It should be >= 1.
* numReplicas is used to place a node on the ring multiple times to distribute it
* more evenly. Increasing numReplicas improves distribution, but also increases memory by
* (numReplicas * N).
* @param[in] numReplicas The number of replicas
* @param[in] hash_fn The hash function to use. HASH_FUNCTION_SHA1 or HASH_FUNCTION_MD5
* @returns a new hash ring or NULL if it couldn't be created.
hash_ring_t *hash_ring_create(uint32_t numReplicas, HASH_FUNCTION hash_fn);
* Frees the hash ring and all memory associated with it.
void hash_ring_free(hash_ring_t *ring);
* Adds a node into the ring. The node is specified by passing an opaque
* array of bytes in the name parameter. The name should be used consistently for clients using the ring.
* This function is idempotent, a node will only ever exist in the ring once, regardless
* of how many times it is added.
* @returns HASH_RING_OK if the node was added, HASH_RING_ERR if an error occurred.
int hash_ring_add_node(hash_ring_t *ring, uint8_t *name, uint32_t nameLen);
* Gets the node specified by name from the ring.
* @returns the node or NULL if it cannot be found.
hash_ring_node_t *hash_ring_get_node(hash_ring_t *ring, uint8_t *name, uint32_t nameLen);
* Finds the node by hashing the given key and searching the ring.
* This is the function that is typically called the most from your clients. Once the ring is created, it is
* usually not modified (unless you want to deal with re-hashing -- which isn't bad necessarily bad, i.e memcached).
hash_ring_node_t *hash_ring_find_node(hash_ring_t *ring, uint8_t *key, uint32_t keyLen);
* Find the next highest item for the given num.
* This function is invoked by hash_ring_find_node to locate a key on the ring. If you want to do your own hashing on
* the keys, you might call this function, but probably not.
hash_ring_item_t *hash_ring_find_next_highest_item(hash_ring_t *ring, uint64_t num);
* Removes a node from the ring.
* @returns HASH_RING_OK if the node was removed, or HASH_RING_ERR if it does not exist.
int hash_ring_remove_node(hash_ring_t *ring, uint8_t *name, uint32_t nameLen);
* Print the hash ring to stdout.
void hash_ring_print(hash_ring_t *ring);
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