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//! An implementation of Rendezvous (a.k.a, highest random weight) hashing algorithm. //! //! # References //! //! - [Rendezvous hashing (Wikipedia)](https://en.wikipedia.org/wiki/Rendezvous_hashing) //! - [Weighted Distributed Hash Tables] //! (https://pdfs.semanticscholar.org/8c55/282dc37d1e3b46b15c2d97f60568ccb9c9cd.pdf) //! - This paper describes an efficient method for //! calculating consistent hash values for heterogeneous nodes. //! //! # Examples //! //! For homogeneous nodes: //! //! ``` //! use rendezvous_hash::RendezvousNodes; //! //! // Constructs a node (a.k.a., server, site, etc) set. //! let mut nodes = RendezvousNodes::default(); //! nodes.insert("foo"); //! nodes.insert("bar"); //! nodes.insert("baz"); //! nodes.insert("qux"); //! //! // Finds candidate nodes for an item (a.k.a., object). //! assert_eq!(nodes.calc_candidates(&1).collect::<Vec<_>>(), //! [&"bar", &"baz", &"foo", &"qux"]); //! assert_eq!(nodes.calc_candidates(&"key").collect::<Vec<_>>(), //! [&"qux", &"bar", &"foo", &"baz"]); //! //! // Update the node set. //! // (The relative order between existing nodes are preserved) //! nodes.remove(&"baz"); //! assert_eq!(nodes.calc_candidates(&1).collect::<Vec<_>>(), //! [&"bar", &"foo", &"qux"]); //! assert_eq!(nodes.calc_candidates(&"key").collect::<Vec<_>>(), //! [&"qux", &"bar", &"foo"]); //! ``` //! //! For heterogeneous nodes: //! //! ``` //! use std::collections::HashMap; //! use rendezvous_hash::RendezvousNodes; //! use rendezvous_hash::{WeightedNode, Capacity}; //! //! let mut nodes = RendezvousNodes::default(); //! nodes.insert(WeightedNode::new("foo", Capacity::new(70.0).unwrap())); //! nodes.insert(WeightedNode::new("bar", Capacity::new(20.0).unwrap())); //! nodes.insert(WeightedNode::new("baz", Capacity::new(9.0).unwrap())); //! nodes.insert(WeightedNode::new("qux", Capacity::new(1.0).unwrap())); //! //! let mut counts = HashMap::new(); //! for item in 0..10000 { //! let node = nodes.calc_candidates(&item).nth(0).unwrap(); //! *counts.entry(node.node.to_string()).or_insert(0) += 1; //! } //! assert_eq!(((counts["foo"] as f64) / 100.0).round(), 70.0); //! assert_eq!(((counts["bar"] as f64) / 100.0).round(), 20.0); //! assert_eq!(((counts["baz"] as f64) / 100.0).round(), 9.0); //! assert_eq!(((counts["qux"] as f64) / 100.0).round(), 1.0); //! ``` #![warn(missing_docs)] extern crate siphasher; use std::borrow::Borrow; use std::collections::hash_map::DefaultHasher; use std::hash::{Hash, Hasher}; pub use node::{Capacity, IdNode, KeyValueNode, Node, WeightedNode}; mod iterators_impl; mod node; pub mod iterators { //! `Iterator` trait implementations. pub use crate::iterators_impl::Candidates; pub use crate::iterators_impl::IntoIter; pub use crate::iterators_impl::Iter; } pub mod types { //! Miscellaneous types. pub use crate::node::SignPositiveF64; } /// This trait allows calculating the hash value of a node for a specific item. pub trait NodeHasher<N> { /// Returns the hash value for the combination of `node` and `item`. fn hash<T: Hash>(&self, node: &N, item: &T) -> u64; } /// The default `NodeHasher` implementation. /// /// This uses `DefaultHasher` to hash nodes and items. /// `DefaultHasher` is provided by Rust standard library. /// /// To hash a combination of a node and an item, /// `DefaultNodeHasher` hashes the item at first, /// then hashes the node, /// and finally returns the resulting hash value /// (as follows). /// /// ```no_run /// use std::collections::hash_map::DefaultHasher; /// # use std::hash::{Hash, Hasher}; /// # let item = (); /// # let node = (); /// /// let mut hasher = DefaultHasher::new(); /// item.hash(&mut hasher); /// node.hash(&mut hasher); /// hasher.finish() /// # ; /// ``` #[derive(Debug, Default, Clone)] pub struct DefaultNodeHasher(()); impl DefaultNodeHasher { /// Makes a new `DefaultNodeHasher` instance. pub fn new() -> Self { DefaultNodeHasher(()) } } impl<N: Hash> NodeHasher<N> for DefaultNodeHasher { fn hash<T: Hash>(&self, node: &N, item: &T) -> u64 { let mut hasher = DefaultHasher::new(); item.hash(&mut hasher); node.hash(&mut hasher); hasher.finish() } } /// A candidate node set of a rendezvous for clients that are requiring the same item. pub struct RendezvousNodes<N: Node, H> { nodes: Vec<node::WithHashCode<N>>, hasher: H, } impl<N, H> RendezvousNodes<N, H> where N: Node, H: NodeHasher<N::NodeId>, { /// Makes a new `RendezvousNodes` instance. pub fn new(hasher: H) -> Self { RendezvousNodes { nodes: Vec::new(), hasher, } } /// Returns the candidate nodes for `item`. /// /// The higher priority node is located in front of the returned candidate sequence. /// /// Note that this method takes `O(n log n)` steps /// (where `n` is the return value of `self.len()`). pub fn calc_candidates<T: Hash>(&mut self, item: &T) -> iterators::Candidates<N> { let hasher = &self.hasher; for n in self.nodes.iter_mut() { let code = n.node.hash_code(hasher, &item); n.hash_code = Some(code); } self.nodes.sort_by(|a, b| { (&b.hash_code, b.node.node_id()).cmp(&(&a.hash_code, a.node.node_id())) }); iterators_impl::candidates(self.nodes.iter()) } /// Returns the candidate nodes for `item`. /// /// The higher priority node is located in front of the returned candidate sequence. /// /// Note that this method takes `O(n log n)` steps /// (where `n` is the return value of `self.len()`). /// /// This is equivalent to `calc_candidates` method except this allocates /// `n * (size_of<usize>() + size_of<N::HashCode>())` memory internally. pub fn calc_candidates_immut<T: Hash>(&self, item: &T) -> impl Iterator<Item = &N> { let hasher = &self.hasher; let mut nodes = Vec::with_capacity(self.nodes.len()); for n in &self.nodes { let code = n.node.hash_code(hasher, &item); nodes.push(node::WithHashCode { node: &n.node, hash_code: Some(code), }); } nodes.sort_by(|a, b| { (&b.hash_code, b.node.node_id()).cmp(&(&a.hash_code, a.node.node_id())) }); nodes.into_iter().map(|n| n.node) } } impl<N: Node, H> RendezvousNodes<N, H> { /// Inserts a new candidate node. /// /// If a node which has an identifier equal to `node` exists, /// it will be removed and returned as `Some(N)`. pub fn insert(&mut self, node: N) -> Option<N> { let old = self.remove(node.node_id()); self.nodes.push(node::WithHashCode::new(node)); old } /// Removes the specified node from the candidates. /// /// If the node does not exist, this method will return `None`. pub fn remove<M>(&mut self, node_id: &M) -> Option<N> where N::NodeId: Borrow<M>, M: PartialEq, { if let Some(i) = self .nodes .iter() .position(|n| n.node.node_id().borrow() == node_id) { Some(self.nodes.swap_remove(i).node) } else { None } } /// Returns `true` if the specified node exists in this candidate set, otherwise `false`. pub fn contains<M>(&self, node_id: &M) -> bool where N::NodeId: Borrow<M>, M: PartialEq, { self.nodes .iter() .any(|n| n.node.node_id().borrow() == node_id) } /// Returns `true` if there are no candidate nodes. pub fn is_empty(&self) -> bool { self.nodes.is_empty() } /// Returns the count of the candidate nodes. pub fn len(&self) -> usize { self.nodes.len() } /// Returns an iterator over the nodes of this candidate set. pub fn iter(&self) -> iterators::Iter<N> { iterators_impl::iter(self.nodes.iter()) } } impl<N: Node> Default for RendezvousNodes<N, DefaultNodeHasher> { fn default() -> Self { Self::new(DefaultNodeHasher::new()) } } impl<N: Node, H> IntoIterator for RendezvousNodes<N, H> { type Item = N; type IntoIter = iterators::IntoIter<N>; fn into_iter(self) -> Self::IntoIter { iterators_impl::into_iter(self.nodes.into_iter()) } } impl<N: Node, H> Extend<N> for RendezvousNodes<N, H> { fn extend<T>(&mut self, iter: T) where T: IntoIterator<Item = N>, { for n in iter { let _ = self.insert(n); } } } #[cfg(test)] mod tests { use super::*; use std::collections::HashMap; macro_rules! assert_calc_candidates { ($nodes:expr, $key:expr, $candidates:expr) => { assert_eq!( $nodes.calc_candidates($key).collect::<Vec<_>>(), $candidates ); assert_eq!( $nodes.calc_candidates_immut($key).collect::<Vec<_>>(), $candidates ); }; } #[test] fn it_works() { let mut nodes = RendezvousNodes::default(); nodes.insert("foo"); nodes.insert("bar"); nodes.insert("baz"); nodes.insert("qux"); assert_calc_candidates!(nodes, &1, [&"bar", &"baz", &"foo", &"qux"]); assert_calc_candidates!(nodes, &"key", [&"qux", &"bar", &"foo", &"baz"]); nodes.remove(&"baz"); assert_calc_candidates!(nodes, &1, [&"bar", &"foo", &"qux"]); assert_calc_candidates!(nodes, &"key", [&"qux", &"bar", &"foo"]); nodes.remove(&"bar"); assert_calc_candidates!(nodes, &1, [&"foo", &"qux"]); assert_calc_candidates!(nodes, &"key", [&"qux", &"foo"]); nodes.insert("bar"); nodes.insert("baz"); let mut counts = HashMap::new(); for item in 0..1000 { let node = nodes.calc_candidates(&item).nth(0).unwrap(); *counts.entry(node.to_string()).or_insert(0) += 1; } assert_eq!(counts["foo"], 246); assert_eq!(counts["bar"], 266); assert_eq!(counts["baz"], 237); assert_eq!(counts["qux"], 251); } #[test] fn kv_nodes() { let mut nodes = RendezvousNodes::default(); nodes.insert(KeyValueNode::new("foo", ())); nodes.insert(KeyValueNode::new("bar", ())); nodes.insert(KeyValueNode::new("baz", ())); nodes.insert(KeyValueNode::new("qux", ())); assert_eq!( nodes .calc_candidates(&1) .map(|n| &n.key) .collect::<Vec<_>>(), [&"bar", &"baz", &"foo", &"qux"] ); assert_eq!( nodes .calc_candidates(&"key") .map(|n| &n.key) .collect::<Vec<_>>(), [&"qux", &"bar", &"foo", &"baz"] ); } #[test] fn heterogeneous_nodes() { let mut nodes = RendezvousNodes::default(); nodes.insert(WeightedNode::new("foo", Capacity::new(70.0).unwrap())); nodes.insert(WeightedNode::new("bar", Capacity::new(20.0).unwrap())); nodes.insert(WeightedNode::new("baz", Capacity::new(9.0).unwrap())); nodes.insert(WeightedNode::new("qux", Capacity::new(1.0).unwrap())); let mut counts = HashMap::new(); for item in 0..10000 { let node = nodes.calc_candidates(&item).nth(0).unwrap(); *counts.entry(node.node.to_string()).or_insert(0) += 1; } assert_eq!(((counts["foo"] as f64) / 100.0).round(), 70.0); assert_eq!(((counts["bar"] as f64) / 100.0).round(), 20.0); assert_eq!(((counts["baz"] as f64) / 100.0).round(), 9.0); assert_eq!(((counts["qux"] as f64) / 100.0).round(), 1.0); } }