Struct immutable_chunkmap::map::Map

pub struct Map<K: Ord + Clone, V: Clone> { /* fields omitted */ }

This Map uses a similar strategy to BTreeMap to ensure cache efficient performance on modern hardware while still providing log(N) get, insert, and remove operations.

For good performance, it is very important to understand that clone is a fundamental operation, it needs to be fast for your key and data types, because it's going to be called a lot whenever you change the map. If your key and data types are cheap to clone (like e.g. Arc), and you perform your update operations in largish batches, then it is possible to get very good performance, even approaching that of a standard HashMap.

Why

Which begs the question, why would anyone ever want to use a data structure where very careful structuring of key and data type, and careful batching, MIGHT APPROACH the performance of a plain old HashMap, it seems a silly thing to work on. I know of two cases.

1. Multiple threads can read this structure even while one thread is updating it.

2. You can take a snapshot and e.g. write it to disk, or replicate it to another process without stopping reads or writes.

There is some nuance to #1, because HashMap is generally faster to read than a BTree. In a pure read application it's the obvious choice when you don't require sorted data. In a mixed read/write scenario at 4 reads for every write HashMap is already the same speed as chunkmap for reading a 10M entry map. That's a pretty write heavy application, and wouldn't be news by itself. The real killer of the mutable strucures is large operations, any kind of housekeeping operation that's going to touch a large number of keys can be death for availability, holding onto a write lock for multiple hundreds of milliseconds, even seconds, even longer. Sure it's possible to amortize this in some cases by doing your housekeeping in small batches, but that can be complex, and it isn't always possible, and readers still pay a price even if it's amortized.

That brings us to #2, which is really the mother of all housekeeping operations. There is no way to amortize taking a consistent snapshot, the best you can possibly do is hold the write lock long enough to make a complete copy of the data, if you even have the memory for that. God help you if you miscalculate and start swapping while you're making that copy, holding the write lock while your disk or if you're lucky SSD churns away moving pages back and forth between main memory, you may be holding that lock for a long long time. Chunkmap gives you free snapshots in exchange for slower writes, which, carefully considered don't even need to be that much slower.

Examples

use std::string::String;
use self::immutable_chunkmap::map::Map;

let m =
   Map::new()
   .insert(String::from("1"), 1).0
   .insert(String::from("2"), 2).0
   .insert(String::from("3"), 3).0;

assert_eq!(m.get("1"), Option::Some(&1));
assert_eq!(m.get("2"), Option::Some(&2));
assert_eq!(m.get("3"), Option::Some(&3));
assert_eq!(m.get("4"), Option::None);

for (k, v) in &m {
  println!("key {}, val: {}", k, v)
}

Methods

impl<K, V> Map<K, V> where     K: Ord + Clone,     V: Clone,

pub fn new() -> Self

Create a new empty map

pub fn insert_many<E: IntoIterator<Item = (K, V)>>(&self, elts: E) -> Self

This will insert many elements at once, and is potentially a lot faster than inserting one by one, especially if the data is sorted. It is just a wrapper around the more general update_many method.

#Examples

 use self::immutable_chunkmap::map::Map;

 let mut v = vec![(1, 3), (10, 1), (-12, 2), (44, 0), (50, -1)];
 v.sort_unstable_by_key(|&(k, _)| k);

 let m = Map::new().insert_many(v.iter().map(|(k, v)| (*k, *v)));

 for (k, v) in &v {
   assert_eq!(m.get(k), Option::Some(v))
 }

pub fn update_many<Q, D, E, F>(&self, elts: E, f: &mut F) -> Self where     E: IntoIterator<Item = (Q, D)>,     Q: Ord,     K: Borrow<Q>,     F: FnMut(Q, D, Option<(&K, &V)>) -> Option<(K, V)>,

This method updates multiple bindings in one call. Given an iterator of an arbitrary type (Q, D), where Q is any borrowed form of K, an update function taking Q, D, the current binding in the map, if any, and producing the new binding, if any, this method will produce a new map with updated bindings of many elements at once. It will skip intermediate node allocations where possible. If the data in elts is sorted, it will be able to skip many more intermediate allocations, and can produce a speedup of about 10x compared to inserting/updating one by one. In any case it should always be faster than inserting elements one by one, even with random unsorted keys.

#Examples

use self::immutable_chunkmap::map::Map;

let m = Map::new().insert_many((0..4).map(|k| (k, k)));
let m = m.update_many(
    (0..4).map(|x| (x, ())),
    &mut |k, (), cur| cur.map(|(_, c)| (k, c + 1))
);
assert_eq!(
    m.into_iter().map(|(k, v)| (*k, *v)).collect::<Vec<_>>(),
    vec![(0, 1), (1, 2), (2, 3), (3, 4)]
);

pub fn insert(&self, k: K, v: V) -> (Self, Option<V>)

return a new map with (k, v) inserted into it. If k already exists in the old map, the old binding will be returned, and the new map will contain the new binding. In fact this method is just a wrapper around update.

pub fn update<Q, D, F>(&self, q: Q, d: D, f: &mut F) -> (Self, Option<V>) where     Q: Ord,     K: Borrow<Q>,     F: FnMut(Q, D, Option<(&K, &V)>) -> Option<(K, V)>,

return a new map with the binding for q, which can be any borrowed form of k, updated to the result of f. If f returns None, the binding will be removed from the new map, otherwise it will be inserted. This function is more efficient than calling get and then insert, since it makes only one tree traversal instead of two. This method runs in log(N) time and space where N is the size of the map.

Examples

use self::immutable_chunkmap::map::Map;

let (m, _) = Map::new().update(0, 0, &mut |k, d, _| Some((k, d)));
let (m, _) = m.update(1, 1, &mut |k, d, _| Some((k, d)));
let (m, _) = m.update(2, 2, &mut |k, d, _| Some((k, d)));
assert_eq!(m.get(&0), Some(&0));
assert_eq!(m.get(&1), Some(&1));
assert_eq!(m.get(&2), Some(&2));

let (m, _) = m.update(0, (), &mut |k, (), v| v.map(move |(_, v)| (k, v + 1)));
assert_eq!(m.get(&0), Some(&1));
assert_eq!(m.get(&1), Some(&1));
assert_eq!(m.get(&2), Some(&2));

let (m, _) = m.update(1, (), &mut |_, (), _| None);
assert_eq!(m.get(&0), Some(&1));
assert_eq!(m.get(&1), None);
assert_eq!(m.get(&2), Some(&2));

pub fn get<'a, Q: ?Sized + Ord>(&'a self, k: &Q) -> Option<&'a V> where     K: Borrow<Q>,

lookup the mapping for k. If it doesn't exist return None. Runs in log(N) time and constant space. where N is the size of the map.

pub fn get_key<'a, Q: ?Sized + Ord>(&'a self, k: &Q) -> Option<&'a K> where     K: Borrow<Q>,

lookup the mapping for k. Return the key. If it doesn't exist return None. Runs in log(N) time and constant space. where N is the size of the map.

pub fn get_full<'a, Q: ?Sized + Ord>(&'a self, k: &Q) -> Option<(&'a K, &'a V)> where     K: Borrow<Q>,

lookup the mapping for k. Return both the key and the value. If it doesn't exist return None. Runs in log(N) time and constant space. where N is the size of the map.

pub fn remove<Q: Sized + Ord>(&self, k: &Q) -> (Self, Option<V>) where     K: Borrow<Q>,

return a new map with the mapping under k removed. If the binding existed in the old map return it. Runs in log(N) time and log(N) space, where N is the size of the map.

pub fn len(&self) -> usize

get the number of elements in the map O(1) time and space

pub fn range<'a, Q>(     &'a self,     lbound: Bound<Q>,     ubound: Bound<Q> ) -> Iter<'a, Q, K, V> where     Q: Ord,     K: Borrow<Q>,

return an iterator over the subset of elements in the map that are within the specified range.

The returned iterator runs in O(log(N) + M) time, and constant space. N is the number of elements in the tree, and M is the number of elements you examine.

if lbound >= ubound the returned iterator will be empty

Trait Implementations

impl<K: Clone + Ord + Clone, V: Clone + Clone> Clone for Map<K, V>

fn clone(&self) -> Map<K, V>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<K, V> Hash for Map<K, V> where     K: Hash + Ord + Clone,     V: Hash + Clone,

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where     H: Hasher,

Feeds a slice of this type into the given [Hasher].

impl<K, V> Default for Map<K, V> where     K: Ord + Clone,     V: Clone,

fn default() -> Map<K, V>

Returns the "default value" for a type.

impl<K, V> PartialEq for Map<K, V> where     K: PartialEq + Ord + Clone,     V: PartialEq + Clone,

fn eq(&self, other: &Map<K, V>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl<K, V> Eq for Map<K, V> where     K: Eq + Ord + Clone,     V: Eq + Clone,

impl<K, V> PartialOrd for Map<K, V> where     K: Ord + Clone,     V: PartialOrd + Clone,

fn partial_cmp(&self, other: &Map<K, V>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<K, V> Ord for Map<K, V> where     K: Ord + Clone,     V: Ord + Clone,

fn cmp(&self, other: &Map<K, V>) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

impl<K, V> Debug for Map<K, V> where     K: Debug + Ord + Clone,     V: Debug + Clone,

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<'a, Q, K, V> Index<&'a Q> for Map<K, V> where     Q: Ord,     K: Ord + Clone + Borrow<Q>,     V: Clone,

type Output = V

The returned type after indexing.

fn index(&self, k: &Q) -> &V

Performs the indexing (container[index]) operation.

impl<K, V> FromIterator<(K, V)> for Map<K, V> where     K: Ord + Clone,     V: Clone,

fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self

Creates a value from an iterator.

impl<'a, K, V> IntoIterator for &'a Map<K, V> where     K: 'a + Borrow<K> + Ord + Clone,     V: 'a + Clone,

type Item = (&'a K, &'a V)

The type of the elements being iterated over.

type IntoIter = Iter<'a, K, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.