A multithreaded and single threaded string interner that allows strings to be cached with a minimal memory footprint, associating them with a unique key that can be used to retrieve them at any time. A Rodeo allows O(1) internment and resolution and can be turned into a RodeoReader to allow for contention-free resolutions with both key to str and str to key operations. It can also be turned into a RodeoResolver with only key to str operations for the lowest possible memory usage.

Which interner do I use?

For single-threaded workloads Rodeo is encouraged, while multi-threaded applications should use ThreadedRodeo. Both of these are the only way to intern strings, but most applications will hit a stage where they are done interning strings, and at that point is where the choice between RodeoReader and RodeoResolver. If the user needs to get keys for strings still, then they must use the RodeoReader (although they can still transfer into a RodeoResolver) at this point. For users who just need key to string resolution, the RodeoResolver gives contention-free access at the minimum possible memory usage. Note that to gain access to ThreadedRodeo the multi-threaded feature is required.

Interner	Thread-safe	Intern String	str to key	key to str	Contention Free	Memory Usage
Rodeo	❌	✅	✅	✅	N/A	Medium
ThreadedRodeo	✅	✅	✅	✅	❌	Most
RodeoReader	✅	❌	✅	✅	✅	Medium
RodeoResolver	✅	❌	❌	✅	✅	Least

Cargo Features

By default lasso has one dependency, hashbrown, and only Rodeo is exposed. Hashbrown is used since the raw_entry api is currently unstable in the standard library's hashmap. The raw hashmap API is used for custom hashing within the hashmaps, which works to dramatically reduce memory usage To make use of ThreadedRodeo, you must enable the multi-threaded feature.

• multi-threaded - Enables ThreadedRodeo, the interner for multi-threaded tasks
• ahasher - Use ahash's RandomState as the default hasher
• no-std - Enables no_std + alloc support for Rodeo and ThreadedRodeo
  • Automatically enables the following required features:
    • ahasher - no_std hashing function
• serialize - Implements Serialize and Deserialize for all Spur types and all interners
• inline-more - Annotate external apis with #[inline]

Example: Using Rodeo

use lasso::Rodeo;

let mut rodeo = Rodeo::default();
let key = rodeo.get_or_intern("Hello, world!");

// Easily retrieve the value of a key and find the key for values
assert_eq!("Hello, world!", rodeo.resolve(&key));
assert_eq!(Some(key), rodeo.get("Hello, world!"));

// Interning the same string again will yield the same key
let key2 = rodeo.get_or_intern("Hello, world!");

assert_eq!(key, key2);

Example: Using ThreadedRodeo

use lasso::ThreadedRodeo;
use std::{thread, sync::Arc};

let rodeo = Arc::new(ThreadedRodeo::default());
let key = rodeo.get_or_intern("Hello, world!");

// Easily retrieve the value of a key and find the key for values
assert_eq!("Hello, world!", rodeo.resolve(&key));
assert_eq!(Some(key), rodeo.get("Hello, world!"));

// Interning the same string again will yield the same key
let key2 = rodeo.get_or_intern("Hello, world!");

assert_eq!(key, key2);

// ThreadedRodeo can be shared across threads
let moved = Arc::clone(&rodeo);
let hello = thread::spawn(move || {
    assert_eq!("Hello, world!", moved.resolve(&key));
    moved.get_or_intern("Hello from the thread!")
})
.join()
.unwrap();

assert_eq!("Hello, world!", rodeo.resolve(&key));
assert_eq!("Hello from the thread!", rodeo.resolve(&hello));

Example: Creating a RodeoReader

use lasso::Rodeo;

// Rodeo and ThreadedRodeo are interchangeable here
let mut rodeo = Rodeo::default();

let key = rodeo.get_or_intern("Hello, world!");
assert_eq!("Hello, world!", rodeo.resolve(&key));

let reader = rodeo.into_reader();

// Reader keeps all the strings from the parent
assert_eq!("Hello, world!", reader.resolve(&key));
assert_eq!(Some(key), reader.get("Hello, world!"));

// The Reader can now be shared across threads, no matter what kind of Rodeo created it

Example: Creating a RodeoResolver

use lasso::Rodeo;

// Rodeo and ThreadedRodeo are interchangeable here
let mut rodeo = Rodeo::default();

let key = rodeo.get_or_intern("Hello, world!");
assert_eq!("Hello, world!", rodeo.resolve(&key));

let resolver = rodeo.into_resolver();

// Resolver keeps all the strings from the parent
assert_eq!("Hello, world!", resolver.resolve(&key));

// The Resolver can now be shared across threads, no matter what kind of Rodeo created it

Example: Making a custom-ranged key

Sometimes you want your keys to only inhabit (or not inhabit) a certain range of values so that you can have custom niches. This allows you to pack more data into what would otherwise be unused space, which can be critical for memory-sensitive applications.

use lasso::{Key, Rodeo};

// First make our key type, this will be what we use as handles into our interner
#[derive(Copy, Clone, PartialEq, Eq)]
struct NicheKey(u32);

// This will reserve the upper 255 values for us to use as niches
const NICHE: usize = 0xFF000000;

// Implementing `Key` is unsafe and requires that anything given to `try_from_usize` must produce the
// same `usize` when `into_usize` is later called
unsafe impl Key for NicheKey {
    fn into_usize(self) -> usize {
        self.0 as usize
    }

    fn try_from_usize(int: usize) -> Option<Self> {
        if int < NICHE {
            // The value isn't in our niche range, so we're good to go
            Some(Self(int as u32))
        } else {
            // The value interferes with our niche, so we return `None`
            None
        }
    }
}

// To make sure we're upholding `Key`'s safety contract, let's make two small tests
#[test]
fn value_in_range() {
    let key = NicheKey::try_from_usize(0).unwrap();
    assert_eq!(key.into_usize(), 0);

    let key = NicheKey::try_from_usize(NICHE - 1).unwrap();
    assert_eq!(key.into_usize(), NICHE - 1);
}

#[test]
fn value_out_of_range() {
    let key = NicheKey::try_from_usize(NICHE);
    assert!(key.is_none());

    let key = NicheKey::try_from_usize(u32::max_value() as usize);
    assert!(key.is_none());
}

// And now we're done and can make `Rodeo`s or `ThreadedRodeo`s that use our custom key!
let mut rodeo: Rodeo<NicheKey> = Rodeo::new();
let key = rodeo.get_or_intern("It works!");
assert_eq!(rodeo.resolve(&key), "It works!");

Example: Creation using FromIterator

use lasso::Rodeo;
use core::iter::FromIterator;

// Works for both `Rodeo` and `ThreadedRodeo`
let rodeo = Rodeo::from_iter(vec![
    "one string",
    "two string",
    "red string",
    "blue string",
]);

assert!(rodeo.contains("one string"));
assert!(rodeo.contains("two string"));
assert!(rodeo.contains("red string"));
assert!(rodeo.contains("blue string"));

use lasso::Rodeo;
use core::iter::FromIterator;

// Works for both `Rodeo` and `ThreadedRodeo`
let rodeo: Rodeo = vec!["one string", "two string", "red string", "blue string"]
    .into_iter()
    .collect();

assert!(rodeo.contains("one string"));
assert!(rodeo.contains("two string"));
assert!(rodeo.contains("red string"));
assert!(rodeo.contains("blue string"));

Benchmarks

Benchmarks were gathered with Criterion.rs
OS: Windows 10
CPU: Ryzen 9 3900X at 3800Mhz
RAM: 3200Mhz
Rustc: Stable 1.44.1

Rodeo

STD RandomState

Method	Time	Throughput
resolve	1.9251 μs	13.285 GiB/s
try_resolve	1.9214 μs	13.311 GiB/s
resolve_unchecked	1.4356 μs	17.816 GiB/s
get_or_intern (empty)	60.350 μs	433.96 MiB/s
get_or_intern (filled)	57.415 μs	456.15 MiB/s
try_get_or_intern (empty)	58.978 μs	444.06 MiB/s
try_get_or_intern (filled)	57.421 μs	456.10 MiB/s
get (empty)	37.288 μs	702.37 MiB/s
get (filled)	55.095 μs	475.36 MiB/s

AHash

Method	Time	Throughput
try_resolve	1.9282 μs	13.264 GiB/s
resolve	1.9404 μs	13.181 GiB/s
resolve_unchecked	1.4328 μs	17.851 GiB/s
get_or_intern (empty)	38.029 μs	688.68 MiB/s
get_or_intern (filled)	33.650 μs	778.30 MiB/s
try_get_or_intern (empty)	39.392 μs	664.84 MiB/s
try_get_or_intern (filled)	33.435 μs	783.31 MiB/s
get (empty)	12.565 μs	2.0356 GiB/s
get (filled)	26.545 μs	986.61 MiB/s

FXHash

Method	Time	Throughput
resolve	1.9014 μs	13.451 GiB/s
try_resolve	1.9278 μs	13.267 GiB/s
resolve_unchecked	1.4449 μs	17.701 GiB/s
get_or_intern (empty)	32.523 μs	805.27 MiB/s
get_or_intern (filled)	30.281 μs	864.88 MiB/s
try_get_or_intern (empty)	31.630 μs	828.00 MiB/s
try_get_or_intern (filled)	31.002 μs	844.78 MiB/s
get (empty)	12.699 μs	2.0141 GiB/s
get (filled)	29.220 μs	896.28 MiB/s

ThreadedRodeo

STD RandomState

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
resolve	54.336 μs	482.00 MiB/s	364.27 μs	71.897 MiB/s
try_resolve	54.582 μs	479.82 MiB/s	352.67 μs	74.261 MiB/s
get_or_intern (empty)	266.03 μs	98.447 MiB/s	N\A	N\A
get_or_intern (filled)	103.04 μs	254.17 MiB/s	441.42 μs	59.331 MiB/s
try_get_or_intern (empty)	261.80 μs	100.04 MiB/s	N\A	N\A
try_get_or_intern (filled)	102.61 μs	255.25 MiB/s	447.42 μs	58.535 MiB/s
get (empty)	80.346 μs	325.96 MiB/s	N\A	N\A
get (filled)	92.669 μs	282.62 MiB/s	439.24 μs	59.626 MiB/s

AHash

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
resolve	22.261 μs	1.1489 GiB/s	265.46 μs	98.658 MiB/s
try_resolve	22.378 μs	1.1429 GiB/s	268.58 μs	97.513 MiB/s
get_or_intern (empty)	157.86 μs	165.91 MiB/s	N\A	N\A
get_or_intern (filled)	56.320 μs	465.02 MiB/s	357.13 μs	73.335 MiB/s
try_get_or_intern (empty)	161.46 μs	162.21 MiB/s	N\A	N\A
try_get_or_intern (filled)	55.874 μs	468.73 MiB/s	360.25 μs	72.698 MiB/s
get (empty)	43.520 μs	601.79 MiB/s	N\A	N\A
get (filled)	53.720 μs	487.52 MiB/s	360.66 μs	72.616 MiB/s

FXHash

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
try_resolve	17.289 μs	1.4794 GiB/s	238.29 μs	109.91 MiB/s
resolve	19.833 μs	1.2896 GiB/s	237.05 μs	110.48 MiB/s
get_or_intern (empty)	130.97 μs	199.97 MiB/s	N\A	N\A
get_or_intern (filled)	42.630 μs	614.35 MiB/s	301.60 μs	86.837 MiB/s
try_get_or_intern (empty)	129.30 μs	202.55 MiB/s	N\A	N\A
try_get_or_intern (filled)	42.508 μs	616.12 MiB/s	337.29 μs	77.648 MiB/s
get (empty)	28.001 μs	935.30 MiB/s	N\A	N\A
get (filled)	37.700 μs	694.68 MiB/s	292.15 μs	89.645 MiB/s

RodeoReader

STD RandomState

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
resolve	1.9398 μs	13.185 GiB/s	4.3153 μs	5.9269 GiB/s
try_resolve	1.9315 μs	13.242 GiB/s	4.1956 μs	6.0959 GiB/s
resolve_unchecked	1.4416 μs	17.741 GiB/s	3.1204 μs	8.1964 GiB/s
get (empty)	38.886 μs	673.50 MiB/s	N\A	N\A
get (filled)	56.271 μs	465.42 MiB/s	105.12 μs	249.14 MiB/s

AHash

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
resolve	1.9404 μs	13.181 GiB/s	4.1881 μs	6.1069 GiB/s
try_resolve	1.8932 μs	13.509 GiB/s	4.2410 μs	6.0306 GiB/s
resolve_unchecked	1.4128 μs	18.103 GiB/s	3.1691 μs	8.0703 GiB/s
get (empty)	11.952 μs	2.1399 GiB/s	N\A	N\A
get (filled)	27.093 μs	966.65 MiB/s	56.269 μs	465.44 MiB/s

FXHash

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
resolve	1.8987 μs	13.471 GiB/s	4.2117 μs	6.0727 GiB/s
try_resolve	1.9103 μs	13.389 GiB/s	4.2254 μs	6.0529 GiB/s
resolve_unchecked	1.4469 μs	17.677 GiB/s	3.0923 μs	8.2709 GiB/s
get (empty)	12.994 μs	1.9682 GiB/s	N\A	N\A
get (filled)	29.745 μs	880.49 MiB/s	52.387 μs	499.93 MiB/s

RodeoResolver

Method	Time (1 Thread)	Throughput (1 Thread)	Time (24 Threads)	Throughput (24 Threads)
resolve	1.9416 μs	13.172 GiB/s	3.9114 μs	6.5387 GiB/s
try_resolve	1.9264 μs	13.277 GiB/s	3.9289 μs	6.5097 GiB/s
resolve_unchecked	1.6638 μs	15.372 GiB/s	3.1741 μs	8.0578 GiB/s