Caching structures and simplified function memoization
cached provides implementations of several caching structures as well as a handy macros
for defining memoized functions.
Memoized functions defined using #[cached]/#[once]/#[io_cached]/cached! macros are thread-safe with the backing
function-cache wrapped in a mutex/rwlock, or externally synchronized in the case of #[io_cached].
By default, the function-cache is not locked for the duration of the function's execution, so initial (on an empty cache)
concurrent calls of long-running functions with the same arguments will each execute fully and each overwrite
the memoized value as they complete. This mirrors the behavior of Python's functools.lru_cache. To synchronize the execution and caching
of un-cached arguments, specify #[cached(sync_writes = "default")] / #[once(sync_writes = true)] (not supported by #[io_cached].
- See
cached::storesdocs cache stores available. - See
proc_macrofor more procedural macro examples. - See
macrosfor more declarative macro examples.
Features
default: Includeproc_macroandahashfeaturesproc_macro: Include proc macrosahash: Enable the optionalahashhasher as default hashing algorithm.async: Include support for async functions and async cache storesasync_tokio_rt_multi_thread: Enabletokio's optionalrt-multi-threadfeature.redis_store: Include Redis cache storeredis_async_std: Include async Redis support usingasync-stdandasync-stdtls support, impliesredis_storeandasyncredis_tokio: Include async Redis support usingtokioandtokiotls support, impliesredis_storeandasyncredis_connection_manager: Enable the optionalconnection-managerfeature ofredis. Any async redis caches created will use a connection manager instead of aMultiplexedConnectionredis_ahash: Enable the optionalahashfeature ofredisdisk_store: Include disk cache storewasm: Enable WASM support. Note that this feature is incompatible withtokio's multi-thread runtime (async_tokio_rt_multi_thread) and all Redis features (redis_store,redis_async_std,redis_tokio,redis_ahash)
The procedural macros (#[cached], #[once], #[io_cached]) offer more features, including async support.
See the proc_macro and macros modules for more samples, and the
examples directory for runnable snippets.
Any custom cache that implements cached::Cached/cached::CachedAsync can be used with the #[cached]/#[once]/cached! macros in place of the built-ins.
Any custom cache that implements cached::IOCached/cached::IOCachedAsync can be used with the #[io_cached] macro.
The basic usage looks like:
use cached::proc_macro::cached;
/// Defines a function named `fib` that uses a cache implicitly named `FIB`.
/// By default, the cache will be the function's name in all caps.
/// The following line is equivalent to #[cached(name = "FIB", unbound)]
#[cached]
fn fib(n: u64) -> u64 {
if n == 0 || n == 1 { return n }
fib(n-1) + fib(n-2)
}use std::thread::sleep;
use std::time::Duration;
use cached::proc_macro::cached;
use cached::SizedCache;
/// Use an explicit cache-type with a custom creation block and custom cache-key generating block
#[cached(
ty = "SizedCache<String, usize>",
create = "{ SizedCache::with_size(100) }",
convert = r#"{ format!("{}{}", a, b) }"#
)]
fn keyed(a: &str, b: &str) -> usize {
let size = a.len() + b.len();
sleep(Duration::new(size as u64, 0));
size
}use cached::proc_macro::once;
/// Only cache the initial function call.
/// Function will be re-executed after the cache
/// expires (according to `time` seconds).
/// When no (or expired) cache, concurrent calls
/// will synchronize (`sync_writes`) so the function
/// is only executed once.
#[once(time=10, option = true, sync_writes = true)]
fn keyed(a: String) -> Option<usize> {
if a == "a" {
Some(a.len())
} else {
None
}
}use cached::proc_macro::cached;
/// Cannot use sync_writes and result_fallback together
#[cached(
result = true,
time = 1,
sync_writes = "default",
result_fallback = true
)]
fn doesnt_compile() -> Result<String, ()> {
Ok("a".to_string())
}
use cached::proc_macro::io_cached;
use cached::AsyncRedisCache;
use thiserror::Error;
#[derive(Error, Debug, PartialEq, Clone)]
enum ExampleError {
#[error("error with redis cache `{0}`")]
RedisError(String),
}
/// Cache the results of an async function in redis. Cache
/// keys will be prefixed with `cache_redis_prefix`.
/// A `map_error` closure must be specified to convert any
/// redis cache errors into the same type of error returned
/// by your function. All `io_cached` functions must return `Result`s.
#[io_cached(
map_error = r##"|e| ExampleError::RedisError(format!("{:?}", e))"##,
ty = "AsyncRedisCache<u64, String>",
create = r##" {
AsyncRedisCache::new("cached_redis_prefix", 1)
.set_refresh(true)
.build()
.await
.expect("error building example redis cache")
} "##
)]
async fn async_cached_sleep_secs(secs: u64) -> Result<String, ExampleError> {
std::thread::sleep(std::time::Duration::from_secs(secs));
Ok(secs.to_string())
}use cached::proc_macro::io_cached;
use cached::DiskCache;
use thiserror::Error;
#[derive(Error, Debug, PartialEq, Clone)]
enum ExampleError {
#[error("error with disk cache `{0}`")]
DiskError(String),
}
/// Cache the results of a function on disk.
/// Cache files will be stored under the system cache dir
/// unless otherwise specified with `disk_dir` or the `create` argument.
/// A `map_error` closure must be specified to convert any
/// disk cache errors into the same type of error returned
/// by your function. All `io_cached` functions must return `Result`s.
#[io_cached(
map_error = r##"|e| ExampleError::DiskError(format!("{:?}", e))"##,
disk = true
)]
fn cached_sleep_secs(secs: u64) -> Result<String, ExampleError> {
std::thread::sleep(std::time::Duration::from_secs(secs));
Ok(secs.to_string())
}Functions defined via macros will have their results cached using the
function's arguments as a key, a convert expression specified on a procedural macros,
or a Key block specified on a cached_key! declarative macro.
When a macro-defined function is called, the function's cache is first checked for an already computed (and still valid) value before evaluating the function body.
Due to the requirements of storing arguments and return values in a global cache:
- Function return types:
- For all store types, except Redis, must be owned and implement
Clone - For the Redis store type, must be owned and implement
serde::Serialize + serde::DeserializeOwned
- For all store types, except Redis, must be owned and implement
- Function arguments:
- For all store types, except Redis, must either be owned and implement
Hash + Eq + Clone, the cached_key!macro is used with aKeyblock specifying key construction, or aconvertexpression is specified on a procedural macro to specify how to construct a key of aHash + Eq + Clonetype. - For the Redis store type, must either be owned and implement
Display, or thecached_key!&Keyor procedural macro &convertexpression used to specify how to construct a key of aDisplaytype.
- For all store types, except Redis, must either be owned and implement
- Arguments and return values will be
clonedin the process of insertion and retrieval. Except for Redis where arguments are formatted intoStringsand values are de/serialized. - Macro-defined functions should not be used to produce side-effectual results!
- Macro-defined functions cannot live directly under
implblocks since macros expand to aonce_cellinitialization and one or more function definitions. - Macro-defined functions cannot accept
Selftypes as a parameter.
License: MIT