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 = true)]
/ #[once(sync_writes = true)]
(not supported by #[io_cached]
.
cached::stores
docs cache stores available.proc_macro
for more procedural macro examples.macros
for more declarative macro examples.Features
default
: Include proc_macro
and ahash
featuresproc_macro
: Include proc macrosahash
: Enable the optional ahash
hasher as default hashing algorithm.async
: Include support for async functions and async cache storesasync_tokio_rt_multi_thread
: Enable tokio
's optional rt-multi-thread
feature.redis_store
: Include Redis cache storeredis_async_std
: Include async Redis support using async-std
and async-std
tls support, implies redis_store
and async
redis_tokio
: Include async Redis support using tokio
and tokio
tls support, implies redis_store
and async
redis_connection_manager
: Enable the optional connection-manager
feature of redis
. Any async redis caches created
will use a connection manager instead of a MultiplexedConnection
redis_ahash
: Enable the optional ahash
feature of redis
disk_store
: Include disk cache storewasm
: Enable WASM support. Note that this feature is incompatible with tokio
'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 = true,
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:
Clone
serde::Serialize + serde::DeserializeOwned
Hash + Eq + Clone
,
the cached_key!
macro is used with a Key
block specifying key construction, or
a convert
expression is specified on a procedural macro to specify how to construct a key
of a Hash + Eq + Clone
type.Display
, or the cached_key!
& Key
or procedural macro & convert
expression used to specify how to construct a key of a Display
type.cloned
in the process of insertion and retrieval. Except for Redis
where arguments are formatted into Strings
and values are de/serialized.impl
blocks since macros expand to a
once_cell
initialization and one or more function definitions.Self
types as a parameter.License: MIT