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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].

Features

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:

License: MIT