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Caching structures and simplified function memoization

cached provides implementations of several caching structures as well as a handy macrosfor defining memoized functions.

Memoized functions defined using#[cached]/#[once]/#[io_cached]/cached! macros are thread-safe with the backingfunction-cache wrapped in a mutex/rwlock, or externally synchronized in the case of#[io_cached].By default, the function-cache isnot 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 overwritethe memoized value as they complete. This mirrors the behavior of Python'sfunctools.lru_cache. To synchronize the execution and cachingof un-cached arguments, specify#[cached(sync_writes = "default")] /#[once(sync_writes = true)] (not supported by#[io_cached].

• Seecached::stores docs cache stores available.
• Seeproc_macro for more procedural macro examples.
• Seemacros for more declarative macro examples.

Features

• default: Includeproc_macro andahash features
• proc_macro: Include proc macros
• ahash: Enable the optionalahash hasher as default hashing algorithm.
• async: Include support for async functions and async cache stores
• async_tokio_rt_multi_thread: Enabletokio's optionalrt-multi-thread feature.
• redis_store: Include Redis cache store
• redis_async_std: Include async Redis support usingasync-std andasync-std tls support, impliesredis_store andasync
• redis_tokio: Include async Redis support usingtokio andtokio tls support, impliesredis_store andasync
• redis_connection_manager: Enable the optionalconnection-manager feature ofredis. Any async redis caches createdwill use a connection manager instead of aMultiplexedConnection
• redis_ahash: Enable the optionalahash feature ofredis
• disk_store: Include disk cache store
• wasm: Enable WASM support. Note that this feature is incompatible withtokio's multi-threadruntime (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 theproc_macro andmacros modules for more samples, and theexamples directory for runnable snippets.

Any custom cache that implementscached::Cached/cached::CachedAsync can be used with the#[cached]/#[once]/cached! macros in place of the built-ins.Any custom cache that implementscached::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]fnfib(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) }"#)]fnkeyed(a:&str,b:&str) ->usize{let size = a.len() + b.len();sleep(Duration::new(sizeasu64,0));    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)]fnkeyed(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)]enumExampleError{#[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")    } "##)]asyncfnasync_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)]enumExampleError{#[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)]fncached_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 thefunction's arguments as a key, aconvert expression specified on a procedural macros,or aKey block specified on acached_key! declarative macro.

When a macro-defined function is called, the function's cache is first checked for an alreadycomputed (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 implementClone
  • For the Redis store type, must be owned and implementserde::Serialize + serde::DeserializeOwned
• Function arguments:
  • For all store types, except Redis, must either be owned and implementHash + Eq + Clone,thecached_key! macro is used with aKey block specifying key construction, oraconvert expression is specified on a procedural macro to specify how to construct a keyof aHash + Eq + Clone type.
  • For the Redis store type, must either be owned and implementDisplay, or thecached_key! &Keyor procedural macro &convert expression used to specify how to construct a key of aDisplay type.
• Arguments and return values will becloned in the process of insertion and retrieval. Except for Rediswhere arguments are formatted intoStrings and values are de/serialized.
• Macro-defined functions should not be used to produce side-effectual results!
• Macro-defined functions cannot live directly underimpl blocks since macros expand to aonce_cell initialization and one or more function definitions.
• Macro-defined functions cannot acceptSelf types as a parameter.

License: MIT