cached
Caching structures and simplified function memoization
cached
provides implementations of several caching structures as well as a handy macro
for defining memoized functions.
Memoized functions defined using #[cached]
/#[once]
/cached!
macros are thread-safe with the backing function-cache wrapped in a mutex/rwlock.
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)]
.
See cached::stores
docs for details about the
cache stores available.
Features
proc_macro
: (default) pull in proc macro supportasync
: (default) AddCachedAsync
trait
Defining memoized functions using macros, #[cached]
, #[once]
, & cached!
Note:
It is recommended you use the two proc-macros (
#[cached]
,#[once]
) as these work with async functions and have more options/features. See theexamples/
directory for more sample usage, andcached_proc_macro/src/lib.rs
for the full list of available proc-macro arguments.The declarative macros (
cached!
and co.) are still available, but are less maintained and have fewer features.
The basic usage looks like:
use cached;
/// Defines a function named `fib` that uses a cache implicitly named `FIB`.
/// By default, the cache will be the function's in all caps.
/// The following line is equivalent to #[cached(name = "FIB", unbound)]
use sleep;
use Duration;
use cached;
/// Use an lru cache with size 100 and a `(String, String)` cache key
use sleep;
use Duration;
use cached;
/// Use a timed-lru cache with size 1, a TTL of 60s,
/// and a `(usize, usize)` cache key
use sleep;
use Duration;
use cached;
/// Use a timed cache with a TTL of 60s
/// that refreshes the entry TTL on cache hit,
/// and a `(String, String)` cache key
use cached;
/// Cache a fallible function. Only `Ok` results are cached.
use cached;
/// Cache an optional function. Only `Some` results are cached.
use cached;
/// Cache an optional function. Only `Some` results are cached.
/// When called concurrently, duplicate argument-calls will be
/// synchronized so as to only run once - the remaining concurrent
/// calls return a cached value.
use cached;
use Return;
/// Get a `cached::Return` value that indicates
/// whether the value returned came from the cache:
/// `cached::Return.was_cached`.
/// Use an LRU cache and a `String` cache key.
use cached;
use Return;
/// Same as the previous, but returning a Result
use cached;
use Return;
/// Same as the previous, but returning an Option
use sleep;
use Duration;
use cached;
use SizedCache;
/// Use an explicit cache-type with a custom creation block and custom cache-key generating block
use 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.
use sleep;
use Duration;
use cached;
/// Use a timed cache with a TTL of 60s.
/// Run a background thread to continuously refresh a specific key.
use sleep;
use Duration;
use once;
/// Run a background thread to continuously refresh a singleton.
use sleep;
use Duration;
use cached;
/// Run a background thread to continuously refresh every key of a cache
#[cached]
/cached!
defined functions will have their results cached using the function's arguments as a key
(or a specific expression when using cached_key!
).
When a cached!
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 must be owned and implement
Clone
- Function arguments must either be owned and implement
Hash + Eq + Clone
OR thecached_key!
macro must be used to convert arguments into an owned +Hash + Eq + Clone
type. - Arguments and return values will be
cloned
in the process of insertion and retrieval. #[cached]
/cached!
functions should not be used to produce side-effectual results!#[cached]
/cached!
functions cannot live directly underimpl
blocks sincecached!
expands to aonce_cell
initialization and a function definition.#[cached]
/cached!
functions cannot acceptSelf
types as a parameter.
NOTE: Any custom cache that implements cached::Cached
can be used with the cached
macros in place of the built-ins.
See examples
for basic usage of proc-macro &
macro-rules macros and an example of implementing a custom cache-store.
cached!
and cached_key!
Usage & Options:
There are several options depending on how explicit you want to be. See below for a full syntax breakdown.
1.) Using the shorthand will use an unbounded cache.
extern crate cached;
/// Defines a function named `fib` that uses a cache named `FIB`
cached!
2.) Using the full syntax requires specifying the full cache type and providing
an instance of the cache to use. Note that the cache's key-type is a tuple
of the function argument types. If you would like fine grained control over
the key, you can use the cached_key!
macro.
The following example uses a SizedCache
(LRU):
extern crate cached;
use sleep;
use Duration;
use SizedCache;
/// Defines a function `compute` that uses an LRU cache named `COMPUTE` which has a
/// size limit of 50 items. The `cached!` macro will implicitly combine
/// the function arguments into a tuple to be used as the cache key.
cached!
3.) The cached_key
macro functions identically, but allows you to define the
cache key as an expression.
extern crate cached;
use sleep;
use Duration;
use SizedCache;
/// Defines a function named `length` that uses an LRU cache named `LENGTH`.
/// The `Key = ` expression is used to explicitly define the value that
/// should be used as the cache key. Here the borrowed arguments are converted
/// to an owned string that can be stored in the global function cache.
cached_key!
4.) The cached_result
and cached_key_result
macros function similarly to cached
and cached_key
respectively but the cached function needs to return Result
(or some type alias like io::Result
). If the function returns Ok(val)
then val
is cached, but errors are not. Note that only the success type needs to implement
Clone
, not the error type. When using cached_result
and cached_key_result
,
the cache type cannot be derived and must always be explicitly specified.
extern crate cached;
use UnboundCache;
/// Cache the successes of a function.
/// To use `cached_key_result` add a key function as in `cached_key`.
cached_result!
Syntax
The common macro syntax is:
cached_key!
Where:
CACHE_NAME
is the unique name used to hold astatic ref
to the cacheCacheType
is the full type of the cacheCacheInstance
is any expression that yields an instance ofCacheType
to be used as the cache-store, followed by;
- When using the
cached_key!
macro, the "Key" line must be specified. This line must start with the literal tokensKey =
, followed by an expression that evaluates to the key, followed by;
fn func_name(arg1: arg_type) -> return_type
is the same form as a regular function signature, with the exception that functions with no return value must be explicitly stated (e.g.fn func_name(arg: arg_type) -> ()
)- The expression following
=
is the function body assigned tofunc_name
. Note, the function body can make recursive calls to its cached-self (func_name
).
Fine grained control using cached_control!
The cached_control!
macro allows you to provide expressions that get plugged into key areas
of the memoized function. While the cached
and cached_result
variants are adequate for most
scenarios, it can be useful to have the ability to customize the macro's functionality.
extern crate cached;
use UnboundCache;
/// The following usage plugs in expressions to make the macro behave like
/// the `cached_result!` macro.
cached_control!
License: MIT