Crate persistentcache [−] [src]
Macros for persistently caching function calls
The values are cached either in files or on Redis. Two storages, FileStorage
and RedisStorage
are provided.
Caching is performed based on the function name and function parameters, meaning that for every
combination of function and parameters, the returned value is stored in a storage. Subsequent
calls of this function with the same parameters are not computed, but instead fetched from the
storage. This can lead to an decrease in computing time in case the function call is
computationally more expensive than fetching the value from the storage. The storages are
persistent (stored on disk) and can be shared between different threads and processes.
All Parameters to the function need to be Hashable. The return value needs to be serializeable
by the crate bincode
.
Setup
Add the following dependencies to your projet:
[dependencies]
lazy_static = "*"
bincode = "*"
persistentcache = "*"
Caching function calls with cache!
The macro cache!
caches a function call. The advantage of this approach over the macro
cache_func
is that different storages can be used for different calls. Furthermore the
function can still be called without caching if desired.
However, in case of recursive functions, this will most likely not work as expected because the
recursive calls will not be cached.
The macro expects the function to return a value of type Result<T, Box<std::error::Error>>
.
Example
#![allow(redundant_closure_call)] extern crate bincode; #[macro_use] extern crate persistentcache; use persistentcache::*; fn add_two(a: u64) -> Result<u64, Box<std::error::Error>> { println!("Calculating {} + 2...", a); Ok(a + 2) } fn main() { let s = storage::redis::RedisStorage::new("redis://127.0.0.1").unwrap(); // Function is called and will print "Calculating 2 + 2..." and "4" println!("{}", cache!(s, add_two(2)).unwrap()); // Value will be cached from Redis, will only print "4" println!("{}", cache!(s, add_two(2)).unwrap()); // Function is called and will print "Calculating 3 + 2..." and "5" println!("{}", cache!(s, add_two(3)).unwrap()); // Value will be cached from Redis, will only print "5" println!("{}", cache!(s, add_two(3)).unwrap()); }
This will print:
Calculating 2 + 2...
4
4
Calculating 3 + 2...
5
5
Caching a function with cache_func!
The macro cache_func!
is wrapped around a function definition and modifies the function such
that the function body is executed and the resulting value is both returned and stored in a
provided storage in case the given combination of parameters hasn't been evaluated before.
Subsequent calls to the function with already evaluated parameters are then fetched from the
storage.
The advantage of this approach over cache!
is that the function is modified and hence every
call to the function will automatically take care of the caching. Furthermore it works with
recursive calls. However, caching cannot be 'turned off' anymore.
No assumption about the return type are made in this case. The function returns the same type
as the initial function definition.
Example
#[macro_use] extern crate lazy_static; #[macro_use] extern crate persistentcache; extern crate bincode; use persistentcache::*; // Either store it in a `FileStorage`... cache_func!(File, "test_dir", fn add_two_file(a: u64) -> u64 { println!("Calculating {} + 2...", a); a + 2 }); // ... or in a `RedisStorage` cache_func!(Redis, "redis://127.0.0.1", fn add_two_redis(a: u64) -> u64 { println!("Calculating {} + 2...", a); a + 2 }); fn main() { /*// Function is called and will print "Calculating 2 + 2..." and "4" println!("{}", s, add_two_file(2)); // Value will be cached from Redis, will only print "4" println!("{}", s, add_two_file(2)); // Function is called and will print "Calculating 3 + 2..." and "5" println!("{}", s, add_two_redis(3)); // Value will be cached from Redis, will only print "5" println!("{}", s, add_two_redis(3));*/ }
This will print:
Calculating 2 + 2...
4
4
Calculating 3 + 2...
5
5
Implementing other storages
Storages need to implement the PersistentCache
trait.
Running the tests
The tests should be run in a single thread because the Storages are regularly flushed.
cargo test --features clippy -- --test-threads=1
A Redis server needs to be running and listening at 127.0.0.1
for the tests to work.
History
This crate is inspired by owls-cache and its primary goal is to teach myself Rust. While working on it, I realised that a similar crate already exists: cached-rs. I've borrowed a couple of ideas from there. Have a look at it, it looks much more professional than this crate and almost certainly has better developers. Unfortunately it lacks the 'persistent' part and the caches cannot be shared between processes/threads, but it should be fairly easy to extend it.
Modules
persistentcache |
Implementation of the macros |
storage |
Implementation of different persistent storages. Currently on disk ( |
Macros
cache |
Cache a single function call. |
cache_func |
Cache an entire function. |
Constants
PREFIX |
Every stored variable is prefixed by this string. Currently, the flush functions depend on this in order to decide which variable to flush from the storage. Keeping track of the used variable internally is not an option because they are persistent and may come from another process. |
Traits
PersistentCache |
Traits which need to be implemented by any storage |