deadpool
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Dead simple pool implementation for rust with async-await
Deadpool
![Rust 1.54+ Rust 1.54+](https://img.shields.io/badge/rustc-1.54+-lightgray.svg)
Deadpool is a dead simple async pool for connections and objects of any type.
This crate provides two implementations:
-
Managed pool (
deadpool::managed::Pool
)- Creates and recycles objects as needed
- Useful for database connection pools
- Enabled via the
managed
feature in yourCargo.toml
-
Unmanaged pool (
deadpool::unmanaged::Pool
)- All objects either need to be created by the user and added to the pool manually. It is also possible to create a pool from an existing collection of objects.
- Enabled via the
unmanaged
feature in yourCargo.toml
Features
Feature | Description | Extra dependencies | Default |
---|---|---|---|
managed |
Enable managed pool implementation | async-trait |
yes |
unmanaged |
Enable unmanaged pool implementation | - | yes |
rt_tokio_1 |
Enable support for tokio crate | tokio/time |
no |
rt_async-std_1 |
Enable support for async-std crate | async-std |
no |
serde |
Enable support for deserializing pool config | serde/derive |
no |
The runtime features (rt_*
) are only needed if you need support for
timeouts. If you try to use timeouts without specifying a runtime at
pool creation the pool get methods will return an
PoolError::NoRuntimeSpecified
error.
Managed pool (aka. connection pool)
This is the obvious choice for connection pools of any kind. Deadpool already comes with a couple of database connection pools which work out of the box.
Example
use async_trait::async_trait;
use deadpool::managed;
#[derive(Debug)]
enum Error { Fail }
struct Computer {}
impl Computer {
async fn get_answer(&self) -> i32 {
42
}
}
struct Manager {}
#[async_trait]
impl managed::Manager for Manager {
type Type = Computer;
type Error = Error;
async fn create(&self) -> Result<Computer, Error> {
Ok(Computer {})
}
async fn recycle(&self, _: &mut Computer) -> managed::RecycleResult<Error> {
Ok(())
}
}
type Pool = managed::Pool<Manager>;
#[tokio::main]
async fn main() {
let mgr = Manager {};
let pool = Pool::builder(mgr).build().unwrap();
let mut conn = pool.get().await.unwrap();
let answer = conn.get_answer().await;
assert_eq!(answer, 42);
}
Database connection pools
Deadpool supports various database backends by implementing the
deadpool::managed::Manager
trait. The following backends are
currently supported:
Backend | Crate | Latest Version |
---|---|---|
bolt-client | deadpool-bolt | |
tokio-postgres | deadpool-postgres | |
lapin (AMQP) | deadpool-lapin | |
redis | deadpool-redis | |
async-memcached | deadpool-memcached | |
rusqlite | deadpool-sqlite | |
diesel | deadpool-diesel | |
r2d2 | deadpool-r2d2 | |
rbatis | rbatis |
Reasons for yet another connection pool
Deadpool is by no means the only pool implementation available. It does things a little different and that is the main reason for it to exist:
-
Deadpool is compatible with any executor. Objects are returned to the pool using the
Drop
trait. The health of those objects is checked upon next retrieval and not when they are returned. Deadpool never performs any actions in the background. This is the reason why deadpool does not need to spawn futures and does not rely on a background thread or task of any type. -
Identical startup and runtime behaviour. When writing long running application there usually should be no difference between startup and runtime if a database connection is temporarily not available. Nobody would expect an application to crash if the database becomes unavailable at runtime. So it should not crash on startup either. Creating the pool never fails and errors are only ever returned when calling
Pool::get()
.If you really want your application to crash on startup if objects can not be created on startup simply call
pool.get().await.expect("DB connection failed")
right after creating the pool. -
Deadpool is fast. Whenever working with locking primitives they are held for the shortest duration possible. When returning an object to the pool a single mutex is locked and when retrieving objects from the pool a Semaphore is used to make this Mutex as little contested as possible.
-
Deadpool is simple. Dead simple. There is very little API surface. The actual code is barely 100 lines of code and lives in the two functions
Pool::get
andObject::drop
. -
Deadpool is extensible. By using
post_create
,pre_recycle
andpost_recycle
hooks you can customize object creation and recycling to fit your needs. -
Deadpool provides insights. All objects track
Metrics
and the pool provides astatus
method that can be used to find out details about the inner workings. -
Deadpool is resizable. You can grow and shrink the pool at runtime without requiring an application restart.
Unmanaged pool
An unmanaged pool is useful when you can't write a manager for the objects
you want to pool or simply don't want to. This pool implementation is slightly
faster than the managed pool because it does not use a Manager
trait to
create
and recycle
objects but leaves it up to the user.
Unmanaged pool example
use deadpool::unmanaged::Pool;
struct Computer {}
impl Computer {
async fn get_answer(&self) -> i32 {
42
}
}
#[tokio::main]
async fn main() {
let pool = Pool::from(vec![
Computer {},
Computer {},
]);
let s = pool.get().await.unwrap();
assert_eq!(s.get_answer().await, 42);
}
FAQ
Why does deadpool depend on tokio
? I thought it was runtime agnostic...
Deadpool depends on tokio::sync::Semaphore
. This does not mean that
the tokio runtime or anything else of tokio is being used or will be part
of your build. You can easily check this by running the following command
in your own code base:
cargo tree --format "{p} {f}"
License
Licensed under either of
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.