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//! # Deadpool [![Latest Version](https://img.shields.io/crates/v/deadpool.svg)](https://crates.io/crates/deadpool) [![Build Status](https://travis-ci.org/bikeshedder/deadpool.svg?branch=master)](https://travis-ci.org/bikeshedder/deadpool) //! //! 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](#database-connection-pools) //! - Enabled via the `managed` feature in your `Cargo.toml` //! //! - Unmanaged pool (`deadpool::unmanaged::Pool`) //! - All objects either need to 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 your `Cargo.toml` //! //! ## Features //! //! | Feature | Description | Extra dependencies | Default | //! | ------- | ----------- | ------------------ | ------- | //! | `managed` | Enable managed pool implementation | – | yes | //! | `unmanaged` | Enable unmanaged pool implementation | `async-trait` | yes | //! | `config` | Enable support for [config](https://crates.io/crates/config) crate | `config`, `serde/derive` | yes | //! //! ## 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](#database-connection-pools) //! which work out of the box. //! //! ### Example //! //! ```rust //! use async_trait::async_trait; //! //! #[derive(Debug)] //! enum Error { Fail } //! //! struct Computer {} //! struct Manager {} //! type Pool = deadpool::managed::Pool<Computer, Error>; //! //! impl Computer { //! async fn get_answer(&self) -> i32 { //! 42 //! } //! } //! //! #[async_trait] //! impl deadpool::managed::Manager<Computer, Error> for Manager { //! async fn create(&self) -> Result<Computer, Error> { //! Ok(Computer {}) //! } //! async fn recycle(&self, conn: &mut Computer) -> deadpool::managed::RecycleResult<Error> { //! Ok(()) //! } //! } //! //! #[tokio::main] //! async fn main() { //! let mgr = Manager {}; //! let pool = Pool::new(mgr, 16); //! 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 //! ----------------------------------------------------------- | ----- //! [tokio-postgres](https://crates.io/crates/tokio-postgres) | [deadpool-postgres](https://crates.io/crates/deadpool-postgres) //! [lapin](https://crates.io/crates/lapin) (AMQP) | [deadpool-lapin](https://crates.io/crates/deadpool-lapin) //! [redis](https://crates.io/crates/redis) | [deadpool-redis](https://crates.io/crates/deadpool-redis) //! //! ### 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.** The code which returns connections to the pool //! contains no blocking code and retrival uses only one locking primitive. //! //! - **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` and `Object::drop`. //! //! ### Differences to other connection pool implementations //! //! - [`r2d2`](https://crates.io/crates/r2d2) provides a lot more configuration //! options but only provides a synchroneous interface. //! //! - [`bb8`](https://crates.io/crates/bb8) uses a callback based interface (See //! [`pool.run`](https://docs.rs/bb8/0.3.1/bb8/struct.Pool.html#method.run)) //! and provides the same configuration options as `r2d2`. At the time of //! writing there is no official release which supports `async/.await`. //! //! - [`mobc`](https://crates.io/crates/mobc) provides an `async/.await` based //! interface and provides a lot more configuration options. It requires an //! executor though and the code is a lot more complex. //! //! ## 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 //! //! ```rust //! 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; //! assert_eq!(s.get_answer().await, 42); //! } //! ``` //! //! ## License //! //! Licensed under either of //! //! - Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or <http://www.apache.org/licenses/LICENSE-2.0)> //! - MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT)> //! //! at your option. #![warn(missing_docs)] #[cfg(feature = "managed")] mod compat_0_4; #[cfg(feature = "managed")] pub mod managed; #[cfg(feature = "managed")] pub use compat_0_4::*; #[cfg(feature = "unmanaged")] pub mod unmanaged; #[derive(Debug)] /// The current pool status. pub struct Status { /// The maximum size of the pool pub max_size: usize, /// The current size of the pool pub size: usize, /// The number of available objects in the pool. If there are no /// objects in the pool this number can become negative and stores the /// number of futures waiting for an object. pub available: isize, }