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//! # Deadpool [](https://crates.io/crates/deadpool) [](https://github.com/bikeshedder/deadpool/actions?query=workflow%3ARust)
//!
//!
//! 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 | `async-trait` | yes |
//! | `unmanaged` | Enable unmanaged pool implementation | - | yes |
//! | `config` | Enable support for [config](https://crates.io/crates/config) crate | `config`, `serde/derive` | yes |
//! | `rt_tokio_1` | Enable support for [tokio](https://crates.io/crates/tokio) crate | `tokio/time` | no |
//! | `rt_async-std_1` | Enable support for [async-std](https://crates.io/crates/config) crate | `async-std` | 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](#database-connection-pools)
//! which work out of the box.
//!
//! ### Example
//!
//! ```rust,ignore
//! use async_trait::async_trait;
//!
//! #[derive(Debug)]
//! enum Error { Fail }
//!
//! struct Computer {}
//! struct Manager {}
//! type Pool = deadpool::managed::Pool<Manager>;
//!
//! impl Computer {
//! async fn get_answer(&self) -> i32 {
//! 42
//! }
//! }
//!
//! #[async_trait]
//! impl deadpool::managed::Manager for Manager {
//! type Type = Computer;
//! type Error = Error;
//! 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 | Latest Version |
//! ------- | ----- | -------------- |
//! [tokio-postgres](https://crates.io/crates/tokio-postgres) | [deadpool-postgres](https://crates.io/crates/deadpool-postgres) | [](https://crates.io/crates/deadpool-postgres) |
//! [lapin](https://crates.io/crates/lapin) (AMQP) | [deadpool-lapin](https://crates.io/crates/deadpool-lapin) | [](https://crates.io/crates/deadpool-lapin) |
//! [redis](https://crates.io/crates/redis) | [deadpool-redis](https://crates.io/crates/deadpool-redis) | [](https://crates.io/crates/deadpool-redis) |
//! [async-memcached](https://crates.io/crates/async-memcached) | [deadpool-memcached](https://crates.io/crates/deadpool-memcached) | [](https://crates.io/crates/deadpool-memcached) |
//!
//! ### 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` 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) provides an `async/.await` based
//! interface and provides the same configuration options as `r2d2`. It
//! depends on the tokio executor though and the code is more complex.
//!
//! - [`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,ignore
//! 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:
//!
//! ```shell
//! cargo tree --format "{p} {f}"
//! ```
//!
//! ## 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.
pub use Runtime;
/// The current pool status.