# piscina

A simple generic pool that supports both sync and async.

[![crate_version](https://img.shields.io/crates/v/piscina.svg?style=flat)](https://crates.io/crates/piscina)
[![docs_version](https://img.shields.io/badge/docs-latest-blue.svg?style=flat)](https://docs.rs/piscina/latest/piscina/)

Two types of pools are provided:

- [`Pool`]: A simple pool that supports both sync and async.
- [`PriorityPool`]: A pool of items with priorities and supports both sync and async.

This crate internally utilizes `futures_channel::oneshot` and is thus lock-free.

## Features

```toml
default = []
```

The features below are related to logging errors, which should be unreachable.

- `log`: Enables logging using the `log` crate.
- `tracing`: Enables logging using the `tracing` crate.

## Examples

Non-async [`Pool`] example:

```rust
use piscina::Pool;

let mut pool = Pool::new();
pool.put(1);
pool.put(2);

let item1 = pool.try_get();
assert!(item1.is_some());

let item2 = pool.blocking_get();

let none = pool.try_get();
assert!(none.is_none());

drop(item1); // Return the item to the pool by dropping it
let item3 = pool.try_get();
assert!(item3.is_some());
```

Async [`Pool`] example:

```rust
use piscina::Pool;

futures::executor::block_on(async {
    let mut pool = Pool::new();
    pool.put(1);
    pool.put(2);

    let item1 = pool.get().await;
    let item2 = pool.get().await;

    let none = pool.try_get();
    assert!(none.is_none());

    drop(item1); // Return the item to the pool by dropping it
    let item3 = pool.get().await;
});
```

Non-async [`PriorityPool`] example:

```rust
use piscina::PriorityPool;

let mut pool = PriorityPool::new();
pool.put("hello", 1);
pool.put("world", 2); // Larger value means higher priority.

// Get the highest priority item.
let item = pool.try_get();
assert!(item.is_some());
let item = item.unwrap();
assert_eq!(item.item(), &"world");

let another_item = pool.try_get();
assert!(another_item.is_some());
let another_item = another_item.unwrap();
assert_eq!(another_item.item(), &"hello");

// The pool is now empty.
let empty_item = pool.try_get();
assert!(empty_item.is_none());

drop(another_item); // Return the item back to the pool by dropping it.
let hello = pool.try_get();
assert!(hello.is_some());
assert_eq!(hello.unwrap().item(), &"hello");
```

Async [`PriorityPool`] example:

```rust
use piscina::PriorityPool;

let mut pool = PriorityPool::new();
pool.put("hello", 1);
pool.put("world", 2); // Larger value means higher priority.

futures::executor::block_on(async {
    // Get the highest priority item.
    let world = pool.get().await;
    assert_eq!(world.item(), &"world");

    let hello = pool.get().await;
    assert_eq!(hello.item(), &"hello");

    // The pool is now empty.
    drop(hello); // Return the item back to the pool by dropping it.
    let item = pool.get().await;
    assert_eq!(item.item(), &"hello");
});
```

## Safety

Instead of using an `Option`, this crate uses unsafe code `ManuallyDrop` in `PooledItem`.
And the only use of unsafe code `ManuallyDrop::take()` occurs when `PooledItem` is dropped.

License: MIT/Apache-2.0