# Locker Room
### Readers-writer access to individual cells of your collection!

## LockerRoom and LockerRoomAsync
The central features of the crate is implemented by these structures. More specifically, they provide such functionality:
1. Shared readers access to single cell of collection with `LockerRoom::read_cell` and `LockerRoomAsync::read_cell`;
2. Exclusive writer access to single cell of collection with `LockerRoom::write_cell` and `LockerRoomAsync::write_cell`;
3. Exclusive writer access to whole collection with `LockerRoom::lock_room` and `LockerRoomAsync::lock_room`.

But `LockerRoomAsync` is optional - you need to enable feature `async` to use it. It depends on
[`tokio`](https://docs.rs/tokio/latest/tokio/index.html)'s [`RwLock`](https://docs.rs/tokio/latest/tokio/sync/struct.RwLock.html).

### LockerRoom example
```rust
let v = vec![0, 1, 2, 3, 4, 5];
let locker_room: LockerRoom<_> = v.into();
let locker_room = Arc::new(locker_room);
thread::scope(|scope| {
    scope.spawn(|| *locker_room.write_cell(0).unwrap() += 1);
    scope.spawn(|| *locker_room.write_cell(0).unwrap() += 2);
});
assert_eq!(3, *locker_room.read_cell(0).unwrap());
```

### LockerRoomAsync example
```rust
let v = vec![0, 1, 2, 3, 4, 5];
let locker_room: LockerRoomAsync<_> = v.into();
let locker_room = Arc::new(locker_room);

let locker_room_cloned = Arc::clone(&locker_room);
let join1 = spawn(async move { *locker_room_cloned.write_cell(0).await.unwrap() += 1 });

let locker_room_cloned = Arc::clone(&locker_room);
let join2 = spawn(async move { *locker_room_cloned.write_cell(0).await.unwrap() += 2 });

join!(join1, join2);
assert_eq!(3, *locker_room.read_cell(0).await.unwrap());
```

### Deadlock example
Carefully block multiple cells in one scope. Otherwise, situation like this may occur:
```text
// Thread 1                            |  // Thread 2
let _w1 = locker_room.write_cell(0);   |
                                       |  let _w1 = locker_room.write_cell(1);
// will block
let _w2 = locker_room.write_cell(1);   |
                                       |  // will deadlock
                                       |  let _w2 = locker_room.write_cell(0);
```

### Collections?
By default you can create `LockerRoom` and `LockerRoomAsync` from `array`, `Vec`, `VecDeque`, `HashMap` and `BTreeMap`.

But the crate provides traits, by which implementing to your collection, you can make it compatible with `LockerRoom` and `LockerRoomAsync`.

## Collection
Crucial part of the crate that helps your collection to be compatible with `LockerRoom` and `LockerRoomAsync`.

Just implement it into your collection and everything will work!

### Example
Let's implement the trait for the struct from `Index`'s [example](https://doc.rust-lang.org/std/ops/trait.Index.html#examples):
```rust
enum Nucleotide {
    C,
    A,
    G,
    T,
}

struct NucleotideCount {
    pub a: usize,
    pub c: usize,
    pub g: usize,
    pub t: usize,
}

impl Collection for NucleotideCount {
    type Output = usize;
    type Idx = Nucleotide;
    type ShadowLocks = NucleotideShadowLocks;

    fn index(&self, index: impl Borrow<Self::Idx>) -> Option<&Self::Output> {
        Some(match index.borrow() {
            Nucleotide::A => &self.a,
            Nucleotide::C => &self.c,
            Nucleotide::G => &self.g,
            Nucleotide::T => &self.t,
        })
    }

    fn index_mut(&mut self, index: impl Borrow<Self::Idx>) -> Option<&mut Self::Output> {
        Some(match index.borrow() {
            Nucleotide::A => &mut self.a,
            Nucleotide::C => &mut self.c,
            Nucleotide::G => &mut self.g,
            Nucleotide::T => &mut self.t,
        })
    }

    fn indices(&self) -> impl Iterator<Item = Self::Idx> {
        [Nucleotide::A, Nucleotide::C, Nucleotide::G, Nucleotide::T].into_iter()
    }

    fn shadow_locks(&self) -> Self::ShadowLocks {
        Default::default()
    }
}

struct NucleotideShadowLocks {
    a: RwLock<()>,
    c: RwLock<()>,
    g: RwLock<()>,
    t: RwLock<()>,
}

impl ShadowLocksCollection for NucleotideShadowLocks {
    type Idx = Nucleotide;

    fn index(&self, index: impl Borrow<Self::Idx>) -> Option<&RwLock<()>> {
        Some(match index.borrow() {
            Nucleotide::A => &self.a,
            Nucleotide::C => &self.c,
            Nucleotide::G => &self.g,
            Nucleotide::T => &self.t,
        })
    }

    fn update_indices(&mut self, _indices: impl Iterator<Item = Self::Idx>) {
        // No need to reindex because NucleotideShadowLocks has static structure.
    }
}
```

If feature `async` is enabled, `Collection` must also include `Collection::ShadowLocksAsync` type and `Collection::shadow_locks_async` method. 
Thus `ShadowLocksCollectionAsync` must be implemented.
```rust
impl Collection for NucleotideCount {
    // ...
    type ShadowLocksAsync = NucleotideShadowLocksAsync;
    // ...
    fn shadow_locks_async(&self) -> Self::ShadowLocksAsync {
        Default::default()
    }
}

struct NucleotideShadowLocksAsync {
    a: tokio::sync::RwLock<()>,
    c: tokio::sync::RwLock<()>,
    g: tokio::sync::RwLock<()>,
    t: tokio::sync::RwLock<()>,
}

impl ShadowLocksCollectionAsync for NucleotideShadowLocksAsync {
    type Idx = Nucleotide;

    fn index(&self, index: impl Borrow<Self::Idx>) -> Option<&tokio::sync::RwLock<()>> {
        Some(match index.borrow() {
            Nucleotide::A => &self.a,
            Nucleotide::C => &self.c,
            Nucleotide::G => &self.g,
            Nucleotide::T => &self.t,
        })
    }

    fn update_indices(&mut self, _indices: impl Iterator<Item = Self::Idx>) {
        // No need to reindex because NucleotideShadowLocksAsync has static structure.
    }
}
```