Struct RwLock

pub struct RwLock<T: ?Sized> { /* private fields */ }

An async reader-writer lock.

This type of lock allows multiple readers or one writer at any point in time.

The locking strategy is write-preferring, which means writers are never starved. Releasing a write lock wakes the next blocked reader and the next blocked writer.

Examples

use async_lock::RwLock;

let lock = RwLock::new(5);

// Multiple read locks can be held at a time.
let r1 = lock.read().await;
let r2 = lock.read().await;
assert_eq!(*r1, 5);
assert_eq!(*r2, 5);
drop((r1, r2));

// Only one write lock can be held at a time.
let mut w = lock.write().await;
*w += 1;
assert_eq!(*w, 6);

Implementations

impl<T> RwLock<T>

pub const fn new(t: T) -> RwLock<T>

Creates a new reader-writer lock.

Examples

use async_lock::RwLock;

let lock = RwLock::new(0);

pub fn into_inner(self) -> T

Unwraps the lock and returns the inner value.

Examples

use async_lock::RwLock;

let lock = RwLock::new(5);
assert_eq!(lock.into_inner(), 5);

impl<T: ?Sized> RwLock<T>

pub fn try_read(&self) -> Option<RwLockReadGuard<'_, T>>

Attempts to acquire a read lock.

If a read lock could not be acquired at this time, then None is returned. Otherwise, a guard is returned that releases the lock when dropped.

Examples

use async_lock::RwLock;

let lock = RwLock::new(1);

let reader = lock.read().await;
assert_eq!(*reader, 1);

assert!(lock.try_read().is_some());

pub async fn read(&self) -> RwLockReadGuard<'_, T>

Acquires a read lock.

Returns a guard that releases the lock when dropped.

Note that attempts to acquire a read lock will block if there are also concurrent attempts to acquire a write lock.

Examples

use async_lock::RwLock;

let lock = RwLock::new(1);

let reader = lock.read().await;
assert_eq!(*reader, 1);

assert!(lock.try_read().is_some());

pub fn try_upgradable_read(&self) -> Option<RwLockUpgradableReadGuard<'_, T>>

Attempts to acquire a read lock with the possiblity to upgrade to a write lock.

If a read lock could not be acquired at this time, then None is returned. Otherwise, a guard is returned that releases the lock when dropped.

Upgradable read lock reserves the right to be upgraded to a write lock, which means there can be at most one upgradable read lock at a time.

Examples

use async_lock::{RwLock, RwLockUpgradableReadGuard};

let lock = RwLock::new(1);

let reader = lock.upgradable_read().await;
assert_eq!(*reader, 1);
assert_eq!(*lock.try_read().unwrap(), 1);

let mut writer = RwLockUpgradableReadGuard::upgrade(reader).await;
*writer = 2;

pub async fn upgradable_read(&self) -> RwLockUpgradableReadGuard<'_, T>

Attempts to acquire a read lock with the possiblity to upgrade to a write lock.

Returns a guard that releases the lock when dropped.

Upgradable read lock reserves the right to be upgraded to a write lock, which means there can be at most one upgradable read lock at a time.

Note that attempts to acquire an upgradable read lock will block if there are concurrent attempts to acquire another upgradable read lock or a write lock.

Examples

use async_lock::{RwLock, RwLockUpgradableReadGuard};

let lock = RwLock::new(1);

let reader = lock.upgradable_read().await;
assert_eq!(*reader, 1);
assert_eq!(*lock.try_read().unwrap(), 1);

let mut writer = RwLockUpgradableReadGuard::upgrade(reader).await;
*writer = 2;

pub fn try_write(&self) -> Option<RwLockWriteGuard<'_, T>>

Attempts to acquire a write lock.

If a write lock could not be acquired at this time, then None is returned. Otherwise, a guard is returned that releases the lock when dropped.

Examples

use async_lock::RwLock;

let lock = RwLock::new(1);

assert!(lock.try_write().is_some());
let reader = lock.read().await;
assert!(lock.try_write().is_none());

pub async fn write(&self) -> RwLockWriteGuard<'_, T>

Acquires a write lock.

Returns a guard that releases the lock when dropped.

Examples

use async_lock::RwLock;

let lock = RwLock::new(1);

let writer = lock.write().await;
assert!(lock.try_read().is_none());

pub fn get_mut(&mut self) -> &mut T

Returns a mutable reference to the inner value.

Since this call borrows the lock mutably, no actual locking takes place. The mutable borrow statically guarantees no locks exist.

Examples

use async_lock::RwLock;

let mut lock = RwLock::new(1);

*lock.get_mut() = 2;
assert_eq!(*lock.read().await, 2);

Trait Implementations

impl<T: Debug + ?Sized> Debug for RwLock<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: Default + ?Sized> Default for RwLock<T>

fn default() -> RwLock<T>

Returns the “default value” for a type.

impl<T> From<T> for RwLock<T>

fn from(val: T) -> RwLock<T>

Converts to this type from the input type.

impl<T: Send + ?Sized> Send for RwLock<T>

impl<T: Send + Sync + ?Sized> Sync for RwLock<T>