Struct tokio::sync::OwnedRwLockWriteGuard

pub struct OwnedRwLockWriteGuard<T: ?Sized> { /* fields omitted */ }

This is supported on crate feature sync only.

Owned RAII structure used to release the exclusive write access of a lock when dropped.

This structure is created by the write_owned method on RwLock.

Implementations

impl<T: ?Sized> OwnedRwLockWriteGuard<T>

pub fn map<F, U: ?Sized>(this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, U> where
    F: FnOnce(&mut T) -> &mut U, 

Make a new OwnedRwLockMappedWriteGuard for a component of the locked data.

This operation cannot fail as the OwnedRwLockWriteGuard passed in already locked the data.

This is an associated function that needs to be used as OwnedRwLockWriteGuard::map(..). A method would interfere with methods of the same name on the contents of the locked data.

Examples

use std::sync::Arc;
use tokio::sync::{RwLock, OwnedRwLockWriteGuard};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Foo(u32);

let lock = Arc::new(RwLock::new(Foo(1)));

{
    let lock = Arc::clone(&lock);
    let mut mapped = OwnedRwLockWriteGuard::map(lock.write_owned().await, |f| &mut f.0);
    *mapped = 2;
}

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

pub fn try_map<F, U: ?Sized>(
    this: Self,
    f: F
) -> Result<OwnedRwLockMappedWriteGuard<T, U>, Self> where
    F: FnOnce(&mut T) -> Option<&mut U>, 

Attempts to make a new OwnedRwLockMappedWriteGuard for a component of the locked data. The original guard is returned if the closure returns None.

This operation cannot fail as the OwnedRwLockWriteGuard passed in already locked the data.

This is an associated function that needs to be used as OwnedRwLockWriteGuard::try_map(...). A method would interfere with methods of the same name on the contents of the locked data.

Examples

use std::sync::Arc;
use tokio::sync::{RwLock, OwnedRwLockWriteGuard};

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Foo(u32);

let lock = Arc::new(RwLock::new(Foo(1)));

{
    let guard = Arc::clone(&lock).write_owned().await;
    let mut guard = OwnedRwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
    *guard = 2;
}

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

pub fn into_mapped(this: Self) -> OwnedRwLockMappedWriteGuard<T>

Converts this OwnedRwLockWriteGuard into an OwnedRwLockMappedWriteGuard. This method can be used to store a non-mapped guard in a struct field that expects a mapped guard.

This is equivalent to calling OwnedRwLockWriteGuard::map(guard, |me| me).

pub fn downgrade(self) -> OwnedRwLockReadGuard<T>

Atomically downgrades a write lock into a read lock without allowing any writers to take exclusive access of the lock in the meantime.

Note: This won’t necessarily allow any additional readers to acquire locks, since RwLock is fair and it is possible that a writer is next in line.

Returns an RAII guard which will drop this read access of the RwLock when dropped.

Examples

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

let n = lock.clone().write_owned().await;

let cloned_lock = lock.clone();
let handle = tokio::spawn(async move {
    *cloned_lock.write_owned().await = 2;
});

let n = n.downgrade();
assert_eq!(*n, 1, "downgrade is atomic");

drop(n);
handle.await.unwrap();
assert_eq!(*lock.read().await, 2, "second writer obtained write lock");

Trait Implementations

impl<T: ?Sized> Debug for OwnedRwLockWriteGuard<T> where
    T: Debug, 

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

Formats the value using the given formatter.

impl<T: ?Sized> Deref for OwnedRwLockWriteGuard<T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<T: ?Sized> DerefMut for OwnedRwLockWriteGuard<T>

fn deref_mut(&mut self) -> &mut T

Mutably dereferences the value.

impl<T: ?Sized> Display for OwnedRwLockWriteGuard<T> where
    T: Display, 

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

Formats the value using the given formatter.

impl<T: ?Sized> Drop for OwnedRwLockWriteGuard<T>

fn drop(&mut self)

Executes the destructor for this type.

impl<T: ?Sized> Send for OwnedRwLockWriteGuard<T> where
    T: Send + Sync, 

impl<T: ?Sized> Sync for OwnedRwLockWriteGuard<T> where
    T: Send + Sync,