Struct tokio::sync::RwLockMappedWriteGuard

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pub struct RwLockMappedWriteGuard<'a, T: ?Sized> { /* private fields */ }

Expand description

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

This structure is created by mapping an RwLockWriteGuard. It is a separate type from RwLockWriteGuard to disallow downgrading a mapped guard, since doing so can cause undefined behavior.

Implementations§

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impl<'a, T: ?Sized> RwLockMappedWriteGuard<'a, T>

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pub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockMappedWriteGuard<'a, U>
where F: FnOnce(&mut T) -> &mut U,

Makes a new RwLockMappedWriteGuard for a component of the locked data.

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

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

This is an asynchronous version of RwLockWriteGuard::map from the parking_lot crate.

§Examples

use tokio::sync::{RwLock, RwLockWriteGuard};

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

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

{
    let mut mapped = RwLockWriteGuard::map(lock.write().await, |f| &mut f.0);
    *mapped = 2;
}

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

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pub fn try_map<F, U: ?Sized>( this: Self, f: F, ) -> Result<RwLockMappedWriteGuard<'a, U>, Self>
where F: FnOnce(&mut T) -> Option<&mut U>,

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

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

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

This is an asynchronous version of RwLockWriteGuard::try_map from the parking_lot crate.

§Examples

use tokio::sync::{RwLock, RwLockWriteGuard};

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

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

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

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