Struct tokio::sync::OwnedRwLockWriteGuard
source · pub struct OwnedRwLockWriteGuard<T: ?Sized> { /* private fields */ }Expand description
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§
source§impl<T: ?Sized> OwnedRwLockWriteGuard<T>
impl<T: ?Sized> OwnedRwLockWriteGuard<T>
sourcepub fn map<F, U: ?Sized>(this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, U>where
F: FnOnce(&mut T) -> &mut U,
pub fn map<F, U: ?Sized>(this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, U>where F: FnOnce(&mut T) -> &mut U,
Makes 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);sourcepub fn downgrade_map<F, U: ?Sized>(
this: Self,
f: F
) -> OwnedRwLockReadGuard<T, U>where
F: FnOnce(&T) -> &U,
pub fn downgrade_map<F, U: ?Sized>( this: Self, f: F ) -> OwnedRwLockReadGuard<T, U>where F: FnOnce(&T) -> &U,
Makes a new OwnedRwLockReadGuard 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::downgrade_map(..). A method would interfere with methods of
the same name on the contents of the locked data.
Inside of f, you retain exclusive access to the data, despite only being given a &T. Handing out a
&mut T would result in unsoundness, as you could use interior mutability.
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 mapped = OwnedRwLockWriteGuard::downgrade_map(guard, |f| &f.0);
let foo = lock.read_owned().await;
assert_eq!(foo.0, *mapped);sourcepub fn try_map<F, U: ?Sized>(
this: Self,
f: F
) -> Result<OwnedRwLockMappedWriteGuard<T, U>, Self>where
F: FnOnce(&mut T) -> Option<&mut U>,
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);sourcepub fn try_downgrade_map<F, U: ?Sized>(
this: Self,
f: F
) -> Result<OwnedRwLockReadGuard<T, U>, Self>where
F: FnOnce(&T) -> Option<&U>,
pub fn try_downgrade_map<F, U: ?Sized>( this: Self, f: F ) -> Result<OwnedRwLockReadGuard<T, U>, Self>where F: FnOnce(&T) -> Option<&U>,
Attempts to make a new OwnedRwLockReadGuard 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_downgrade_map(...). A method would interfere with
methods of the same name on the contents of the locked data.
Inside of f, you retain exclusive access to the data, despite only being given a &T. Handing out a
&mut T would result in unsoundness, as you could use interior mutability.
If this function returns Err(...), the lock is never unlocked nor downgraded.
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 guard = OwnedRwLockWriteGuard::try_downgrade_map(guard, |f| Some(&f.0)).expect("should not fail");
let foo = lock.read_owned().await;
assert_eq!(foo.0, *guard);sourcepub fn into_mapped(this: Self) -> OwnedRwLockMappedWriteGuard<T>
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).
sourcepub fn downgrade(self) -> OwnedRwLockReadGuard<T>
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");