Struct tokio::sync::RwLockWriteGuard
source · [−]pub struct RwLockWriteGuard<'a, T: ?Sized> { /* private fields */ }Expand description
Implementations
sourceimpl<'a, T: ?Sized> RwLockWriteGuard<'a, T>
impl<'a, T: ?Sized> RwLockWriteGuard<'a, T>
sourcepub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockMappedWriteGuard<'a, U>where
F: FnOnce(&mut T) -> &mut U,
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 RwLockWriteGuard passed in already
locked the data.
This is an associated function that needs to be used as
RwLockWriteGuard::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);sourcepub fn downgrade_map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, U>where
F: FnOnce(&T) -> &U,
pub fn downgrade_map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, U>where
F: FnOnce(&T) -> &U,
Makes a new RwLockReadGuard for a component of the locked data.
This operation cannot fail as the RwLockWriteGuard passed in already
locked the data.
This is an associated function that needs to be used as
RwLockWriteGuard::downgrade_map(..). A method would interfere with methods of
the same name on the contents of the locked data.
This is equivalent to a combination of asynchronous RwLockWriteGuard::map and RwLockWriteGuard::downgrade
from the parking_lot crate.
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 tokio::sync::{RwLock, RwLockWriteGuard};
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Foo(u32);
let lock = RwLock::new(Foo(1));
let mapped = RwLockWriteGuard::downgrade_map(lock.write().await, |f| &f.0);
let foo = lock.read().await;
assert_eq!(foo.0, *mapped);sourcepub fn try_map<F, U: ?Sized>(
this: Self,
f: F
) -> Result<RwLockMappedWriteGuard<'a, U>, Self>where
F: FnOnce(&mut T) -> Option<&mut U>,
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 RwLockWriteGuard passed in already
locked the data.
This is an associated function that needs to be
used as RwLockWriteGuard::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);sourcepub fn try_downgrade_map<F, U: ?Sized>(
this: Self,
f: F
) -> Result<RwLockReadGuard<'a, U>, Self>where
F: FnOnce(&T) -> Option<&U>,
pub fn try_downgrade_map<F, U: ?Sized>(
this: Self,
f: F
) -> Result<RwLockReadGuard<'a, U>, Self>where
F: FnOnce(&T) -> Option<&U>,
Attempts to make a new RwLockReadGuard for a component of
the locked data. The original guard is returned if the closure returns
None.
This operation cannot fail as the RwLockWriteGuard passed in already
locked the data.
This is an associated function that needs to be
used as RwLockWriteGuard::try_downgrade_map(...). A method would interfere with
methods of the same name on the contents of the locked data.
This is equivalent to a combination of asynchronous RwLockWriteGuard::try_map and RwLockWriteGuard::downgrade
from the parking_lot crate.
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 tokio::sync::{RwLock, RwLockWriteGuard};
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct Foo(u32);
let lock = RwLock::new(Foo(1));
let guard = RwLockWriteGuard::try_downgrade_map(lock.write().await, |f| Some(&f.0)).expect("should not fail");
let foo = lock.read().await;
assert_eq!(foo.0, *guard);sourcepub fn into_mapped(this: Self) -> RwLockMappedWriteGuard<'a, T>
pub fn into_mapped(this: Self) -> RwLockMappedWriteGuard<'a, T>
Converts this RwLockWriteGuard into an RwLockMappedWriteGuard. 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 RwLockWriteGuard::map(guard, |me| me).
sourcepub fn downgrade(self) -> RwLockReadGuard<'a, T>
pub fn downgrade(self) -> RwLockReadGuard<'a, 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.write().await;
let cloned_lock = lock.clone();
let handle = tokio::spawn(async move {
*cloned_lock.write().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");