Struct tokio::sync::RwLockWriteGuard
source · pub struct RwLockWriteGuard<'a, T: ?Sized> { /* private fields */ }
sync
only.Expand description
Implementations§
source§impl<'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>
pub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockMappedWriteGuard<'a, 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>
pub fn downgrade_map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, 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>
pub fn try_map<F, U: ?Sized>( this: Self, f: F, ) -> Result<RwLockMappedWriteGuard<'a, U>, Self>
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>
pub fn try_downgrade_map<F, U: ?Sized>( this: Self, f: F, ) -> Result<RwLockReadGuard<'a, U>, Self>
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");