Struct tokio::sync::RwLockWriteGuard

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pub struct RwLockWriteGuard<'a, T: ?Sized> { /* private fields */ }
Available on crate feature sync only.
Expand description

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

This structure is created by the write method on RwLock.

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impl<'a, T: ?Sized> RwLockWriteGuard<'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 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);
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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);
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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 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);
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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);
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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).

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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");

Trait Implementations§

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impl<'a, T> Debug for RwLockWriteGuard<'a, T>
where T: Debug + ?Sized,

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

Formats the value using the given formatter. Read more
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impl<T: ?Sized> Deref for RwLockWriteGuard<'_, T>

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type Target = T

The resulting type after dereferencing.
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fn deref(&self) -> &T

Dereferences the value.
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impl<T: ?Sized> DerefMut for RwLockWriteGuard<'_, T>

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

Mutably dereferences the value.
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impl<'a, T> Display for RwLockWriteGuard<'a, T>
where T: Display + ?Sized,

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

Formats the value using the given formatter. Read more
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impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T>

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fn drop(&mut self)

Executes the destructor for this type. Read more
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impl<T> Send for RwLockWriteGuard<'_, T>
where T: ?Sized + Send + Sync,

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impl<T> Sync for RwLockWriteGuard<'_, T>
where T: ?Sized + Send + Sync,

Auto Trait Implementations§

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impl<'a, T> Freeze for RwLockWriteGuard<'a, T>
where T: ?Sized,

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impl<'a, T> !RefUnwindSafe for RwLockWriteGuard<'a, T>

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impl<'a, T> Unpin for RwLockWriteGuard<'a, T>
where T: ?Sized,

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impl<'a, T> !UnwindSafe for RwLockWriteGuard<'a, T>

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToString for T
where T: Display + ?Sized,

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default fn to_string(&self) -> String

Converts the given value to a String. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more