# RwLockUpgradableGuard in spin::rw_lock - Rust
A guard that provides immutable data access but can be upgraded to [`RwLockWriteGuard`].
Keywords: rust, rustlang, rust-lang, RwLockUpgradableGuard

# Struct spin::rw_lock::RwLockUpgradableGuard

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

Expand description

A guard that provides immutable data access but can be upgraded to `RwLockWriteGuard`.

No writers or other upgradeable guards can exist while this is in scope. New reader creation is prevented (to alleviate writer starvation) but there may be existing readers when the lock is acquired.

When the guard falls out of scope it will release the lock.

## Implementations

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### impl<'rwlock, T: ?Sized> RwLockUpgradableGuard<'rwlock, T>

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#### pub fn upgrade(self) -> RwLockWriteGuard<'rwlock, T>

Upgrades an upgradeable lock guard to a writable lock guard.

    let mylock = spin::RwLock::new(0);

    let upgradeable = mylock.upgradeable_read(); // Readable, but not yet writable
    let writable = upgradeable.upgrade();

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#### pub fn try_upgrade(self) -> Result<RwLockWriteGuard<'rwlock, T>, Self>

Tries to upgrade an upgradeable lock guard to a writable lock guard.

    let mylock = spin::RwLock::new(0);
    let upgradeable = mylock.upgradeable_read(); // Readable, but not yet writable

    match upgradeable.try_upgrade() {
        Ok(writable) => /* upgrade successful - use writable lock guard */ (),
        Err(upgradeable) => /* upgrade unsuccessful */ (),
    };

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#### pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T>

Downgrades the upgradeable lock guard to a readable, shared lock guard. Cannot fail and is guaranteed not to spin.

    let mylock = spin::RwLock::new(1);

    let upgradeable = mylock.upgradeable_read();
    assert!(mylock.try_read().is_none());
    assert_eq!(*upgradeable, 1);

    let readable = upgradeable.downgrade(); // This is guaranteed not to spin
    assert!(mylock.try_read().is_some());
    assert_eq!(*readable, 1);

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#### pub fn leak(this: Self) -> &'rwlock T

Leak the lock guard, yielding a reference to the underlying data.

Note that this function will permanently lock the original lock.

    let mylock = spin::RwLock::new(0);

    let data: &i32 = spin::RwLockUpgradableGuard::leak(mylock.upgradeable_read());

    assert_eq!(*data, 0);

## Trait Implementations

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### impl<'rwlock, T: ?Sized + Debug> Debug for RwLockUpgradableGuard<'rwlock, T>

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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<'rwlock, T: ?Sized> Deref for RwLockUpgradableGuard<'rwlock, T>

#### type Target = T

The resulting type after dereferencing.

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#### fn deref(&self) -> &T

Dereferences the value.

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### impl<'rwlock, T: ?Sized + Display> Display for RwLockUpgradableGuard<'rwlock, T>

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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<'rwlock, T: ?Sized> Drop for RwLockUpgradableGuard<'rwlock, T>

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#### fn drop(&mut self)

Executes the destructor for this type. Read more

## Auto Trait Implementations

### impl<'a, T> !RefUnwindSafe for RwLockUpgradableGuard<'a, T>

### impl<'a, T: ?Sized> Send for RwLockUpgradableGuard<'a, T> where
T: Send + Sync,

### impl<'a, T: ?Sized> Sync for RwLockUpgradableGuard<'a, T> where
T: Send + Sync,

### impl<'a, T: ?Sized> Unpin for RwLockUpgradableGuard<'a, T>

### impl<'a, T> !UnwindSafe for RwLockUpgradableGuard<'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,

const: unstable · source

#### 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,

const: unstable · source

#### 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

const: unstable · source

#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T where
U: From<T>,

const: unstable · source

#### 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, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### 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>,

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

The type returned in the event of a conversion error.

const: unstable · source

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.