# Struct std::sync::OnceState

1.51.0 · source ·

    pub struct OnceState { /* private fields */ }

Expand description

State yielded to `Once::call_once_force()`’s closure parameter. The state can be used to query the poison status of the `Once`.

## Implementations§

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### impl OnceState

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#### pub fn is_poisoned(&self) -> bool

Returns `true` if the associated `Once` was poisoned prior to the invocation of the closure passed to `Once::call_once_force()`.

##### Examples

A poisoned `Once`:

    use std::sync::Once;
    use std::thread;

    static INIT: Once = Once::new();

    // poison the once
    let handle = thread::spawn(|| {
        INIT.call_once(|| panic!());
    });
    assert!(handle.join().is_err());

    INIT.call_once_force(|state| {
        assert!(state.is_poisoned());
    });

Run

An unpoisoned `Once`:

    use std::sync::Once;

    static INIT: Once = Once::new();

    INIT.call_once_force(|state| {
        assert!(!state.is_poisoned());
    });

Run

## Trait Implementations§

1.16.0 · source§

### impl Debug for OnceState

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

Formats the value using the given formatter. Read more

## Auto Trait Implementations§

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### impl !RefUnwindSafe for OnceState

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### impl Send for OnceState

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### impl !Sync for OnceState

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### impl Unpin for OnceState

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### impl UnwindSafe for OnceState

## Blanket Implementations§

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### impl<T> Any for Twhere 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 Twhere 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 Twhere 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, U> Into<U> for Twhere 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, U> TryFrom<U> for Twhere 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 Twhere 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.