Struct `LocalKey`

struct LocalKey<T: 'static> { ... }

A key for task-local data.

This type is generated by the task_local! macro.

Unlike std::thread::LocalKey, tokio::task::LocalKey will not lazily initialize the value on first access. Instead, the value is first initialized when the future containing the task-local is first polled by a futures executor, like Tokio.

Examples

# async fn dox() {
tokio::task_local! {
    static NUMBER: u32;
}

NUMBER.scope(1, async move {
    assert_eq!(NUMBER.get(), 1);
}).await;

NUMBER.scope(2, async move {
    assert_eq!(NUMBER.get(), 2);

    NUMBER.scope(3, async move {
        assert_eq!(NUMBER.get(), 3);
    }).await;
}).await;
# }

Implementations

`impl<T: 'static> LocalKey<T>`

fn scope<F>(self: &'static Self, value: T, f: F) -> TaskLocalFuture<T, F> where F: Future

Sets a value T as the task-local value for the future F.

On completion of scope, the task-local will be dropped.

Panics

If you poll the returned future inside a call to with or try_with on the same LocalKey, then the call to poll will panic.

Examples

# async fn dox() {
tokio::task_local! {
    static NUMBER: u32;
}

NUMBER.scope(1, async move {
    println!("task local value: {}", NUMBER.get());
}).await;
# }

fn sync_scope<F, R>(self: &'static Self, value: T, f: F) -> R where F: FnOnce() -> R

Sets a value T as the task-local value for the closure F.

On completion of sync_scope, the task-local will be dropped.

Panics

This method panics if called inside a call to with or try_with on the same LocalKey.

Examples

# async fn dox() {
tokio::task_local! {
    static NUMBER: u32;
}

NUMBER.sync_scope(1, || {
    println!("task local value: {}", NUMBER.get());
});
# }

fn with<F, R>(self: &'static Self, f: F) -> R where F: FnOnce(&T) -> R

Accesses the current task-local and runs the provided closure.

Panics

This function will panic if the task local doesn't have a value set.

fn try_with<F, R>(self: &'static Self, f: F) -> Result<R, AccessError> where F: FnOnce(&T) -> R

Accesses the current task-local and runs the provided closure.

If the task-local with the associated key is not present, this method will return an AccessError. For a panicking variant, see with.

`impl<T: Clone + 'static> LocalKey<T>`

fn get(self: &'static Self) -> T

Returns a copy of the task-local value if the task-local value implements Clone.

Panics

This function will panic if the task local doesn't have a value set.

`impl<T> Any for LocalKey<T>`

fn type_id(self: &Self) -> TypeId

`impl<T> Borrow for LocalKey<T>`

fn borrow(self: &Self) -> &T

`impl<T> BorrowMut for LocalKey<T>`

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

`impl<T> Freeze for LocalKey<T>`

`impl<T> From for LocalKey<T>`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T> RefUnwindSafe for LocalKey<T>`

`impl<T> Send for LocalKey<T>`

`impl<T> Sync for LocalKey<T>`

`impl<T> Unpin for LocalKey<T>`

`impl<T> UnsafeUnpin for LocalKey<T>`

`impl<T> UnwindSafe for LocalKey<T>`

`impl<T, U> Into for LocalKey<T>`

fn into(self: Self) -> U

Calls U::from(self).

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

`impl<T, U> TryFrom for LocalKey<T>`

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

`impl<T, U> TryInto for LocalKey<T>`

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

`impl<T: 'static> Debug for LocalKey<T>`

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