Struct LocalKey

pub struct LocalKey<T>
where
    T: 'static,
{ /* private fields */ }

Available on crate features dep_tokio and std only.

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

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> LocalKey<T>

where T: 'static,

pub fn scope<F>(&'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

tokio::task_local! {
    static NUMBER: u32;
}

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

pub fn sync_scope<F, R>(&'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

tokio::task_local! {
    static NUMBER: u32;
}

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

pub fn with<F, R>(&'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.

pub fn try_with<F, R>(&'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> LocalKey<T>

where T: Clone + 'static,

pub fn get(&'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.

Trait Implementations

impl<T> Debug for LocalKey<T>

where T: 'static,

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

Formats the value using the given formatter.