pub struct LocalKey<T: 'static> { /* private fields */ }
Expand description

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

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;

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());
});

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.

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.

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

Panics

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

Trait Implementations

Formats the value using the given formatter. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

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

The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.