Struct futures::task::LocalKey

pub struct LocalKey<T> { /* fields omitted */ }

A key for task-local data stored in a future’s task.

This type is generated by the task_local! macro and performs very similarly to the thread_local! macro and std::thread::LocalKey types. Data associated with a LocalKey<T> is stored inside of a future’s task, and the data is destroyed when the future is completed and the task is destroyed.

Task-local data can migrate between threads and hence requires a Send bound. Additionally, task-local data also requires the 'static bound to ensure it lives long enough. When a key is accessed for the first time the task’s data is initialized with the provided initialization expression to the macro.

Implementations

impl<T: Send + 'static> LocalKey<T>

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

Access this task-local key, running the provided closure with a reference to the value.

This function will access this task-local key to retrieve the data associated with the current task and this key. If this is the first time this key has been accessed on this task, then the key will be initialized with the initialization expression provided at the time the task_local! macro was called.

The provided closure will be provided a shared reference to the underlying data associated with this task-local-key. The data itself is stored inside of the current task.

Panics

This function can possibly panic for a number of reasons:

• If there is not a current task.
• If the initialization expression is run and it panics
• If the closure provided panics

Trait Implementations

impl<T: Debug> Debug for LocalKey<T>

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

Formats the value using the given formatter.