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§
source§impl<T: 'static> LocalKey<T>
impl<T: 'static> LocalKey<T>
sourcepub fn scope<F>(&'static self, value: T, f: F) -> TaskLocalFuture<T, F> ⓘwhere
F: Future,
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;
sourcepub fn sync_scope<F, R>(&'static self, value: T, f: F) -> Rwhere
F: FnOnce() -> R,
pub fn sync_scope<F, R>(&'static self, value: T, f: F) -> Rwhere
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());
});