Struct GuardUsable

pub struct GuardUsable {
    u: Option<Receiver<bool>>,
}

A future used to see if we have “permission” to use a guard.

For efficiency, the GuardMgr implementation sometimes gives out lower-priority guards when it is not certain whether higher-priority guards are running. After having built a circuit with such a guard, the caller must wait on this future to see whether the circuit is usable or not.

The circuit may be usable immediately (as happens if the guard was of sufficient priority, or if all higher-priority guards are known to be down). It may eventually become usable (if all of the higher-priority guards are discovered to be down). Or it may eventually become unusable (if we find a higher-priority guard that works).

Any GuardRestrictions that were used to select this guard may influence whether it is usable: if higher priority guards were ignored because of a restriction, then we might use a guard that we otherwise wouldn’t.

Fields

u: Option<Receiver<bool>>

If present, then this is a future to wait on to see whether the guard is usable.

If absent, then the guard is ready immediately and no waiting is needed.

Implementations

impl GuardUsable

pub(crate) fn project<'pin>( self: Pin<&'pin mut Self>, ) -> __GuardUsableProjection<'pin>

pub(crate) fn project_ref<'pin>( self: Pin<&'pin Self>, ) -> __GuardUsableProjectionRef<'pin>

impl GuardUsable

pub(crate) fn new_usable_immediately() -> Self

Create a new GuardUsable for a primary guard or a fallback directory.

(Circuits built through these are usable immediately, independently of whether other guards succeed or fail, so we don’t need a way to report whether such guards/fallbacks are usable.)

pub(crate) fn new_uncertain() -> (Self, Sender<bool>)

Create a new GuardUsable for a guard with undecided usability status.

(We use this constructor when a circuit is built through a non-primary guard, and there are other guards we would prefer to use, if they turn out to work. If such a circuit succeeds, the caller must still use this GuardUsable to wait until the GuardMgr sees whether the more-preferred guards have succeeded or failed.)

Trait Implementations

impl Future for GuardUsable

type Output = Result<bool, Canceled>

The type of value produced on completion.

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>

Attempts to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.

impl<'pin> Unpin for GuardUsable

where PinnedFieldsOf<__GuardUsable<'pin>>: Unpin,