completable
A [Future] value that resolves once it's explicitly completed, potentially
from a different thread or task, similar to Java's CompletableFuture.
Currently, this is implemented using [Mutex][parking_lot::Mutex] from the [parking_lot] crate.
Examples
Create an incomplete [ControlledFuture] and explicitly complete it with the
completer:
let = new;
completer.complete.unwrap;
assert_eq!;
Create an initially complete [ControlledFuture] that can be immediately
resolved:
assert_eq!;