Module Eio.Promise Source A promise is a placeholder for result that will arrive in the future.
Unlike lazy values, you cannot "force" promises; a promise is resolved when the maker of the promise is ready.
Promises are thread-safe and so can be shared between domains and used to communicate between them.
Example:
let promise, resolver = Promise.create () in
Fiber.both
(fun () -> traceln "Got %d" (Promise.await promise))
(fun () -> Promise.resolve resolver 42)An 'a t is a promise for a value of type 'a.
An 'a u is a resolver for a promise of type 'a.
Source val create : ?label :string -> unit -> 'a t 'a u create () is a fresh promise/resolver pair. The promise is initially unresolved.
Source val create_resolved : 'a -> 'a t create_resolved x is a promise that is already resolved with result x.
await t blocks until t is resolved. If t is already resolved then this returns immediately.
Source val resolve : 'a u -> 'a -> resolve u v resolves u's promise with the value v. Any threads waiting for the result will be added to the run queue.
peek t is Some v if the promise has been resolved to v, or None otherwise. If the result is None then it may change in future, otherwise it won't. If another domain has access to the resolver then the state may have already changed by the time this call returns.
Source val is_resolved : 'a t -> is_resolved t is Option.is_some (peek t).
resolve_ok u x is resolve u (Ok x).
resolve_error u x is resolve u (Error x).
await_exn t is like await t, but if the result is Error ex then it raises ex.