Delayed evaluation.
This is like Stdlib.Lazy, but multiple fibers or domains can force at once.
val from_fun : cancel:[ `Restart | `Record | `Protect ] -> (unit -> 'a) -> 'a tfrom_fun ~cancel fn is a lazy value that runs fn () the first time it is forced.
cancel determines how cancellation is handled while forcing:
`Restart : if the forcing fiber is cancelled, the next waiting fiber runs fn again.`Record : the failure is recorded and the lazy value will always report cancelled if used.`Protect : the forcing fiber is protected from cancellation while running.val from_val : 'a -> 'a tfrom_val v is a lazy value that is already forced.
It is equivalent to from_fun (fun () -> v).
val force : 'a t -> 'aforce t returns the result of running the function passed to from_fun.
If the function is currently running, this waits for it to finish and then retries. If the function has already completed then it returns the saved result. If the function returned an exception then force re-raises it.