Module Fiber.Maybe

An unboxed optional fiber.

type t

Either a fiber or nothing.

val nothing : t

Not a fiber.

val of_fiber : fiber -> t

of_fiber fiber casts the fiber into an optional fiber.

🏎️ This performs no allocations.

val to_fiber : t -> fiber

to_fiber casts the optional fiber to a fiber.

  • raises Invalid_argument

    in case the optional fiber is nothing.

val current_if : bool option -> t

current_if checked returns nothing in case checked is Some false and otherwise of_fiber (Fiber.current ()).

val current_and_check_if : bool option -> t

current_check_if checked returns nothing in case checked is Some false and otherwise of_fiber (Fiber.current ()) and also calls Fiber.check on the fiber.

val or_current : t -> t

or_current maybe returns of_fiber (Fiber.current ()) in case maybe is nothing and otherwise returns maybe.

val to_fiber_or_current : t -> fiber

to_fiber_or_current maybe returns Fiber.current () in case maybe is nothing and otherwise returns the fiber that maybe was cast from.

val check : t -> unit

check maybe returns immediately if maybe is nothing and otherwise calls Fiber.check on the fiber.

val equal : t -> t -> bool

equal l r determines whether l and r are maybe equal. Specifically, if either l or r or both is nothing, then they are considered (maybe) equal. Otherwise l and r are compared for physical equality.

val unequal : t -> t -> bool

equal l r determines whether l and r are maybe unequal. Specifically, if either l or r or both is nothing, then they are considered (maybe) unequal. Otherwise l and r are compared for physical equality.

Design rationale

The fiber identity is often needed only for the purpose of dynamically checking against programming errors. Unfortunately it can be relative expensive to obtain the current fiber.

As a data point, in a benchmark that increments an int ref protected by a mutex, obtaining the fiber identity for the lock and unlock operations — that only need it for error checking purposes — roughly tripled the cost of an increment on a machine.

Using GADTs internally allows an optional fiber to be provided without adding overhead to operations on non-optional fibers and allows optional fibers to used without allocations at a very low cost.