Module Imandrakit_thread.Fut

Future

type 'a or_error = ('a, Moonpool.Exn_bt.t) result
type 'a t = 'a Moonpool.Fut.t

A future with a result of type 'a.

type 'a promise = 'a Moonpool.Fut.promise

A promise, which can be fulfilled exactly once to set the corresponding future

val make : unit -> 'a t * 'a promise

Make a new future with the associated promise.

val on_result : 'a t -> ('a or_error -> unit) -> unit

on_result fut f registers f to be called in the future when fut is set ; or calls f immediately if fut is already set.

exception Already_fulfilled
val fulfill : 'a promise -> 'a or_error -> unit

Fullfill the promise, setting the future at the same time.

val fulfill_idempotent : 'a promise -> 'a or_error -> unit

Fullfill the promise, setting the future at the same time. Does nothing if the promise is already fulfilled.

val return : 'a -> 'a t

Already settled future, with a result

val fail : exn -> Stdlib.Printexc.raw_backtrace -> _ t

Already settled future, with a failure

val fail_exn_bt : Moonpool.Exn_bt.t -> _ t

Fail from a bundle of exception and backtrace

  • since 0.6
val of_result : 'a or_error -> 'a t
val is_resolved : _ t -> bool

is_resolved fut is true iff fut is resolved.

val peek : 'a t -> 'a or_error option

peek fut returns Some r if fut is currently resolved with r, and None if fut is not resolved yet.

exception Not_ready
  • since 0.2
val get_or_fail : 'a t -> 'a or_error

get_or_fail fut obtains the result from fut if it's fulfilled (i.e. if peek fut returns Some res, get_or_fail fut returns res).

  • since 0.2
val get_or_fail_exn : 'a t -> 'a

get_or_fail_exn fut obtains the result from fut if it's fulfilled, like get_or_fail. If the result is an Error _, the exception inside is re-raised.

  • since 0.2
val is_done : _ t -> bool

Is the future resolved? This is the same as peek fut |> Option.is_some.

  • since 0.2
val is_success : _ t -> bool

Checks if the future is resolved with Ok _ as a result.

  • since 0.6
val is_failed : _ t -> bool

Checks if the future is resolved with Error _ as a result.

  • since 0.6
val raise_if_failed : _ t -> unit

raise_if_failed fut raises e if fut failed with e.

  • since 0.6

Combinators

val spawn : on:Moonpool.Runner.t -> (unit -> 'a) -> 'a t

spaw ~on f runs f() on the given runner on, and return a future that will hold its result.

val spawn_on_current_runner : (unit -> 'a) -> 'a t

This must be run from inside a runner, and schedules the new task on it as well.

See Runner.get_current_runner to see how the runner is found.

  • since 0.5
  • raises Failure

    if run from outside a runner.

val map : ?on:Moonpool.Runner.t -> f:('a -> 'b) -> 'a t -> 'b t

map ?on ~f fut returns a new future fut2 that resolves with f x if fut resolved with x; and fails with e if fut fails with e or f x raises e.

  • parameter on

    if provided, f runs on the given runner

val bind : ?on:Moonpool.Runner.t -> f:('a -> 'b t) -> 'a t -> 'b t

bind ?on ~f fut returns a new future fut2 that resolves like the future f x if fut resolved with x; and fails with e if fut fails with e or f x raises e.

  • parameter on

    if provided, f runs on the given runner

val join : 'a t t -> 'a t

join fut is fut >>= Fun.id. It joins the inner layer of the future.

  • since 0.2
val both : 'a t -> 'b t -> ('a * 'b) t

both a b succeeds with x, y if a succeeds with x and b succeeds with y, or fails if any of them fails.

val choose : 'a t -> 'b t -> ('a, 'b) Either.t t

choose a b succeeds Left x or Right y if a succeeds with x or b succeeds with y, or fails if both of them fails. If they both succeed, it is not specified which result is used.

val choose_same : 'a t -> 'a t -> 'a t

choose_same a b succeeds with the value of one of a or b if they succeed, or fails if both fail. If they both succeed, it is not specified which result is used.

val join_array : 'a t array -> 'a array t

Wait for all the futures in the array. Fails if any future fails.

val join_list : 'a t list -> 'a list t

Wait for all the futures in the list. Fails if any future fails.

module Advanced = Moonpool.Fut.Advanced
val map_list : f:('a -> 'b t) -> 'a list -> 'b list t

map_list ~f l is like join_list @@ List.map f l.

  • since 0.5.1
val wait_array : _ t array -> unit t

wait_array arr waits for all futures in arr to resolve. It discards the individual results of futures in arr. It fails if any future fails.

val wait_list : _ t list -> unit t

wait_list l waits for all futures in l to resolve. It discards the individual results of futures in l. It fails if any future fails.

val for_ : on:Moonpool.Runner.t -> int -> (int -> unit) -> unit t

for_ ~on n f runs f 0, f 1, …, f (n-1) on the runner, and returns a future that resolves when all the tasks have resolved, or fails as soon as one task has failed.

val for_array : on:Moonpool.Runner.t -> 'a array -> (int -> 'a -> unit) -> unit t

for_array ~on arr f runs f 0 arr.(0), …, f (n-1) arr.(n-1) in the runner (where n = Array.length arr), and returns a future that resolves when all the tasks are done, or fails if any of them fails.

  • since 0.2
val for_list : on:Moonpool.Runner.t -> 'a list -> ('a -> unit) -> unit t

for_list ~on l f is like for_array ~on (Array.of_list l) f.

  • since 0.2

Await

NOTE This is only available on OCaml 5.

val await : 'a t -> 'a

await fut suspends the current tasks until fut is fulfilled, then resumes the task on this same runner (but possibly on a different thread/domain).

  • since 0.3

This must only be run from inside the runner itself. The runner must support Suspend_. NOTE: only on OCaml 5.x

Blocking

val wait_block : 'a t -> 'a or_error

wait_block fut blocks the current thread until fut is resolved, and returns its value.

NOTE: A word of warning: this will monopolize the calling thread until the future resolves. This can also easily cause deadlocks, if enough threads in a pool call wait_block on futures running on the same pool or a pool depending on it.

A good rule to avoid deadlocks is to run this from outside of any pool, or to have an acyclic order between pools where wait_block is only called from a pool on futures evaluated in a pool that comes lower in the hierarchy. If this rule is broken, it is possible for all threads in a pool to wait for futures that can only make progress on these same threads, hence the deadlock.

val wait_block_exn : 'a t -> 'a

Same as wait_block but re-raises the exception if the future failed.

Infix operators

These combinators run on either the current pool (if present), or on the same thread that just fulfilled the previous future if not.

They were previously present as module Infix_local and val infix, but are now simplified.

module Infix = Moonpool.Fut.Infix
include module type of Infix
  • since 0.5
  • since 0.5
val (>|=) : 'a Moonpool.Fut.t -> ('a -> 'b) -> 'b Moonpool.Fut.t
val (>>=) : 'a Moonpool.Fut.t -> ('a -> 'b Moonpool.Fut.t) -> 'b Moonpool.Fut.t
val let+ : 'a Moonpool.Fut.t -> ('a -> 'b) -> 'b Moonpool.Fut.t
val and+ : 'a Moonpool.Fut.t -> 'b Moonpool.Fut.t -> ('a * 'b) Moonpool.Fut.t
val let* : 'a Moonpool.Fut.t -> ('a -> 'b Moonpool.Fut.t) -> 'b Moonpool.Fut.t
val and* : 'a Moonpool.Fut.t -> 'b Moonpool.Fut.t -> ('a * 'b) Moonpool.Fut.t
module Infix_local = Moonpool.Fut.Infix
type exn_with_bt = exn * Stdlib.Printexc.raw_backtrace

Helpers

val peek_exn : 'a t -> 'a option
val unwrap : ('a, exn_with_bt) result -> 'a

Unwrap result by raising in case of error

val raise_with_bt : exn -> backtrace -> 'a
val map_iter : f:('a -> 'b t) -> 'a Iter.t -> 'b Iter.t t
val map_l : f:('a -> 'b t) -> 'a list -> 'b list t
val protect : finally:(unit -> unit t) -> (unit -> 'a t) -> 'a t
val reify_error : 'a t -> 'a or_error t
val bind_reify_error : ?on:Executor.t -> f:('a or_error -> 'b t) -> 'a t -> 'b t
val wait_vec : (_ t, _) Imandrakit.Vec.t -> unit t

Wait for all futures in the vector to be done

val map_vec_array : ('a t, _) Imandrakit.Vec.t -> 'a array t

Type erasure

type any =
  1. | Any : _ t -> any
val any_is_resolved : any -> bool
val any_is_success : any -> bool
val any_is_failed : any -> bool
val any_raise_if_failed : any -> unit