ocaml-containers/future.mli

(*
Copyright (c) 2013, Simon Cruanes
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*)

(** {1 Futures for concurrency} *)

exception SendTwice
  (** Exception raised when a future is evaluated several time *)

(** {2 MVar: a zero-or-one element thread-safe box} *)

module MVar : sig
  type 'a t

  val empty : unit -> 'a t
    (** Create an empty box *)

  val full : 'a -> 'a t
    (** Create a full box *)

  val is_empty : _ t -> bool
    (** Is the box currently empty? *)

  val take : 'a t -> 'a
    (** Take value out of the box. Wait if necessary *)

  val put : 'a t -> 'a -> unit
    (** Put a value in the box. Waits if the box is already empty *)

  val update : 'a t -> ('a -> 'a * 'b) -> 'b
    (** Use given function to atomically update content, and return a value *)

  val peek : 'a t -> 'a
    (** Look at the value, without removing it *)
end

(** {2 Signature} *)

module type S = sig
  type 'a t
    (** A future value of type 'a *)

  val run : (unit -> unit) -> unit
    (** Use the underlying thread pool to run this job *)

  val finish : unit -> unit
    (** Kill threads in the pool. The pool won't be usable any more. *)

  (** {2 Basic low-level Future functions} *)

  type 'a state =
    | NotKnown
    | Success of 'a
    | Failure of exn

  val state : 'a t -> 'a state
    (** Current state of the future *)

  val is_done : 'a t -> bool
    (** Is the future evaluated (success/failure)? *)

  (** {2 Combinators} *)

  val on_success : 'a t -> ('a -> unit) -> unit
    (** Attach a handler to be called upon success *)

  val on_failure : _ t -> (exn -> unit) -> unit
    (** Attach a handler to be called upon failure *)

  val on_finish : _ t -> (unit -> unit) -> unit
    (** Attach a handler to be called when the future is evaluated *)

  val flatMap : ('a -> 'b t) -> 'a t -> 'b t
    (** Monadic combination of futures *)

  val andThen : 'a t -> (unit -> 'b t) -> 'b t
    (** Wait for the first future to succeed, then launch the second *)

  val sequence : 'a t list -> 'a list t
    (** Future that waits for all previous sequences to terminate *)

  val choose : 'a t list -> 'a t
    (** Choose among those futures (the first to terminate) *)

  val map : ('a -> 'b) -> 'a t -> 'b t
    (** Maps the value inside the future *)

  (** {2 Future constructors} *)

  val return : 'a -> 'a t
    (** Future that is already computed *)

  val spawn : (unit -> 'a) -> 'a t
    (** Spawn a thread that wraps the given computation *)

  val spawn_process : ?stdin:string -> cmd:string ->
                      (int * string * string) t
    (** Spawn a sub-process with the given command [cmd] (and possibly input);
        returns a future containing (returncode, stdout, stderr) *)

  val sleep : float -> unit t
    (** Future that returns with success in the given amount of seconds *)

  (** {2 Event timer} *)

  module Timer : sig
    val at : float -> (unit -> unit) -> unit
      (** [schedule_at ~at act] will run [act] at the Unix echo [at] *)

    val after : float -> (unit -> unit) -> unit
      (** [schedule_after ~after act] will run [act] in [after] seconds *)
  end

  module Infix : sig
    val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
    val (>>) : 'a t -> (unit -> 'b t) -> 'b t
  end

  val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
  val (>>) : 'a t -> (unit -> 'b t) -> 'b t
end

(** {2 Functor} *)

module type CONFIG = sig
  val min_size : int  (** Minimum (initial) number of threads *)
  val max_size : int  (** Maximum number of active threads *)
end

module DefaultConfig : CONFIG

module Make(C : CONFIG) : S

(** Standard (default) pool *)
module Std : S