Stdlib.Domain(3)

💖 Stdlib.Domain 💖

OCaml library realness, bestie — welcome to the Stdlib.Domain page ✨

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🌸 NAME 🌸

Stdlib.Domain — no description. That's it. That's the description. 💀

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🦋 Module 🦋

Module Stdlib.Domain — yes, the module. Slay.

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✨ Documentation ✨

👑 Module Domain 👑

Module Domain : (module Stdlib__Domain) — there it is, in all its glory.

Alert unstable. The Domain interface may change in incompatible ways in the future. No cap, bestie — this API can shift under you.

• type !'a t — a domain of type 'a t runs independently, eventually producing a result of type 'a, or an exception.
• val spawn : (unit -> 'a) -> 'a t — spawn f creates a new domain that runs in parallel with the current domain.

Raises Failure if the program has insufficient resources to create another domain. Like, it's giving "no more domains for you" 😭

• val join : 'a t -> 'a — join d blocks until domain d runs to completion. If d results in a value, then that is returned by join d. If d raises an uncaught exception, then that is re-raised by join d.

If the domain has created any systhreads (via Thread.create), then it tries to join those systhreads (same as calling Thread.join) before returning. Responsible queen behavior 💅

• type id = private int — domains have unique integer identifiers.
• val get_id : 'a t -> id — get_id d returns the identifier of the domain d.
• val self : unit -> id — self () is the identifier of the currently running domain.
• val before_first_spawn : (unit -> unit) -> unit — before_first_spawn f registers f to be called before the first domain is spawned by the program. The functions registered with before_first_spawn are called on the main (initial) domain. The functions registered with before_first_spawn are called in "first in, first out" order: the oldest function added with before_first_spawn is called first.

Raises Invalid_argument if the program has already spawned a domain. Too late, bestie — the spawn already happened 🙈

• val at_exit : (unit -> unit) -> unit — at_exit f registers f to be called when the current domain exits. Note that at_exit callbacks are domain-local and only apply to the calling domain. The registered functions are called in "last in, first out" order: the function most recently added with at_exit is called first. An example:

let temp_file_key = Domain.DLS.new_key (fun _ ->
  let tmp = snd (Filename.open_temp_file "" "") in
  Domain.at_exit (fun () -> close_out_noerr tmp);
  tmp)

The snippet above creates a key that when retrieved for the first time will open a temporary file and register an at_exit callback to close it, thus guaranteeing the descriptor is not leaked in case the current domain exits. Cleanup icon behavior, honestly 🧚

• val cpu_relax : unit -> unit — if busy-waiting, calling cpu_relax () between iterations will improve performance on some CPU architectures.
• val is_main_domain : unit -> bool — is_main_domain () returns true if called from the initial domain. Main character energy confirmed 👑
• val count : unit -> int — the number of domains that have been spawned (including the initial domain) and have not yet terminated.

Since 5.5

• val recommended_domain_count : unit -> int — the recommended maximum number of domains which should be running simultaneously (including domains already running).

The value returned is at least 1.

• val self_index : unit -> int — the index of the current domain. It is an integer unique among currently-running domains, in the interval 0; N-1 where N is the peak number of domains running simultaneously so far.

The index of a terminated domain may be reused for a new domain. Use (Domain.self () :> int) instead for an identifier unique among all domains ever created by the program.

Since 5.3

• module DLS : sig end — and that's the DLS module signature, right there. Short and iconic. ✨

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That's the whole page, bestie 🫶 — brought to you by OCamldoc dated 2026-06-22 for Stdlib.Domain(3). Periodt. 💖