Module Moonpool.Immediate_runner

Runner that runs tasks immediately in the caller thread.

Whenever a task is submitted to this runner via Runner.run_async r task, the task is run immediately in the caller thread as task(). There are no background threads, no resource, this is just a trivial implementation of the interface.

This can be useful when an implementation needs a runner, but there isn't enough work to justify starting an actual full thread pool.

Another situation is when threads cannot be used at all (e.g. because you plan to call Unix.fork later).

include module type of Runner
type task = unit -> unit
type t

A runner.

If a runner is no longer needed, shutdown can be used to signal all worker threads in it to stop (after they finish their work), and wait for them to stop.

The threads are distributed across a fixed domain pool (whose size is determined by Domain.recommended_domain_count on OCaml 5, and simple the single runtime on OCaml 4).

val size : t -> int

Number of threads/workers.

val num_tasks : t -> int

Current number of tasks. This is at best a snapshot, useful for metrics and debugging.

val shutdown : t -> unit

Shutdown the runner and wait for it to terminate. Idempotent.

val shutdown_without_waiting : t -> unit

Shutdown the pool, and do not wait for it to terminate. Idempotent.

exception Shutdown
val run_async : t -> task -> unit

run_async pool f schedules f for later execution on the runner in one of the threads. f() will run on one of the runner's worker threads/domains.

  • raises Shutdown

    if the runner was shut down before run_async was called.

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

run_wait_block pool f schedules f for later execution on the pool, like run_async. It then blocks the current thread until f() is done executing, and returns its result. If f() raises an exception, then run_wait_block pool f will raise it as well.

NOTE be careful with deadlocks (see notes in Fut.wait_block about the required discipline to avoid deadlocks).

module For_runner_implementors : sig ... end

This module is specifically intended for users who implement their own runners. Regular users of Moonpool should not need to look at it.

val get_current_runner : unit -> t option

Access the current runner. This returns Some r if the call happens on a thread that belongs in a runner.

  • since 0.5
val runner : t

The trivial runner that actually runs tasks at the calling point.