moonpool 0.2 · OCaml Package

Thread pool.

type t

A pool of threads. The pool contains a fixed number of threads that wait for work items to come, process these, and loop.

If a pool is no longer needed, shutdown can be used to signal all 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).

type thread_loop_wrapper =
  thread:Thread.t ->
  pool:t ->
  (unit -> unit) ->
  unit ->
  unit

A thread wrapper f takes the current thread, the current pool, and the worker function loop : unit -> unit which is the worker's main loop, and returns a new loop function. By default it just returns the same loop function but it can be used to install tracing, effect handlers, etc.

val add_global_thread_loop_wrapper : thread_loop_wrapper -> unit

add_global_thread_loop_wrapper f installs f to be installed in every new pool worker thread, for all existing pools, and all new pools created with create. These wrappers accumulate: they all apply, but their order is not specified.

val create : 
  ?on_init_thread:(dom_id:int -> t_id:int -> unit -> unit) ->
  ?on_exit_thread:(dom_id:int -> t_id:int -> unit -> unit) ->
  ?thread_wrappers:thread_loop_wrapper list ->
  ?on_exn:(exn -> Printexc.raw_backtrace -> unit) ->
  ?around_task:((t -> 'a) * (t -> 'a -> unit)) ->
  ?min:int ->
  ?per_domain:int ->
  unit ->
  t

create () makes a new thread pool.

parameter on_init_thread
called at the beginning of each new thread in the pool.

parameter min
minimum size of the pool. It will be at least 1 internally, so 0 or negative values make no sense.

parameter per_domain
is the number of threads allocated per domain in the fixed domain pool. The default value is 0, but setting, say, ~per_domain:2 means that if there are 8 domains (which might be the case on an 8-core machine) then the minimum size of the pool is 16. If both min and per_domain are specified, the maximum of both min and per_domain * num_of_domains is used.

parameter on_exit_thread
called at the end of each thread in the pool

parameter thread_wrappers
a list of thread_loop_wrapper functions to use for this pool's workers.

parameter around_task
a pair of before, after, where before pool is called before a task is processed, on the worker thread about to run it, and returns x; and after pool x is called by the same thread after the task is over. (since 0.2)

val size : t -> int

Number of threads

val num_tasks : t -> int

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

since 0.2

val shutdown : t -> unit

Shutdown the pool 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.

since 0.2

exception Shutdown

val run : t -> (unit -> unit) -> unit

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

raises Shutdown
if the pool was shut down before run was called.

package moonpool