Module Eio.Pool

A pool of resources.

This is useful to manage a collection of resources where creating new ones is expensive and so you want to reuse them where possible.


let buffer_pool = Eio.Pool.create 10 (fun () -> Bytes.create 1024) in
Eio.Pool.use buffer_pool (fun buf -> ...)

Note: If you just need to limit how many resources are in use, it is simpler to use Eio.Semaphore instead.

type 'a t
val create : ?validate:('a -> bool) -> ?dispose:('a -> unit) -> int -> (unit -> 'a) -> 'a t

create n alloc is a fresh pool which allows up to n resources to be live at a time. It uses alloc to create new resources as needed. If alloc raises an exception then that use fails, but future calls to use will retry.

The alloc function is called in the context of the fiber trying to use the pool.

You should take care about handling cancellation in alloc, since resources are typically attached to a switch with the lifetime of the pool, meaning that if alloc fails then they won't be freed automatically until the pool itself is finished.

  • parameter validate

    If given, this is used to check each resource before using it. If it returns false, the pool removes it with dispose and then allocates a fresh resource.

  • parameter dispose

    Used to free resources rejected by validate. If it raises, the exception is passed on to the user, but resource is still considered to have been disposed.

val use : 'a t -> ?never_block:bool -> ('a -> 'b) -> 'b

use t fn waits for some resource x to be available and then runs f x. Afterwards (on success or error), x is returned to the pool.

  • parameter never_block

    If true and the pool has reached maximum capacity, then a fresh resource is created to ensure that this use call does not wait for a resource to become available. This resource is immediately disposed after f x returns.