Resource Pool🔗ℹ

This module provides a generic blocking resource pool implementation. Useful for managing things such as database and HTTP connections. Resource pools are both thread-safe and kill-safe.

procedure
(pool? v) → boolean?
  v : any/c
procedure
(make-pool make-resource
[ destroy-resource
#:max-size max-size
#:idle-ttl idle-ttl]) → pool?
  make-resource : (-> any/c)
  destroy-resource : (-> any/c void?) = void
  max-size : exact-positive-integer? = 8
   idle-ttl : (or/c +inf.0 exact-positive-integer?)
= (* 3600 1000)

The make-pool procedure returns a new resource pool that lazily creates new resources using make-resource. The resulting pool can contain up to #:max-size resources. The make-resource procedure must not raise an exception.

The #:idle-ttl argument controls how long a resource can remain idle before destroy-resource is applied to it and it is removed from the pool.

procedure
(call-with-pool-resource p
proc
#:timeout timeout) → any/c
  p : pool?
  proc : (-> any/c any)
  timeout : (or/c #f exact-nonnegative-integer?)

Leases a resource from p and applies proc to it, returning the leased value back into the pool once proc finishes executing.

The #:timeout behaves the same as in pool-take!, except that if the timeout is hit, an exn:fail:pool? is raised and #f is not executed.

procedure
(pool-take! p [timeout]) → (or/c #f any/c)
p : pool?
timeout : (or/c #f exact-nonnegative-integer?) = #f

Waits for a resource to become available and then leases it from p. If the timeout argument is provided, the pool-take! will block for at most timeout milliseconds before returning. On timeout, #f is returned.

procedure
(pool-take!-evt p) → evt?
p : pool?

Returns a synchronizable event that is ready for synchronization when a pool resource becomes available.

Added in version 0.3 of package resource-pool-lib.

procedure
(pool-release! p v) → void?
p : pool?
v : any/c

Releases v back into p. If v was not leased from p, then an exn:fail:pool? error is raised.

procedure
(pool-close! p) → void?
p : pool?

Closes p. If pool-close is called before all of the leased resources have been returned to the pool, an exn:fail:pool? error is raised and the pool remains open.

Raises an exception if p has already been closed.

procedure
(exn:fail:pool? v) → boolean?
v : any/c

Returns #t when v is a resource pool error.