feat apool: add init_size option for create

Author: c-cube

src/core/apool.ml

@@ -11,22 +11,33 @@ type 'a t = {
   items: 'a list_ A.t;
 }
 
-let create ?(clear = ignore) ~mk_item ?(max_size = 512) () : _ t =
-  { mk_item; clear; max_size; items = A.make Nil }
+let[@inline] size_ = function
+  | Cons (sz, _, _) -> sz
+  | Nil -> 0
+
+let create ?(clear = ignore) ~mk_item ?(init_size = 0) ?(max_size = 512) () :
+    _ t =
+  let@ _sp = Trace.with_span ~__FILE__ ~__LINE__ "apool.create" in
+  if max_size < init_size then invalid_arg "apool: max_size < init_size";
+  let items = ref Nil in
+  for _i = 0 to init_size - 1 do
+    let@ _sp = Trace.with_span ~__FILE__ ~__LINE__ "apool.create.mk-item" in
+    let item = mk_item () in
+    items := Cons (size_ !items + 1, item, !items)
+  done;
+  { mk_item; clear; max_size; items = A.make !items }
 
 let rec acquire_ self =
   match A.get self.items with
-  | Nil -> self.mk_item ()
+  | Nil ->
+    let@ _sp = Trace.with_span ~__FILE__ ~__LINE__ "apool.acquire.mk-item" in
+    self.mk_item ()
   | Cons (_, x, tl) as l ->
     if A.compare_and_set self.items l tl then
       x
     else
       acquire_ self
 
-let[@inline] size_ = function
-  | Cons (sz, _, _) -> sz
-  | Nil -> 0
-
 let release_ self x : unit =
   self.clear x;
   while

src/core/apool.mli

@@ -9,11 +9,17 @@ type 'a t
 (** Pool of values of type ['a] *)
 
 val create :
-  ?clear:('a -> unit) -> mk_item:(unit -> 'a) -> ?max_size:int -> unit -> 'a t
+  ?clear:('a -> unit) ->
+  mk_item:(unit -> 'a) ->
+  ?init_size:int ->
+  ?max_size:int ->
+  unit ->
+  'a t
 (** Create a new pool.
     @param mk_item produce a new item in case the pool is empty
     @param max_size maximum number of item in the pool before we start
       dropping resources on the floor. This controls resource consumption.
+    @param init_size initial number of items to create (default 0). This must be <= max_size.
     @param clear a function called on items before recycling them.
  *)