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Avoid an allocation on Hashtbl.remove #135

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merged 1 commit into from
Dec 10, 2023
Merged

Avoid an allocation on Hashtbl.remove #135

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39 changes: 18 additions & 21 deletions src/kcas_data/hashtbl.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,6 @@ open Kcas

(** Optimized operations on internal association lists with custom equality. *)
module Assoc = struct
type change = Nop | Removed | Replaced | Added
type ('k, 'v) t = Nil | Cons of { k : 'k; v : 'v; kvs : ('k, 'v) t }

let[@inline] cons k v kvs = Cons { k; v; kvs }
Expand Down Expand Up @@ -44,14 +43,15 @@ module Assoc = struct
| Nil -> false
| Cons r -> equal r.k k' || mem equal k' r.kvs

let[@tail_mod_cons] rec remove equal change k' = function
| Nil -> Nil
exception Not_found

let[@tail_mod_cons] rec remove equal k' = function
| Nil -> raise_notrace Not_found
| Cons r ->
if equal r.k k' then begin
change := Removed;
r.kvs
end
else Cons { k = r.k; v = r.v; kvs = remove equal change k' r.kvs }
if equal r.k k' then r.kvs
else Cons { k = r.k; v = r.v; kvs = remove equal k' r.kvs }

type change = Nop | Replaced | Added

let[@tail_mod_cons] rec replace equal change k' v' = function
| Nil ->
Expand Down Expand Up @@ -338,19 +338,16 @@ module Xt = struct
let buckets = r.buckets in
let mask = Array.length buckets - 1 in
let bucket = Array.unsafe_get buckets (r.hash k land mask) in
let change = ref Assoc.Nop in
Xt.unsafe_modify ~xt bucket (fun kvs ->
let kvs' = Assoc.remove r.equal change k kvs in
if !change != Assoc.Nop then kvs' else kvs);
if !change == Assoc.Removed then begin
Accumulator.Xt.decr ~xt r.length;
if r.min_buckets <= mask && Random.bits () land mask = 0 then
let capacity = mask + 1 in
let length = Accumulator.Xt.get ~xt r.length in
if length * 4 < capacity then
Xt.set ~xt t
{ r with pending = make_rehash capacity (capacity asr 1) }
end
match Xt.unsafe_modify ~xt bucket (Assoc.remove r.equal k) with
| () ->
Accumulator.Xt.decr ~xt r.length;
if r.min_buckets <= mask && Random.bits () land mask = 0 then
let capacity = mask + 1 in
let length = Accumulator.Xt.get ~xt r.length in
if length * 4 < capacity then
Xt.set ~xt t
{ r with pending = make_rehash capacity (capacity asr 1) }
| exception Assoc.Not_found -> ()

let add ~xt t k v =
let r = perform_pending ~xt t in
Expand Down