cache.ml

open Prelude

module StdHashtbl = Hashtbl

open ExtLib
open Printf

module type Lock = sig
  type t
  val create : unit -> t
  val locked : t -> (unit -> 'a) -> 'a
end

module NoLock = struct
  type t = unit
  let create () = ()
  let locked () f = f ()
end

module TimeLimited2(E: Set.OrderedType)
  (Lock: sig type t val create : unit -> t val locked : t -> (unit -> 'a) -> 'a end) = struct

  type time = Int64.t

  let fixed f = 10000. *. f |> Int64.of_float
  let current () = Unix.gettimeofday () |> fixed

  module Value = struct
    type t = E.t * time
    let compare (v1,_) (v2,_) = E.compare v1 v2
  end

  module M = Set.Make(Value)

  type t = { limit : time; mutable next : time; lock : Lock.t; mutable m : M.t; }

  let private_purge t =
    let cur = current () in
    if cur >= t.next then
    begin
      t.next <- Int64.add t.limit cur;
      t.m <- M.filter (fun (_,t) -> t > cur) t.m
    end

  let create limit = { limit = fixed limit; next = 0L; lock = Lock.create (); m = M.empty }

  let add t x =
    let expire = Int64.add t.limit (current ()) in
    (* FIXME replace not add *)
    Lock.locked t.lock (fun () -> private_purge t; t.m <- M.add (x, expire) t.m)

  let get t v =
    (* lock is not needed *)
    Lock.locked t.lock (fun () -> M.find_opt (v, t.limit) t.m)

  let count t = Lock.locked t.lock (fun () -> M.cardinal t.m)

  let iter t f = Lock.locked t.lock (fun () -> M.iter (fun (x,_) -> f x) t.m)

end

module Count = struct
  open Hashtbl
  type 'a t = ('a, int ref) Hashtbl.t
  let create () : 'a t = create 16
  let clear = Hashtbl.clear
  let entry t x = match find t x with r -> r | exception Not_found -> let r = ref 0 in Hashtbl.add t x r; r
  let plus t x n = entry t x += n
  let minus t x n = entry t x -= n
  let of_enum e = let h = create () in Enum.iter (fun (k,n) -> plus h k n) e; h
  let of_list l = of_enum @@ List.enum l
  let add t x = plus t x 1
  let del t x = minus t x 1
  let enum t = enum t |> Enum.map (fun (k,n) -> k, !n)
  let iter t f = iter (fun k n -> f k !n) t
  let fold t f acc = Hashtbl.fold (fun k n acc -> f k !n acc) t acc
  let count t k = match Hashtbl.find t k with n -> !n | exception Not_found -> 0
  let count_all t = Hashtbl.fold (fun _ n acc -> acc + !n) t 0
  let size = Hashtbl.length
  let show t ?(sep=" ") f = enum t |>
    List.of_enum |> List.sort ~cmp:(Action.compare_by fst) |>
    List.map (fun (x,n) -> sprintf "%S: %u" (f x) n) |>
    String.concat sep
  let show_sorted t ?limit ?(sep="\n") f = enum t |>
    List.of_enum |> List.sort ~cmp:(flip @@ Action.compare_by snd) |>
    (match limit with None -> id | Some n -> List.take n) |>
    List.map (fun (x,n) -> sprintf "%6d : %S" n (f x)) |>
    String.concat sep
  let stats t ?(cmp=compare) f =
    if Hashtbl.length t = 0 then
      "<empty>"
    else
      let a = Array.of_enum (enum t) in
      let total = Array.fold_left (fun t (_,n) -> t + n) 0 a in
      let half = total / 2 in
      let cmp (x,_) (y,_) = cmp x y in
      Array.sort cmp a;
      let med = ref None in
      let (mi,ma,_) = Array.fold_left begin fun (mi,ma,sum) x ->
        let sum = sum + snd x in
        if !med = None && half <= sum then med := Some x;
        let mi = if snd x < snd mi then x else mi in
        let ma = if snd x > snd ma then x else ma in
        mi, ma, sum
      end ((fst a.(0), max_int), (fst a.(0),min_int), 0) a
      in
      let show (x,n) = sprintf "%S (%d)" (f x) n in
      sprintf "total %d median %s min %s max %s"
        total (match !med with None -> "?" | Some x -> show x) (show mi) (show ma)
  let distrib t =
    if Hashtbl.length t = 0 then
      [||]
    else
      let a = Array.of_enum (enum t) in
      let total = Array.fold_left (fun t (_,n) -> t + n) 0 a in
      let limits = Array.init 10 (fun i -> total * (i + 1) / 10) in
      let cmp (x,_) (y,_) = compare (x:float) y in
      Array.sort cmp a;
      let distrib = limits |> Array.map begin fun limit ->
        let (v,_) = Array.fold_left begin fun (found,sum) (v,n) ->
          let sum = sum + n in
          if found = None && limit <= sum then Some v, sum else (found,sum)
        end (None,0) a in
        match v with
        | None -> nan
        | Some v -> v
      end
      in
      distrib
  let show_distrib ?(sep="\n") t =
    distrib t |> Array.mapi (fun i v -> sprintf "%d%% <= %f" ((i + 1) * 10) v) |> Array.to_list |> String.concat sep
  let report t ?limit ?cmp ?(sep="\n") f =
    let data = show_sorted t ?limit ~sep f in
    let stats = stats t ?cmp f in
    stats^sep^data
  let names (t : 'a t) = List.of_enum @@ Hashtbl.keys t
end


(*
  Generationnal LRU cache.
  Elements are store in a first fifo, and get evicted in order.
  If an element is reused while in the first fifo, it is promoted to a second fifo, from which elements are also evicted in order.
  Hits from the second fifo puts back the element in the back of this fifo.

  The goal is to avoid low hit rate due to large workload with some regularly used elements which would get evicted from the LRU
  before being reused
*)
module LRU (Keys : StdHashtbl.HashedType) = struct
  module Hashtbl = StdHashtbl.Make(Keys)
  module Queue = struct
    exception Empty

    type 'a elem = 'a Dllist.node_t
    type 'a t = 'a elem option ref

    let create () = ref None

    let unwrap = Dllist.get

    let is_singleton list = Dllist.next list == list

    let drop elem =
      match is_singleton elem with
      | true -> None
      | false -> Some (Dllist.rev_drop elem)

    let append t value =
      match !t with
      | None -> t := Some (value)
      | Some queue ->
        Dllist.splice value (Dllist.next queue);
        Dllist.splice queue value

    let push t value =
      let node = Dllist.create value in
      append t node;
      node

    let pop t =
      match !t with
      | None -> raise Empty
      | Some queue ->
        t := drop queue;
        queue

    let remove t elem =
      match !t with
      | None -> ()
      | Some queue when elem == queue ->
        t := drop queue
      | Some _ ->
        Dllist.remove elem
  end

  type 'v entry = {
    key : Hashtbl.key;
    mutable value : 'v;
    mutable queue : [`Lru | `Lfu ];
  }

  type 'v t = {
    table : 'v entry Queue.elem Hashtbl.t;
    mutable lru_avaibl : int;
    mutable lfu_avaibl : int;
    lru : 'v entry Queue.t;
    lfu : 'v entry Queue.t;
    mutable hit : int;
    mutable miss : int;
  }

  let create size =
    assert (size > 0);
    {
      table = Hashtbl.create size;
      lru = Queue.create ();
      lfu = Queue.create ();
      hit = 0;
      miss = 0;
      lru_avaibl = size;
      lfu_avaibl = size;
    }

  let size cache = Hashtbl.length cache.table

  let iter f cache = Hashtbl.iter (fun key value -> f key (Queue.unwrap value).value) cache.table

  let miss cache = cache.miss
  let hit cache = cache.hit

  let replace cache key value =
    try
      let entry = Hashtbl.find cache.table key |> Queue.unwrap in
      entry.value <- value
    with Not_found -> ()

  let get_evicted cache key =
    try
      let node = Hashtbl.find cache.table key in
      let entry = Queue.unwrap node in
      cache.hit <- cache.hit + 1;
      (* first remove the entry from the current queue *)
      begin match entry.queue with
      | `Lru ->
        (* if the node is in the lru queuen it will be moved to the lfu queue *)
        cache.lru_avaibl <- cache.lru_avaibl + 1;
        entry.queue <- `Lfu;
        Queue.remove cache.lru node;
      | `Lfu ->
        cache.lfu_avaibl <- cache.lfu_avaibl + 1;
        Queue.remove cache.lfu node
      end;
      (* If the queue is full, drop one entry *)
      let evicted = 
        if cache.lfu_avaibl <= 0 then begin
          let evicted = Queue.unwrap (Queue.pop cache.lfu) in
          Hashtbl.remove cache.table evicted.key;
          Some (evicted.key, evicted.value)
        end else begin
          cache.lfu_avaibl <- cache.lfu_avaibl - 1;
          None
        end
      in
      Queue.append cache.lfu node;
      entry.value, evicted
    with Not_found -> cache.miss <- cache.miss + 1; raise Not_found

  let find cache key =
    let entry = Queue.unwrap @@ Hashtbl.find cache.table key in
    entry.value

  let get cache key =
    fst @@ get_evicted cache key

  let mem cache key = Hashtbl.mem cache.table key
  let lru_free cache = cache.lru_avaibl
  let lfu_free cache = cache.lfu_avaibl

  let put_evicted cache key value =
    try
      let node = Hashtbl.find cache.table key |> Queue.unwrap in
      node.value <- value;
      None
    with Not_found ->
      let evicted =
        if cache.lru_avaibl = 0 then begin
          let evicted = Queue.unwrap (Queue.pop cache.lru) in
          Hashtbl.remove cache.table evicted.key;
          Some (evicted.key, evicted.value)
        end else begin
          cache.lru_avaibl <- cache.lru_avaibl - 1;
          None
        end
      in
      let node = Queue.push cache.lru { key;  value; queue = `Lru } in
      Hashtbl.add cache.table key node;
      evicted

  let put cache key value = put_evicted cache key value |> ignore

  let remove cache key =
    try
      let node = Hashtbl.find cache.table key in
      Hashtbl.remove cache.table key;
      match (Queue.unwrap node).queue with
      | `Lru ->
        cache.lru_avaibl <- cache.lru_avaibl + 1;
        Queue.remove cache.lru node
      | `Lfu ->
        cache.lfu_avaibl <- cache.lfu_avaibl + 1;
        Queue.remove cache.lfu node
    with Not_found -> ()
end

module Group = struct
  type ('a,'b) t = ('b,'a list) Hashtbl.t * ('a -> 'b)
  let by f = Hashtbl.create 32, f
  let add (h,f) x = let k = f x in try Hashtbl.replace h k (x :: Hashtbl.find h k) with Not_found -> Hashtbl.add h k [x]
  let get (h,_) k = try Hashtbl.find h k with Not_found -> []
  let iter (h,_) k = Hashtbl.iter k h
  let keys (h,_) = Hashtbl.keys h
end

let group_fst e =
  let h = Hashtbl.create 10 in
  Enum.iter (fun (k,v) -> Hashtbl.replace h k (try v :: Hashtbl.find h k with Not_found -> [v])) e;
  Hashtbl.enum h

module Assoc = struct
  type ('a,'b) t = ('a,'b) Hashtbl.t
  let create () = Hashtbl.create 32
  let add h k v =
    assert (false = Hashtbl.mem h k);
    Hashtbl.add h k v
  let get = Hashtbl.find
  let try_get = Hashtbl.find_option
  let del h k =
    try
      let v = Hashtbl.find h k in
      Hashtbl.remove h k; v
    with
      Not_found -> assert false
  let remove h k =
    assert (true = Hashtbl.mem h k);
    Hashtbl.remove h k
  let size = Hashtbl.length

  let fold = Hashtbl.fold
end

module Lists = struct
type ('a,'b) t = ('a,'b list) Hashtbl.t
let create () = Hashtbl.create 16
let get h k = try Hashtbl.find h k with Not_found -> []
let set = Hashtbl.replace
let add h k v = Hashtbl.replace h k (v::get h k)
let enum = Hashtbl.enum
let clear = Hashtbl.clear
let count_keys = Hashtbl.length
let count_all h = Hashtbl.fold (fun _ l acc -> acc + List.length l) h 0
end

class ['a] cache (cb : ('a list -> unit)) ~limit =
object(self)
  val mutable l = []
  method name = "cache"
  method add x =
    l <- x :: l;
    if List.length l >= limit then
    begin
      cb l;
      self#clear
    end
  method get = l
  method dump = cb l; l <- []
  method clear = l <- []
  method to_list = l
  method size = List.length l
end

type 'a reused = { cache : 'a Stack.t; create : (unit -> 'a); reset : ('a -> unit); }
let reuse create reset = { cache = Stack.create (); create; reset; }
let use t = if Stack.is_empty t.cache then t.create () else Stack.pop t.cache
let recycle t x = t.reset x; Stack.push x t.cache

module ReuseLocked(L : Lock)(T : sig type t val create : unit -> t val reset : t -> unit end) : sig
type t = T.t
val get : unit -> t
val release : t -> unit
end = struct
type t = T.t
type cache = { cache : t Stack.t; lock : L.t }
let cache = { cache = Stack.create (); lock = L.create () }
let get' () = if Stack.is_empty cache.cache then T.create () else Stack.pop cache.cache
let get () = L.locked cache.lock get'
let release x = L.locked cache.lock (fun () -> T.reset x; Stack.push x cache.cache)
end

module Reuse = ReuseLocked(NoLock)