Source file distributor.ml
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open Serverset
open Lwt.Infix
open Util
module type S = sig
type param
type state
type peer
val pick: state -> param -> peer Lwt.t
val use: state -> param -> (Node.t -> 'a Lwt.t) -> 'a Lwt.t
end
module type Fanout = sig
val fanout: int
end
module type Checksum = sig
val sum64: Cstruct.t -> int64
end
module P2C = struct
type state = LoadedNodes.t
type param = unit
type peer = LoadedNode.t
open LoadedNode
let pick state () =
SyncVar.read state >>= fun set ->
let elements = LoadedSet.elements set in
let select () =
Random.int ( List.length elements )
|> fun i -> List.nth elements i
in
let (a, b) =
select (), select ()
in
if a.load <= b.load then
Lwt.return a
else
Lwt.return b
let use t () f =
pick t () >>= fun n ->
Counter64.incr n.load;
Util.ensure (f n.node) ( fun () ->
Counter64.decr n.load;
()
)
end
module RoundRobin = struct
type state = RRQueue.t
type param = unit
type peer = Node.t
let pick state () =
RRQueue.take state
let use state () f =
pick state () >>= fun node ->
Util.ensure (f node) (fun () ->
RRQueue.add state node;
()
)
end
module CHash (C: Checksum) = struct
type param = Cstruct.t
type state = Nodes.t
type peer = Node.t
let pick state key =
SyncVar.read state >>= fun s ->
let nodes = NodeSet.elements s in
Chash.lookup nodes (C.sum64 key) |> Lwt.return
let use state key f =
pick state key >>= fun node ->
f node
end
module CHashLeastLoaded (C: Checksum) (F: Fanout) = struct
type param = Cstruct.t
type state = LoadedNodes.t
type peer = LoadedNode.t
open LoadedNode
let min nodes =
let rec aux hosts m =
match hosts with
| hd :: tl when m.load < hd.load ->
aux tl hd
| hd :: tl ->
aux tl m
| [] -> m
in
aux nodes (List.hd nodes)
let pick state key =
SyncVar.read state >>= fun s ->
let nodes =
let a = LoadedSet.elements s in
Chash.shards a (C.sum64 key) F.fanout
in
let n = min nodes in
Lwt.return n
let use state key f =
pick state key >>= fun n ->
Counter64.incr n.load ;
ensure (f n.node) (fun () ->
Counter64.decr n.load;
()
)
end
module P2C_PKG (C1: Checksum) (C2: Checksum) = struct
type param = Cstruct.t
type state = LoadedNodes.t
type peer = LoadedNode.t
let lookup e hf key =
let size = List.length e in
let a = Int64.to_int (hf key) in
a mod size |> List.nth e
let pick t key =
SyncVar.read t >>= fun x ->
let e = LoadedSet.elements x in
let (a, b) =
( lookup e C1.sum64 key), ( lookup e C2.sum64 key)
in
if a.load <= b.load then
Lwt.return a
else
Lwt.return b
let use state key f =
pick state key >>= fun n ->
Counter64.incr n.load ;
ensure (f n.node) (fun () ->
Counter64.decr n.load;
()
)
end