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open Core
open Lwt
open Base
open State
let mode = Some CANDIDATE
let lock = Lwt_mutex.create ()
type t = {
conf : Conf.t;
logger : Logger.t;
apply_log : apply_log;
state : State.common;
mutable next_mode : mode option;
}
let init ~conf ~apply_log ~state =
{
conf;
logger =
Logger.create ~node_id:conf.node_id ~mode ~output_path:conf.log_file
~level:conf.log_level;
apply_log;
state;
next_mode = None;
}
let request_vote t =
let persistent_state = t.state.persistent_state in
let persistent_log = t.state.persistent_log in
let request_json =
let last_log = PersistentLog.last_log persistent_log in
let r : Params.request_vote_request =
{
term = PersistentState.current_term persistent_state;
candidate_id = t.conf.node_id;
last_log_term = last_log.term;
last_log_index = last_log.index;
}
in
Params.request_vote_request_to_yojson r
in
let request =
Request_sender.post ~node_id:t.conf.node_id ~logger:t.logger
~url_path:"request_vote" ~request_json
~timeout_millis:t.conf.request_timeout_millis
~converter:(fun response_json ->
match Params.request_vote_response_of_yojson response_json with
| Ok param ->
if PersistentState.detect_new_leader persistent_state
~logger:t.logger ~other_term:param.term
then t.next_mode <- Some FOLLOWER;
Ok (Params.REQUEST_VOTE_RESPONSE param)
| Error _ as err -> err)
in
Lwt_list.map_p request (Conf.peer_nodes t.conf)
let request_handlers t ~election_timer =
let handlers = Stdlib.Hashtbl.create 2 in
let open Params in
Stdlib.Hashtbl.add handlers
(`POST, "/append_entries")
( (fun json ->
match append_entries_request_of_yojson json with
| Ok x -> Ok (APPEND_ENTRIES_REQUEST x)
| Error _ as e -> e),
function
| APPEND_ENTRIES_REQUEST x ->
Append_entries_handler.handle ~conf:t.conf ~state:t.state
~logger:t.logger ~apply_log:t.apply_log
~cb_valid_request:(fun () -> Timer.update election_timer)
~cb_new_leader:(fun () -> t.next_mode <- Some FOLLOWER)
~param:x
| _ -> failwith "Unexpected state" );
Stdlib.Hashtbl.add handlers
(`POST, "/request_vote")
( (fun json ->
match request_vote_request_of_yojson json with
| Ok x -> Ok (REQUEST_VOTE_REQUEST x)
| Error _ as e -> e),
function
| REQUEST_VOTE_REQUEST x ->
Request_vote_handler.handle ~state:t.state ~logger:t.logger
~cb_valid_request:(fun () -> ())
~cb_new_leader:(fun () -> t.next_mode <- Some FOLLOWER)
~param:x
| _ -> failwith "Unexpected state" );
handlers
let collect_votes t ~election_timer ~vote_request =
( vote_request >>= fun responses ->
List.fold_left ~init:1
~f:(fun a r ->
match r with
| Some param -> (
match param with
| Params.REQUEST_VOTE_RESPONSE param ->
if param.vote_granted then a + 1 else a
| _ -> failwith "Unexpected state"
)
| None -> a)
responses
|> Lwt.return )
>>= fun n ->
let majority = Conf.majority_of_nodes t.conf in
if n >= majority
then (
Logger.info t.logger
(Printf.sprintf
"Received majority votes (received: %d, majority: %d). Moving to Leader"
n majority);
Timer.stop election_timer;
t.next_mode <- Some LEADER
)
else (
Logger.info t.logger
(Printf.sprintf
"Didn't receive majority votes (received: %d, majority: %d). Trying again"
n majority);
Timer.stop election_timer;
t.next_mode <- Some CANDIDATE
);
Lwt.return ()
let next_mode t =
match t.next_mode with
| Some LEADER -> LEADER
| Some CANDIDATE -> CANDIDATE
| Some _ ->
Logger.error t.logger "Unexpected state: FOLLOWER";
CANDIDATE
| _ ->
Logger.error t.logger "Unexpected state";
CANDIDATE
let run t () =
let persistent_state = t.state.persistent_state in
Logger.info t.logger "### Candidate: Start ###";
PersistentState.increment_current_term persistent_state;
PersistentState.set_voted_for persistent_state ~logger:t.logger
~voted_for:(Some t.conf.node_id);
State.log t.state ~logger:t.logger;
let election_timer =
Timer.create ~logger:t.logger ~timeout_millis:t.conf.election_timeout_millis
in
let handlers = request_handlers t ~election_timer in
let server, stopper =
Request_dispatcher.create ~port:(Conf.my_node t.conf).port ~logger:t.logger
~lock ~table:handlers
in
let vote_request = Lwt_mutex.with_lock lock (fun () -> request_vote t) in
let received_votes = collect_votes t ~election_timer ~vote_request in
let election_timer_thread =
Timer.start election_timer ~on_stop:(fun () ->
Lwt.wakeup stopper ();
Lwt.cancel vote_request)
in
Lwt.join [ election_timer_thread; received_votes; server ] >>= fun () ->
Lwt.return (next_mode t)