topic Erlang API: action init callback not implemented? in NSO Developer Hub Discussions

Erlang API: action init callback not implemented?

alex-filippov — Thu, 31 Oct 2019 02:52:23 GMT

Trying to write an action in Erlang API and wanted to spawn a new worker in init() callback for each new action invocation.
Action init callback seems to be not implemented in Erlang API: confd_action_cb record in econfd.hrl has no "init" field.
NSO versions 4.7.4.3 and 5.1.

Re: Erlang API: action init callback not implemented?

sunge — Thu, 31 Oct 2019 05:34:24 GMT

Hi,

I guess you want to avoid a long running action to block other user session invocations of the action?

Using the erlang api, you do not have to handle that case as you would in the C-api.

econfd:init_daemon(...):

Starts and links to a gen_server which connects to ConfD/NSO. This gen_server holds two sockets to ConfD/NSO, one so called control socket and one worker socket (See confd_lib_dp(3) for an explanation of those sockets.)

To avoid blocking control socket callback requests due to long-running worker socket callbacks, the control socket callbacks are run in the gen_server, while the worker socket callbacks are run in a separate process that is spawned by the gen_server. This means that applications must not share e.g. MAAPI sockets between transactions, since this could result in simultaneous use of a socket by the gen_server and the spawned process.

...

Re: Erlang API: action init callback not implemented?

alex-filippov — Thu, 31 Oct 2019 15:02:58 GMT

Thank you. Yes, that blocking is what I try to avoid. And that was initially my hope that Erlang API does not need the init callback for actions, because it somehow spawns workers as needed. But so far I am stuck with only one worker, which blocks other users while it executes one action.

The problem seems to be that there is only one worker socket and only one worker process. The daemon does not spawn a new worker for each incoming action, does not maintain a pool of workers (like Java and Python API do, I think), and there is no way for me to spawn workers myself (like in C API) because action init callback is not supported.

Re: Erlang API: action init callback not implemented?

sunge — Wed, 06 Nov 2019 19:22:21 GMT

Hi,

I had a talk with the developers responsible for the Erlang API, and they suspect your findings are correct.

That said, I'm not entirely sure how to help you bypass the issue.

Re: Erlang API: action init callback not implemented?

sunge — Mon, 09 Dec 2019 12:20:41 GMT

Quick question.

After calling init_daemon(...), did you run econfd:controlliing_process() to make sure the

worker process is being called?

Re: Erlang API: action init callback not implemented?

alex-filippov — Mon, 09 Dec 2019 17:04:51 GMT

No, I did not run that.

The worker process worked well without it. The action was doing its job.

Re: Erlang API: action init callback not implemented?

radioman — Fri, 11 Feb 2022 12:54:21 GMT

Hi,

Sorry for reviving this old thread, but I am running into exactly the same problem with NSO 5.6.2.

I can't get actions callback's written with the Erlang API to run concurrently.

Is it still the case there is no way to spawn new workers for action calls ?

Re: Erlang API: action init callback not implemented?

radioman — Tue, 15 Feb 2022 13:07:49 GMT

Hi,

Seems like there there is limited interest in the Erlang API. But I found this thread when I hit the problem so might be useful for others.

Of all the API's I could not accept the Erlang API, to have no action concurrency options at all. So I made a workaround/hack around this problem, it does re-implement some internal stuff from the econfd application, So would be appreciated if this could be fixed properly upstream at some point in time.

This code will spawn a new process for every action call, to limit the amount of code that needed to be re-implemented, the process is stopped with timer:exit_after/2.

-module(ec_cfs_test_action_server).

-behaviour(gen_server).

%% API
-export([
         start_link/0
        ]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
         terminate/2, code_change/3, call_action/4]).

-include_lib("econfd/include/econfd.hrl").
-include_lib("econfd/include/econfd_errors.hrl").
-include_lib("econfd/src/econfd_proto.hrl").

-define(SERVER, ?MODULE).

% from econfd_internal.hrl
-define(CLIENT_CAPI,         3).

%%%===================================================================
%%% API
%%%===================================================================

start_link() ->
    gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================

init([]) ->
    process_flag(trap_exit, true), % Triggers call to terminate/2
    Host = {127,0,0,1},
    {ok, Dx} = econfd_daemon:init([?MODULE,?CONFD_SILENT, user, {}, Host, ?NCS_PORT]),

    % While we are in the init state of the gen_server, we can't use the econfd functions,
    % since they rely in the gen_server to be ready.
    {reply, ok, Dx1} = econfd_daemon:handle_call({register_action_cb,
                                                  #confd_action_cb{actionpoint = 'cfs-test-action-erl-ap',
                                                    action = fun call_action/4}
                                                 }, self(), Dx),
    {reply, ok, Dx2} = econfd_daemon:handle_call(register_done, self(), Dx1),
    log(info, "Server started", []),
    {ok, Dx2}.

%%--------------------------------------------------------------------
handle_call(Req, From, State) ->
    econfd_daemon:handle_call(Req, From, State).

%%--------------------------------------------------------------------
handle_cast(Msg, State) ->
    econfd_daemon:handle_cast(Msg, State).

%%--------------------------------------------------------------------
handle_info(State={tcp, _Socket, Data}, Dx) ->
    case econfd_internal:term_get(Data) of
        _ET={_Op=?CONFD_PROTO_NEW_ACTION, _Qref, _Did, _Usid, _CallPoint, _Index, _TH} ->
            {ok, Socket} = econfd_internal:connect(Dx#confd_daemon_ctx.ip, Dx#confd_daemon_ctx.port, ?CLIENT_CAPI, [{active, true}]),
            Int = incr(),
            ok= econfd_internal:term_write(Socket, {?CONFD_PROTO_WORKER, Dx#confd_daemon_ctx.daemon_id, Int}),
            Worker = proc_lib:spawn_link(econfd_daemon, worker, [Dx]),
            % Have some failsafe to not have the worker hanning around forever.
            timer:exit_after(300*1000, Worker,worker_exit),
            Dx1 = Dx#confd_daemon_ctx{ wint=Int, worker=Socket, worker_pid=Worker},
            econfd:controlling_process(Socket, Worker),
            econfd_daemon:handle_info(State, Dx1),
            % Keep using original daemon state since action worker is for one-time usage.
            {noreply, Dx};
        _ ->
            econfd_daemon:handle_info(State, Dx)
    end;
handle_info({'EXIT',_,worker_exit}, State) ->
    {noreply,State};
handle_info(Info, State) ->
    econfd_daemon:handle_info(Info, State).

%%--------------------------------------------------------------------
terminate(Reason, State) ->
    log(info, "Server stopped - ~p", [Reason]),
    econfd_daemon:terminate(Reason, State).

%%--------------------------------------------------------------------
code_change(OldVsn, State, Extra) ->
    econfd_daemon:code_change(OldVsn, State, Extra).

%%%===================================================================
%%% Internal functions
%%%===================================================================

incr() ->
    X = get(sock_int),
    put(sock_int, X+1),
    X.

%%--------------------------------------------------------------------
call_action(_,[_|'test-action'],_,Args) ->
    log(info,"Args ~p ~p",[self(),Args]),
    % Do some heavy lifting :-)
    timer:sleep(10000),
    timer:exit_after(500,worker_exit),
    ok;

call_action(A1,A2,A3,A4) ->
    log(error,"Unknow call ~p ~p ~p ~p",[A1,A2,A3,A4]),
    timer:exit_after(500,worker_exit),
    ok.

%%--------------------------------------------------------------------
log(error, Format, Args) ->
    econfd:log(?CONFD_LEVEL_ERROR, "~p: " ++ Format, [?SERVER | Args]);
log(info, Format, Args) ->
    econfd:log(?CONFD_LEVEL_INFO,  "~p: " ++ Format, [?SERVER | Args]);
log(trace, Format, Args) ->
    econfd:log(?CONFD_LEVEL_TRACE, "~p: " ++ Format, [?SERVER | Args]).