path: root/lib/stdlib/src/gen_fsm.erl

%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2018. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(gen_fsm).

%%%-----------------------------------------------------------------
%%%   
%%% This state machine is somewhat more pure than state_lib.  It is
%%% still based on State dispatching (one function per state), but
%%% allows a function handle_event to take care of events in all states.
%%% It's not that pure anymore :(  We also allow synchronized event sending.
%%%
%%% If the Parent process terminates the Module:terminate/2
%%% function is called.
%%%
%%% The user module should export:
%%%
%%%   init(Args)
%%%     ==> {ok, StateName, StateData}
%%%         {ok, StateName, StateData, Timeout}
%%%         ignore
%%%         {stop, Reason}
%%%
%%%   StateName(Msg, StateData)
%%%
%%%    ==> {next_state, NewStateName, NewStateData}
%%%        {next_state, NewStateName, NewStateData, Timeout}
%%%        {stop, Reason, NewStateData}
%%%              Reason = normal | shutdown | Term terminate(State) is called
%%%
%%%   StateName(Msg, From, StateData)
%%%
%%%    ==> {next_state, NewStateName, NewStateData}
%%%        {next_state, NewStateName, NewStateData, Timeout}
%%%        {reply, Reply, NewStateName, NewStateData}
%%%        {reply, Reply, NewStateName, NewStateData, Timeout}
%%%        {stop, Reason, NewStateData}
%%%              Reason = normal | shutdown | Term terminate(State) is called
%%%
%%%   handle_event(Msg, StateName, StateData)
%%%
%%%    ==> {next_state, NewStateName, NewStateData}
%%%        {next_state, NewStateName, NewStateData, Timeout}
%%%        {stop, Reason, Reply, NewStateData}
%%%        {stop, Reason, NewStateData}
%%%              Reason = normal | shutdown | Term terminate(State) is called
%%%
%%%   handle_sync_event(Msg, From, StateName, StateData)
%%%
%%%    ==> {next_state, NewStateName, NewStateData}
%%%        {next_state, NewStateName, NewStateData, Timeout}
%%%        {reply, Reply, NewStateName, NewStateData}
%%%        {reply, Reply, NewStateName, NewStateData, Timeout}
%%%        {stop, Reason, Reply, NewStateData}
%%%        {stop, Reason, NewStateData}
%%%              Reason = normal | shutdown | Term terminate(State) is called
%%%
%%%   handle_info(Info, StateName) (e.g. {'EXIT', P, R}, {nodedown, N}, ...
%%%
%%%    ==> {next_state, NewStateName, NewStateData}
%%%        {next_state, NewStateName, NewStateData, Timeout}
%%%        {stop, Reason, NewStateData}
%%%              Reason = normal | shutdown | Term terminate(State) is called
%%%
%%%   terminate(Reason, StateName, StateData) Let the user module clean up
%%%        always called when server terminates
%%%
%%%    ==> the return value is ignored
%%%
%%%
%%% The work flow (of the fsm) can be described as follows:
%%%
%%%   User module                           fsm
%%%   -----------                          -------
%%%     start              ----->             start
%%%     init               <-----              .
%%%
%%%                                           loop
%%%     StateName          <-----              .
%%%
%%%     handle_event       <-----              .
%%%
%%%     handle__sunc_event <-----              .
%%%
%%%     handle_info        <-----              .
%%%
%%%     terminate          <-----              .
%%%
%%%
%%% ---------------------------------------------------

-include("logger.hrl").

-export([start/3, start/4,
	 start_link/3, start_link/4,
	 stop/1, stop/3,
	 send_event/2, sync_send_event/2, sync_send_event/3,
	 send_all_state_event/2,
	 sync_send_all_state_event/2, sync_send_all_state_event/3,
	 reply/2,
	 start_timer/2,send_event_after/2,cancel_timer/1,
	 enter_loop/4, enter_loop/5, enter_loop/6, wake_hib/7]).

%% Internal exports
-export([init_it/6,
	 system_continue/3,
	 system_terminate/4,
	 system_code_change/4,
	 system_get_state/1,
	 system_replace_state/2,
	 format_status/2]).

%% logger callback
-export([format_log/1]).

-deprecated({start, 3, eventually}).
-deprecated({start, 4, eventually}).
-deprecated({start_link, 3, eventually}).
-deprecated({start_link, 4, eventually}).
-deprecated({stop, 1, eventually}).
-deprecated({stop, 3, eventually}).
-deprecated({send_event, 2, eventually}).
-deprecated({sync_send_event, 2, eventually}).
-deprecated({sync_send_event, 3, eventually}).
-deprecated({send_all_state_event, 2, eventually}).
-deprecated({sync_send_all_state_event, 2, eventually}).
-deprecated({sync_send_all_state_event, 3, eventually}).
-deprecated({reply, 2, eventually}).
-deprecated({start_timer, 2, eventually}).
-deprecated({send_event_after, 2, eventually}).
-deprecated({cancel_timer, 1, eventually}).
-deprecated({enter_loop, 4, eventually}).
-deprecated({enter_loop, 5, eventually}).
-deprecated({enter_loop, 6, eventually}).

%%% ---------------------------------------------------
%%% Interface functions.
%%% ---------------------------------------------------

-callback init(Args :: term()) ->
    {ok, StateName :: atom(), StateData :: term()} |
    {ok, StateName :: atom(), StateData :: term(), timeout() | hibernate} |
    {stop, Reason :: term()} | ignore.
-callback handle_event(Event :: term(), StateName :: atom(),
                       StateData :: term()) ->
    {next_state, NextStateName :: atom(), NewStateData :: term()} |
    {next_state, NextStateName :: atom(), NewStateData :: term(),
     timeout() | hibernate} |
    {stop, Reason :: term(), NewStateData :: term()}.
-callback handle_sync_event(Event :: term(), From :: {pid(), Tag :: term()},
                            StateName :: atom(), StateData :: term()) ->
    {reply, Reply :: term(), NextStateName :: atom(), NewStateData :: term()} |
    {reply, Reply :: term(), NextStateName :: atom(), NewStateData :: term(),
     timeout() | hibernate} |
    {next_state, NextStateName :: atom(), NewStateData :: term()} |
    {next_state, NextStateName :: atom(), NewStateData :: term(),
     timeout() | hibernate} |
    {stop, Reason :: term(), Reply :: term(), NewStateData :: term()} |
    {stop, Reason :: term(), NewStateData :: term()}.
-callback handle_info(Info :: term(), StateName :: atom(),
                      StateData :: term()) ->
    {next_state, NextStateName :: atom(), NewStateData :: term()} |
    {next_state, NextStateName :: atom(), NewStateData :: term(),
     timeout() | hibernate} |
    {stop, Reason :: normal | term(), NewStateData :: term()}.
-callback terminate(Reason :: normal | shutdown | {shutdown, term()}
		    | term(), StateName :: atom(), StateData :: term()) ->
    term().
-callback code_change(OldVsn :: term() | {down, term()}, StateName :: atom(),
		      StateData :: term(), Extra :: term()) ->
    {ok, NextStateName :: atom(), NewStateData :: term()}.
-callback format_status(Opt, StatusData) -> Status when
      Opt :: 'normal' | 'terminate',
      StatusData :: [PDict | State],
      PDict :: [{Key :: term(), Value :: term()}],
      State :: term(),
      Status :: term().

-optional_callbacks(
    [handle_info/3, terminate/3, code_change/4, format_status/2]).

%%% ---------------------------------------------------
%%% Starts a generic state machine.
%%% start(Mod, Args, Options)
%%% start(Name, Mod, Args, Options)
%%% start_link(Mod, Args, Options)
%%% start_link(Name, Mod, Args, Options) where:
%%%    Name ::= {local, atom()} | {global, term()} | {via, atom(), term()}
%%%    Mod  ::= atom(), callback module implementing the 'real' fsm
%%%    Args ::= term(), init arguments (to Mod:init/1)
%%%    Options ::= [{debug, [Flag]}]
%%%      Flag ::= trace | log | {logfile, File} | statistics | debug
%%%          (debug == log && statistics)
%%% Returns: {ok, Pid} |
%%%          {error, {already_started, Pid}} |
%%%          {error, Reason}
%%% ---------------------------------------------------
start(Mod, Args, Options) ->
    gen:start(?MODULE, nolink, Mod, Args, Options).

start(Name, Mod, Args, Options) ->
    gen:start(?MODULE, nolink, Name, Mod, Args, Options).

start_link(Mod, Args, Options) ->
    gen:start(?MODULE, link, Mod, Args, Options).

start_link(Name, Mod, Args, Options) ->
    gen:start(?MODULE, link, Name, Mod, Args, Options).

stop(Name) ->
    gen:stop(Name).

stop(Name, Reason, Timeout) ->
    gen:stop(Name, Reason, Timeout).

send_event({global, Name}, Event) ->
    catch global:send(Name, {'$gen_event', Event}),
    ok;
send_event({via, Mod, Name}, Event) ->
    catch Mod:send(Name, {'$gen_event', Event}),
    ok;
send_event(Name, Event) ->
    Name ! {'$gen_event', Event},
    ok.

sync_send_event(Name, Event) ->
    case catch gen:call(Name, '$gen_sync_event', Event) of
	{ok,Res} ->
	    Res;
	{'EXIT',Reason} ->
	    exit({Reason, {?MODULE, sync_send_event, [Name, Event]}})
    end.

sync_send_event(Name, Event, Timeout) ->
    case catch gen:call(Name, '$gen_sync_event', Event, Timeout) of
	{ok,Res} ->
	    Res;
	{'EXIT',Reason} ->
	    exit({Reason, {?MODULE, sync_send_event, [Name, Event, Timeout]}})
    end.

send_all_state_event({global, Name}, Event) ->
    catch global:send(Name, {'$gen_all_state_event', Event}),
    ok;
send_all_state_event({via, Mod, Name}, Event) ->
    catch Mod:send(Name, {'$gen_all_state_event', Event}),
    ok;
send_all_state_event(Name, Event) ->
    Name ! {'$gen_all_state_event', Event},
    ok.

sync_send_all_state_event(Name, Event) ->
    case catch gen:call(Name, '$gen_sync_all_state_event', Event) of
	{ok,Res} ->
	    Res;
	{'EXIT',Reason} ->
	    exit({Reason, {?MODULE, sync_send_all_state_event, [Name, Event]}})
    end.

sync_send_all_state_event(Name, Event, Timeout) ->
    case catch gen:call(Name, '$gen_sync_all_state_event', Event, Timeout) of
	{ok,Res} ->
	    Res;
	{'EXIT',Reason} ->
	    exit({Reason, {?MODULE, sync_send_all_state_event,
			   [Name, Event, Timeout]}})
    end.

%% Designed to be only callable within one of the callbacks
%% hence using the self() of this instance of the process.
%% This is to ensure that timers don't go astray in global
%% e.g. when straddling a failover, or turn up in a restarted
%% instance of the process.

%% Returns Ref, sends event {timeout,Ref,Msg} after Time 
%% to the (then) current state.
start_timer(Time, Msg) ->
    erlang:start_timer(Time, self(), {'$gen_timer', Msg}).

%% Returns Ref, sends Event after Time to the (then) current state.
send_event_after(Time, Event) ->
    erlang:start_timer(Time, self(), {'$gen_event', Event}).

%% Returns the remaining time for the timer if Ref referred to
%% an active timer/send_event_after, false otherwise.
cancel_timer(Ref) ->
    case erlang:cancel_timer(Ref) of
	false ->
	    receive {timeout, Ref, _} -> 0
	    after 0 -> false 
	    end;
	RemainingTime ->
	    RemainingTime
    end.

%% enter_loop/4,5,6
%% Makes an existing process into a gen_fsm.
%% The calling process will enter the gen_fsm receive loop and become a
%% gen_fsm process.
%% The process *must* have been started using one of the start functions
%% in proc_lib, see proc_lib(3).
%% The user is responsible for any initialization of the process,
%% including registering a name for it.
enter_loop(Mod, Options, StateName, StateData) ->
    enter_loop(Mod, Options, StateName, StateData, self(), infinity).

enter_loop(Mod, Options, StateName, StateData, {Scope,_} = ServerName)
  when Scope == local; Scope == global ->
    enter_loop(Mod, Options, StateName, StateData, ServerName,infinity);
enter_loop(Mod, Options, StateName, StateData, {via,_,_} = ServerName) ->
    enter_loop(Mod, Options, StateName, StateData, ServerName,infinity);
enter_loop(Mod, Options, StateName, StateData, Timeout) ->
    enter_loop(Mod, Options, StateName, StateData, self(), Timeout).

enter_loop(Mod, Options, StateName, StateData, ServerName, Timeout) ->
    Name = gen:get_proc_name(ServerName),
    Parent = gen:get_parent(),
    Debug = gen:debug_options(Name, Options),
	HibernateAfterTimeout = gen:hibernate_after(Options),
    loop(Parent, Name, StateName, StateData, Mod, Timeout, HibernateAfterTimeout, Debug).

%%% ---------------------------------------------------
%%% Initiate the new process.
%%% Register the name using the Rfunc function
%%% Calls the Mod:init/Args function.
%%% Finally an acknowledge is sent to Parent and the main
%%% loop is entered.
%%% ---------------------------------------------------
init_it(Starter, self, Name, Mod, Args, Options) ->
    init_it(Starter, self(), Name, Mod, Args, Options);
init_it(Starter, Parent, Name0, Mod, Args, Options) ->
    Name = gen:name(Name0),
    Debug = gen:debug_options(Name, Options),
	HibernateAfterTimeout = gen:hibernate_after(Options),
	case catch Mod:init(Args) of
	{ok, StateName, StateData} ->
	    proc_lib:init_ack(Starter, {ok, self()}), 	    
	    loop(Parent, Name, StateName, StateData, Mod, infinity, HibernateAfterTimeout, Debug);
	{ok, StateName, StateData, Timeout} ->
	    proc_lib:init_ack(Starter, {ok, self()}), 	    
	    loop(Parent, Name, StateName, StateData, Mod, Timeout, HibernateAfterTimeout, Debug);
	{stop, Reason} ->
	    gen:unregister_name(Name0),
	    proc_lib:init_ack(Starter, {error, Reason}),
	    exit(Reason);
	ignore ->
	    gen:unregister_name(Name0),
	    proc_lib:init_ack(Starter, ignore),
	    exit(normal);
	{'EXIT', Reason} ->
	    gen:unregister_name(Name0),
	    proc_lib:init_ack(Starter, {error, Reason}),
	    exit(Reason);
	Else ->
	    Error = {bad_return_value, Else},
	    proc_lib:init_ack(Starter, {error, Error}),
	    exit(Error)
    end.

%%-----------------------------------------------------------------
%% The MAIN loop
%%-----------------------------------------------------------------
loop(Parent, Name, StateName, StateData, Mod, hibernate, HibernateAfterTimeout, Debug) ->
    proc_lib:hibernate(?MODULE,wake_hib,
		       [Parent, Name, StateName, StateData, Mod, HibernateAfterTimeout,
			Debug]);

loop(Parent, Name, StateName, StateData, Mod, infinity, HibernateAfterTimeout, Debug) ->
	receive
		Msg ->
			decode_msg(Msg,Parent, Name, StateName, StateData, Mod, infinity, HibernateAfterTimeout, Debug, false)
	after HibernateAfterTimeout ->
		loop(Parent, Name, StateName, StateData, Mod, hibernate, HibernateAfterTimeout, Debug)
	end;

loop(Parent, Name, StateName, StateData, Mod, Time, HibernateAfterTimeout, Debug) ->
    Msg = receive
	      Input ->
		    Input
	  after Time ->
		  {'$gen_event', timeout}
	  end,
    decode_msg(Msg,Parent, Name, StateName, StateData, Mod, Time, HibernateAfterTimeout, Debug, false).

wake_hib(Parent, Name, StateName, StateData, Mod, HibernateAfterTimeout, Debug) ->
    Msg = receive
	      Input ->
		  Input
	  end,
    decode_msg(Msg, Parent, Name, StateName, StateData, Mod, hibernate, HibernateAfterTimeout, Debug, true).

decode_msg(Msg,Parent, Name, StateName, StateData, Mod, Time, HibernateAfterTimeout, Debug, Hib) ->
    case Msg of
        {system, From, Req} ->
	    sys:handle_system_msg(Req, From, Parent, ?MODULE, Debug,
				  [Name, StateName, StateData, Mod, Time, HibernateAfterTimeout], Hib);
	{'EXIT', Parent, Reason} ->
	    terminate(
              Reason, Name, undefined, Msg, Mod, StateName, StateData, Debug);
	_Msg when Debug =:= [] ->
	    handle_msg(Msg, Parent, Name, StateName, StateData, Mod, Time, HibernateAfterTimeout);
	_Msg ->
	    Debug1 = sys:handle_debug(Debug, fun print_event/3,
				      {Name, StateName}, {in, Msg}),
	    handle_msg(Msg, Parent, Name, StateName, StateData,
		       Mod, Time, HibernateAfterTimeout, Debug1)
    end.

%%-----------------------------------------------------------------
%% Callback functions for system messages handling.
%%-----------------------------------------------------------------
system_continue(Parent, Debug, [Name, StateName, StateData, Mod, Time, HibernateAfterTimeout]) ->
    loop(Parent, Name, StateName, StateData, Mod, Time, HibernateAfterTimeout, Debug).

-spec system_terminate(term(), _, _, [term(),...]) -> no_return().

system_terminate(Reason, _Parent, Debug,
		 [Name, StateName, StateData, Mod, _Time, _HibernateAfterTimeout]) ->
    terminate(Reason, Name, undefined, [], Mod, StateName, StateData, Debug).

system_code_change([Name, StateName, StateData, Mod, Time, HibernateAfterTimeout],
		   _Module, OldVsn, Extra) ->
    case catch Mod:code_change(OldVsn, StateName, StateData, Extra) of
	{ok, NewStateName, NewStateData} ->
	    {ok, [Name, NewStateName, NewStateData, Mod, Time, HibernateAfterTimeout]};
	Else -> Else
    end.

system_get_state([_Name, StateName, StateData, _Mod, _Time, _HibernateAfterTimeout]) ->
    {ok, {StateName, StateData}}.

system_replace_state(StateFun, [Name, StateName, StateData, Mod, Time, HibernateAfterTimeout]) ->
    Result = {NStateName, NStateData} = StateFun({StateName, StateData}),
    {ok, Result, [Name, NStateName, NStateData, Mod, Time, HibernateAfterTimeout]}.

%%-----------------------------------------------------------------
%% Format debug messages.  Print them as the call-back module sees
%% them, not as the real erlang messages.  Use trace for that.
%%-----------------------------------------------------------------
print_event(Dev, {in, Msg}, {Name, StateName}) ->
    case Msg of
	{'$gen_event', Event} ->
	    io:format(Dev, "*DBG* ~tp got event ~tp in state ~tw~n",
		      [Name, Event, StateName]);
	{'$gen_all_state_event', Event} ->
	    io:format(Dev,
		      "*DBG* ~tp got all_state_event ~tp in state ~tw~n",
		      [Name, Event, StateName]);
	{timeout, Ref, {'$gen_timer', Message}} ->
	    io:format(Dev,
		      "*DBG* ~tp got timer ~tp in state ~tw~n",
		      [Name, {timeout, Ref, Message}, StateName]);
	{timeout, _Ref, {'$gen_event', Event}} ->
	    io:format(Dev,
		      "*DBG* ~tp got timer ~tp in state ~tw~n",
		      [Name, Event, StateName]);
	_ ->
	    io:format(Dev, "*DBG* ~tp got ~tp in state ~tw~n",
		      [Name, Msg, StateName])
    end;
print_event(Dev, {out, Msg, To, StateName}, Name) ->
    io:format(Dev, "*DBG* ~tp sent ~tp to ~tw~n"
	           "      and switched to state ~tw~n",
	      [Name, Msg, To, StateName]);
print_event(Dev, return, {Name, StateName}) ->
    io:format(Dev, "*DBG* ~tp switched to state ~tw~n",
	      [Name, StateName]).

handle_msg(Msg, Parent, Name, StateName, StateData, Mod, _Time, HibernateAfterTimeout) -> %No debug here
    From = from(Msg),
    case catch dispatch(Msg, Mod, StateName, StateData) of
	{next_state, NStateName, NStateData} ->	    
	    loop(Parent, Name, NStateName, NStateData, Mod, infinity, HibernateAfterTimeout, []);
	{next_state, NStateName, NStateData, Time1} ->
	    loop(Parent, Name, NStateName, NStateData, Mod, Time1, HibernateAfterTimeout, []);
        {reply, Reply, NStateName, NStateData} when From =/= undefined ->
	    reply(From, Reply),
	    loop(Parent, Name, NStateName, NStateData, Mod, infinity, HibernateAfterTimeout, []);
        {reply, Reply, NStateName, NStateData, Time1} when From =/= undefined ->
	    reply(From, Reply),
	    loop(Parent, Name, NStateName, NStateData, Mod, Time1, HibernateAfterTimeout, []);
	{stop, Reason, NStateData} ->
	    terminate(Reason, Name, From, Msg, Mod, StateName, NStateData, []);
	{stop, Reason, Reply, NStateData} when From =/= undefined ->
	    {'EXIT', R} = (catch terminate(Reason, Name, From, Msg, Mod,
					   StateName, NStateData, [])),
	    reply(From, Reply),
	    exit(R);
        {'EXIT', {undef, [{Mod, handle_info, [_,_,_], _}|_]}} ->
            ?LOG_WARNING(#{label=>{gen_fsm,no_handle_info},
                           module=>Mod,
                           message=>Msg},
                         #{domain=>[otp],
                           report_cb=>fun gen_fsm:format_log/1,
                           error_logger=>#{tag=>warning_msg}}),
            loop(Parent, Name, StateName, StateData, Mod, infinity, HibernateAfterTimeout, []);
	{'EXIT', What} ->
	    terminate(What, Name, From, Msg, Mod, StateName, StateData, []);
	Reply ->
	    terminate({bad_return_value, Reply},
		      Name, From, Msg, Mod, StateName, StateData, [])
    end.

handle_msg(Msg, Parent, Name, StateName, StateData, Mod, _Time, HibernateAfterTimeout, Debug) ->
    From = from(Msg),
    case catch dispatch(Msg, Mod, StateName, StateData) of
	{next_state, NStateName, NStateData} ->
	    Debug1 = sys:handle_debug(Debug, fun print_event/3,
				      {Name, NStateName}, return),
	    loop(Parent, Name, NStateName, NStateData, Mod, infinity, HibernateAfterTimeout, Debug1);
	{next_state, NStateName, NStateData, Time1} ->
	    Debug1 = sys:handle_debug(Debug, fun print_event/3,
				      {Name, NStateName}, return),
	    loop(Parent, Name, NStateName, NStateData, Mod, Time1, HibernateAfterTimeout, Debug1);
        {reply, Reply, NStateName, NStateData} when From =/= undefined ->
	    Debug1 = reply(Name, From, Reply, Debug, NStateName),
	    loop(Parent, Name, NStateName, NStateData, Mod, infinity, HibernateAfterTimeout, Debug1);
        {reply, Reply, NStateName, NStateData, Time1} when From =/= undefined ->
	    Debug1 = reply(Name, From, Reply, Debug, NStateName),
	    loop(Parent, Name, NStateName, NStateData, Mod, Time1, HibernateAfterTimeout, Debug1);
	{stop, Reason, NStateData} ->
	    terminate(
              Reason, Name, From, Msg, Mod, StateName, NStateData, Debug);
	{stop, Reason, Reply, NStateData} when From =/= undefined ->
	    {'EXIT', R} = (catch terminate(Reason, Name, From, Msg, Mod,
					   StateName, NStateData, Debug)),
	    _ = reply(Name, From, Reply, Debug, StateName),
	    exit(R);
	{'EXIT', What} ->
	    terminate(What, Name, From, Msg, Mod, StateName, StateData, Debug);
	Reply ->
	    terminate({bad_return_value, Reply},
		      Name, From, Msg, Mod, StateName, StateData, Debug)
    end.

dispatch({'$gen_event', Event}, Mod, StateName, StateData) ->
    Mod:StateName(Event, StateData);
dispatch({'$gen_all_state_event', Event}, Mod, StateName, StateData) ->
    Mod:handle_event(Event, StateName, StateData);
dispatch({'$gen_sync_event', From, Event}, Mod, StateName, StateData) ->
    Mod:StateName(Event, From, StateData);
dispatch({'$gen_sync_all_state_event', From, Event},
	 Mod, StateName, StateData) ->
    Mod:handle_sync_event(Event, From, StateName, StateData);
dispatch({timeout, Ref, {'$gen_timer', Msg}}, Mod, StateName, StateData) ->
    Mod:StateName({timeout, Ref, Msg}, StateData);
dispatch({timeout, _Ref, {'$gen_event', Event}}, Mod, StateName, StateData) ->
    Mod:StateName(Event, StateData);
dispatch(Info, Mod, StateName, StateData) ->
    Mod:handle_info(Info, StateName, StateData).

from({'$gen_sync_event', From, _Event}) -> From;
from({'$gen_sync_all_state_event', From, _Event}) -> From;
from(_) -> undefined.

%% Send a reply to the client.
reply({To, Tag}, Reply) ->
    catch To ! {Tag, Reply}.

reply(Name, {To, Tag}, Reply, Debug, StateName) ->
    reply({To, Tag}, Reply),
    sys:handle_debug(Debug, fun print_event/3, Name,
		     {out, Reply, To, StateName}).

%%% ---------------------------------------------------
%%% Terminate the server.
%%% ---------------------------------------------------

-spec terminate(term(), _, _, _, atom(), _, _, _) -> no_return().

terminate(Reason, Name, From, Msg, Mod, StateName, StateData, Debug) ->
    case erlang:function_exported(Mod, terminate, 3) of
	true ->
	    case catch Mod:terminate(Reason, StateName, StateData) of
		{'EXIT', R} ->
		    FmtStateData = format_status(terminate, Mod, get(), StateData),
		    error_info(
                      R, Name, From, Msg, StateName, FmtStateData, Debug),
		    exit(R);
		_ ->
		    ok
	    end;
	false ->
	    ok
    end,
    case Reason of
	normal ->
	    exit(normal);
	shutdown ->
	    exit(shutdown);
 	{shutdown,_}=Shutdown ->
 	    exit(Shutdown);
	_ ->
	    FmtStateData1 = format_status(terminate, Mod, get(), StateData),
	    error_info(
              Reason, Name, From, Msg, StateName, FmtStateData1, Debug),
	    exit(Reason)
    end.

error_info(Reason, Name, From, Msg, StateName, StateData, Debug) ->
    Log = [{Event, State} || {Event, State, _FormFunc} <- sys:get_log(Debug)],
    ?LOG_ERROR(#{label=>{gen_fsm,terminate},
                 name=>Name,
                 last_message=>Msg,
                 state_name=>StateName,
                 state_data=>StateData,
                 log=>Log,
                 reason=>Reason,
                 client_info=>client_stacktrace(From)},
               #{domain=>[otp],
                 report_cb=>fun gen_fsm:format_log/1,
                 error_logger=>#{tag=>error}}),
    ok.

client_stacktrace(undefined) ->
    undefined;
client_stacktrace({Pid,_Tag}) ->
    client_stacktrace(Pid);
client_stacktrace(Pid) when is_pid(Pid), node(Pid) =:= node() ->
    case process_info(Pid, [current_stacktrace, registered_name]) of
        undefined ->
            {Pid,dead};
        [{current_stacktrace, Stacktrace}, {registered_name, []}]  ->
            {Pid,{Pid,Stacktrace}};
        [{current_stacktrace, Stacktrace}, {registered_name, Name}]  ->
            {Pid,{Name,Stacktrace}}
    end;
client_stacktrace(Pid) when is_pid(Pid) ->
    {Pid,remote}.


format_log(#{label:={gen_fsm,terminate},
             name:=Name,
             last_message:=Msg,
             state_name:=StateName,
             state_data:=StateData,
             log:=Log,
             reason:=Reason,
             client_info:=ClientInfo}) ->
    Reason1 = 
	case Reason of
	    {undef,[{M,F,A,L}|MFAs]} ->
		case code:is_loaded(M) of
		    false ->
			{'module could not be loaded',[{M,F,A,L}|MFAs]};
		    _ ->
			case erlang:function_exported(M, F, length(A)) of
			    true ->
				Reason;
			    false ->
				{'function not exported',[{M,F,A,L}|MFAs]}
			end
		end;
	    _ ->
		Reason
	end,
    {ClientFmt,ClientArgs} = format_client_log(ClientInfo),
    {"** State machine ~tp terminating \n" ++
         get_msg_str(Msg) ++
     "** When State == ~tp~n"
     "**      Data  == ~tp~n"
     "** Reason for termination ==~n** ~tp~n" ++
         case Log of
             [] -> [];
             _ -> "** Log ==~n** ~tp~n"
         end ++ ClientFmt,
     [Name|error_logger:limit_term(get_msg(Msg))] ++
         [StateName,
          error_logger:limit_term(StateData),
          error_logger:limit_term(Reason1) |
          case Log of
              [] -> [];
              _ -> [[error_logger:limit_term(D) || D <- Log]]
          end] ++ ClientArgs};
format_log(#{label:={gen_fsm,no_handle_info},
             module:=Mod,
             message:=Msg}) ->
    {"** Undefined handle_info in ~p~n"
     "** Unhandled message: ~tp~n",
     [Mod, error_logger:limit_term(Msg)]}.

get_msg_str({'$gen_event', _Event}) ->
    "** Last event in was ~tp~n";
get_msg_str({'$gen_sync_event', _From, _Event}) ->
    "** Last sync event in was ~tp from ~p~n";
get_msg_str({'$gen_all_state_event', _Event}) ->
    "** Last event in was ~tp (for all states)~n";
get_msg_str({'$gen_sync_all_state_event', _From, _Event}) ->
    "** Last sync event in was ~tp (for all states) from ~p~n";
get_msg_str({timeout, _Ref, {'$gen_timer', _Msg}}) ->
    "** Last timer event in was ~tp~n";
get_msg_str({timeout, _Ref, {'$gen_event', _Msg}}) ->
    "** Last timer event in was ~tp~n";
get_msg_str(_Msg) ->
    "** Last message in was ~tp~n".

get_msg({'$gen_event', Event}) -> [Event];
get_msg({'$gen_sync_event', From, Event}) -> [Event,From];
get_msg({'$gen_all_state_event', Event}) -> [Event];
get_msg({'$gen_sync_all_state_event', From, Event}) -> [Event,From];
get_msg({timeout, Ref, {'$gen_timer', Msg}}) -> [{timeout, Ref, Msg}];
get_msg({timeout, _Ref, {'$gen_event', Event}}) -> [Event];
get_msg(Msg) -> [Msg].

format_client_log(undefined) ->
    {"", []};
format_client_log({From,dead}) ->
    {"** Client ~p is dead~n", [From]};
format_client_log({From,remote}) ->
    {"** Client ~p is remote on node ~p~n", [From, node(From)]};
format_client_log({_From,{Name,Stacktrace}}) ->
    {"** Client ~tp stacktrace~n"
     "** ~tp~n",
     [Name, error_logger:limit_term(Stacktrace)]}.

%%-----------------------------------------------------------------
%% Status information
%%-----------------------------------------------------------------
format_status(Opt, StatusData) ->
    [PDict, SysState, Parent, Debug, [Name, StateName, StateData, Mod, _Time, _HibernateAfterTimeout]] =
	StatusData,
    Header = gen:format_status_header("Status for state machine",
                                      Name),
    Log = [{Ev, St} || {Ev, St, _FormFunc} <- sys:get_log(Debug)],
    Specfic = format_status(Opt, Mod, PDict, StateData),
    Specfic = case format_status(Opt, Mod, PDict, StateData) of
		  S when is_list(S) -> S;
		  S -> [S]
	      end,
    [{header, Header},
     {data, [{"Status", SysState},
	     {"Parent", Parent},
	     {"Logged events", Log},
	     {"StateName", StateName}]} |
     Specfic].

format_status(Opt, Mod, PDict, State) ->
    DefStatus = case Opt of
		    terminate -> State;
		    _ -> [{data, [{"StateData", State}]}]
		end,
    case erlang:function_exported(Mod, format_status, 2) of
	true ->
	    case catch Mod:format_status(Opt, [PDict, State]) of
		{'EXIT', _} -> DefStatus;
		Else -> Else
	    end;
	_ ->
	    DefStatus
    end.