supervisor:start_child returns child,undefined - erlang

seem to be running in to an issue when calling add_location
-module(test_sup).
-version(1.0).
-behaviour(supervisor).
-export([start_link/0,add_location/3]).
-export([init/1]).
-define(SERVER, ?MODULE).
start_link() ->
supervisor:start_link({local,?SERVER}, ?MODULE, no_args).
add_location(SupPid, Spaces, Occupied) ->
supervisor:start_child(SupPid, child(test_location, [Spaces, Occupied])).
init(no_args) ->
{ok, {{rest_for_one, 5, 2000}, []}}.
child(Module, Args) ->
{Module, {Module, start_link, Args},
permanent, brutal_kill, worker, [Module]}.
I call....
{_, SupPid} = test_sup:start_link().
{Success, LocRef} = test_sup:add_location(SupPid, 1, 0)
But add_location is always returning an error..
{child,undefined,test_location,
{test_location,start_link,[1,0]},
permanent,brutal_kill,worker,
[zc_pickup_location]}}
Any ideas why?

My Error - The method start_link in test_location was returning something the supervisor didnt understand.

Related

Returning State from a gen_server cast

I am following http://learnyousomeerlang.com/static/erlang/kitty_gen_server.erl .
I have my application logic inside of temple.erl. All of this code is tested & runs as I expect it to. My land.erl is intended to be the server that contains the Temple.
My understanding (please correct any ignorance) is that I can use gen_server to abstract message passing and keep track of state with minimal overhead.
I understand that the second tuplevalue in my init function
init([]) -> {ok, temple:new()}. is my server's state - in this case, the return value of temple:new().
So I c(land). (code below), and try this:
19> {ok, Pid2} = land:start_link().
{ok,<0.108.0>}
20> land:join(Pid2, a).
ok
and I just get the atom ok back when I send the join message From reading the code and comparing my experiences running the kitty_gen_server, I think the state is updated correctly with the value temple:join(Temple, Name), but the ok atom is the response value from
handle_call({join, Name}, _From, Temple) ->
{reply, ok, temple:join(Temple, Name)};
how can I update my state with temple:join(Temple, Name), and then return this value to the client? I don't want to call the same function twice eg.
handle_call({join, Name}, _From, Temple) ->
{reply, temple:join(Temple, Name), temple:join(Temple, Name)};
So looking at the kitty_gen_server I tried
handle_call({join, Name}, _From, Temple) ->
[{reply, JoinedTemple, JoinedTemple} || JoinedTemple <- temple:join(Temple, Name)];
and I get a function clause crash when I try this with a message about syntax error ||, and then I see this is only for list comprehensions..
how can I compute the value of temple:join(Temple, Name)] and return to the caller of land:join and update the Land's state?
-module(land).
-behaviour(gen_server).
-export([start_link/0, join/2, input/3, fight/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
start_link() ->
gen_server:start_link(?MODULE, [], []).
join(Pid, Name) ->
gen_server:call(Pid, {join, Name}).
input(Pid, Action, Target) ->
gen_server:call(Pid, {input, Action, Target}).
fight(Pid) ->
gen_server:call(Pid, fight).
init([]) -> {ok, temple:new()}.
handle_call({join, Name}, _From) ->
{reply, ok, temple:join(Name)}.
handle_call({join, Name}, _From, Temple) ->
{reply, temple:join(Temple, Name), temple:join(Temple, Name)};
handle_call(terminate, _From, Temple) ->
{stop, normal, ok, Temple}.
handle_info(Msg, Temple) ->
io:format("Unexpected message: ~p~n",[Msg]),
{noreply, Temple }.
terminate(normal, Temple) ->
io:format("Temple bathed in blood.~p~n", [Temple]),
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
handle_cast(_, Temple) ->
{noreply, Temple}.
You can store the new state in a variable and then return a tuple containing that variable twice:
handle_call({join, Name}, _From, Temple) ->
NewTemple = temple:join(Temple, Name),
{reply, NewTemple, NewTemple};

How do I start yaws to run in embedded mode?

I've spent several hours trying to troubleshoot this issue using the yaws documentation and web searches. The existing threads here haven't helped me.
I am new to erlang and I am trying to run yaws in embedded mode using the sample code provided on http://yaws.hyber.org/embed.yaws. I am missing something because I cannot get it to work. I have four files:
ybed.app
{application, ybed_app,
[
{description, "Yaws Embedded Application Test"},
{vsn, "0.1.0"},
{registered, []},
{applications, [kernel, stdlib, yaws]},
{mod, {ybed_app, []}},
{env, []}
]}.
ybed_app.erl
-module(ybed_app).
-behaviour(application).
%% Application callbacks
-export([start/2,
stop/1]).
start(_StartType, _StartArgs) ->
case ybed_sup:start_link() of
{ok, Pid} ->
{ok, Pid};
Other ->
{error, Other}
end.
stop(_State) ->
ok.
ybed_sup.erl
-module(ybed_sup).
-behaviour(supervisor).
%% API
-export([start_link/0]).
%% Supervisor callbacks
-export([init/1]).
start_link() ->
supervisor:start_link({local, ?MODULE}, ?MODULE, []).
init([]) ->
YBed = {ybed, {ybed,start,[]},
permanent,2000,worker,[ybed]},
{ok,{{one_for_all,0,1}, [YBed]}}.
ybed.erl
-module(ybed).
-compile(export_all).
start() ->
{ok, spawn(?MODULE, run, [])}.
run() ->
Id = "embedded",
GconfList = [{id, Id}],
Docroot = "/tmp",
SconfList = [{port, 8000},
{servername, "foobar"},
{listen, {127,0,0,1}},
{docroot, Docroot}],
{ok, SCList, GC, ChildSpecs} =
yaws_api:embedded_start_conf(Docroot, SconfList, GconfList, Id),
[supervisor:start_child(ybed_sup, Ch) || Ch <- ChildSpecs],
yaws_api:setconf(GC, SCList),
{ok, self()}.
When I compile it (successfully) and try to start the application, I get a return value:
{error,{not_loaded,yaws}}
When I try to run the compiled ybed.erl, ybed:run(), I get:
** exception error: undefined function yaws_api:embedded_start_conf/4
in function ybed:run/0 (src/ybed.erl, line 16)
If I start yaws before I start the application, it still doesn't work.
I am not trying to build releases yet, just compile and test yaws in embedded mode. Can anyone tell me what I'm missing?
Thanks in advance
When you get error
** exception error: undefined function yaws_api:embedded_start_conf/4
in function ybed:run/0 (src/ybed.erl, line 16)
You clearly don't have yaws_api.beam in your code server search path. Start your erl with proper -pa argument or call code:add_patha/1 in your application initialization if you are not planning use embedded mode.
BTW there is a neat way how to start yaws under your own supervisor described in yaws documentation but without complete code so here we go in one module and with neat debugging resource and preparation for REST servicing.
-module(ybed_yaws).
-behaviour(supervisor).
-include_lib("yaws/include/yaws_api.hrl").
%% API
-export([start_link/0]).
%% Supervisor callbacks
-export([init/1]).
%% Internal functions export
-export([init_yaws/1, out/1]).
%%%===================================================================
%%% Defaults
%%%===================================================================
default_global() ->
#{id => "yaws", logdir => "log"}.
default_server() ->
#{port => 9900,
listen => {0,0,0,0},
docroot => "www",
appmods => [{"/", ?MODULE}]}.
%%%===================================================================
%%% API functions
%%%===================================================================
start_link() ->
supervisor:start_link(?MODULE, []).
%%%===================================================================
%%% Supervisor callbacks
%%%===================================================================
init([]) ->
{ok,
{{one_for_all, 0, 1},
[#{id => init_yaws,
start => {?MODULE, init_yaws, [self()]},
restart => transient}]
}}.
%%%===================================================================
%%% Internal functions
%%%===================================================================
init_yaws(Sup) ->
{ok, proc_lib:spawn_link(fun() -> config(Sup) end)}.
ensure_dir(Dir) ->
{ok, App} = application:get_application(),
D = filename:join([code:priv_dir(App), Dir])
filelib:ensure_dir(filename:join([D, "foo"])),
D.
config(Supervisor) ->
#{id := Id} = GCMap = default_global(),
#{docroot := DR} = SCMap = default_server(),
Docroot = ensure_dir(DR),
{ok, SC, GC, ChildSpecs} =
yaws_api:embedded_start_conf(
Docroot,
maps:to_list(SCMap#{docroot => Docroot}),
maps:to_list(GCMap),
Id),
[supervisor:start_child(Supervisor, Ch) || Ch <- ChildSpecs],
yaws_api:setconf(GC, SC),
ok.
-compile({inline, [h/1, f/2]}).
h(A) when is_atom(A) -> h(atom_to_binary(A, latin1));
h(S) -> yaws_api:htmlize(S).
f(Fmt, Args) -> yaws_api:f(Fmt, Args).
box(Str) ->
{'div',[{class,"box"}],
{pre, [], h(Str)}}.
out(A) ->
PathString = case A#arg.pathinfo of
undefined -> "";
P -> P
end,
Path = string:tokens(PathString, "/"),
Method = A#arg.req#http_request.method,
out(A, Method, Path).
out(A, Method, Path) ->
{ehtml,
{html, [],
[{head},
{body, [],
[
{h5, [], "Paths:"},
{hr},
box(f("Method = ~p~n"
"Path = ~p~n"
"A#arg.querydata = ~p~n",
[Method,
Path,
A#arg.querydata])),
{h5, [], "Headers:"},
{hr},
{ol, [], yaws_api:reformat_header(
A#arg.headers,
fun(H, V)->
{li, [], [h(H), ": ", {code, [], h(V)}]}
end
)}
]}
]}
}.
Note the way how is yaws initialised in OTP compliant transient process but without gen_server.
Add {yaws, [{embedded, true}]} to your .config file to keep yaws application common services from starting. It will work even without it but it will not be fully embedded.

How to stop a tcp_listener implemented as a gen_server in erlang

I implemented a tcp_listener as a gen_server(). I have a function called start_link(Port) creates a tcp_listener at that port. Now, I have trouble understanding how to tell the tcp_listener to stop listening through stop().
I tried calling a function like this with stop.
stop() -> gen_server:cast(?MODULE, shutdown)
in the terminate/2 function I tried closing the listening socket but failed.
terminate(_Reason, State = #state{lsocket = LSocket}) ->
gen_tcp:close(LSocket),
NewState = State#state{lsocket = null},
{ok, NewState}.
If I close the listening socket, what happens to the accepted connections that I spawned.
Thank you!
start_link(Port) when is_integer(Port) ->
State = #state{port = Port},
gen_server:start_link({local, ?MODULE}, ?MODULE, State, []).
init(State = #state{port = Port}) ->
io:format("Supervisor started me and I am listening at ~p ~n", [Port]),
case gen_tcp:listen(Port, ?TCP_OPTIONS) of
{ok, LSocket} ->
NewState = State#state{lsocket = LSocket},
spawn(fun() -> accept(NewState) end),
{ok, NewState};
{error, Reason} ->
{stop, Reason}
end.
accept(State = #state{lsocket = LSocket}) ->
case gen_tcp:accept(LSocket) of
{ok, Socket} ->
Pid = spawn(fun() ->
io:format("Connection accepted ~n"),
loop(Socket)
end),
gen_tcp:controlling_process(Socket, Pid),
accept(State);
{error, closed} -> error
end.
loop(Socket) ->
case gen_tcp:recv(Socket, 0) of
{ok, Data} ->
gen_tcp:send(Socket, Data),
loop(Socket);
{error, closed} ->
ok
end.
I recommend you have a look at this chapter in the Learn You Some Erlang book, in particular:
Both sockets can send messages in the same way, and can then be closed with gen_tcp:close(Socket). Note that closing an accept socket will close that socket alone, and closing a listen socket will close none of the related and established accept sockets, but will interrupt currently running accept calls by returning {error, closed}.
So it should be just a matter of calling gen_tcp:close(Socket) on all sockets.

About a client for pusher written in Erlang

I want to write a module which need to be able to push message to pusher in Erlang. I found this repo https://github.com/bradfordw/pusherl, which is not maintained anymore, but I think I can adapt to make it work. I followed the README, and I ran successfully all the Rebar command. Then I open the rebar console by the command
./rel/pusherl/bin/pusherl console
So the server should start. But then when I try to call
gen_server:call(pusherl_server, {push, {"ChannelName", "EventName", "Payload"}}).
Then it throws error:
exception exit: {noproc,{gen_server,call,
[pusherl_server,
{push,
{"ChannelName","EventName","Payload"}}]}}
in function gen_server:call/2 (gen_server.erl, line 182)
I'm quite new with Erlang and OTP, and it takes me half of the day to make it work but not successful. Please help me to solve this. I really appreciate.
By the way, if you know any other pusher client, please suggest me. Thanks a lot.
Here is the code to for gen_server callback:
-module(pusherl_server).
-behaviour(gen_server).
-define(SERVER, ?MODULE).
-define(JP, fun(K,V) -> string:join([K,V],"=") end).
-record(state,{app_id, key, secret}).
-export([start_link/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
start_link() ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
init(_) ->
{ok, PusherAppId} = application:get_env(pusher_app_id),
{ok, PusherKey} = application:get_env(pusher_key),
{ok, PusherSecret} = application:get_env(pusher_secret),
{ok, #state{app_id=PusherAppId, key=PusherKey, secret=PusherSecret}}.
handle_call({push, {ChannelName, EventName, Payload}}, _From, State) ->
case http_request(ChannelName, EventName, Payload, State) of
{ok, _} -> {reply, ok, State};
{error, _} -> {reply, error, State}
end;
handle_call(_Request, _From, State) ->
{noreply, ok, State}.
handle_cast({push, {ChannelName, EventName, Payload}}, State) ->
case http_request(ChannelName, EventName, Payload, State) of
{ok, _} -> {noreply, ok, State};
{error, _} -> {noreply, error, State}
end;
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
http_request(ChannelName, EventName, Payload, Config) when is_list(ChannelName), is_record(Config, state) ->
{ok, ReqProps} = http_request_props(Payload, EventName, ChannelName, Config),
httpc:request(post, ReqProps, [], []).
http_request_props(Payload, EventName, ChannelName, #state{app_id=AppId, key=AppKey, secret=AppSecret}) ->
Md5String = lists:flatten([io_lib:format("~2.16.0b",[N]) || <<N>> <= crypto:md5(Payload)]),
ToSign = ["POST",
lists:flatten(["/apps/", AppId, "/channels/", ChannelName, "/events"]),
string:join([?JP("auth_key", AppKey),
?JP("auth_timestamp", get_time_as_string()),
?JP("auth_version", "1.0"),
?JP("body_md5", Md5String),
?JP("name", EventName)
],"&")
],
AuthSignature = signed_params(ToSign, AppSecret),
QueryParams = [
?JP("auth_key", AppKey),
?JP("auth_timestamp", get_time_as_string()),
?JP("auth_version","1.0"),
?JP("body_md5", Md5String),
?JP("auth_signature", AuthSignature),
?JP("name", EventName)
],
Url = http_api_url(AppId, ChannelName, QueryParams),
{ok, {Url, [], "application/x-www-form-urlencoded", Payload}}.
http_api_url(AppId, ChannelName, QueryParams) ->
QueryString = string:join(QueryParams,"&"),
lists:flatten(["http://api.pusherapp.com/apps/",AppId,"/channels/",ChannelName,"/events?", QueryString]).
get_time_as_string() ->
{M, S, _} = now(),
integer_to_list(((M * 1000000) + S)).
signed_params(Params, Secret) ->
lists:flatten([io_lib:format("~2.16.0b",[N]) || <<N:8>> <= sha2:hmac_sha256(Secret, string:join(Params,"\n"))]).
noproc means that the process you're trying to call is not running. You need to start it with:
pusherl_server:start_link().
Note that this will link the pusherl_server process to the calling process. If you're running this in the shell, and then do something that causes an error, the error will propagate across the link to the pusherl_server process and kill it, so then you have to start it again.
To avoid that, you can either unlink the process after starting it:
{ok, Pid} = pusherl_server:start_link().
unlink(Pid).
or add a start function to the module, that does the same as start_link except it calls gen_server:start instead of gen_server:start_link.

Erlang: list all records

Please help me, (btw my English is not very good). I want to list all records that have been created for a gen_server, for example, if a had the following code:
-module(mod).
-record(person, {name, phone}).
start_link(Param1, Param2) ->
gen_server:start_link(?MODULE, [Param1, Param2], []).
init([Param1, Param2]) ->
{ok, #person{name=Param1,phone=Param2}}.
I can called:
mod:start_link(Maria,22222).
mod:start_link(Jose,9348).
mod:start_link(lol,232).
After that i want to see all the records that i have created and put it on a list. How can i do this?
You should read this doc: http://www.erlang.org/doc/man/gen_server.html#start_link-3.
The start_link/3 just start the gen_server, do store the record data.
-module(record_make).
-compile(export_all).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
-behaviour(gen_server).
-define(SERVER, ?MODULE).
-record(state, {persons = []}).
-record(person, {name, phone}).
start_link() ->
gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
init([]) ->
{ok, #state{}}.
handle_call({create, Name, Phone}, _Frome, State = #state{persons = Persons}) ->
NewPerson = #person{name = Name, phone = Phone},
{reply, ok, State#state{persons = [NewPerson | Persons]}};
handle_call(list, _From, State = #state{persons = Persons}) ->
io:format("~p~n", [Persons]),
{reply, ok, State};
handle_call(_Request, _From, State) ->
Reply = ok,
{reply, Reply, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
create(Name, Phone) ->
gen_server:call(?MODULE, {create, Name, Phone}).
list() ->
gen_server:call(?MODULE, list).
You can do like this:
1> c(record_make)
1> .
{ok,record_make}
2> record_make:start_link().
{ok,<0.41.0>}
3> record_make:create("yang", "123").
ok
4> record_make:create("zhang", "456").
ok
5> record_make:list().
[{person,"zhang","456"},{person,"yang","123"}]
ok
6>
No chance to get the information in this way: there is one record per gen_server and the information is lost as soon as the sever die. If you need this information you shold add a dedicated process to keep the information ({Pid,Record} or record number ...). The information can be updated during the init and the terminate function via function such as record_manager:create/1 and record_manager:delete/1. You can also store them in a shared ets.

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