Starting and Terminating child of simple
I have a simple application target_interceptor that upon receiving register and unregister messages, starts or terminates workers under simple_one_for_one rpc_server_supervisor .
The code of supervisor rpc_server_supervisor :
init([]) ->
MaxRestart = 5,
MaxTime = 3600,
{ok, {{simple_one_for_one, MaxRestart, MaxTime},
[{rbmq_rpc_server,
{rbmq_rpc_server, start_link, []},
temporary,
10000,
worker,
[rbmq_rpc_server]}]}}.
register message of target_interceptor :
handle_cast({register, Args}, S = #state{channel = Channel, supervisor=Sup, refs=R, qs_link = QSLinks}) ->
{Connection, QueueName, Node} = Args,
{Ok, Pid} = supervisor:start_child(Sup, [Connection, QueueName, Node]),
Ref = erlang:monitor(process, Pid),
{noreply, S#state{refs=gb_sets:add(Ref,R), qs_link=orddict:append(binary_to_list(QueueName),Pid,QSLinks)}};
unregister message of target_interceptor :
handle_cast({unregister,{QueueName}}, S = #state{supervisor = Sup, qs_link = QSLinks}) ->
Pid = orddict:fetch(QueueName,QSLinks)
case supervisor:terminate_child(Sup,Pid) of
ok -> Success = true;
Error -> io:format("Error ~p~n",[Error]),
Success = false
end,
{noreply, S#state{qs_link=orddict:erase(QueueName,QSLinks)}}
my version of Erlang is : R15B01
The first problem is when handling register action the tuple {OK, Pid} = {error, <0.57.0>}; even though it indicates that something went wrong, the gen_server rbmq_rpc_server on Pid 57 is working correctly and responding to messages. Why is the return value of start_child function error? What went wrong?
The second problem is when handling unregister action, where supervisor:terminate_child(Sup,Pid) returns {error,simple_one_for_one) even though I reference Pid not ChildID. Why is it behaving like this and how could I dynamically and individually terminate children of my supervisor?
EDIT: Both target_interceptor and rpc_server_supervisor are supervised by rbmq_sup_sup supervisor :
init({Nodeid, Node}) ->
MaxRestart = 1,
MaxTime = 3600,
{ok, {{rest_for_one, MaxRestart, MaxTime},
[{server,
{target_interceptor, start_link, [target, self(), {Nodeid, Node}]},
permanent,
5000,
worker,
[target_interceptor]}]}}.
EDIT: rpc_server_supervisor is called in target_interceptor init() function (Sup here is rbmq_sup_sup supervisor):
handle_info({start_worker_supervisor, Sup}, S = #state{}) ->
{ok, Pid} = supervisor:start_child(Sup, ?SPEC),
link(Pid),
{noreply, S#state{sup=Pid}};
-define(SPEC,
{rpc_server_sup,
{rpc_server_sup, start_link, []},
temporary,
10000,
supervisor,
[rpc_server_sup]}).
I will add to this as I get time.
A first point is that {Ok,Pid} matches any tuple even {error,Error} so calling the variable Ok might not be the best choice.
A quick question: in handle_cast({register,Args}, ... you do binary_to_list(QueueName) for the key but in handle_cast({unregister,{QueueName}}, ... you just use QueueName for the key. Why? Why do you keep a list of pids for each QueueName as unregister seems to clear them all? This will also mean that when you do Pid = orddict:fetch(QueueName,QSLinks) Pid will be a list of pids not one.
In rbmq_sup_sup you only start target_interceptor .
Are the rbmq_rpc_server processes registered?
EDIT:
I think the reason for error when doing unregister is that you have saved the pid with orddict:append/3 which saves the value in a list, even the first time, while you are getting the value with orddict:fetch/2 which returns the whole list in this case. So Pid is a list. You then try kill the child with Pid which is a list of the pid not the pid which is what supervisor:terminate_child/2 is complaining about.
If you only have one pid per QueueName then you should do orddict:store(binary_to_list(QueueName), Pid, QSLinks) instead. Then orddict:fetch/2 will return the pid.
PS The idea behind orddict:append/3 is that you can add more values to the same key and it keeps a list of all the values.
上一篇: 使用多个erlang行为
下一篇: 开始和终止简单的孩子