ndrean
I am circling around with the following problem and no post helped me so far.
I have a GenServer module named MyApp.Repo here that runs GenServer.cast but GenServer.call returns an error and kills the process.
GenServer MyApp.Repo terminating
** (ArgumentError) unknown registry: MyApp.Repo
When I start the app, I check:
iex> Enum.member?(Process.registered(), MyApp.Repo)
=> true
The GenServer module MyApp.Repo is supervised as a child by the Application supervisor.
children = [
MyAppWeb.Telemetry,
{Phoenix.PubSub, name: MyApp.PubSub, adapter: Phoenix.PubSub.PG2},
MyApp.Repo,
MyAppWeb.Endpoint
...
MyApp.Repo module is a basic GenServer that registers a :name:
def start_link(),
do: GenServer.start_link(__MODULE__, [], name: __MODULE__)
def save_with_cast(user),
do: GenServer.cast(__MODULE__, {:new, user})
def save_with_call(user) do
IO.inspect(user, label: "CALL______")
GenServer.call(__MODULE__, {:new, user})
end
def handle_call({:new, user}, _from,_state) do
IO.puts("CALL______")
Phoenix.PubSub.broadcast_from(MyApp.PubSub, self(), @topic, {:perform_new, user})
{:reply, user, [])
end
def handle_cast({:new, user}, _state) do
Phoenix.PubSub.broadcast_from(MyApp.PubSub, self(), @topic, {:perform_new, user})
{:noreply, []}
end
def handle_info({:perform_new, message}, _state) do
...
MyApp.save_with_cast(user) runs :ok but not MyApp.save_with_call(user).
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msimonborg
Can you paste the implementations of
handle_cast/2andhandle_call/3, and the stacktrace of theArgumentError?ndrean
I added some code above, and the stacktrace is below:
msimonborg
Where does the
messagevariable come from?Is
MyApp.Repopubsub broadcasting to itself?What is in your
terminate/2callback? It looks like you might be trying to unregister from a nonexistent registry withRegistry.unregister(__MODULE__, key)ndrean
messagewasuserin fact, I copied the wrong one. I changed the names to be more readable.Then I added this because I saw this somewhere and wasn’t sure
OK, I removed this. Now I have a different error:
This was my inspiration
It was a typo (
:nwinstead of:newin thehandle_call).castandcallrun normal. Thanks for the guidance on thisterminatefunction. So the typo killed or stopped and the termination function destroyed things I believe.msimonborg
There it is!
unsubscribe/2, likebroadcastandsubscribeand friends, needs a valid PubSub name as the first argument.Phoenix.PubSub.unsubscribe(MyApp.PubSub, @topic)would be correct, it infers thepidto unsubscribe automatically. That is the cause of your** (ArgumentError) unknown registry: MyApp.Repo. Unsubscribing in theterminate/2callback is not necessary by the way, you are subscribed bypidwhich is automatically cleaned up if the process restarts. Also you do not need pubsub at all to send messages to yourself, just usesend(self(), {:perform_new, user})ifMyApp.Repois the only process interested in the message. And even then, you only need to do this if you require async execution, otherwise you can implement theperform_newdirectly in the original callback. Having separatecallandcasthandlers that implement the same message sending toself()like this is kind of an anti-pattern in my opinion,callimplies that it’s a synchronous operation but you are forcing it to be async so there’s no reason to have acallimplementation.All that said, this error is raising because your process is already crashing somewhere else. If you remove this
terminate/2callback entirely you may get a more helpful error message about what the real problem is.msimonborg
Double check the
handle_call/3function head, this is indicating you made a mistake there. Or you might need torecompile()your project if you’ve added this function since starting your sessionmsimonborg
With the way you’re editing your posts as you solve your problem it makes the thread harder to follow for anyone else reading it, and makes it look like I’m replying to a problem you already solved lol. Might want to post new developments as new comments especially if previous posts have already been replied to.
ndrean
ok! Thanks!
ndrean
Yes, this needs an explanation. I am “pubsubing” to other nodes, not sending messages to self()
msimonborg
Gotcha, that makes sense