Thanks for enlightening me. I will dig into the PartitionSupervisor. Many tools with OTP! It seems to make powerful and lightweight apps. It is surprising it’s not more widely used, for web apps I mean.
ndrean
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ndrean
Progressing slowly with Elixir. If I don’t use state in a module but only use the messaging part, I understand I may not need a Genserver. I used a supervised Task and use a receive do loop in the module. This seems to work (you can subscribe and receive the event/data between distributed nodes). However, this looks like I’m using Genserver with more complications and no benefit, aren’t I?
# some module broadcasts an event/payload:
Phoenix.PubSub.broadcast(MyApp.PubSub, "node_up", {:new data})
# the "listener" module is started in the "children" array of the app supervisor
children = [..., {MyApp.Listener, opts},...]
defmodule MyApp.Listener
# no need "child_spec"
use Task, restart: : permanent
def start_link(opts) do
task = Task.start_link(__MODULE__, :start, [opts])
IO.inspect(task, label: "start_link")
end
def start(opts) do
do_something_with(opts)
Phoenix.PubSub.subscribe(MyApp.PubSub, "node_up")
monitor()
end
def monitor() do
receive do
{:new, payload} ->
IO.inspect(payload, label: "Node UP -> action with: ")
monitor()
end
end
end
Side note: I can’t reach for Process.whereis(MyApp.Listener) == nil, however the process appears by pid under the supervision tree.
0
msimonborg
My take on this comment that I think you’re referencing was that it’s guiding you to consider not using a GenServer for bare function calls when the GenServer’s state is being ignored. The original code you posted didn’t have any use for the GenServer state, nor was the GenServer receiving and responding to any pubsub messages, so it could have been written as a module and functions to allow parallel execution from any process, rather than serial execution from a single process.
Now that it’s clear you need a process to listen for and respond to changes in cluster membership, it is appropriate to use a GenServer for that. I think the way you’re using the Task as a replacement is a misunderstanding of the basis for that original comment, and a misuse of Tasks, which are really an abstraction for one-off computations. A GenServer is a general-purpose abstraction for listening to and handling messages in a loop, so it’s the right tool for the job IMO.
AFAIK you can’t register a name for a Task, precisely because they’re not meant to be used as this type of long running “reachable” process
0
ndrean
Yes, when I read about the Task, it seemed like an inappropriate tool, that’s why I posted this. It was however instructive! Now it makes sense. Thanks.
1