Elixir: How to send notification to server in handle_cast?

Question

I am making basic Elixir server/client module that can send/receive asynchronous messages. The module looks like following.

defmodule Bitcoin.WorkerOne do
use GenServer

def start_link(opts) do
    IO.puts " - Worker 1 started - "
    GenServer.start_link(__MODULE__,:ok, opts)
end

def set_message(server, name, mid) do
    GenServer.cast(server, {:set_message, name})
end

#callbacks
def init(:ok) do
    names = []
    {:ok, names}
end

def handle_cast({:set_message, name},names) do
    IO.puts "- new state is - " 
    names = names ++name
    IO.inspect names
    {:noreply,names}
end

end

I am initiating the processes through iex console using.

{:ok, pid1} = Bitcoin.WorkerOne.start_link([])
Bitcoin.WorkerOne.get_message(pid1, ["one"])

After the above , the state gets change to ['one'] (initially empty list). I want to send a notification back to the server that the state has been updated. Can I call 'Genserver.cast' inside the handle_cast, in order to send a message back?

Answer 1

You should include the sender's pid in the message to the server when using casts where you want to send a notification, but it's better to use calls combined with GenServer.reply/2, returning {:noreply, state} in the handle_call callback for that use case, to get the guarantee that the server received the request. Manually reimplementing replies is a lot of work depending on what guarantees you need, so you should avoid it.