I was writing one last night…
Maybe it can help You.
defmodule EventStore.Core.ListenersProvider do
use GenServer
require Logger
@name __MODULE__
def start_link(_) do
GenServer.start_link(@name, nil, name: @name)
end
def register(pid, filter_fun \\ fn _ -> true end)
def register(pid, filter_fun) when is_function(filter_fun) do
GenServer.call(@name, {:register, pid, filter_fun})
end
def unregister(pid) do
GenServer.cast(@name, {:unregister, pid})
end
def get_listeners do
@name
|> :ets.match_object({:"$1", :"$2", :_})
|> Enum.map(fn {pid, filter_fun, _ref} -> {pid, filter_fun} end)
end
def stop, do: GenServer.cast(@name, :stop)
@impl GenServer
def init(_) do
Logger.debug(fn -> "#{@name} is starting}" end)
#
Process.flag :trap_exit, true
:ets.new(@name, [:set, :protected, :named_table])
{:ok, nil}
end
@impl GenServer
def handle_call({:register, pid, filter_fun}, _from, _state) do
ref = Process.monitor(pid)
:ets.insert_new(@name, {pid, filter_fun, ref})
{:reply, :ok, nil}
end
@impl GenServer
def handle_cast({:unregister, pid}, _state) do
case :ets.match(@name, {pid, :_, :"$1"}) do
[[ref]] when is_reference(ref) -> Process.demonitor(ref)
_ -> nil
end
:ets.delete(@name, pid)
{:noreply, nil}
end
@impl GenServer
def handle_cast(:stop, _state), do: {:stop, :normal, nil}
@impl GenServer
def handle_info({:DOWN, _ref, :process, pid, _status}, _state) do
:ets.delete(@name, pid)
{:noreply, nil}
end
@impl GenServer
def terminate(reason, _state) do
Logger.debug(fn -> "#{@name} is stopping : #{inspect reason}" end)
#
:ets.delete(@name)
:ok
end
end
