registering_a_genserver_with_gproc.ex

defmodule Name do
  use GenServer

  def start_link(data) do
    GenServer.start_link(__MODULE__, data, name: via_name(data))
  end

  # do what ever you need to do with data
  defp via_name(data),
    do: {:via, :gproc, gproc_name(data)}

  defp gproc_name(data),
    do: {:n, :l, {__MODULE__, :something, data}}
    # it is good to keep __MODULE__ in the registration name for later debugging in prod

  # ... the rest of the GenServer implementation
end

from twitter, not tested. The thing here is to use MODULE or similar to ensure your Gen* are cleanly separated in gproc. You probably want tighter restrictions on data (e.g. simple short binary or similar) to avoid refcount issues or just things getting too confusing :-)

defmodule Name do
  use GenServer

  def start_link(data) do
    registry = {:via, :gproc, {:n, :l, {__MODULE__, data}}}
    GenServer.start_link(__MODULE__, data, name: registry)
  end

  # ... the rest of the GenServer implementation
end

I usually have a Name.start/1 call that either spawns a new GenServer if not already started, or returns pid of the existing one if found.

I like the idea of that. It simplifies the api a great deal when it comes to using it. 99% of the time I would like to just get the process.