GenServer.call produces "no process" error

Question

I have this GenServer/client implementation for a naive cache using ETS:

defmodule Cache do
    use GenServer

    def start_link() do
        GenServer.start_link(__MODULE__, [])
    end

    def fetch(key, def_value) do
        case get(key) do
            {:not_found} -> set(key, def_value)
            {:found, result} -> result
        end
    end

    defp get(key) do
        case GenServer.call(__MODULE__, {:get, key}) do
            [] -> {:not_found}
            [{_, result}] -> {:found, result}
        end
    end

    defp set(key, value) do
        GenServer.call(__MODULE__, {:set, key, value})
    end

    # GenServer callbacks

    def handle_call({:get, key}, _from, state) do
        result = :ets.lookup(:my_table, key)
        {:reply, result, state}
    end

    def handle_call({:set, key, value}, _from, state) do
        true = :ets.insert(:my_table, {key, value})
        {:reply, value, state}
    end

    def init(_args) do
        :ets.new(:my_table, [:named_table, :set, :private])
        {:ok, %{}}
    end

end

I'm starting the server with:

$ iex -S mix
$ {:ok, pid} = Cache.start_link
{:ok, #PID<0.139.0>}

But when I call some function:

$ Cache.fetch(:key, "value")

I'm getting this error:

** (exit) exited in: GenServer.call(Cache, {:get, 1}, 5000) ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started

Dogbert Dogbert · Accepted Answer · 2017-10-17T08:03:25

Based on your GenServer.call calls, I'm assuming you wanted to start a process registered with the same name as the module. In that case, you forgot to pass name: __MODULE__ to the GenServer.start_link call in Cache.start_link:

def start_link do
  GenServer.start_link(__MODULE__, [], name: __MODULE__)
end

GenServer.call produces "no process" error

1 Answers