Created
September 6, 2024 13:26
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Two (very simple) process registries written in Elixir, one with is fully based on GenServer, while the other stores its state in an ETS table
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| defmodule RegistryEts do | |
| use GenServer | |
| def register(key, pid \\ self()), | |
| do: GenServer.call(__MODULE__, {:register, key, pid}) | |
| def whereis(key) do | |
| case :ets.lookup(__MODULE__, key) do | |
| [{^key, pid}] -> pid | |
| _ -> nil | |
| end | |
| end | |
| def start_link(), | |
| do: GenServer.start_link(__MODULE__, :ok, name: __MODULE__) | |
| @impl GenServer | |
| def init(:ok) do | |
| :ets.new(__MODULE__, [:named_table, :protected, :set]) | |
| {:ok, nil} | |
| end | |
| @impl GenServer | |
| def handle_call({:register, key, pid}, _from, state) do | |
| if is_nil(whereis(key)) do | |
| Process.monitor(pid) | |
| :ets.insert(__MODULE__, {key, pid}) | |
| {:reply, :ok, state} | |
| else | |
| {:reply, :error, state} | |
| end | |
| end | |
| @impl GenServer | |
| def handle_info({:DOWN, _ref, :process, pid, _reason}, state) do | |
| :ets.match_delete(__MODULE__, {:_, pid}) | |
| {:noreply, state} | |
| end | |
| end |
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| defmodule RegistryGen do | |
| use GenServer | |
| def register(key), | |
| do: GenServer.call(__MODULE__, {:register, key, self()}) | |
| def whereis(key), | |
| do: GenServer.call(__MODULE__, {:whereis, key}) | |
| def start_link(), | |
| do: GenServer.start_link(__MODULE__, :ok, name: __MODULE__) | |
| @impl GenServer | |
| def init(:ok) do | |
| Process.flag(:trap_exit, true) | |
| {:ok, %{}} | |
| end | |
| @impl GenServer | |
| def handle_call({:register, key, pid}, _from, processes) do | |
| if Map.has_key?(processes, key) do | |
| {:reply, :error, processes} | |
| else | |
| Process.link(pid) | |
| {:reply, :ok, Map.put_new(processes, key, pid)} | |
| end | |
| end | |
| @impl GenServer | |
| def handle_call({:whereis, key}, _from, processes), | |
| do: {:reply, Map.get(processes, key), processes} | |
| @impl GenServer | |
| def handle_info({:EXIT, pid, _reason}, processes), | |
| do: {:noreply, processes |> Enum.reject(fn {_, v} -> v == pid end) |> Map.new()} | |
| end |
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