lecture 05

lectures/05/dynamic_counters/lib/counter/worker.ex

@@ -0,0 +1,52 @@
+defmodule Counter.Worker do
+  use GenServer
+
+  @registry Counter.Registry
+  @table Counter.Table
+
+  ### Client API ###
+  def start_link(name) do
+	GenServer.start_link(__MODULE__, name, name: via(name))
+  end
+
+  def value(name) do
+	GenServer.call(via(name), :value)
+  end
+
+  def inc(name, amt \\ 1) do
+	GenServer.cast(via(name), {:inc, amt})
+  end
+
+  # wrap the name in a triple to use the Registry to get the
+  # process ID by name
+  defp via(name) do
+	{:via, Registry, {@registry, {__MODULE__, name}}}
+  end
+
+  ### Server Impl ###
+  @impl true
+  def init(arg) do
+	name = {__MODULE__, arg}
+	value = case :ets.lookup(@table, name) do
+		[] -> 0
+		[{_, v}] -> v
+	end
+   {:ok, {name, value}}
+  end
+
+  @impl true
+  def handle_call(:value, _from, {_, value} = state) do
+	{:reply, value, state}
+  end
+
+  @impl true
+  def handle_cast({:inc, amt}, {name, value}) do
+	{:noreply, {name, value + amt}}
+  end
+
+  # save state to term table when process terminates
+  @impl true
+  def terminate(_, state) do
+	:ets.insert(@table, state)
+  end
+end