prevent dead-lock during garbage-collection

lib/floof/packet_spool.ex

@@ -46,10 +46,6 @@ defmodule Floof.PacketSpool do
   @impl true
   def init(state) do
     :ok = File.mkdir_p(state)
-
-    # in 5 seconds
-    Process.send_after(self(), :collect_garbage, 5 * 1000)
-
     {:ok, state}
   end
 
@@ -134,22 +130,7 @@ defmodule Floof.PacketSpool do
   end
 
   @impl true
-  def handle_cast({:drop, hash}, state) do
-    case File.rm(hash_to_path(hash, state)) do
-      :ok -> nil
-      {:error, e} -> Logger.error("spool: unable to remove #{inspect(hash)}: #{inspect(e)}")
-    end
-
-    {:noreply, state}
-  end
-
-  @impl true
-  def handle_info(:collect_garbage, state) do
-    case GenServer.call(Floof.SessionManager, :get_keep_only, :infinity) do
-      :error ->
-        nil
-
-      {:ok, to_keep} ->
+  def handle_call({:collect_garbage_keep_only, to_keep}, _, state) do
     {:ok, items} = File.ls(state)
 
     present =
@@ -182,10 +163,16 @@ defmodule Floof.PacketSpool do
         end
       end
     end
+
+    {:noreply, state}
   end
 
-    # do this again in 15 seconds
-    Process.send_after(self(), :collect_garbage, 15 * 1000)
+  @impl true
+  def handle_cast({:drop, hash}, state) do
+    case File.rm(hash_to_path(hash, state)) do
+      :ok -> nil
+      {:error, e} -> Logger.error("spool: unable to remove #{inspect(hash)}: #{inspect(e)}")
+    end
 
     {:noreply, state}
   end

lib/floof/session_manager.ex

@@ -15,6 +15,7 @@ defmodule Floof.SessionManager do
   @impl true
   def init({file, opts}) do
     {:ok, file} = :dets.open_file(file, opts ++ [type: :bag])
+    Process.send_after(self(), :collect_garbage, 5 * 1000)
     {:ok, %Floof.SessionManager{dets_file: file}}
   end
 
@@ -143,16 +144,19 @@ defmodule Floof.SessionManager do
   end
 
   @impl true
-  def handle_call(:get_keep_only, _, state) do
-    {:reply,
+  def handle_info(:collect_garbage, state) do
     case :dets.match(state.dets_file, {'_', '$2'}) do
       {:error, e} ->
         Logger.error("garbage collection error: #{inspect(e)}")
-         :error
+        Process.send_after(self(), :collect_garbage, 60 * 1000)
 
       keys ->
-         {:ok, Enum.map(keys, fn [x] -> x end)}
-     end, state}
+        to_keep = Enum.map(keys, fn [x] -> x end)
+        GenServer.call(Floof.PacketSpool, {:collect_garbage_keep_only, to_keep}, :infinity)
+        Process.send_after(self(), :collect_garbage, 15 * 1000)
+    end
+
+    {:noreply, state}
   end
 
   defp all_session_keys(state) do