Handle shutdown process (#45)

* Test: workers stop before the pool

* Stop supervisor on pool terminating

* Destroy monitoring table on pool terminating

* Update CHANGELOG

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix the shutdown process: stop workers before the pool ([issue](https://github.com/general-CbIC/poolex/issues/44)).
+
 ## [0.7.0] - 2023-04-13
 
 ### Added

lib/poolex.ex

@@ -472,4 +472,12 @@ defmodule Poolex do
         {:noreply, %{state | waiting_callers_state: new_waiting_callers_state}}
     end
   end
+
+  @impl GenServer
+  def terminate(reason, %State{} = state) do
+    DynamicSupervisor.stop(state.supervisor, reason)
+    Monitoring.stop(state.monitor_id)
+
+    :ok
+  end
 end

lib/poolex/monitoring.ex

@@ -11,6 +11,14 @@ defmodule Poolex.Monitoring do
     {:ok, monitor_id}
   end
 
+  @spec stop(monitor_id()) :: :ok
+  @doc false
+  def stop(monitor_id) do
+    :ets.delete(monitor_id)
+
+    :ok
+  end
+
   @spec add(monitor_id(), pid(), kind_of_process()) :: :ok
   @doc false
   def add(monitor_id, process_pid, kind_of_process) do

test/poolex_test.exs

@@ -372,6 +372,30 @@ defmodule PoolexTest do
     end
   end
 
+  describe "shutdown process" do
+    test "workers stop before the pool", %{pool_name: pool_name} do
+      {:ok, pool_pid} =
+        Poolex.start_link(pool_id: pool_name, worker_module: SomeWorker, workers_count: 1)
+
+      state = Poolex.get_state(pool_name)
+
+      supervisor_pid = state.supervisor
+      worker_pid = Poolex.run!(pool_name, fn pid -> pid end)
+
+      pool_monitor_ref = Process.monitor(pool_pid)
+      supervisor_monitor_ref = Process.monitor(supervisor_pid)
+      worker_monitor_ref = Process.monitor(worker_pid)
+
+      GenServer.stop(pool_name)
+
+      {:messages, [message_1, message_2, message_3]} = Process.info(self(), :messages)
+
+      assert message_1 == {:DOWN, worker_monitor_ref, :process, worker_pid, :shutdown}
+      assert message_2 == {:DOWN, supervisor_monitor_ref, :process, supervisor_pid, :normal}
+      assert message_3 == {:DOWN, pool_monitor_ref, :process, pool_pid, :normal}
+    end
+  end
+
   defp pool_name do
     1..10
     |> Enum.map(fn _ -> Enum.random(?a..?z) end)