Gun Connection Pool: successfully retry after reclaiming the pool

changelog.d/gun_pool4.fix

@@ -0,0 +1 @@
+Gun Connection Pool was not retrying to acquire a connection if the pool was full and stale connections were reclaimed

lib/pleroma/gun/connection_pool/worker_supervisor.ex

@@ -5,6 +5,9 @@
 defmodule Pleroma.Gun.ConnectionPool.WorkerSupervisor do
   @moduledoc "Supervisor for pool workers. Does not do anything except enforce max connection limit"
 
+  alias Pleroma.Config
+  alias Pleroma.Gun.ConnectionPool.Worker
+
   use DynamicSupervisor
 
   def start_link(opts) do
@@ -14,21 +17,28 @@ defmodule Pleroma.Gun.ConnectionPool.WorkerSupervisor do
   def init(_opts) do
     DynamicSupervisor.init(
       strategy: :one_for_one,
-      max_children: Pleroma.Config.get([:connections_pool, :max_connections])
+      max_children: Config.get([:connections_pool, :max_connections])
     )
   end
 
-  def start_worker(opts, last_attempt \\ false) do
-    case DynamicSupervisor.start_child(__MODULE__, {Pleroma.Gun.ConnectionPool.Worker, opts}) do
-      {:error, :max_children} ->
-        funs = [fn -> last_attempt end, fn -> match?(:error, free_pool()) end]
+  def start_worker(opts, last_attempt \\ false)
 
-        if Enum.any?(funs, fn fun -> fun.() end) do
-          :telemetry.execute([:pleroma, :connection_pool, :provision_failure], %{opts: opts})
-          {:error, :pool_full}
-        else
-          start_worker(opts, true)
-        end
+  def start_worker(opts, true) do
+    case DynamicSupervisor.start_child(__MODULE__, {Worker, opts}) do
+      {:error, :max_children} ->
+        :telemetry.execute([:pleroma, :connection_pool, :provision_failure], %{opts: opts})
+        {:error, :pool_full}
+
+      res ->
+        res
+    end
+  end
+
+  def start_worker(opts, false) do
+    case DynamicSupervisor.start_child(__MODULE__, {Worker, opts}) do
+      {:error, :max_children} ->
+        spawn(fn -> free_pool() end)
+        start_worker(opts, true)
 
       res ->
         res

test/pleroma/gun/connection_pool_test.exs

@@ -46,7 +46,6 @@ defmodule Pleroma.Gun.ConnectionPoolTest do
       end
   end
 
-  @tag :erratic
   test "connection limit is respected with concurrent requests" do
     clear_config([:connections_pool, :max_connections]) do
       clear_config([:connections_pool, :max_connections], 1)