From c765fcbe7e907dd5ac1f8b559bf65ab477dfe0f0 Mon Sep 17 00:00:00 2001
From: Mark Felder <feld@feld.me>
Date: Thu, 20 Jun 2024 14:03:22 -0400
Subject: [PATCH 1/2] Gun Connection Pool: successfully retry after reclaiming
 the pool

---
 changelog.d/gun_pool4.fix                     |  1 +
 .../gun/connection_pool/worker_supervisor.ex  | 32 ++++++++++++-------
 test/pleroma/gun/connection_pool_test.exs     |  1 -
 3 files changed, 22 insertions(+), 12 deletions(-)
 create mode 100644 changelog.d/gun_pool4.fix

diff --git a/changelog.d/gun_pool4.fix b/changelog.d/gun_pool4.fix
new file mode 100644
index 000000000..f68c1c970
--- /dev/null
+++ b/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
diff --git a/lib/pleroma/gun/connection_pool/worker_supervisor.ex b/lib/pleroma/gun/connection_pool/worker_supervisor.ex
index eb83962d8..dabb15b08 100644
--- a/lib/pleroma/gun/connection_pool/worker_supervisor.ex
+++ b/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
diff --git a/test/pleroma/gun/connection_pool_test.exs b/test/pleroma/gun/connection_pool_test.exs
index e0c9e9904..f3670760d 100644
--- a/test/pleroma/gun/connection_pool_test.exs
+++ b/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)

From 9ef021e2dae1a0bc07e997489304875b0d45ec07 Mon Sep 17 00:00:00 2001
From: Mark Felder <feld@feld.me>
Date: Thu, 20 Jun 2024 14:17:28 -0400
Subject: [PATCH 2/2] Switch the reclaimer to GenServer.start so it is not
 linked

---
 lib/pleroma/gun/connection_pool/reclaimer.ex         | 2 +-
 lib/pleroma/gun/connection_pool/worker_supervisor.ex | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/pleroma/gun/connection_pool/reclaimer.ex b/lib/pleroma/gun/connection_pool/reclaimer.ex
index 35e7f4b2e..3580d38f5 100644
--- a/lib/pleroma/gun/connection_pool/reclaimer.ex
+++ b/lib/pleroma/gun/connection_pool/reclaimer.ex
@@ -9,7 +9,7 @@ defmodule Pleroma.Gun.ConnectionPool.Reclaimer do
 
   def start_monitor do
     pid =
-      case GenServer.start_link(__MODULE__, [], name: {:via, Registry, {registry(), "reclaimer"}}) do
+      case GenServer.start(__MODULE__, [], name: {:via, Registry, {registry(), "reclaimer"}}) do
         {:ok, pid} ->
           pid
 
diff --git a/lib/pleroma/gun/connection_pool/worker_supervisor.ex b/lib/pleroma/gun/connection_pool/worker_supervisor.ex
index dabb15b08..b9dedf61e 100644
--- a/lib/pleroma/gun/connection_pool/worker_supervisor.ex
+++ b/lib/pleroma/gun/connection_pool/worker_supervisor.ex
@@ -37,7 +37,7 @@ defmodule Pleroma.Gun.ConnectionPool.WorkerSupervisor do
   def start_worker(opts, false) do
     case DynamicSupervisor.start_child(__MODULE__, {Worker, opts}) do
       {:error, :max_children} ->
-        spawn(fn -> free_pool() end)
+        free_pool()
         start_worker(opts, true)
 
       res ->