From 66c3813ea6388e9933af2b15e903f1cf6254cd3a Mon Sep 17 00:00:00 2001
From: Lain Iwakura <lain@soykaf.club>
Date: Tue, 5 Dec 2017 18:21:30 +0100
Subject: [PATCH] Add basic queue prioritization.

---
 lib/pleroma/web/federator/federator.ex | 21 +++++++++++++++------
 test/web/federator_test.exs            | 20 ++++++++++++++++++++
 2 files changed, 35 insertions(+), 6 deletions(-)
 create mode 100644 test/web/federator_test.exs

diff --git a/lib/pleroma/web/federator/federator.ex b/lib/pleroma/web/federator/federator.ex
index 9f6f983aa..f384b313c 100644
--- a/lib/pleroma/web/federator/federator.ex
+++ b/lib/pleroma/web/federator/federator.ex
@@ -15,8 +15,8 @@ def start_link do
       enqueue(:refresh_subscriptions, nil)
     end)
     GenServer.start_link(__MODULE__, %{
-          in: {:sets.new(), :queue.new()},
-          out: {:sets.new(), :queue.new()}
+          in: {:sets.new(), [],
+          out: {:sets.new(), []}
                          }, name: __MODULE__)
   end
 
@@ -88,8 +88,8 @@ def enqueue(type, payload) do
   end
 
   def maybe_start_job(running_jobs, queue) do
-    if (:sets.size(running_jobs) < @max_jobs) && !:queue.is_empty(queue) do
-      {{:value, {type, payload}}, queue} = :queue.out(queue)
+    if (:sets.size(running_jobs) < @max_jobs) && queue != [] do
+      {{:value, {type, payload}}, queue} = queue_pop(queue)
       {:ok, pid} = Task.start(fn -> handle(type, payload) end)
       mref = Process.monitor(pid)
       {:sets.add_element(mref, running_jobs), queue}
@@ -100,14 +100,14 @@ def maybe_start_job(running_jobs, queue) do
 
   def handle_cast({:enqueue, type, payload}, state) when type in [:incoming_doc] do
     %{in: {i_running_jobs, i_queue}, out: {o_running_jobs, o_queue}} = state
-    i_queue = :queue.in({type, payload}, i_queue)
+    i_queue = enqueue_sorted(i_queue, {type, payload}, 1)
     {i_running_jobs, i_queue} = maybe_start_job(i_running_jobs, i_queue)
     {:noreply, %{in: {i_running_jobs, i_queue}, out: {o_running_jobs, o_queue}}}
   end
 
   def handle_cast({:enqueue, type, payload}, state) do
     %{in: {i_running_jobs, i_queue}, out: {o_running_jobs, o_queue}} = state
-    o_queue = :queue.in({type, payload}, o_queue)
+    o_queue = enqueue_sorted(o_queue, {type, payload}, 1)
     {o_running_jobs, o_queue} = maybe_start_job(o_running_jobs, o_queue)
     {:noreply, %{in: {i_running_jobs, i_queue}, out: {o_running_jobs, o_queue}}}
   end
@@ -126,4 +126,13 @@ def handle_info({:DOWN, ref, :process, _pid, _reason}, state) do
 
     {:noreply, %{in: {i_running_jobs, i_queue}, out: {o_running_jobs, o_queue}}}
   end
+
+  def enqueue_sorted(queue, element, priority) do
+    [%{item: element, priority: priority} | queue]
+    |> Enum.sort_by(fn (%{priority: priority}) -> priority end)
+  end
+
+  def queue_pop([%{item: element} | queue]) do
+    {element, queue}
+  end
 end
diff --git a/test/web/federator_test.exs b/test/web/federator_test.exs
new file mode 100644
index 000000000..09533362a
--- /dev/null
+++ b/test/web/federator_test.exs
@@ -0,0 +1,20 @@
+defmodule Pleroma.Web.FederatorTest do
+  alias Pleroma.Web.Federator
+  use Pleroma.DataCase
+
+  test "enqueues an element according to priority" do
+    queue = [%{item: 1, priority: 2}]
+
+    new_queue = Federator.enqueue_sorted(queue, 2, 1)
+    assert new_queue == [%{item: 2, priority: 1}, %{item: 1, priority: 2}]
+
+    new_queue = Federator.enqueue_sorted(queue, 2, 3)
+    assert new_queue == [%{item: 1, priority: 2}, %{item: 2, priority: 3}]
+  end
+
+  test "pop first item" do
+    queue = [%{item: 2, priority: 1}, %{item: 1, priority: 2}]
+
+    assert {2, [%{item: 1, priority: 2}]} = Federator.queue_pop(queue)
+  end
+end