Revert "Parallelize template rendering"

This reverts commit 1ad71592ad.

Since it had no limit on the number on concurrent processes it OOM killed
instances while rendering hellthreads. When I tried introducing a
concurrency limit with Task.async_stream/manual folds it lead to about 3 times
worse performance on threads larger than 1000 activities (we are talking
30s vs 1.2 minutes), I think this is not worth the about 1.5 times
performance increase on smaller threads when using it.

lib/mix/tasks/pleroma/benchmark.ex

@@ -37,37 +37,17 @@ def run(["render_timeline", nickname]) do
       |> Map.put("blocking_user", user)
       |> Map.put("muting_user", user)
       |> Map.put("user", user)
-      |> Map.put("limit", 80)
       |> Pleroma.Web.ActivityPub.ActivityPub.fetch_public_activities()
       |> Enum.reverse()
 
-    inputs = %{
-      "One activity" => Enum.take_random(activities, 1),
-      "Ten activities" => Enum.take_random(activities, 10),
-      "Twenty activities" => Enum.take_random(activities, 20),
-      "Forty activities" => Enum.take_random(activities, 40),
-      "Eighty activities" => Enum.take_random(activities, 80)
-    }
-
-    Benchee.run(
-      %{
-        "Parallel rendering" => fn activities ->
-          Pleroma.Web.MastodonAPI.StatusView.render("index.json", %{
-            activities: activities,
-            for: user,
-            as: :activity
-          })
-        end,
-        "Standart rendering" => fn activities ->
-          Pleroma.Web.MastodonAPI.StatusView.render("index.json", %{
-            activities: activities,
-            for: user,
-            as: :activity,
-            parallel: false
-          })
-        end
-      },
-      inputs: inputs
-    )
+    Benchee.run(%{
+      "render_timeline" => fn ->
+        Pleroma.Web.MastodonAPI.StatusView.render("index.json", %{
+          activities: activities,
+          for: user,
+          as: :activity
+        })
+      end
+    })
   end
 end

lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -73,14 +73,12 @@ defp reblogged?(activity, user) do
 
   def render("index.json", opts) do
     replied_to_activities = get_replied_to_activities(opts.activities)
-    parallel = unless is_nil(opts[:parallel]), do: opts[:parallel], else: true
 
     opts.activities
     |> safe_render_many(
       StatusView,
       "status.json",
-      Map.put(opts, :replied_to_activities, replied_to_activities),
-      parallel
+      Map.put(opts, :replied_to_activities, replied_to_activities)
     )
   end
 

lib/pleroma/web/web.ex

@@ -66,23 +66,9 @@ def safe_render(view, template, assigns \\ %{}) do
       end
 
       @doc """
-      Same as `render_many/4` but wrapped in rescue block and parallelized (unless disabled by passing false as a fifth argument).
+      Same as `render_many/4` but wrapped in rescue block.
       """
-      def safe_render_many(collection, view, template, assigns \\ %{}, parallel \\ true)
-
-      def safe_render_many(collection, view, template, assigns, true) do
-        Enum.map(collection, fn resource ->
-          Task.async(fn ->
-            as = Map.get(assigns, :as) || view.__resource__
-            assigns = Map.put(assigns, as, resource)
-            safe_render(view, template, assigns)
-          end)
-        end)
-        |> Enum.map(&Task.await(&1, :infinity))
-        |> Enum.filter(& &1)
-      end
-
-      def safe_render_many(collection, view, template, assigns, false) do
+      def safe_render_many(collection, view, template, assigns \\ %{}) do
         Enum.map(collection, fn resource ->
           as = Map.get(assigns, :as) || view.__resource__
           assigns = Map.put(assigns, as, resource)