Improves RetryQueue behavior

reduces to one single timer firing once a second
switches to a parallel worker model

lib/pleroma/web/federator/retry_queue.ex

@@ -7,20 +7,34 @@ defmodule Pleroma.Web.Federator.RetryQueue do
 
   require Logger
 
-  # initial timeout, 5 min
-  @initial_timeout 30_000
+  # seconds
+  @initial_timeout 30
   @max_retries 5
 
+  @max_jobs 20
+
   def init(args) do
-    {:ok, args}
+    queue_table = :ets.new(:pleroma_retry_queue, [:bag, :protected])
+
+    {:ok, %{args | queue_table: queue_table, running_jobs: :sets.new()}}
   end
 
   def start_link() do
-    enabled = Pleroma.Config.get([:retry_queue, :enabled], false)
+    enabled =
+      if Mix.env() == :test, do: true, else: Pleroma.Config.get([:retry_queue, :enabled], false)
 
     if enabled do
       Logger.info("Starting retry queue")
-      GenServer.start_link(__MODULE__, %{delivered: 0, dropped: 0}, name: __MODULE__)
+
+      linkres =
+        GenServer.start_link(
+          __MODULE__,
+          %{delivered: 0, dropped: 0, queue_table: nil, running_jobs: nil},
+          name: __MODULE__
+        )
+
+      maybe_kickoff_timer()
+      linkres
     else
       Logger.info("Retry queue disabled")
       :ignore
@@ -31,6 +45,14 @@ def enqueue(data, transport, retries \\ 0) do
     GenServer.cast(__MODULE__, {:maybe_enqueue, data, transport, retries + 1})
   end
 
+  def get_stats() do
+    GenServer.call(__MODULE__, :get_stats)
+  end
+
+  def reset_stats() do
+    GenServer.call(__MODULE__, :reset_stats)
+  end
+
   def get_retry_params(retries) do
     if retries > @max_retries do
       {:drop, "Max retries reached"}
@@ -39,16 +61,118 @@ def get_retry_params(retries) do
     end
   end
 
-  def handle_cast({:maybe_enqueue, data, transport, retries}, %{dropped: drop_count} = state) do
+  def get_retry_timer_interval() do
+    Pleroma.Config.get([:retry_queue, :interval], 1000)
+  end
+
+  defp ets_count_expires(table, current_time) do
+    :ets.select_count(
+      table,
+      [
+        {
+          {:"$1", :"$2"},
+          [{:"=<", :"$1", {:const, current_time}}],
+          [true]
+        }
+      ]
+    )
+  end
+
+  defp ets_pop_n_expired(table, current_time, desired) do
+    {popped, _continuation} =
+      :ets.select(
+        table,
+        [
+          {
+            {:"$1", :"$2"},
+            [{:"=<", :"$1", {:const, current_time}}],
+            [:"$_"]
+          }
+        ],
+        desired
+      )
+
+    popped
+    |> List.foldl(true, fn e, acc ->
+      :ets.delete_object(table, e)
+      acc
+    end)
+
+    popped
+  end
+
+  def maybe_start_job(running_jobs, queue_table) do
+    # we don't want to hit the ets or the DateTime more times than we have to
+    # could optimize slightly further by not using the count, and instead grabbing
+    # up to N objects early...
+    current_time = DateTime.to_unix(DateTime.utc_now())
+    n_running_jobs = :sets.size(running_jobs)
+
+    if n_running_jobs < @max_jobs do
+      n_ready_jobs = ets_count_expires(queue_table, current_time)
+
+      if n_ready_jobs > 0 do
+        # figure out how many we could start
+        available_job_slots = @max_jobs - n_running_jobs
+        start_n_jobs(running_jobs, queue_table, current_time, available_job_slots)
+      else
+        running_jobs
+      end
+    else
+      running_jobs
+    end
+  end
+
+  defp start_n_jobs(running_jobs, _queue_table, _current_time, 0) do
+    running_jobs
+  end
+
+  defp start_n_jobs(running_jobs, queue_table, current_time, available_job_slots)
+       when available_job_slots > 0 do
+    candidates = ets_pop_n_expired(queue_table, current_time, available_job_slots)
+
+    candidates
+    |> List.foldl(running_jobs, fn {_, e}, rj ->
+      {:ok, pid} = Task.start(fn -> worker(e) end)
+      mref = Process.monitor(pid)
+      :sets.add_element(mref, rj)
+    end)
+  end
+
+  def worker({:send, data, transport, retries}) do
+    case transport.publish_one(data) do
+      {:ok, _} ->
+        GenServer.cast(__MODULE__, :inc_delivered)
+        :delivered
+
+      {:error, _reason} ->
+        enqueue(data, transport, retries)
+        :retry
+    end
+  end
+
+  def handle_call(:get_stats, _from, %{delivered: delivery_count, dropped: drop_count} = state) do
+    {:reply, %{delivered: delivery_count, dropped: drop_count}, state}
+  end
+
+  def handle_call(:reset_stats, _from, %{delivered: delivery_count, dropped: drop_count} = state) do
+    {:reply, %{delivered: delivery_count, dropped: drop_count},
+     %{state | delivered: 0, dropped: 0}}
+  end
+
+  def handle_cast(:reset_stats, state) do
+    {:noreply, %{state | delivered: 0, dropped: 0}}
+  end
+
+  def handle_cast(
+        {:maybe_enqueue, data, transport, retries},
+        %{dropped: drop_count, queue_table: queue_table, running_jobs: running_jobs} = state
+      ) do
     case get_retry_params(retries) do
       {:retry, timeout} ->
-        Process.send_after(
-          __MODULE__,
-          {:send, data, transport, retries},
-          timeout
-        )
-
-        {:noreply, state}
+        :ets.insert(queue_table, {timeout, {:send, data, transport, retries}})
+        running_jobs = maybe_start_job(running_jobs, queue_table)
+        {:noreply, %{state | running_jobs: running_jobs}}
 
       {:drop, message} ->
         Logger.debug(message)
@@ -56,6 +180,20 @@ def handle_cast({:maybe_enqueue, data, transport, retries}, %{dropped: drop_coun
     end
   end
 
+  def handle_cast(:kickoff_timer, state) do
+    retry_interval = get_retry_timer_interval()
+    Process.send_after(__MODULE__, :retry_timer_run, retry_interval)
+    {:noreply, state}
+  end
+
+  def handle_cast(:inc_delivered, %{delivered: delivery_count} = state) do
+    {:noreply, %{state | delivered: delivery_count + 1}}
+  end
+
+  def handle_cast(:inc_dropped, %{dropped: drop_count} = state) do
+    {:noreply, %{state | dropped: drop_count + 1}}
+  end
+
   def handle_info({:send, data, transport, retries}, %{delivered: delivery_count} = state) do
     case transport.publish_one(data) do
       {:ok, _} ->
@@ -67,12 +205,39 @@ def handle_info({:send, data, transport, retries}, %{delivered: delivery_count}
     end
   end
 
+  def handle_info(
+        :retry_timer_run,
+        %{queue_table: queue_table, running_jobs: running_jobs} = state
+      ) do
+    maybe_kickoff_timer()
+    running_jobs = maybe_start_job(running_jobs, queue_table)
+    {:noreply, %{state | running_jobs: running_jobs}}
+  end
+
+  def handle_info({:DOWN, ref, :process, _pid, _reason}, state) do
+    %{running_jobs: running_jobs, queue_table: queue_table} = state
+    running_jobs = :sets.del_element(ref, running_jobs)
+    running_jobs = maybe_start_job(running_jobs, queue_table)
+    {:noreply, %{state | running_jobs: running_jobs}}
+  end
+
   def handle_info(unknown, state) do
     Logger.debug("RetryQueue: don't know what to do with #{inspect(unknown)}, ignoring")
     {:noreply, state}
   end
 
-  defp growth_function(retries) do
-    round(@initial_timeout * :math.pow(retries, 3))
+  if Mix.env() == :test do
+    defp growth_function(_retries) do
+      _shutit = @initial_timeout
+      DateTime.to_unix(DateTime.utc_now()) - 1
+    end
+  else
+    defp growth_function(retries) do
+      round(@initial_timeout * :math.pow(retries, 3)) + DateTime.to_unix(DateTime.utc_now())
+    end
+  end
+
+  defp maybe_kickoff_timer() do
+    GenServer.cast(__MODULE__, :kickoff_timer)
   end
 end

test/web/retry_queue_test.exs

@@ -3,7 +3,8 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule MockActivityPub do
-  def publish_one(ret) do
+  def publish_one({ret, waiter}) do
+    send(waiter, :complete)
     {ret, "success"}
   end
 end
@@ -15,21 +16,33 @@ defmodule Pleroma.Web.Federator.RetryQueueTest do
   @small_retry_count 0
   @hopeless_retry_count 10
 
+  setup do
+    RetryQueue.reset_stats()
+  end
+
+  test "RetryQueue responds to stats request" do
+    assert %{delivered: 0, dropped: 0} == RetryQueue.get_stats()
+  end
+
   test "failed posts are retried" do
     {:retry, _timeout} = RetryQueue.get_retry_params(@small_retry_count)
 
-    assert {:noreply, %{delivered: 1}} ==
-             RetryQueue.handle_info({:send, :ok, MockActivityPub, @small_retry_count}, %{
-               delivered: 0
-             })
+    wait_task =
+      Task.async(fn ->
+        receive do
+          :complete -> :ok
+        end
+      end)
+
+    RetryQueue.enqueue({:ok, wait_task.pid}, MockActivityPub, @small_retry_count)
+    Task.await(wait_task)
+    assert %{delivered: 1, dropped: 0} == RetryQueue.get_stats()
   end
 
   test "posts that have been tried too many times are dropped" do
     {:drop, _timeout} = RetryQueue.get_retry_params(@hopeless_retry_count)
 
-    assert {:noreply, %{dropped: 1}} ==
-             RetryQueue.handle_cast({:maybe_enqueue, %{}, nil, @hopeless_retry_count}, %{
-               dropped: 0
-             })
+    RetryQueue.enqueue({:ok, nil}, MockActivityPub, @hopeless_retry_count)
+    assert %{delivered: 0, dropped: 1} == RetryQueue.get_stats()
   end
 end