Extract Indexer.start_monitor

Rename Indexer.BlockFetcher.monitor_task to Indexer.start_monitor, so
that all fetchers can use it.

apps/explorer/lib/explorer/indexer.ex

@@ -4,7 +4,7 @@ defmodule Explorer.Indexer do
   """
   require Logger
 
-  alias Explorer.Chain
+  alias Explorer.{Chain, Indexer}
 
   @doc """
   The maximum `t:Explorer.Chain.Block.t/0` `number` that was indexed
@@ -79,6 +79,16 @@ defmodule Explorer.Indexer do
     Application.put_env(:explorer, :indexer, Keyword.put(config(), :debug_logs, false))
   end
 
+  @doc """
+  Starts a child task of `Indexer.TaskSupervisor` and monitors it, instead of linking to it.
+  """
+  @spec start_monitor((() -> term())) :: {:ok, pid, reference}
+  def start_monitor(task_function) when is_function(task_function, 0) do
+    {:ok, pid} = Task.Supervisor.start_child(Indexer.TaskSupervisor, task_function)
+    ref = Process.monitor(pid)
+    {:ok, pid, ref}
+  end
+
   defp debug_logs_enabled? do
     Keyword.fetch!(config(), :debug_logs)
   end

apps/explorer/lib/explorer/indexer/block_fetcher.ex

@@ -87,13 +87,13 @@ defmodule Explorer.Indexer.BlockFetcher do
 
   @impl GenServer
   def handle_info(:catchup_index, %{} = state) do
-    {:ok, genesis_task, _ref} = monitor_task(fn -> genesis_task(state) end)
+    {:ok, genesis_task, _ref} = Indexer.start_monitor(fn -> genesis_task(state) end)
 
     {:noreply, %{state | genesis_task: genesis_task}}
   end
 
   def handle_info(:realtime_index, %{} = state) do
-    {:ok, realtime_task, _ref} = monitor_task(fn -> realtime_task(state) end)
+    {:ok, realtime_task, _ref} = Indexer.start_monitor(fn -> realtime_task(state) end)
 
     {:noreply, %{state | realtime_task: realtime_task}}
   end
@@ -315,10 +315,4 @@ defmodule Explorer.Indexer.BlockFetcher do
     Process.send_after(self(), :realtime_index, state.realtime_interval)
     state
   end
-
-  defp monitor_task(task_func) do
-    {:ok, pid} = Task.Supervisor.start_child(Indexer.TaskSupervisor, task_func)
-    ref = Process.monitor(pid)
-    {:ok, pid, ref}
-  end
 end