This was an experiment before running across this PR

derekkraan/horde#271

Long story short, its not a good idea to nest Horde Supervisors in this way, probably a better approach
is have the "sub" processes attached to the main HordeSupervisor (via the project Module) and maybe
monitor that process in the "parent". Or just rethink needing them to be parent/child processes.

horde_background_job/lib/horde_background_job/database_cleaner.ex

@@ -9,30 +9,61 @@ defmodule HordeBackgroundJob.DatabaseCleaner do
     timeout = Keyword.get(opts, :timeout, :timer.seconds(2))
     count = Keyword.get(opts, :count, 0)
 
-    GenServer.start_link(__MODULE__, {timeout, name, count}, name: name)
+    case GenServer.start_link(__MODULE__, {timeout, name, count}, name: name) do
+      {:ok, pid} ->
+        nil # nothing to do
+
+      {:error, {:already_started, pid}} ->
+        # also nothing to do but log it - mostly interested if a name is being set incorrectly
+        log_msg("already started at #{inspect(pid)} for #{ name }")
+    end
   end
 
   @impl GenServer
   def init({timeout, name, count}) do
     Process.set_label(_name(name))
     polisher_name = "#{_name(name)}Polisher"
     log_msg("starting")
+    log_msg("polisher name")
+    log_msg(inspect name)
+    log_msg(inspect polisher_name)
 
     schedule(timeout)
 
     log_msg("starting horde super for the polisher - #{ inspect _name(name) }")
-    {:ok, polish_supervisor} = Horde.DynamicSupervisor.start_link([strategy: :one_for_one, name: :"#{polisher_name}"])
-    log_msg("should have started polish supervisor - #{ inspect polish_supervisor }")
 
-    child_spec = %{
-      id: polisher_name,
-      start: {HordeBackgroundJob.DatabasePolisher, :start_link, [[name: polisher_name, timeout: timeout]]},
-      type: :worker,
-      restart: :temporary,
-      shutdown: 500,
-    }
+    polish_supervisor = \
+      case Horde.DynamicSupervisor.start_link(strategy: :one_for_one, members: :auto, name: :"#{polisher_name}") do
+        {:ok, pid} ->
+          log_msg("success #{ inspect pid }")
+          pid
+
+        {:error, {:already_started, pid}} ->
+          log_msg("already started polisher at #{inspect(pid)} for #{ polisher_name }")
+          pid
+
+        something_else ->
+          log_msg("uh oh - #{ inspect something_else }")
+          nil
+      end
+
+    log_msg("should have started polish supervisor - #{ inspect polish_supervisor }")
 
-    {:ok, _pid} = Horde.DynamicSupervisor.start_child(polish_supervisor, child_spec)
+    # a random number of polishers
+    Enum.map(1..:rand.uniform(4), fn(i) ->
+      polisher_name_x = "#{polisher_name}#{i}"
+
+      child_spec = %{
+        id: polisher_name_x,
+        start: {HordeBackgroundJob.DatabasePolisher, :start_link, [[name: polisher_name_x, timeout: timeout]]},
+        type: :worker,
+        restart: :temporary,
+        shutdown: 500,
+      }
+
+      # keeps returning an :error tuple, but seems the process starts anyway :/
+      IO.inspect Horde.DynamicSupervisor.start_child(:"#{polisher_name}", child_spec)
+    end)
 
     {:ok, {timeout, name, count}}
   end

horde_background_job/lib/horde_background_job/database_polisher.ex

@@ -10,7 +10,14 @@ defmodule HordeBackgroundJob.DatabasePolisher do
 
     log_msg("start_link polisher #{ inspect name}")
 
-    {:ok, _pid} = GenServer.start_link(__MODULE__, {timeout, name}, name: via_tuple(name))
+    case GenServer.start_link(__MODULE__, {timeout, name}, name: via_tuple(name)) do
+      {:ok, pid} ->
+        nil # nothing to do
+
+      {:error, {:already_started, pid}} ->
+        # also nothing to do but log it - mostly interested if a name is being set incorrectly
+        log_msg("already started at #{inspect(pid)} for #{ inspect(via_tuple(name)) }")
+    end
   end
 
   @impl GenServer

horde_background_job/lib/horde_background_job/horde_supervisor.ex

@@ -23,7 +23,4 @@ defmodule HordeBackgroundJob.HordeSupervisor do
     Enum.map([Node.self() | Node.list()], &{__MODULE__, &1})
   end
 
-#  defp via_tuple(name) do
-#    {:via, Horde.Registry, {HordeRegistry, name}}
-#  end
 end