Fix MIDI input lag / hang / occasional crashes

lib/portmidi/input/reader.ex

@@ -1,8 +1,10 @@
 defmodule PortMidi.Input.Reader do
   import PortMidi.Nifs.Input
   alias PortMidi.Input.Server
+  require Logger
 
   @buffer_size Application.get_env(:portmidi, :buffer_size, 256)
+  @input_poll_sleep Application.get_env(:portmidi, :input_poll_sleep, 1)
 
   def start_link(server, device_name) do
     Agent.start_link(fn -> start(server, device_name) end)
@@ -34,12 +36,15 @@ defmodule PortMidi.Input.Reader do
 
   defp loop(server, stream) do
     if do_poll(stream) == :read, do: read_and_send(server, stream)
+    :timer.sleep(@input_poll_sleep)
     loop(server, stream)
   end
 
   defp read_and_send(server, stream) do
-    messages = do_read(stream, @buffer_size)
-    Server.new_messages(server, messages)
+    case do_read(stream, @buffer_size) do
+      {:error, reason} -> Logger.debug("Error Reading Midi: #{reason}")
+      messages -> Server.new_messages(server, messages)
+    end
   end
 
   defp do_stop({_server, stream, task}) do

src/portmidi_in.c

@@ -70,10 +70,13 @@ static ERL_NIF_TERM do_read(ErlNifEnv* env, int arc, const ERL_NIF_TERM argv[])
   if(!enif_get_resource(env, argv[0], streamType, (PortMidiStream **) &stream)) {
     return enif_make_badarg(env);
   }
-
-  int bufferSize = enif_make_int(env, argv[2]);
+  long bufferSize;
+  enif_get_long(env, argv[1], &bufferSize);
   int numEvents = Pm_Read(*stream, buffer, bufferSize);
-
+  if (numEvents < 0) {
+      ERL_NIF_TERM reason = enif_make_atom(env, makePmErrorAtom(numEvents));
+      return enif_make_tuple2(env, enif_make_atom(env, "error"), reason);
+  }
   ERL_NIF_TERM events[numEvents];
   for(int i = 0; i < numEvents; i++) {
     status    = enif_make_int(env, Pm_MessageStatus(buffer[i].message));
@@ -86,7 +89,6 @@ static ERL_NIF_TERM do_read(ErlNifEnv* env, int arc, const ERL_NIF_TERM argv[])
       timestamp
     );
   }
-
   return enif_make_list_from_array(env, events, numEvents);
 }
 
@@ -97,9 +99,7 @@ static ERL_NIF_TERM do_close(ErlNifEnv* env, int arc, const ERL_NIF_TERM argv[])
   if(!enif_get_resource(env, argv[0], streamType, (PortMidiStream **) &stream)) {
     return enif_make_badarg(env);
   }
-
   Pm_Close(*stream);
-
   return enif_make_atom(env, "ok");
 }