Fix smlua memory leaks (#606)

mods/arena/arena-sound.lua

@@ -34,7 +34,6 @@ function handleMusic()
         audioCurSeq = get_current_background_music()
         if audioMain then
             audio_stream_stop(audioMain)
-            audio_stream_destroy(audioMain)
             audioMain = nil
         end
         if bgms[curMap] and bgms[curMap].audio then
@@ -76,7 +75,6 @@ function handleMusic()
     else
         if audioSpecial then
             audio_stream_stop(audioSpecial)
-            audio_stream_destroy(audioSpecial)
             audioSpecial = nil
             if audioMain and audioMainPaused then
                 audioMainPaused = false

src/pc/lua/smlua.c

@@ -344,19 +344,17 @@ void smlua_update(void) {
     audio_sample_destroy_pending_copies();
 
     smlua_call_event_hooks(HOOK_UPDATE);
+
     // Collect our garbage after calling our hooks.
     // If we don't, Lag can quickly build up from our mods.
-    /*lua_gc(L, LUA_GCSTEP, 1);
-    lua_gc(L, LUA_GCSTOP, 0);*/
-
-    // EDIT: uhh, it turns out that is not the case
-    // if we only do incremental garbage collection,
-    // eventually the garbage will build up so much
-    // that the game slows to a crawl. Messing with
-    // the GC setting is what caused Arena to get worse
-    // over time.
+    // Truth is smlua generates so much garbage that the
+    // incremental collection fails to keep up after some time.
+    // So, for now, stop the GC from running during the hooks
+    // and perform a full GC at the end of the frame.
     // The real fix would be to make smlua produce less
     // garbage.
+    lua_gc(L, LUA_GCSTOP, 0);
+    lua_gc(L, LUA_GCCOLLECT, 0);
 }
 
 void smlua_shutdown(void) {