Don't reschedule unmuted actors with no work

src/libponyrt/sched/scheduler.c

@@ -1478,11 +1478,15 @@ bool ponyint_sched_unmute_senders(pony_ctx_t* ctx, pony_actor_t* actor)
  if(!has_flag(to_unmute, FLAG_UNSCHEDULED))
  {
  ponyint_unmute_actor(to_unmute);
- // TODO: we don't want to reschedule if our queue is empty.
- // That's wasteful.
- ponyint_sched_add(ctx, to_unmute);
- DTRACE2(ACTOR_SCHEDULED, (uintptr_t)sched, (uintptr_t)to_unmute);
- actors_rescheduled++;
+
+ // Only reschedule if the queue isn't empty. The queue hasn't been
+ // marked as empty when the actor was muted.
+ if(!ponyint_messageq_markempty(&to_unmute->q))
+ {
+ ponyint_sched_add(ctx, to_unmute);
+ DTRACE2(ACTOR_SCHEDULED, (uintptr_t)sched, (uintptr_t)to_unmute);
+ actors_rescheduled++;
+ }
  }
 
  ponyint_sched_start_global_unmute(ctx->scheduler->index, to_unmute);