Use Process.sentinel, not Process._popen.sentinel

celery/utils/timer2.py

@@ -219,7 +219,7 @@ class Timer(Thread):
     if TIMER_DEBUG:
         def start(self, *args, **kwargs):
             import traceback
-            print("TIMER START")
+            print("- Timer starting")
             traceback.print_stack()
             super(Timer, self).start(*args, **kwargs)
 

celery/worker/consumer.py

@@ -407,11 +407,11 @@ class Consumer(object):
                 self.timer.apply_interval(interval * 1000.0, handler)
 
             def on_process_up(w):
-                hub.add(w._popen.sentinel, self.pool._pool.maintain_pool)
+                hub.add(w.sentinel, self.pool._pool.maintain_pool)
             self.pool.on_process_up = on_process_up
 
             def on_process_down(w):
-                hub.remove(w._popen.sentinel)
+                hub.remove(w.sentinel)
             self.pool.on_process_down = on_process_down
 
             transport.on_poll_init(hub.poller)