setting up to run collabcks is different, libev just refs self, libev needs to start the timer.

fixes test__loop_callback.

src/gevent/_ffi/loop.py

@@ -443,10 +443,13 @@ class AbstractLoop(object):
     def callback(self, priority=None):
         return callback(self, priority)
 
+    def _setup_for_run_callback(self):
+        raise NotImplementedError()
+
     def run_callback(self, func, *args):
         cb = callback(func, args)
         self._callbacks.append(cb)
-        self.ref()
+        self._setup_for_run_callback()
 
         return cb
 

src/gevent/libev/corecffi.py

@@ -267,6 +267,9 @@ class loop(AbstractLoop):
             self.ref()
             libev.ev_check_stop(self._ptr, self._check)
 
+    def _setup_for_run_callback(self):
+        self.ref() # we should go through the loop now
+
     def destroy(self):
         global _default_loop_destroyed
         if self._ptr:

src/gevent/libuv/loop.py

@@ -75,6 +75,10 @@ class loop(AbstractLoop):
         libuv.uv_check_stop(self._check)
         libuv.uv_ref(self._check)
 
+    def _setup_for_run_callback(self):
+        self._start_callback_timer()
+        libuv.uv_ref(self._timer0)
+
     def destroy(self):
         if self._ptr:
             ptr = self._ptr