Account for the stopped callbacks in the leakcheck.

gevent/greenlet.py

@@ -189,6 +189,11 @@ def __cancel_start(self):
             # prevent self from ever being started in the future
             self._start_event = _cancelled_start_event
         # cancel any pending start event
+        # NOTE: If this was a real pending start event, this will leave a
+        # "dangling" callback/timer object in the hub.loop.callbacks list;
+        # depending on where we are in the event loop, it may even be in a local
+        # variable copy of that list (in _run_callbacks). This isn't a problem,
+        # except for the leak-tests.
         self._start_event.stop()
 
     def __handle_death_before_start(self, *args):

greentest/greentest.py

@@ -28,6 +28,7 @@
 import os
 from os.path import basename, splitext
 import gevent
+import gevent.core
 from patched_tests_setup import get_switch_expected
 from gevent.hub import _get_hub
 from functools import wraps
@@ -106,6 +107,12 @@ def type_hist():
             k = type(x)
             if k in IGNORED_TYPES:
                 continue
+            if k == gevent.core.callback and x.callback is None and x.args is None:
+                # these represent callbacks that have been stopped, but
+                # the event loop hasn't cycled around to run them. The only
+                # known cause of this is killing greenlets before they get a chance
+                # to run for the first time.
+                continue
             d[k] += 1
         return d