当我运行下面的代码时，很长一段时间会出现这种错误。
代码：
from gevent import monkey; monkey.patch_all()
from gevent.pywsgi import WSGIServer
sys.modules.pop("threading", None)
异常信息：
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/gevent/greenlet.py", line 375, in _notify_links
link(self)
File "/usr/local/lib/python2.7/dist-packages/gevent/threading.py", line 22, in _cleanup
__threading__._active.pop(id(g))
KeyError: 40406544
(<function _cleanup at 0x1fed0c8>, <Greenlet at 0x2688e10>) failed with KeyError