[Bug 1863021] Re: eventlet monkey patch results in assert len(_active) == 1 AssertionError

[Corey Bryant]

See attached for much more detailed recreation/patching/fixing.

** Attachment added: "nova-eventlet-monkey-patch.txt"
   https://bugs.launchpad.net/nova/+bug/1863021/+attachment/5327763/+files/nova-eventlet-monkey-patch.txt

** Also affects: nova (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: nova (Ubuntu)
       Status: New => Triaged

** Changed in: nova (Ubuntu)
   Importance: Undecided => High

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https://bugs.launchpad.net/bugs/1863021

Title:
  eventlet monkey patch results in assert len(_active) == 1
  AssertionError

Status in OpenStack Compute (nova):
  New
Status in nova package in Ubuntu:
  Triaged

Bug description:
  This appears to be the same issue documented here:
  https://github.com/eventlet/eventlet/issues/592

  However I seem to only hit this with python3.8. Basically nova
  services fail with:

   Exception ignored in: <function _after_fork at 0x7f1100d075e0>
   Traceback (most recent call last):
     File "/usr/lib/python3.8/threading.py", line 1454, in _after_fork
       assert len(_active) == 1
   AssertionError:
   Exception ignored in: <function _after_fork at 0x7f1100d075e0>
   Traceback (most recent call last):
     File "/usr/lib/python3.8/threading.py", line 1454, in _after_fork
       assert len(_active) == 1
   AssertionError:

  Patching nova/monkey_patch.py with the following appears to fix this:

  diff --git a/nova/monkey_patch.py b/nova/monkey_patch.py
  index a07ff91dac..bb7252c643 100644
  --- a/nova/monkey_patch.py
  +++ b/nova/monkey_patch.py
  @@ -59,6 +59,9 @@ def _monkey_patch():
       else:
           eventlet.monkey_patch()
   
  +    import __original_module_threading
  +    import threading
  +    __original_module_threading.current_thread.__globals__['_active'] = threading._active
       # NOTE(rpodolyaka): import oslo_service first, so that it makes eventlet
       # hub use a monotonic clock to avoid issues with drifts of system time (see

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