Iterating over a WeakKeyDictionary isn't thread-safe

[Anthony Lenton]

Working with the latest wsgi-oops, we sometimes get the following
Traceback (most recent call last):
  File "/srv/login.staging.ubuntu.com/staging/framework/django.wsgi", line 46, in application
    return oops(environ, start_response)
  File "/usr/lib/python2.5/site-packages/canonical/oops/wsgi.py", line 70, in __call__
    response_trapper = ResponseTrapper(self.serial, environ, start_response)
  File "/usr/lib/python2.5/site-packages/canonical/oops/wsgi.py", line 88, in __init__
    environ['OOPSID'] = self.oops.assign_id()
  File "/usr/lib/python2.5/site-packages/canonical/oops/oops.py", line 66, in assign_id
    self.id = self._oops_id_factory()
  File "/usr/lib/python2.5/site-packages/canonical/oops/serializer.py", line 171, in get_next_oops_id
    day, sequence = self.get_next_sequence()
  File "/usr/lib/python2.5/site-packages/canonical/oops/serializer.py", line 159, in get_next_sequence
    serializer in self._serializers[self._key])
  File "/usr/lib/python2.5/site-packages/canonical/oops/serializer.py", line 158, in <genexpr>
    sequence = max(serializer.get_initial_sequence() for
  File "/usr/lib/python2.5/weakref.py", line 303, in iterkeys
    for wr in self.data.iterkeys():
RuntimeError: dictionary changed size during iteration

You usually see this error pop up a couple of times during load tests.

[Tim Cole (tcole)]

Apparently iterators obtained from WeakKeyDictionaries aren't threadsafe, since finalization may modify the underlying dict at any time. For now, we can avoid using iterators obtained from WeakKeyDictionaries, but this is arguably a bug in WeakKeyDictionary.

[Anthony Lenton (elachuni)]

Confirmed, the tracebacks go away by avoiding iterators on WeakKeyDictionary.

[Anthony Lenton (elachuni)]

This is an upstream Python bug, http://bugs.python.org/issue839159