Comment 0 for bug 879044

Multiple XenAPI requests can happen at the same time... but there's an issue with that because we only use a single XenAPISession().

I think it's the cause of tracebacks like this periodically:

(nova.rpc): TRACE: File "/usr/local/lib/python2.6/dist-packages/XenAPI.py", line 229, in __call__
(nova.rpc): TRACE: return self.__send(self.__name, args)(nova.rpc): TRACE: File "/usr/local/lib/python2.6/dist-packages/XenAPI.py", line 133, in xenapi_request
(nova.rpc): TRACE: result = _parse_result(getattr(self, methodname)(*full_params))
(nova.rpc): TRACE: File "/usr/local/lib/python2.6/dist-packages/XenAPI.py", line 203, in _parse_result
(nova.rpc): TRACE: raise Failure(result['ErrorDescription'])(nova.rpc): TRACE: Failure: ['HANDLE_INVALID', 'VM', 'OpaqueRef:d1054be1-0ad6-532a-fa87-60ea50b863e2'](nova.rpc): TRACE:

It has been also reported that httplib will sometimes return CannotSendRequest exceptions... when there appears to be multiple XenAPI requests at nearly the same time...