possible race condition for multiattach in Unity driver

Hi Eric,

Actually there is a lock around initialize_connection and terminate_connection. _create_host_and_attach called by initialize_connection and _detach_and_delete_host called by terminate_connection share this lock:

def _create_host_and_attach(self, host_name, lun_or_snap):
 @utils.lock_if(self.to_lock_host, '{lock_name}')
 def _lock_helper(lock_name):
  ...
 return _lock_helper('{unity}-{host}'.format(unity=self.client.host, host=host_name))

def _detach_and_delete_host(self, host_name, lun_or_snap, is_multiattach_to_host=False):
 @utils.lock_if(self.to_lock_host, '{lock_name}')
 def _lock_helper(lock_name):
  ...
 return _lock_helper('{unity}-{host}'.format(unity=self.client.host, host=host_name))

So the Volume B attach should not be impacted by Volume A detach.

And if is_multiattach_to_host is True, self.client.detach(host, lun_or_snap) and self.client.delete_host_wo_lock(host) will not be called in _detach_and_delete_host since the volume still attached to some instances.

So I think the race condition you mentioned may not happen.