'Write data describing a container update notification to a pickle file
in the async_pending directory.
:param device: name of target device
:param account: account name for the object
:param container: container name for the object
:param obj: object name for the object
:param data: update data to be written to pickle file
:param timestamp: a Timestamp
:param policy: the StoragePolicy instance'

def pickle_async_update(self, device, account, container, obj, data, timestamp, policy):

    device_path = self.construct_dev_path(device)
    async_dir = os.path.join(device_path, get_async_dir(policy))
    tmp_dir = os.path.join(device_path, get_tmp_dir(policy))
    mkdirs(tmp_dir)
    ohash = hash_path(account, container, obj)
    write_pickle(data, os.path.join(async_dir, ohash[(-3):], ((ohash + '-') + Timestamp(timestamp).internal)), tmp_dir)
    self.logger.increment('async_pendings')
