Synnefo » snf-ganeti

def ExecWithUnusedUid(fn, all_uids, *args, **kwargs):

  """Execute a callable and provide an unused user-id in its kwargs.

  This wrapper function provides a simple way to handle the requesting,

  unlocking and releasing a user-id.

  "fn" is called by passing a "uid" keyword argument that

  contains an unused user-id (as a string) selected from the set of user-ids

  passed in all_uids.

  If there is an error while executing "fn", the user-id is returned

  to the pool.

  @param fn: a callable

  @param all_uids: a set containing all user-ids in the user-id pool

  """

  uid = RequestUnusedUid(all_uids)

  kwargs["uid"] = str(uid)

  try:

    return_value = fn(*args, **kwargs)

  except:

    # The failure of "callabe" means that starting a process with the uid

    # failed, so let's put the uid back into the pool.

    ReleaseUid(uid)

    raise

  uid.Unlock()

  return return_value