Synnefo » snf-ganeti

{-| Ganeti lock-related types and type classes

-}

{-

Copyright (C) 2014 Google Inc.

This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.

-}

module Ganeti.Locking.Types

  ( Lock

  , lockImplications

  ) where

{-| The type class of being a lock

As usual, locks need to come with an order, the lock order, and

be an instance of Show, so that malformed requests can meaningfully

be reported.

Additionally, in Ganeti we also have group locks, like a lock for all

nodes. While those group locks contain infinitely many locks, the set

of locks a single lock is included in is always finite, and usually

very small. So we take this association from a lock to the locks it

is (strictly) included in as additional data of the type class.

It is a prerequisite that whenever 'a' is implied in 'b', then all locks

that are in the lock order between 'a' and 'b' are also implied in 'b'.

-}

class (Ord a, Show a) => Lock a where

  lockImplications :: a -> [a]