## root / src / Ganeti / HTools / PeerMap.hs @ 6d3d13ab

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{-| Module abstracting the peer map implementation. |
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This is abstracted separately since the speed of peermap updates can |

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be a significant part of the total runtime, and as such changing the |

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implementation should be easy in case it's needed. |

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-} |

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{- |

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Copyright (C) 2009, 2011 Google Inc. |

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

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

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

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(at your option) any later version. |

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

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WITHOUT ANY WARRANTY; without even the implied warranty of |

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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |

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General Public License for more details. |

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

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

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

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02110-1301, USA. |

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-} |

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module Ganeti.HTools.PeerMap |

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( PeerMap |

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, Key |

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, Elem |

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, empty |

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, accumArray |

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, Ganeti.HTools.PeerMap.find |

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, add |

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, remove |

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, maxElem |

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) where |

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import Data.Maybe (fromMaybe) |

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import Data.List |

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import Data.Ord (comparing) |

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import Ganeti.HTools.Types |

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-- * Type definitions |

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-- | Our key type. |

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type Key = Ndx |

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-- | Our element type. |

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type Elem = Int |

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-- | The definition of a peer map. |

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type PeerMap = [(Key, Elem)] |

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-- * Initialization functions |

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-- | Create a new empty map. |

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empty :: PeerMap |

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empty = [] |

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-- | Our reverse-compare function. |

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pmCompare :: (Key, Elem) -> (Key, Elem) -> Ordering |

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pmCompare a b = comparing snd b a |

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-- | Add or update (via a custom function) an element. |

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addWith :: (Elem -> Elem -> Elem) -> Key -> Elem -> PeerMap -> PeerMap |

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addWith fn k v lst = |

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case lookup k lst of |

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Nothing -> insertBy pmCompare (k, v) lst |

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Just o -> insertBy pmCompare (k, fn o v) (remove k lst) |

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-- | Create a PeerMap from an association list, with possible duplicates. |

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accumArray :: (Elem -> Elem -> Elem) -- ^ function used to merge the elements |

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-> [(Key, Elem)] -- ^ source data |

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-> PeerMap -- ^ results |

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accumArray _ [] = empty |

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accumArray fn ((k, v):xs) = addWith fn k v $ accumArray fn xs |

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-- * Basic operations |

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-- | Returns either the value for a key or zero if not found. |

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find :: Key -> PeerMap -> Elem |

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find k = fromMaybe 0 . lookup k |

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-- | Add an element to a peermap, overwriting the previous value. |

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add :: Key -> Elem -> PeerMap -> PeerMap |

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add = addWith (flip const) |

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-- | Remove an element from a peermap. |

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remove :: Key -> PeerMap -> PeerMap |

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remove _ [] = [] |

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remove k ((x@(x', _)):xs) = if k == x' |

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then xs |

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else x:remove k xs |

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-- | Find the maximum element. |

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-- |

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-- Since this is a sorted list, we just get the value at the head of |

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-- the list, or zero for a null list |

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maxElem :: PeerMap -> Elem |

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maxElem (x:_) = snd x |

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maxElem _ = 0 |