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{-| Utilities related to livelocks and death detection

-}

{-

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.Utils.Livelock

  ( Livelock

  , mkLivelockFile

  ) where

import qualified Control.Exception as E

import Control.Monad

import Control.Monad.Error

import System.Directory (doesFileExist)

import System.IO

import System.Posix.IO

import System.Posix.Types (Fd)

import System.Time (ClockTime(..), getClockTime)

import Ganeti.BasicTypes

import Ganeti.Path (livelockFile)

import Ganeti.Utils (lockFile)

type Livelock = FilePath

-- | Appends the current time to the given prefix, creates

-- the lockfile in the appropriate directory, and locks it.

-- Returns its full path and the file's file descriptor.

mkLivelockFile :: (Error e, MonadError e m, MonadIO m)

               => FilePath -> m (Fd, Livelock)

mkLivelockFile prefix = do

  (TOD secs _) <- liftIO getClockTime

  lockfile <- liftIO . livelockFile $ prefix ++ "_" ++ show secs

  fd <- liftIO (lockFile lockfile) >>= \r -> case r of

          Bad msg   -> failError $ "Locking the livelock file " ++ lockfile

                                   ++ ": " ++ msg

          Ok fd     -> return fd

  return (fd, lockfile)