Synnefo » snf-ganeti

    , allocateJobIds

    , allocateJobId

import Control.Concurrent.MVar

import Ganeti.Objects (Node)

import Ganeti.Rpc (executeRpcCall, RpcCallJobqueueUpdate(..))

-- | Allocate new job ids.

-- To avoid races while accessing the serial file, the threads synchronize

-- over a lock, as usual provided by an MVar.

allocateJobIds :: [Node] -> MVar () -> Int -> IO (Result [JobId])

allocateJobIds mastercandidates lock n =

  if n <= 0

    then return . Bad $ "Can only allocate positive number of job ids"

    else do

      takeMVar lock

      rjobid <- readSerialFromDisk

      case rjobid of

        Bad s -> do

          putMVar lock ()

          return . Bad $ s

        Ok jid -> do

          let current = fromJobId jid

              serial_content = show (current + n) ++  "\n"

          serial <- jobQueueSerialFile

          write_result <- try $ atomicWriteFile serial serial_content

                          :: IO (Either IOError ())

          putMVar lock ()

          case write_result of

            Left e -> do

              let msg = "Failed to write serial file: " ++ show e

              logError msg

              return . Bad $ msg 

            Right () -> do

              _ <- executeRpcCall mastercandidates

                     $ RpcCallJobqueueUpdate serial serial_content

              return $ mapM makeJobId [(current+1)..(current+n)]

-- | Allocate one new job id.

allocateJobId :: [Node] -> MVar () -> IO (Result JobId)

allocateJobId mastercandidates lock = do

  jids <- allocateJobIds mastercandidates lock 1

  return (jids >>= monadicThe "Failed to allocate precisely one Job ID")