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{-| Implementation of a reader for the job queue.

-}

{-

Copyright (C) 2013 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.JQScheduler

  ( JQStatus

  , emptyJQStatus

  , initJQScheduler

  , enqueueNewJobs

  ) where

import Control.Arrow

import Control.Concurrent

import Control.Exception

import Control.Monad

import Data.List

import Data.IORef

import Ganeti.BasicTypes

import Ganeti.Constants as C

import Ganeti.JQueue as JQ

import Ganeti.Logging

import Ganeti.Path

import Ganeti.Types

import Ganeti.Utils

data JobWithStat = JobWithStat { jStat :: FStat, jJob :: QueuedJob }

data Queue = Queue { qEnqueued :: [JobWithStat], qRunning :: [JobWithStat] }

{-| Representation of the job queue

We keep two lists of jobs (together with information about the last

fstat result observed): the jobs that are enqueued, but not yet handed

over for execution, and the jobs already handed over for execution. They

are kept together in a single IORef, so that we can atomically update

both, in particular when scheduling jobs to be handed over for execution.

-}

data JQStatus = JQStatus

  { jqJobs :: IORef Queue

  }

emptyJQStatus :: IO JQStatus

emptyJQStatus = do

  jqJ <- newIORef Queue {qEnqueued=[], qRunning=[]}

  return JQStatus { jqJobs=jqJ }

-- | Apply a function on the running jobs.

onRunningJobs :: ([JobWithStat] -> [JobWithStat]) -> Queue -> Queue

onRunningJobs f queue = queue {qRunning=f $ qRunning queue}

-- | Apply a function on the queued jobs.

onQueuedJobs :: ([JobWithStat] -> [JobWithStat]) -> Queue -> Queue

onQueuedJobs f queue = queue {qEnqueued=f $ qEnqueued queue}

-- | Obtain a JobWithStat from a QueuedJob.

unreadJob :: QueuedJob -> JobWithStat

unreadJob job = JobWithStat {jJob=job, jStat=nullFStat}

-- | Reload interval for polling the running jobs for updates in microseconds.

watchInterval :: Int

watchInterval = C.luxidJobqueuePollInterval * 1000000 

-- | Maximal number of jobs to be running at the same time.

maxRunningJobs :: Int

maxRunningJobs = C.luxidMaximalRunningJobs 

-- | Wrapper function to atomically update the jobs in the queue status.

modifyJobs :: JQStatus -> (Queue -> Queue) -> IO ()

modifyJobs qstat f = atomicModifyIORef (jqJobs qstat) (flip (,) ()  . f)

-- | Reread a job from disk, if the file has changed.

readJobStatus :: JobWithStat -> IO (Maybe JobWithStat)

readJobStatus (JobWithStat {jStat=fstat, jJob=job})  = do

  let jid = qjId job

  qdir <- queueDir

  let fpath = liveJobFile qdir jid

  logDebug $ "Checking if " ++ fpath ++ " changed on disk."

  changedResult <- try $ needsReload fstat fpath

                   :: IO (Either IOError (Maybe FStat))

  let changed = either (const $ Just nullFStat) id changedResult

  case changed of

    Nothing -> do

      logDebug $ "File " ++ fpath ++ " not changed on disk."

      return Nothing

    Just fstat' -> do

      let jids = show $ fromJobId jid

      logInfo $ "Rereading job "  ++ jids

      readResult <- loadJobFromDisk qdir True jid

      case readResult of

        Bad s -> do

          logWarning $ "Failed to read job " ++ jids ++ ": " ++ s

          return Nothing

        Ok (job', _) -> do

          logDebug

            $ "Read job " ++ jids ++ ", staus is " ++ show (calcJobStatus job')

          return . Just $ JobWithStat {jStat=fstat', jJob=job'}

-- | Update a job in the job queue, if it is still there. This is the

-- pure function for inserting a previously read change into the queue.

-- as the change contains its time stamp, we don't have to worry about a

-- later read change overwriting a newer read state. If this happens, the

-- fstat value will be outdated, so the next poller run will fix this.

updateJobStatus :: JobWithStat -> [JobWithStat] -> [JobWithStat]

updateJobStatus job' =

  let jid = qjId $ jJob job' in

  map (\job -> if qjId (jJob job) == jid then job' else job)

-- | Update a single job by reading it from disk, if necessary.

updateJob :: JQStatus -> JobWithStat -> IO ()

updateJob state jb = do

  jb' <- readJobStatus jb

  maybe (return ()) (modifyJobs state . onRunningJobs . updateJobStatus) jb'

-- | Sort out the finished jobs from the monitored part of the queue.

-- This is the pure part, splitting the queue into a remaining queue

-- and the jobs that were removed.

sortoutFinishedJobs :: Queue -> (Queue, [QueuedJob])

sortoutFinishedJobs queue =

  let (run', fin) = partition

                      ((<= JOB_STATUS_RUNNING) . calcJobStatus . jJob)

                      . qRunning $ queue

  in (queue {qRunning=run'}, map jJob fin)

-- | Actually clean up the finished jobs. This is the IO wrapper around

-- the pure `sortoutFinishedJobs`.

cleanupFinishedJobs :: JQStatus -> IO ()

cleanupFinishedJobs qstate = do

  finished <- atomicModifyIORef (jqJobs qstate) sortoutFinishedJobs

  let showJob = show . ((fromJobId . qjId) &&& calcJobStatus)

      jlist = commaJoin $ map showJob finished

  unless (null finished)

    . logInfo $ "Finished jobs: " ++ jlist

-- | Decide on which jobs to schedule next for execution. This is the

-- pure function doing the scheduling.

selectJobsToRun :: Queue -> (Queue, [QueuedJob])

selectJobsToRun queue =

  let n = maxRunningJobs - length (qRunning queue)

      (chosen, remain) = splitAt n (qEnqueued queue)

  in (queue {qEnqueued=remain, qRunning=qRunning queue ++ chosen}

     , map jJob chosen)

-- | Requeue jobs that were previously selected for execution

-- but couldn't be started.

requeueJobs :: JQStatus -> [QueuedJob] -> IOError -> IO ()

requeueJobs qstate jobs err = do

  let jids = map qjId jobs

      jidsString = commaJoin $ map (show . fromJobId) jids

      rmJobs = filter ((`notElem` jids) . qjId . jJob)

  logWarning $ "Starting jobs failed: " ++ show err

  logWarning $ "Rescheduling jobs: " ++ jidsString

  modifyJobs qstate (onRunningJobs rmJobs)

  modifyJobs qstate (onQueuedJobs . (++) $ map unreadJob jobs)

-- | Schedule jobs to be run. This is the IO wrapper around the

-- pure `selectJobsToRun`.

scheduleSomeJobs :: JQStatus -> IO ()

scheduleSomeJobs qstate = do

  chosen <- atomicModifyIORef (jqJobs qstate) selectJobsToRun

  unless (null chosen) . logInfo . (++) "Starting jobs: " . commaJoin

    $ map (show . fromJobId . qjId) chosen

  result <- try $ JQ.startJobs chosen

  either (requeueJobs qstate chosen) return result

-- | Format the job queue status in a compact, human readable way.

showQueue :: Queue -> String

showQueue (Queue {qEnqueued=waiting, qRunning=running}) =

  let showids = show . map (fromJobId . qjId . jJob)

  in "Waiting jobs: " ++ showids waiting 

       ++ "; running jobs: " ++ showids running

-- | Time-based watcher for updating the job queue.

onTimeWatcher :: JQStatus -> IO ()

onTimeWatcher qstate = forever $ do

  threadDelay watchInterval

  logDebug "Job queue watcher timer fired"

  jobs <- readIORef (jqJobs qstate)

  mapM_ (updateJob qstate) $ qRunning jobs

  cleanupFinishedJobs qstate

  jobs' <- readIORef (jqJobs qstate)

  logInfo $ showQueue jobs'

  scheduleSomeJobs qstate

-- | Set up the job scheduler. This will also start the monitoring

-- of changes to the running jobs.

initJQScheduler :: JQStatus -> IO ()

initJQScheduler qstate = do

  logInfo "Starting time-based job queue watcher"

  _ <- forkIO $ onTimeWatcher qstate

  return ()

-- | Enqueue new jobs. This will guarantee that the jobs will be executed

-- eventually.

enqueueNewJobs :: JQStatus -> [QueuedJob] -> IO ()

enqueueNewJobs state jobs = do

  logInfo . (++) "New jobs enqueued: " . commaJoin

    $ map (show . fromJobId . qjId) jobs

  let jobs' = map unreadJob jobs

  modifyJobs state (onQueuedJobs (++ jobs'))

  scheduleSomeJobs state