git-annex-3.20120924: Utility/DirWatcher.hs

{- generic directory watching interface
 -
 - Uses either inotify or kqueue to watch a directory (and subdirectories)
 - for changes, and runs hooks for different sorts of events as they occur.
 -
 - Copyright 2012 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

{-# LANGUAGE CPP #-}

module Utility.DirWatcher where

import Utility.Types.DirWatcher

#if WITH_INOTIFY
import qualified Utility.INotify as INotify
import qualified System.INotify as INotify
#endif
#if WITH_KQUEUE
import qualified Utility.Kqueue as Kqueue
import Control.Concurrent
#endif

type Pruner = FilePath -> Bool

canWatch :: Bool
#if (WITH_INOTIFY || WITH_KQUEUE)
canWatch = True
#else
#if defined linux_HOST_OS
#warning "Building without inotify support"
#endif
canWatch = False
#endif

/* With inotify, discrete events will be received when making multiple changes
 * to the same filename. For example, adding it, deleting it, and adding it
 * again will be three events.
 * 
 * OTOH, with kqueue, often only one event is received, indicating the most
 * recent state of the file.
 */
eventsCoalesce :: Bool
#if WITH_INOTIFY
eventsCoalesce = False
#else
#if WITH_KQUEUE
eventsCoalesce = True
#else
eventsCoalesce = undefined
#endif
#endif

/* With inotify, file closing is tracked to some extent, so an add event
 * will always be received for a file once its writer closes it, and
 * (typically) not before. This may mean multiple add events for the same file.
 *
 * OTOH, with kqueue, add events will often be received while a file is
 * still being written to, and then no add event will be received once the
 * writer closes it.
 */
closingTracked :: Bool
#if WITH_INOTIFY
closingTracked = True
#else
#if WITH_KQUEUE
closingTracked = False
#else
closingTracked = undefined
#endif
#endif

/* With inotify, modifications to existing files can be tracked.
 * Kqueue does not support this.
 */
modifyTracked :: Bool
#if WITH_INOTIFY
modifyTracked = True
#else
#if WITH_KQUEUE
modifyTracked = False
#else
modifyTracked = undefined
#endif
#endif

/* Starts a watcher thread. The runStartup action is passed a scanner action
 * to run, that will return once the initial directory scan is complete.
 * Once runStartup returns, the watcher thread continues running,
 * and processing events. Returns a DirWatcherHandle that can be used
 * to shutdown later.  */
#if WITH_INOTIFY
type DirWatcherHandle = INotify.INotify
watchDir :: FilePath -> Pruner -> WatchHooks -> (IO () -> IO ()) -> IO DirWatcherHandle
watchDir dir prune hooks runstartup = do
	i <- INotify.initINotify
	runstartup $ INotify.watchDir i dir prune hooks
	return i
#else
#if WITH_KQUEUE
type DirWatcherHandle = ThreadId
watchDir :: FilePath -> Pruner -> WatchHooks -> (IO Kqueue.Kqueue -> IO Kqueue.Kqueue) -> IO DirWatcherHandle
watchDir dir ignored hooks runstartup = do
	kq <- runstartup $ Kqueue.initKqueue dir ignored
	forkIO $ Kqueue.runHooks kq hooks
#else
type DirWatcherHandle = ()
watchDir :: FilePath -> Pruner -> WatchHooks -> (IO () -> IO ()) -> IO DirWatcherHandle
watchDir = undefined
#endif
#endif

#if WITH_INOTIFY
stopWatchDir :: DirWatcherHandle -> IO ()
stopWatchDir = INotify.killINotify
#else
#if WITH_KQUEUE
stopWatchDir :: DirWatcherHandle -> IO ()
stopWatchDir = killThread
#else
stopWatchDir :: DirWatcherHandle -> IO ()
stopWatchDir = undefined
#endif
#endif