git-annex/CmdLine/Action.hs

{- git-annex command-line actions
 -
 - Copyright 2010-2017 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

{-# LANGUAGE CPP #-}

module CmdLine.Action where

import Annex.Common
import qualified Annex
import Annex.Concurrent
import Types.Command
import Types.Concurrency
import Messages.Concurrent
import Types.Messages
import Remote.List

import Control.Concurrent
import Control.Concurrent.Async
import Control.Concurrent.STM
import Control.Exception (throwIO)
import Data.Either
import qualified Data.Map.Strict as M

#ifdef WITH_CONCURRENTOUTPUT
import qualified System.Console.Regions as Regions
#endif

{- Runs a command, starting with the check stage, and then
 - the seek stage. Finishes by running the continutation, and 
 - then showing a count of any failures. -}
performCommandAction :: Command -> CommandSeek -> Annex () -> Annex ()
performCommandAction Command { cmdcheck = c, cmdname = name } seek cont = do
	mapM_ runCheck c
	Annex.changeState $ \s -> s { Annex.errcounter = 0 }
	seek
	finishCommandActions
	cont
	showerrcount =<< Annex.getState Annex.errcounter
  where
	showerrcount 0 = noop
	showerrcount cnt = giveup $ name ++ ": " ++ show cnt ++ " failed"

{- Runs one of the actions needed to perform a command.
 - Individual actions can fail without stopping the whole command,
 - including by throwing IO errors (but other errors terminate the whole
 - command).
 - 
 - When concurrency is enabled, a thread is forked off to run the action
 - in the background, as soon as a free slot is available.
 
 - This should only be run in the seek stage.
 -}
commandAction :: CommandStart -> Annex ()
commandAction a = go =<< Annex.getState Annex.concurrency
  where
	go (Concurrent n) = do
		ws <- Annex.getState Annex.workers
		(st, ws') <- if null ws
			then do
				-- Generate the remote list now, to avoid
				-- each thread generating it, which would
				-- be more expensive and could cause
				-- threads to contend over eg, calls to
				-- setConfig.
				_ <- remoteList
				st <- dupState
				return (st, replicate (n-1) (Left st))
			else do
				l <- liftIO $ drainTo (n-1) ws
				findFreeSlot l
		w <- liftIO $ async
			$ snd <$> Annex.run st (inOwnConsoleRegion (Annex.output st) run)
		Annex.changeState $ \s -> s { Annex.workers = Right w:ws' }
	go NonConcurrent = run
	run = void $ includeCommandAction a

{- Waits for any forked off command actions to finish.
 -
 - Merge together the cleanup actions of all the AnnexStates used by
 - threads, into the current Annex's state, so they'll run at shutdown.
 -
 - Also merge together the errcounters of the AnnexStates.
 -}
finishCommandActions :: Annex ()
finishCommandActions = do
	ws <- Annex.getState Annex.workers
	Annex.changeState $ \s -> s { Annex.workers = [] }
	l <- liftIO $ drainTo 0 ws
	forM_ (lefts l) mergeState

{- Wait for Asyncs from the list to finish, replacing them with their
 - final AnnexStates, until the list of remaining Asyncs is not larger
 - than the specified size, then returns the new list.
 -
 - If the action throws an exception, it is propigated, but first
 - all other actions are waited for, to allow for a clean shutdown.
 -}
drainTo
	:: Int
	-> [Either Annex.AnnexState (Async Annex.AnnexState)]
	-> IO [Either Annex.AnnexState (Async Annex.AnnexState)]
drainTo sz l
	| null as || sz >= length as = return l
	| otherwise = do
		(done, ret) <- waitAnyCatch as
		let as' = filter (/= done) as
		case ret of
			Left e -> do
				void $ drainTo 0 (map Left sts ++ map Right as')
				throwIO e
			Right st -> do
				drainTo sz $ map Left (st:sts) ++ map Right as'
  where
	(sts, as) = partitionEithers l

findFreeSlot :: [Either Annex.AnnexState (Async Annex.AnnexState)] -> Annex (Annex.AnnexState, [Either Annex.AnnexState (Async Annex.AnnexState)])
findFreeSlot = go []
  where
	go c [] = do
		st <- dupState
		return (st, c)
	go c (Left st:rest) = return (st, c ++ rest)
	go c (v:rest) = go (v:c) rest

{- Like commandAction, but without the concurrency. -}
includeCommandAction :: CommandStart -> CommandCleanup
includeCommandAction a = account =<< tryIO (callCommandAction a)
  where
	account (Right True) = return True
	account (Right False) = incerr
	account (Left err) = do
		toplevelWarning True (show err)
		implicitMessage showEndFail
		incerr
	incerr = do
		Annex.incError
		return False

{- Runs a single command action through the start, perform and cleanup
 - stages, without catching errors. Useful if one command wants to run
 - part of another command. -}
callCommandAction :: CommandStart -> CommandCleanup
callCommandAction = fromMaybe True <$$> callCommandAction' 

{- Like callCommandAction, but returns Nothing when the command did not
 - perform any action. -}
callCommandAction' :: CommandStart -> Annex (Maybe Bool)
callCommandAction' = start
  where
	start   = stage $ maybe skip perform
	perform = stage $ maybe failure cleanup
	cleanup = stage $ status
	stage = (=<<)
	skip = return Nothing
	failure = implicitMessage showEndFail >> return (Just False)
	status r = implicitMessage (showEndResult r) >> return (Just r)

{- Do concurrent output when that has been requested. -}
allowConcurrentOutput :: Annex a -> Annex a
#ifdef WITH_CONCURRENTOUTPUT
allowConcurrentOutput a = go =<< Annex.getState Annex.concurrency
  where
	go NonConcurrent = a
	go (Concurrent _) = ifM (liftIO concurrentOutputSupported)
		( Regions.displayConsoleRegions $
			goconcurrent True
		, goconcurrent False
		)
	goconcurrent b = bracket_ (setup b) cleanup a
	setup = setconcurrentenabled
	cleanup = do
		finishCommandActions
		setconcurrentenabled False
	setconcurrentenabled b = Annex.changeState $ \s ->
		s { Annex.output = (Annex.output s) { concurrentOutputEnabled = b } }
#else
allowConcurrentOutput = id
#endif

{- Ensures that only one thread processes a key at a time.
 - Other threads will block until it's done. -}
onlyActionOn :: Key -> CommandStart -> CommandStart
onlyActionOn k a = onlyActionOn' k run
  where
	run = do
		-- Run whole action, not just start stage, so other threads
		-- block until it's done.
		r <- callCommandAction' a
		case r of
			Nothing -> return Nothing
			Just r' -> return $ Just $ return $ Just $ return r'

onlyActionOn' :: Key -> Annex a -> Annex a
onlyActionOn' k a = go =<< Annex.getState Annex.concurrency
  where
	go NonConcurrent = a
	go (Concurrent _) = do
		tv <- Annex.getState Annex.activekeys
		bracket (setup tv) id (const a)
	setup tv = liftIO $ do
		mytid <- myThreadId
		atomically $ do
			m <- readTVar tv
			case M.lookup k m of
				Just tid
					| tid /= mytid -> retry
					| otherwise -> return (return ())
				Nothing -> do
					writeTVar tv $! M.insert k mytid m
					return $ liftIO $ atomically $
						modifyTVar tv $ M.delete k