git-annex/RunCommand.hs
Joey Hess 34c8af74ba fix inversion of control in CommandSeek (no behavior changes)
I've been disliking how the command seek actions were written for some
time, with their inversion of control and ugly workarounds.

The last straw to fix it was sync --content, which didn't fit the
Annex [CommandStart] interface well at all. I have not yet made it take
advantage of the changed interface though.

The crucial change, and probably why I didn't do it this way from the
beginning, is to make each CommandStart action be run with exceptions
caught, and if it fails, increment a failure counter in annex state.
So I finally remove the very first code I wrote for git-annex, which
was before I had exception handling in the Annex monad, and so ran outside
that monad, passing state explicitly as it ran each CommandStart action.

This was a real slog from 1 to 5 am.

Test suite passes.

Memory usage is lower than before, sometimes by a couple of megabytes, and
remains constant, even when running in a large repo, and even when
repeatedly failing and incrementing the error counter. So no accidental
laziness space leaks.

Wall clock speed is identical, even in large repos.

This commit was sponsored by an anonymous bitcoiner.
2014-01-20 04:57:36 -04:00

64 lines
1.8 KiB
Haskell

{- git-annex running commands
-
- Copyright 2010-2014 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
{-# LANGUAGE BangPatterns #-}
module RunCommand where
import Common.Annex
import qualified Annex
import Types.Command
import qualified Annex.Queue
import Annex.Exception
{- Runs a command, starting with the check stage, and then
- the seek stage. Finishes by printing the number of commandActions that
- failed. -}
performCommand :: Command -> CmdParams -> Annex ()
performCommand Command { cmdseek = seek, cmdcheck = c, cmdname = name } params = do
mapM_ runCheck c
Annex.changeState $ \s -> s { Annex.errcounter = 0 }
seek params
showerrcount =<< Annex.getState Annex.errcounter
where
showerrcount 0 = noop
showerrcount cnt = error $ 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).
-
- This should only be run in the seek stage. -}
commandAction :: CommandStart -> Annex ()
commandAction a = handle =<< tryAnnexIO go
where
go = do
Annex.Queue.flushWhenFull
callCommand a
handle (Right True) = noop
handle (Right False) = incerr
handle (Left err) = do
showErr err
showEndFail
incerr
incerr = Annex.changeState $ \s ->
let ! c = Annex.errcounter s + 1
! s' = s { Annex.errcounter = c }
in s'
{- Runs a single command action through the start, perform and cleanup stages -}
callCommand :: CommandStart -> CommandCleanup
callCommand = start
where
start = stage $ maybe skip perform
perform = stage $ maybe failure cleanup
cleanup = stage $ status
stage = (=<<)
skip = return True
failure = showEndFail >> return False
status r = showEndResult r >> return r