add TList, built on DList

Utility/TList.hs

@@ -0,0 +1,52 @@
+{- Transactional lists
+ -
+ - Based on DLists, a transactional list can quickly and efficiently
+ - have items inserted at either end, or a whole list appended to it.
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -}
+
+{-# LANGUAGE BangPatterns #-}
+
+module Utility.TList where
+
+import Common
+
+import Control.Concurrent.STM
+import qualified Data.DList as D
+
+type TList a = TMVar (D.DList a)
+
+newTList :: STM (TList a)
+newTList = newEmptyTMVar
+
+{- Gets the contents of the TList. Blocks when empty.
+ - TList is left empty. -}
+getTList :: TList a -> STM [a]
+getTList tlist = D.toList <$> takeTMVar tlist
+
+{- Gets anything currently in the TList, without blocking.
+ - TList is left empty. -}
+readTList :: TList a -> STM [a]
+readTList tlist = maybe [] D.toList <$> tryTakeTMVar tlist
+
+{- Mutates a TList. -}
+modifyTList :: TList a -> (D.DList a -> D.DList a) -> STM ()
+modifyTList tlist a = do
+	dl <- fromMaybe D.empty <$> tryTakeTMVar tlist
+	let !dl' = a dl
+	{- The TMVar is left empty when the list is empty.
+	 - Thus attempts to read it automatically block. -}
+	unless (emptyDList dl') $
+		putTMVar tlist dl'
+  where
+  	emptyDList = D.list True (\_ _ -> False)
+
+consTList :: TList a -> a -> STM ()
+consTList tlist v = modifyTList tlist $ \dl -> D.cons v dl
+
+snocTList :: TList a -> a -> STM ()
+snocTList tlist v = modifyTList tlist $ \dl -> D.snoc dl v
+
+appendTList :: TList a -> [a] -> STM ()
+appendTList tlist l = modifyTList tlist $ \dl -> D.append dl (D.fromList l)

debian/control

@@ -17,6 +17,7 @@ Build-Depends:
 	libghc-quickcheck2-dev,
 	libghc-monad-control-dev (>= 0.3),
 	libghc-lifted-base-dev,
+	libghc-dlist-dev,
 	libghc-uuid-dev,
 	libghc-json-dev,
 	libghc-ifelse-dev,

doc/install/fromscratch.mdwn

@@ -13,6 +13,7 @@ quite a lot.
   * [QuickCheck 2](http://hackage.haskell.org/package/QuickCheck)
   * [json](http://hackage.haskell.org/package/json)
   * [IfElse](http://hackage.haskell.org/package/IfElse)
+  * [dlist](http://hackage.haskell.org/package/dlist)
   * [bloomfilter](http://hackage.haskell.org/package/bloomfilter)
   * [edit-distance](http://hackage.haskell.org/package/edit-distance)
   * [hS3](http://hackage.haskell.org/package/hS3) (optional)

git-annex.cabal

@@ -70,7 +70,7 @@ Executable git-annex
    extensible-exceptions, dataenc, SHA, process, json,
    base (>= 4.5 && < 4.8), monad-control, transformers-base, lifted-base,
    IfElse, text, QuickCheck >= 2.1, bloomfilter, edit-distance, process,
-   SafeSemaphore, uuid, random, regex-tdfa
+   SafeSemaphore, uuid, random, regex-tdfa, dlist
   -- Need to list these because they're generated from .hsc files.
   Other-Modules: Utility.Touch Utility.Mounts
   Include-Dirs: Utility