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authorGravatar Joey Hess <joey@kitenet.net>2013-04-24 16:01:01 -0400
committerGravatar Joey Hess <joey@kitenet.net>2013-04-24 16:01:01 -0400
commit6148b926959ce5cbbc12aafc60a119788ca6d97f (patch)
tree738a801b7d4b49dbfee254d0baa6674444f93551 /Utility
parentc7f3bfbc5e25109629cb3df871dc1f4844f6c560 (diff)
add TList, built on DList
Diffstat (limited to 'Utility')
-rw-r--r--Utility/TList.hs52
1 files changed, 52 insertions, 0 deletions
diff --git a/Utility/TList.hs b/Utility/TList.hs
new file mode 100644
index 000000000..33a50b7dd
--- /dev/null
+++ b/Utility/TList.hs
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+{- 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)