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{- git-annex assistant transfer slots
-
- Copyright 2012 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
module Assistant.TransferSlots where
import Control.Exception
import Control.Concurrent
type TransferSlots = QSemN
{- Number of concurrent transfers allowed to be run from the assistant.
-
- Transfers launched by other means, including by remote assistants,
- do not currently take up slots.
-}
numSlots :: Int
numSlots = 1
newTransferSlots :: IO TransferSlots
newTransferSlots = newQSemN numSlots
{- Waits until a transfer slot becomes available, and runs a transfer
- action in the slot. If the action throws an exception, its slot is
- freed here, otherwise it should be freed by the TransferWatcher when
- the transfer is complete.
-}
inTransferSlot :: TransferSlots -> IO a -> IO a
inTransferSlot s a = bracketOnError start abort run
where
start = waitQSemN s 1
abort = const $ transferComplete s
run = const a
{- Call when a transfer is complete. -}
transferComplete :: TransferSlots -> IO ()
transferComplete s = signalQSemN s 1
|
