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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.
-}
{-# LANGUAGE DeriveDataTypeable #-}
module Assistant.TransferSlots where
import qualified Control.Exception as E
import Control.Concurrent
import Data.Typeable
import Common.Annex
import Utility.ThreadScheduler
type TransferSlots = QSemN
{- A special exception that can be thrown to pause or resume a transfer, while
- keeping its slot in use. -}
data TransferException = PauseTransfer | ResumeTransfer
deriving (Show, Eq, Typeable)
instance E.Exception TransferException
{- 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, in its own thread.
-
- Note that the action is subject to being killed when the transfer
- is canceled or paused.
-
- A PauseTransfer exception is handled by letting the action be killed,
- then pausing the thread until a ResumeTransfer exception is raised,
- then rerunning the action.
-}
inTransferSlot :: TransferSlots -> IO () -> IO ThreadId
inTransferSlot s transfer = do
waitQSemN s 1
forkIO $ E.bracket_ noop (signalQSemN s 1) go
where
go = catchPauseResume transfer
pause = catchPauseResume $ runEvery (Seconds 86400) noop
catchPauseResume a = E.catch a handlePauseResume
handlePauseResume PauseTransfer = do
putStrLn "pause"
pause
handlePauseResume ResumeTransfer = do
putStrLn "resume"
go
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