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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 Common.Annex
import Utility.ThreadScheduler
import Assistant.DaemonStatus
import Logs.Transfer
import qualified Control.Exception as E
import Control.Concurrent
import qualified Control.Concurrent.MSemN as MSemN
import Data.Typeable
type TransferSlots = MSemN.MSemN Int
{- 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
type TransferSlotRunner = DaemonStatusHandle -> TransferSlots -> TransferGenerator -> IO ()
type TransferGenerator = IO (Maybe (Transfer, TransferInfo, IO ()))
{- 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 = MSemN.new numSlots
{- Waits until a transfer slot becomes available, then runs a
- TransferGenerator, and then runs the transfer action in its own thread.
-}
inTransferSlot :: TransferSlotRunner
inTransferSlot dstatus s gen = do
MSemN.wait s 1
runTransferThread dstatus s =<< gen
{- Runs a TransferGenerator, and its transfer action,
- without waiting for a slot to become available. -}
inImmediateTransferSlot :: TransferSlotRunner
inImmediateTransferSlot dstatus s gen = do
MSemN.signal s (-1)
runTransferThread dstatus s =<< gen
{- Runs a transfer action, in an already allocated transfer slot.
- Once it finishes, frees the transfer slot.
-
- 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.
-}
runTransferThread :: DaemonStatusHandle -> TransferSlots -> Maybe (Transfer, TransferInfo, IO ()) -> IO ()
runTransferThread _ s Nothing = MSemN.signal s 1
runTransferThread dstatus s (Just (t, info, a)) = do
tid <- forkIO go
updateTransferInfo dstatus t $ info { transferTid = Just tid }
where
go = catchPauseResume a
pause = catchPauseResume $ runEvery (Seconds 86400) noop
{- Note: This must use E.try, rather than E.catch.
- When E.catch is used, and has called go in its exception
- handler, Control.Concurrent.throwTo will block sometimes
- when signaling. Using E.try avoids the problem. -}
catchPauseResume a' = do
r <- E.try a' :: IO (Either E.SomeException ())
case r of
Left e -> case E.fromException e of
Just PauseTransfer -> pause
Just ResumeTransfer -> go
_ -> done
_ -> done
done = MSemN.signal s 1
|
