092041fab0
(With the exception of daemon pid locking.) This fixes at part of #758630. I reproduced the assistant locking eg, a removable drive's annex journal lock file and forking a long-running git-cat-file process that inherited that lock. This did not affect Windows. Considered doing a portable Utility.LockFile layer, but git-annex uses posix locks in several special ways that have no direct Windows equivilant, and it seems like it would mostly be a complication. This commit was sponsored by Protonet.
74 lines
2.3 KiB
Haskell
74 lines
2.3 KiB
Haskell
{- Windows lock files
|
|
-
|
|
- Copyright 2014 Joey Hess <joey@kitenet.net>
|
|
-
|
|
- License: BSD-2-clause
|
|
-}
|
|
|
|
module Utility.WinLock (
|
|
lockShared,
|
|
lockExclusive,
|
|
dropLock,
|
|
waitToLock,
|
|
LockHandle
|
|
) where
|
|
|
|
import System.Win32.Types
|
|
import System.Win32.File
|
|
import Control.Concurrent
|
|
|
|
{- Locking is exclusive, and prevents the file from being opened for read
|
|
- or write by any other process. So for advisory locking of a file, a
|
|
- different LockFile should be used. -}
|
|
type LockFile = FilePath
|
|
|
|
type LockHandle = HANDLE
|
|
|
|
{- Tries to lock a file with a shared lock, which allows other processes to
|
|
- also lock it shared. Fails is the file is exclusively locked. -}
|
|
lockShared :: LockFile -> IO (Maybe LockHandle)
|
|
lockShared = openLock fILE_SHARE_READ
|
|
|
|
{- Tries to take an exclusive lock on a file. Fails if another process has
|
|
- a shared or exclusive lock. -}
|
|
lockExclusive :: LockFile -> IO (Maybe LockHandle)
|
|
lockExclusive = openLock fILE_SHARE_NONE
|
|
|
|
{- Windows considers just opening a file enough to lock it. This will
|
|
- create the LockFile if it does not already exist.
|
|
-
|
|
- Will fail if the file is already open with an incompatable ShareMode.
|
|
- Note that this may happen if an unrelated process, such as a virus
|
|
- scanner, even looks at the file. See http://support.microsoft.com/kb/316609
|
|
-
|
|
- Note that createFile busy-waits to try to avoid failing when some other
|
|
- process briefly has a file open. But that would make checking locks
|
|
- much more expensive, so is not done here. Thus, the use of c_CreateFile.
|
|
-
|
|
- Also, passing Nothing for SECURITY_ATTRIBUTES ensures that the lock file
|
|
- is not inheerited by any child process.
|
|
-}
|
|
openLock :: ShareMode -> LockFile -> IO (Maybe LockHandle)
|
|
openLock sharemode f = do
|
|
h <- withTString f $ \c_f ->
|
|
c_CreateFile c_f gENERIC_READ sharemode security_attributes
|
|
oPEN_ALWAYS fILE_ATTRIBUTE_NORMAL (maybePtr Nothing)
|
|
return $ if h == iNVALID_HANDLE_VALUE
|
|
then Nothing
|
|
else Just h
|
|
where
|
|
security_attributes = maybePtr Nothing
|
|
|
|
dropLock :: LockHandle -> IO ()
|
|
dropLock = closeHandle
|
|
|
|
{- If the initial lock fails, this is a BUSY wait, and does not
|
|
- guarentee FIFO order of waiters. In other news, Windows is a POS. -}
|
|
waitToLock :: IO (Maybe LockHandle) -> IO LockHandle
|
|
waitToLock locker = takelock
|
|
where
|
|
takelock = go =<< locker
|
|
go (Just lck) = return lck
|
|
go Nothing = do
|
|
threadDelay (500000) -- half a second
|
|
takelock
|