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{- Opening files
-
- Copyright 2024 Joey Hess <id@joeyh.name>
-
- License: BSD-2-clause
-}
{-# LANGUAGE CPP #-}
module Utility.OpenFile where
#ifndef mingw32_HOST_OS
import System.IO
import System.Posix.IO
import GHC.IO.FD
import GHC.IO.Handle.FD
import GHC.IO.Device
import Utility.OpenFd
import Utility.RawFilePath
import Utility.FileSystemEncoding
{- Usually, opening a Handle to a file that another thread also has open
- for write is prevented, which avoids a lot of concurrency bugs especially
- with lazy IO.
-
- However, sometimes one thread is writing and another thread really wants
- to read from the same file. This bypasses the usual locking, by claiming
- that an opened FD is a Stream.
-}
openFileBeingWritten :: RawFilePath -> IO Handle
openFileBeingWritten f = do
fd <- openFdWithMode f ReadOnly Nothing defaultFileFlags (CloseOnExecFlag True)
(fd', fdtype) <- mkFD (fromIntegral fd) ReadMode (Just (Stream, 0, 0)) False False
mkHandleFromFD fd' fdtype (fromRawFilePath f) ReadMode False Nothing
#endif
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