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