On Mon, 2005-12-12 at 07:43 +0200, Einar Karttunen wrote:
Hello
It seems that opening the same file multiple times (one writer and multiple readers) is not supported at least on *nix with GHC. I want to use one Handle to use append data till the end of the file while other Handles perform random access IO with seeks on the file.
It states in the Haskell Report 21.2.3: http://haskell.org/onlinereport/io.html Implementations should enforce as far as possible, at least locally to the Haskell process, multiple-reader single-writer locking on files. That is, there may either be many handles on the same file which manage input, or just one handle on the file which manages output. If any open or semi-closed handle is managing a file for output, no new handle can be allocated for that file. If any open or semi-closed handle is managing a file for input, new handles can only be allocated if they do not manage output. Whether two files are the same is implementation-dependent, but they should normally be the same if they have the same absolute path name and neither has been renamed, for example. So yes, what you're trying to do is not supported by the standard IO library. GHC is doing the right thing and hugs is not. I'm not sure which layer implements the file locking so it may be that you can get underneath by using the System.Posix.IO functions. Duncan