Hi all, Haskell currently requires that multiple-reader single-writer locking is used on files. I understand the motivation for this was to try to protect people from running into problems due to lazy IO, but in practice I think it just causes more problems than it solves. The decision may also have been influenced by the belief that this behaviour is enforced for all programs on Windows, but I am told that it is possible to get lock-free behaviour on Windows too. I propose that we remove all the automatic locking from the libraries, and let the user do any locking that they wish to do themselves. Attached are patches for ghc, base, process and unix. (not yet tested on Windows). Suggested discussion period: Until 9 Nov 2011 Related GHC ticket: http://hackage.haskell.org/trac/ghc/ticket/4363 Thanks Ian