[Haskell-cafe] Windows: openFile gives permission denied when file in use

[Steve Schafer]

On Thu, 29 Dec 2011 16:10:03 +1300, chrisyco at gmail.com wrote:

>In fact, this is required behavior according to the Haskell Report:
>
>> 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.

The second sentence somewhat contradicts the first.

The first sentence says, "multiple-reader single-writer" which implies
multiple readers AND at most one writer (i.e., at the same time). This
is pretty typical file-locking behavior, and, from the symptoms, appears
to be the way that Framemaker opens the file.

The second sentence, on the other hand, implies that there can be
multiple readers OR one writer, but not both (which appears to be the
way that GHC operates).

>I guess on Windows, "as far as possible" means locking it across the
>whole system.

Windows does allow finer-grained control (including byte-range locking),
but most applications don't bother.

-Steve Schafer