Re: [Caml-list] memory mapped files with bigarray on windows

[Gabriel Scherer <gabriel.scherer@gmail.com>]

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There were experiments adding an explicit "unmap this bigarray" operation
to the runtime: see Apr 2012 commit

https://github.com/ocaml/ocaml/commit/2330a3b30fe5b910f4776bf9c41f35ce2b980fb1
However, this change was reverted shortly thereafter because of performance
concerns: it changes the invariant that the size of a live bigarray never
changes, which makes it easier to optimize away bound checks.

Could you please create a bug report ( http://caml.inria.fr/mantis/ ) to
keep track of your particular issue with lack of explicit bigarray closure?
I haven't found traces of it in the bugtracker ( the rather old bug
http://caml.inria.fr/mantis/view.php?id=3571 is about the need to call
msync() in a NFS setting, but doesn't touch explicit closure ), so it may
not have been previously known.

On Thu, Sep 18, 2014 at 10:04 AM, Bauer, Christoph <
bauerchristoph@siemens.com> wrote:

>  Dear All,
>
>
>
> my program maps  several blocks of a file into memory with
> Bigarray.Array1.map_file for writing.
>
> Finally the file handle is closed with Unix.close.
>
>
>
> On local files system everything works as expected. But if the file is on
> a network drive,
>
> the resulting file is after the close still  locked [1] and it contains
> just zeros.
>
>
>
> My workaround is, to call  Gc.full_major() before the close. Then all
> remaining bigarrays are
>
> finalized (the finalizer calls caml_ba_unmap_file(), see
> bigarray_stubs.c).
>
>
>
> Calling Gc.full_major () is somewhat dissatisfying. But I’m not sure how
> it could be solved more cleanly.
>
> I would expect that Unix.close should unmap all remaining views of the
> file. But Unix.close knows nothing
>
> about the bigarray mapping.
>
>
>
> Maybe a special Bigarray.unmap is the solution.
>
>
>
> Does anyone has a better idea?
>
>
>
> Thanks,
>
> Christoph Bauer
>
>
>
> [1] You can’t delete it in the windows explorer.
>
>
>
>
>
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