Re: [Boost-users] [interprocess] Memory mapped file based allocator

Subject: Re: [Boost-users] [interprocess] Memory mapped file based allocator
From: Stuart Dootson (stuart.dootson_at_[hidden])
Date: 2009-03-11 04:20:52

On Wed, Mar 11, 2009 at 3:41 AM, dhruva <dhruva_at_[hidden]> wrote:
>
> Hello,
>
> ----- Original Message ----
>> From: Stuart Dootson <stuart.dootson_at_[hidden]>
>> >  I am looking for a memory mapped file based allocator that does not map the
>> whole file into memory. The size may be huge and I would not want to map all the
>
>> One solution (which I've used with files of gigabyte size) that you
>> could consider is writing a class to encapsulate memory mapped files
>> that exposes the file contents only through a custom iterator class.
>> These could work together to map and unmap portions of the file as the
>> iterator position crosses 'page' boundaries. This would give you
>> something close to on-demand paging.
>
> Thank you for the suggestion. I have implemented it on windows using SEH (structured exception handling). Is there something similar in the UNIX world. Adding a signal handler will be for the whole process, I need to check if there is a way to add a signal handler for a specific thread that is doing the read/write and perform the unmap and map sequence to keep moving the read/write window. This would be a great feature to have it tucked somewhere in BOOST. Reading/writing large files is quite common. If I succeed in putting in a solution that works on M$ and NIX world, I will post it.
>
> -dhruva

You don't need to use exceptions at all - in the iterator's
'dereference' method (see the iterator_facade documentation in
Boost.Iterator for what that means), check if the item that the
iterator references is in the currently mapped region. If not, map a
region that does contain that item.

Stuart Dootson