Re: [boost] [Review] Shmem Library

From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2006-02-07 11:47:32

Hi Andrew,

> Just in case I don't get a chance to do a formal review before the 16th,
> I have one brief comment.

  I hope you can find to do a review, since it seems you have experience 
with memory mappings.

> The mmaped_file class merges "a file which has some of its space mapped"
> with "a mapped portion of a file".  While I realise that this is a shared
> memory library, not a general memory mapped file library, it might be
> useful to separate the two.

I'm open to develop a more advanced memory mapped file. I have no 
experience with memory mapping but if you want to help, I'm ready to put 
some effort.

> The problem is that under the current design, mapping two separate parts
> of one file (a common task when trying to be clever with page-structured
> files) requires two file descriptors and two filename lookups.  The other
> option is mapping a region which includes both parts, which wastes address
> space (occasionally to the point of it being impossible; consider mapping a
> 4Gb file on a 32-bit architecture).

If I understand this correctly, you want a class that can map more than 
a fragment of a file holding a single file descriptor, is that right? 
That would require that the memory mapped class should have a list of 
mappings (to unmap them in the destructor, for example). I think we 
should define about the interface you would want for this class. It can 
be implemented in a different class than current (simple) 
boost::shmem::mmapped_file. I don't have experience with this type of 
multi-mapped files but it's surely a good idea.

Regards,

Ion