Re: [Chicken-users] using mmap files as strings?

[Felix]

From: Alan Post <address@hidden>
Subject: [Chicken-users] using mmap files as strings?
Date: Thu, 21 Oct 2010 15:01:10 -0600

> I have the following file:
> 
> <++> mmap.scm
> (use posix)
> (use lolevel)
> 
> (let* ((fd (file-open "mmap.scm" (+ open/rdonly open/nonblock)))
>        (size (file-size fd))
>        (mmap (map-file-to-memory #f size prot/read (+ map/file map/shared) 
> fd))
>        (buf  (memory-mapped-file-pointer mmap)))
>   (write fd)
>   (newline)
>   (write size)
>   (newline)
>   (write mmap)
>   (newline)
>   (write buf)
>   (newline)
>   (write (pointer-s8-ref buf))
>   (newline)
>   (write (integer->char (pointer-s8-ref buf)))
>   (newline))
> <-->
> 
> Which opens itself as an mmap and reads the first byte.  The output
> is:
> 
> <++> csc -o mmap mmap.scm && ./mmap
> 3
> 458
> #<mmap>
> #<pointer 0x8818c000>
> 40
> #\(
> <-->
> 
> So far so good, that is what I would expect.  I'd like to work with
> an mmap buffer like a string.  Is it possible to create an object
> that will treat the mmap area as a string that I can run regular
> string operations on without copying the mmap buffer? 

I can't think of a way in the moment. Strings require a header-word,
and the data pointed to by a pointer doesn't have that header, so it
isn't possible to "sneak in" a pointer as a replacement of a string.

> I'm
> specifically interested in running regular expressions across the
> mmap space.

irregex provides a "chunk" based API, perhaps it is possible to
define chunks over the data represented by the mmap pointer.
Alex or Peter might be able to tell more about this.


cheers,
felix