Tim Bunce writes:
> On Fri, Dec 17, 1999 at 12:55:12PM +0000, Andrew Ford wrote:
> > I have an urgent need for a module to tie an array of integers to an
> > mmap'ed file (a sparse array of several hundred million integers). I
> > have looked at Mmap.pm by Malcolm Beattie and seen the idea for
> > Array::Virtual registered by Larry Wall and have started implementing
> > the module I need. But should it be called Array::Virtual (taking
> > Larry's slot) or Mmap::Array?
> >
> > The interface I have in mind is:
> >
> > use Array::Virtual; # or Mmap::Array
> >
> > my @array;
> > open(FH, "...");
> > my $nel = 42;
> > my $prot = "rw"; # or "ro", or "wo" or should it be PROT_READ?
> > my $shared = 1; # or should it be MAP_SHARED?
> > my $offset = 0; # this would be the default anyway
> > my $type = "int4" # some set of (string) literals for 1, 2, 4, 8
> > # byte integers in native or network byte
> > # order, plus floating point (default probably int4)
> >
> > tie @array, $nel, $prot, $shared, FH, $offset, $type;
> >
> > $array[0] = 42;
> > #etc
> >
> > undef @array;
> >
> > Any thoughts?
>
> The word 'Virtual' doesn't carry much meaning here. Maybe:
>
> Tie::MmapArray
>
> I'd switch to using a hash of named parameters to the tie.
>
> I'd also use pack() letters to describe the element type (which would
> neatly expand to a string of letters for arrays of structures).
>
Thanks for the prompt feedback. I agree about the name and using a
hash for parameters, so the call will now look like:
use Tie::MmapArray;
use Fcntl;
tie @array, { fh => $fh,
eltype => "l",
nels => 42,
mode => O_RDWR, # or "rw"
shared => 1,
offset => 0 };
This raises a couple of issues:
1. If the fh parameter is not specified then this becomes an anonymous
mmap call, which is probably not a sensible default. Should I have
the filehandle as a separate parameter (e.g. tie @array, FH, $href)
and require an explicit undef for anonymous mmap'ing (or require an
explicit undef for the value of the "fh" element of the hash)?
2. The mode could be a numeric parameter with values:
O_RDONLY, O_WRONLY or O_RDWR (from Fcntl). I know that mmap uses
PROT_READ, PROT_WRITE, but not many people are that familiar with
mmap compared to open(2). I could allow both the Fcntl constants
and the strings "ro", "wo" and "rw".
3. using the pack letters does not allow all (sensible) possibilities
(signed/unsigned, network/native, 1/2/4/8 integers or float/double).
specifically it looks like unsigned network order and 8 byte
integers are not covered. I could allow the letters to be
qualified, e.g. i8 would be an eight-byte integer, and c22 would be
an array of 22-character, fixed-length strings.
4. any comments on the naming of the parameters?
Andrew
