Subject: ANNOUNCE: Tie::MmapArray 0.02
From: Andrew Ford <[email-masked]>
Date: 11 Jan 2000 16:35:04 GMT
Newsgroups: comp.lang.perl.announce,comp.lang.perl.modules

I have just uploaded an revised version of Tie::MmapArray to 

	http://www.ford-mason.co.uk/resources/

The module is inspired by Malcolm Beatie's Mmap module, but this one
allows a file to be mapped as an array of integers, f.p. numbers,
fixed-length strings or nested structures (new in 0.02).  The man page
is appended.

Andrew
-- 
Andrew Ford,  Director       Ford & Mason Ltd           +44 1531 829900 (tel)
[email-masked]      South Wing, Compton House  +44 1531 829901 (fax)
http://www.ford-mason.co.uk  Compton Green, Redmarley   +44 385 258278 (mobile)
http://www.refcards.com      Gloucester, GL19 3JB, UK   

NAME
    Tie::MmapArray - mmap a file as a tied array

SYNOPSIS
        use Tie::MmapArray;

        tie @array, 'Tie::MmapArray', $filename;
        tie @array, 'Tie::MmapArray', $filename, $template;
        tie @array, 'Tie::MmapArray', $filename, { template => $template,
                                                   nels     => 0,
                                                   mode     => "rw",
                                                   shared   => 1,
                                                   offset   => 0 };

DESCRIPTION
    The Tie::MmapArray module lets you use mmap to map in a file as a perl
    array rather than reading the file into dynamically allocated memory. It
    depends on your operating system supporting UNIX or POSIX.1b mmap, of
    course. (Code to use the equivalent functions on Win32 platforms has
    been contributed but has not been tested yet.)

    The type of array elements is defined by the *template* argument or
    option. This is a Perl pack()-style template, which defaults to "i". The
    template may be an array reference, in which case the elements are
    defined by pairs of name and template for each element. A template
    string may define multiple fields, in which case that element is
    regarded as an array of fields (which need not be of the same type).

    The following example shows the utmp file on Linux mapped to an array:

        tie @utmp, 'Tie::MmapArray', '/var/log/utmp',
            [
              ut_type    => 's',
              ut_pid     => 'i',    # pid_t
              ut_line    => 'a12',
              ut_id      => 'a4',
              ut_user    => 'a32',
              ut_host    => 'a256',
              ut_exit    => [ # struct exit_status
                              e_termination => 's',
                              e_exit        => 's' ],
              ut_session => 'l',
              ut_tv      => [ # struct timeval
                              tv_sec  => 'l'
                              tv_usec => 'l' ],
              ut_addr_v6 => 'l4',
              pad        => 'a20' ];

    This can be scanned as follows:

        for (my $i = 0; $i < @utmp; $i++) {
            print("pid: %d, user: %s\n",
                  $utmp[$i]->{ut_pid}, $utmp[$i]->{ut_user});
        }

    The following subset of pack() template letters is supported:

    i   signed integer (default)

    I   unsigned integer

    c   signed character (one byte integer)

    c   unsigned character (one byte integer)

    s   signed short integer

    S   unsigned short integer

    n   unsigned short integer in network byte order

    l   signed long integer

    L   unsigned long integer

    N   unsigned long integer in network byte order

    f   float

    d   double

    a*N*
        fixed-length, null-padded ASCII string of length *N*

    A*N*
        fixed-length, space-padded ASCII string of length *N*

    The size of the array is defined by the *nels* option. If this is zero
    then it is calculated as the file size divided by the element size.

    If the file size is smaller than the size required for the requested
    elements then a single zero byte will be written to the final byte of
    the requested size. This seems to prevent the module dying with a
    segmentation or bus error if memory is accessed beyond the end of the
    file and generally results in a file with holes (unallocated blocks).
    Precise details of the behaviour of the module are subject to change.

BUGS, RESTRICTIONS AND FUTURE DIRECTIONS
    This is version 0.02 of the module and there are likely to be many bugs.
    The interface may change as the result of feedback.

    The options *mode* and *shared* are not yet used.

    Not all pack letters are implemented yet.

    push, pop, shift, unshift, and splice operations are not yet supported.
    It is debateable whether they should be as they could be very expensive
    if the mmaped file was large (say a Gigabyte or two). Perhaps there
    should be an option to explicitly allow these operations.

AUTHOR
    Andrew Ford <[email-masked]>, 27 December 1999.

CREDITS
    The module was inspired by Malcolm Beatie's Mmap module.

    Reini Urban <[email-masked]> provided intial code for Win32 platforms.