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README
		   Mmap perl module, version alpha2

		 Copyright (c) 1996, Malcolm Beattie
                  Copyright (c) 2002, Scott Walters

    This program is free software; you can redistribute it and/or modify
    it under the terms of either:

	a) the GNU General Public License as published by the Free
	Software Foundation; either version 1, or (at your option) any
	later version, or

	b) the "Artistic License" which comes with this kit.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See either
    the GNU General Public License or the Artistic License for more details.

    You should have received a copy of the Artistic License with this kit,
    in the file named "Artistic".  If not, you can get one from the Perl
    distribution. You should also have received a copy of the GNU General
    Public License, in the file named "Copying". If not, you can get one
    from the Perl distribution or else write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

DESCRIPTION

The Mmap module lets you use mmap to map in a file as a perl variable
rather than reading the file into dynamically allocated memory. 
Multiple programs may map the same file into memory, and immediately
see changes by each other.  Memory may be allocated not attached to a file, 
and shared with subprocesses.

It depends on your operating system supporting UNIX or POSIX.1b mmap, of
course. 

You may use the new OO interface, or the old map() and unmap() 
interface. If you use the old interface, you need to be careful. Some
programming constructs may create copies of a string which, while
unimportant for smallish strings, are far less welcome if you're
mapping in a file which is a few gigabytes big. If you use PROT_WRITE
and attempt to write to the file via the variable you need to be even
more careful. One of the few ways in which you can safely write to the
string in-place is by using substr as an lvalue and ensuring that the
part of the string that you replace is exactly the same length.
The new interface does not suffer from these problems.

INSTALLATION

Prerequisites are perl 5.002 and an operating system that has an
implementation of mmap(2) with either the traditional or the
POSIX.1b API. Perl 5.7.2 was tested with this release.

Type
    perl Makefile.PL
to write a personalised Makefile for your system.
If your platform supports dynamic loading then just type
    make
    make test
and provided you see "All tests successful" you can install it with
    make install

If you need/want instead to make a statically linked perl which
contains the module, then type
    make perl
    make test

Documentation is included in pod format in Mmap.pm itself. The
"make install" step will install an Mmap(3) man page or else you
can use
    perldoc Mmap
which will find the documentation whether it has been installed or
if you run it from the Mmap distribution directory.

BUGS

You must explicitly use munmap() rather than letting perl itself
clean up after you since perl 5.002 can't cope with variables
whose string contents live in non-malloc'd memory.

Malcolm Beattie
21 Jun 1996

Documentation updated to include information on OO interface
6/2002
Scott Walters
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