NAME
Data::UUID::MT - Fast random UUID generator using the Mersenne Twister
algorithm
VERSION
version 1.001
SYNOPSIS
use Data::UUID::MT;
my $ug1 = Data::UUID::MT->new( version => 4 ); # "1", "4" or "4s"
my $ug2 = Data::UUID::MT->new(); # default is "4"
# method interface
my $uuid1 = $ug->create(); # 16 byte binary string
my $uuid2 = $ug->create_hex();
my $uuid3 = $ug->create_string();
# iterator -- avoids some method call overhead
my $next = $ug->iterator;
my $uuid4 = $next->();
DESCRIPTION
This UUID generator uses the excellent Math::Random::MT::Auto module as
a source of fast, high-quality (pseudo) random numbers.
Three different types of UUIDs are supported. Two are consistent with
RFC 4122 and one is a custom variant that provides a 'sequential UUID'
that can be advantageous when used as a primary database key.
Note: The Mersenne Twister pseudo-random number generator has excellent
statistical properties, but it is not considered cryptographically
secure. Pseudo-random UUIDs are not recommended for use as security
authentication tokens in cookies or other user-visible session
identifiers.
Version 1 UUIDs
The UUID generally follows the "version 1" spec from the RFC, however
the clock sequence and MAC address are randomly generated each time.
(This is permissible within the spec of the RFC.) The generated MAC
address has the the multicast bit set as mandated by the RFC to ensure
it does not conflict with real MAC addresses. This UUID has 60 bits of
timestamp data, 61 bits of pseudo-random data and 7 mandated bits
(multicast bit, "variant" field and "version" field).
Version 4 UUIDs
The UUID follows the "version 4" spec, with 122 pseudo-random bits and 6
mandated bits ("variant" field and "version" field).
Version 4s UUIDs
This is a custom UUID form that resembles "version 4" form, but that
overlays the first 60 bits with a timestamp akin to "version 1", Unlike
"version 1", this custom version preserves the ordering of bits from
high to low, whereas "version 1" puts the low 32 bits of the timestamp
first, then the middle 16 bits, then multiplexes the high bits with
version field. This "4s" variant provides a "sequential UUID" with the
timestamp providing order and the remaining random bits making collision
with other UUIDs created at the exact same microsecond highly unlikely.
This UUID has 60 timestamp bits, 62 pseudo-random bits and 6 mandated
bits ("variant" field and "version" field).
Unsupported: Versions 2, 3 and 5
This module focuses on generation of UUIDs with random elements and does
not support UUID versions 2, 3 and 5.
METHODS
new
my $ug = Data::UUID::MT->new( version => 4 );
Creates a UUID generator object. The only allowed versions are "1", "4"
and "4s". If no version is specified, it defaults to "4".
create
my $uuid = $ug->create;
Returns a UUID packed into a 16 byte string.
create_hex
my $uuid = $ug->create_hex();
Returns a UUID as a lowercase hex string, prefixed with "0x", e.g.
0xb0470602a64b11da863293ebf1c0e05a
create_string
my $uuid = $ug->create_string(); #
Returns UUID as a lowercase string in "standard" format, e.g.
"b0470602-a64b-11da-8632-93ebf1c0e05a"
iterator
my $next = $ug->iterator;
my $uuid = $next->();
Returns a reference to the internal UUID generator function. Because
this avoids method call overhead, it is slightly faster than calling
"create".
reseed
$ug->reseed;
Reseeds the internal pseudo-random number generator. This happens
automatically after a fork or thread creation (assuming
Scalar::Util::weaken), but may be called manually if desired for some
reason.
Any arguments provided are passed to Math::Random::MT::Auto::srand() for
custom seeding.
$ug->reseed('hotbits' => 250, '/dev/random');
UUID STRING REPRESENTATIONS
A UUID contains 16 bytes. A hex string representation looks like
0xb0470602a64b11da863293ebf1c0e05a. A "standard" representation looks
like "b0470602-a64b-11da-8632-93ebf1c0e05a". Sometimes these are seen in
upper case and on Windows the standard format is often seen wrapped in
parentheses.
Converting back and forth is easy with "pack" and "unpack".
# string to 16 bytes
$string =~ s/^0x//i; # remove leading "0x"
$string =~ tr/()-//d; # strip '-' and parentheses
$binary = pack("H*", $string);
# 16 bytes to uppercase string formats
$hex = "0x" . uc unpack("H*", $binary);
$std = uc join "-", unpack("H8H4H4H4H12", $binary);
If you need a module that provides these conversions for you, consider
UUID::Tiny.
COMPARISON TO OTHER UUID MODULES
At the time of writing, there are five other general purpose UUID
generators on CPAN that I consider potential alternatives.
Data::UUID::MT is included in the discussion below for comparison.
* Data::GUID - version 1 UUIDs (wrapper around Data::UUID)
* Data::UUID - version 1 or 3 UUIDs (derived from RFC 4122 code)
* Data::UUID::LibUUID - version 1 or 4 UUIDs (libuuid)
* UUID - version 1 or 4 UUIDs (libuuid)
* UUID::Tiny - versions 1, 3, 4, or 5 (pure perl)
* Data::UUID::MT - version 1 or 4 (or custom sequential "4s")
"libuuid" based UUIDs may generally be either version 4 (preferred) or
version 1 (fallback), depending on the availability of a good random bit
source (e.g. /dev/random). "libuuid" version 1 UUIDs could also be
provided by the "uuidd" daemon if available.
UUID.pm leaves the choice of version up to "libuuid".
Data::UUID::LibUUID does so by default, but also allows specifying a
specific version. Note that Data::UUID::LibUUID incorrectly refers to
version 1 UUIDs as version 2 UUIDs. For example, to get a version 1
binary UUID explicitly, you would call
Data::UUID::LibUUID::new_uuid_binary(2).
In addition to differences mentioned below, there are additional slight
difference in how the modules (or "libuuid") treat the "clock sequence"
field and otherwise attempt to keep state between calls, but this is
generally immaterial.
Use of Ethernet MAC addresses
Version 1 UUID generators differ in whether they include the Ethernet
MAC address as a "node identifier" as specified in RFC 4122. Including
the MAC has security implications as Version 1 UUIDs can then be traced
to a particular machine at a particular time.
For "libuuid" based modules, Version 1 UUIDs will include the actual MAC
address, if available, or will substitute a random MAC (with multicast
bit set).
Data::UUID version 1 UUIDs do not contain the MAC address, but replace
it with an MD5 hash of data including the hostname and host id (possibly
just the IP address), modified with the multicast bit.
Both UUID::Tiny and Data::UUID::MT version 1 UUIDs do not contain the
actual MAC address, but replace it with a random multicast MAC address.
Source of random bits
All the modules differ in the source of random bits.
"libuuid" based modules get random bits from "/dev/random" or
"/dev/urandom" or fall back to a pseudo-random number generator.
Data::UUID only uses random data to see the clock sequence and gets bits
from the C "rand()" function.
UUID::Tiny uses Perl's "rand()" function.
Data::UUID::MT gets random bits from Math::Random::MT::Auto, which uses
the Mersenne Twister algorithm. Math::Random::MT::Auto seeds from system
sources (including Win32 specific ones on that platform) if available
and falls back to other less ideal sources if not.
Fork and thread safety
Pseudo-random number generators used in generating UUIDs should be
reseeded if the process forks or if threads are created.
Data::UUID::MT checks if the process ID has changed before generating a
UUID and reseeds if necessary. If Scalar::Util is installed and provides
"weaken()", Data::UUID::MT will also reseed its objects on thread
creation.
Data::UUID::LibUUID will reseed on fork on Mac OSX.
I have not explored further whether other UUID generators are
fork/thread safe.
Benchmarks
The examples/bench.pl program included with this module does some simple
benchmarking of UUID generation speeds. Here is the output from my
desktop system (AMD Phenom II X6 1045T CPU). Note that "v?" is used
where the choice is left to "libuuid" -- which will result in version 4
UUIDs on my system.
Benchmark on Perl v5.14.0 for x86_64-linux with 8 byte integers.
Key:
U => UUID 0.02
UT => UUID::Tiny 1.03
DG => Data::GUID 0.046
DU => Data::UUID 1.217
DULU => Data::UUID::LibUUID 0.05
DUMT => Data::UUID::MT 0.001
Benchmarks are marked as to which UUID version is generated.
Some modules offer method ('meth') and function ('func') interfaces.
UT|v1 85229/s
UT|v4 110652/s
DULU|v1 177495/s
DULU|v? 178629/s
DUMT|v4s|meth 274905/s
DUMT|v1|meth 281942/s
U|v? 288136/s
DULU|v4 295107/s
DUMT|v4s|func 307575/s
DUMT|v1|func 313538/s
DG|v1|func 335333/s
DG|v1|meth 373515/s
DUMT|v4|meth 450845/s
DUMT|v4|func 588573/s
DU|v1 1312946/s
SEE ALSO
* RFC 4122 A Universally Unique IDentifier (UUID) URN Namespace
SUPPORT
Bugs / Feature Requests
Please report any bugs or feature requests through the issue tracker at
automatically of any progress on your issue.
Source Code
This is open source software. The code repository is available for
public review and contribution under the terms of the license.
AUTHOR
David Golden <dagolden@cpan.org>
CONTRIBUTOR
Matt Koscica <matt.koscica@gmail.com>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2011 by David Golden.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004