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    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
        <http://www.apps.ietf.org/rfc/rfc4122.html>

SUPPORT
  Bugs / Feature Requests
    Please report any bugs or feature requests through the issue tracker at
    <https://github.com/dagolden/data-uuid-mt/issues>. You will be notified
    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.

    <https://github.com/dagolden/data-uuid-mt>

      git clone git://github.com/dagolden/data-uuid-mt.git

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: