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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
C<Data::UUID::LibUUID::new_uuid_binary(2)>.

In addition to differences mentioned below, there are additional slight
difference in how the modules (or C<libuuid>) treat the "clock sequence" field
and otherwise attempt to keep state between calls, but this is generally
immaterial.

=head2 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 C<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.

=head2 Source of random bits

All the modules differ in the source of random bits.

C<libuuid> based modules get random bits from C</dev/random> or C</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 C<rand()> function.

UUID::Tiny uses Perl's C<rand()> function.

Data::UUID::MT gets random bits from L<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.

=head2 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 L<Scalar::Util> is installed and provides
C<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.

=head2 Benchmarks

The F<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 C<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

=head1 SEE ALSO

=over 4

=item *

L<RFC 4122 A Universally Unique IDentifier (UUID) URN Namespace|http://www.apps.ietf.org/rfc/rfc4122.html>

=back

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=head1 SUPPORT

=head2 Bugs / Feature Requests

Please report any bugs or feature requests through the issue tracker
at L<https://github.com/dagolden/data-uuid-mt/issues>.
You will be notified automatically of any progress on your issue.

=head2 Source Code

This is open source software.  The code repository is available for
public review and contribution under the terms of the license.

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

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