=encoding utf8

=head1 NAME

perl51910delta - what is new for perl v5.19.10

=head1 DESCRIPTION

This document describes differences between the 5.19.9 release and the 5.19.10
release.

If you are upgrading from an earlier release such as 5.19.8, first read
L<perl5199delta>, which describes differences between 5.19.8 and 5.19.9.

=head1 Deprecations

=head2 Discouraged features

=over 4

=item *

The "interpreter-based threads" provided by Perl are not the fast, lightweight
system for multitasking that one might expect or hope for.  Threads are
implemented in a way that make them easy to misuse.  Few people know how to
use them correctly or will be able to provide help.

The use of interpreter-based threads in perl is officially
L<discouraged|perlpolicy/discouraged>.

=back

=head1 Performance Enhancements

=over 4

=item *

When doing a global regex match on a string that came from the C<readline>
or C<E<lt>E<gt>> operator, the data is no longer copied unnecessarily.
[perl #121259]

=item *

Executing a regex that contains the C<^> anchor (or its variant under the
C</m> flag) has been made much faster in several situations.

=item *

It is now faster to create certain sorts of lists, including array and hash
slices.

=item *

The optimisation for arrays indexed with a small constant integer is now
applied for integers in the range -128..127, rather than 0..255. This should
speed up Perl code using expressions like C<$x[-1]>, at the expense of
(presumably much rarer) code using expressions like C<$x[200]>.

=item *

Dereferencing (as in C<$obj-E<gt>[0]> or C<$obj-E<gt>{k}>) is now faster
when C<$obj> is an instance of a class that has overloaded methods, but
doesn't overload any of the dereferencing methods C<@{}>, C<%{}>, and so on.

=item *

The first iteration over a large hash (using C<keys> or C<each>) is now
faster. This is achieved by preallocating the hash's internal iterator
state, rather than lazily creating it when the hash is first iterated. (For
small hashes, the iterator is still created only when first needed. The
assumption is that small hashes are more likely to be used as objects, and
therefore never allocated. For large hashes, that's less likely to be true,
and the cost of allocating the iterator is swamped by the cost of allocating
space for the hash itself.)

=item *

Perl's optimiser no longer skips optimising code that follows certain
C<eval {}> expressions (including those with an apparent infinite loop).

=item *

The implementation now does a better job of avoiding meaningless work at
runtime. Internal effect-free "null" operations (created as a side-effect of
parsing Perl programs) are normally deleted during compilation. That
deletion is now applied in some situations that weren't previously handled.

=item *

A few micro-optimisations have been applied to performance-sensitive parts
of the implementation, including subroutine invocation and scope exit.

=item *

Perl now does less disk I/O when dealing with Unicode properties that cover
up to three ranges of consecutive code points.

=back

=head1 Modules and Pragmata

=head2 Updated Modules and Pragmata

=over 4

=item *

L<Attribute::Handlers> has been upgraded from version 0.95 to 0.96.

=item *

L<autouse> has been upgraded from version 1.07 to 1.08.

=item *

L<B::Deparse> has been upgraded from version 1.25 to 1.26.

=item *

L<base> has been upgraded from version 2.21 to 2.22.

Co-exist more gracefully with C<CORE::GLOBAL::require>
overrides. [perl #121196]

=item *

L<Carp> has been upgraded from version 1.32 to 1.33.

=item *

L<charnames> has been upgraded from version 1.39 to 1.40.

=item *

L<CPAN> has been upgraded from version 2.03 to 2.04.

Fixes a bug preventing "force install" from working. [cpan #91706]

Fixes an infinite-loop bug when using the C<make> command in the CPAN
shell. [cpan #86915]

=item *

L<CPAN::Meta> has been upgraded from version 2.133380 to 2.140640.

Added a C<load_string()> method that guesses whether the string is YAML or JSON.

=item *

L<CPAN::Meta::YAML> has been upgraded from version 0.011 to 0.012.

=item *

L<Data::Dumper> has been upgraded from version 2.150 to 2.151.

=item *

L<Devel::PPPort> has been upgraded from version 3.21 to 3.22.

=item *

L<Digest::SHA> has been upgraded from version 5.87 to 5.88.

=item *

L<ExtUtils::Install> has been upgraded from version 1.62 to 1.63.

=item *

L<ExtUtils::MakeMaker> has been upgraded from version 6.88 to 6.92.

=item *

L<ExtUtils::ParseXS> has been upgraded from version 3.23 to 3.24.

=item *

L<ExtUtils::Typemaps> has been upgraded from version 3.23 to 3.24.

=item *

L<feature> has been upgraded from version 1.35 to 1.36.

=item *

L<File::Find> has been upgraded from version 1.26 to 1.27.

=item *

L<Filter::Simple> has been upgraded from version 0.90 to 0.91.

=item *

L<Hash::Util::FieldHash> has been upgraded from version 1.14 to 1.15.

=item *

L<HTTP::Tiny> has been upgraded from version 0.042 to 0.043.

No longer sends absolute request URI when tunneling SSL via proxy and fixes
regression in setting host name to verify SSL.

=item *

L<IO> has been upgraded from version 1.30 to 1.31.

=item *

L<IO::Socket::IP> has been upgraded from version 0.28 to 0.29.

=item *

L<Locale::Codes> has been upgraded from version 3.29 to 3.30.

Fixed a problem that was preventing rename_* functions to work.  [cpan #92680]

=item *

L<Module::CoreList> has been upgraded from version 3.06 to 3.09.

=item *

L<Module::Load> has been upgraded from version 0.30 to 0.32.

Fix tests to support statically built perls.

=item *

L<mro> has been upgraded from version 1.15 to 1.16.

=item *

L<Parse::CPAN::Meta> has been upgraded from version 1.4413 to 1.4414.

Added C<load_string>, which uses heuristics to guess YAML/JSON content.
C<load_file> will now attempt to detect YAML/JSON content if the suffix is not
.json, .yml or .yaml.

=item *

L<Pod::Perldoc> has been upgraded from version 3.21 to 3.23.

=item *

L<POSIX> has been upgraded from version 1.38_02 to 1.38_03.

=item *

L<Thread::Queue> has been upgraded from version 3.02 to 3.05.

=item *

L<threads> has been upgraded from version 1.92 to 1.93.

=item *

L<warnings> has been upgraded from version 1.22 to 1.23.

=item *

L<XS::Typemap> has been upgraded from version 0.12 to 0.13.

=back

=head1 Documentation

=head2 Changes to Existing Documentation

=over 4

=item *

The L<perllexwarn> documentation used to describe the hierarchy of warning
categories understood by the L<warnings> pragma. That description has now
been moved to the L<warnings> documentation itself, leaving L<perllexwarn>
as a stub that points to it. This change consolidates all documentation for
lexical warnings in a single place.

=back

=head1 Diagnostics

The following changes have been made to diagnostic output,
including warnings and fatal error messages.  For the complete list of
diagnostic messages, see L<perldiag>.

=head2 Changes to Existing Diagnostics

=over 4

=item *

When C<use re "debug"> executes a regex containing a backreference, the
debugging output now shows what string is being matched.

=back

=head1 Configuration and Compilation

=over 4

=item *

Where possible, the build now avoids recursive invocations of F<make> when
building pure-Perl extensions, without removing any parallelism from the
build. Currently around 80 extensions can be processed directly by the
F<make_ext.pl> tool, meaning that 80 invocations of F<make> and 160
invocations of F<miniperl> are no longer made.

=item *

The build system now works correctly when compiling under GCC or Clang with
link-time optimization enabled (the C<-flto> option). [perl #113022]

=back

=head1 Testing

=over 4

=item *

The test suite no longer fails when the user's interactive shell maintains a
C<$PWD> environment variable, but the F</bin/sh> used for running tests
doesn't.

=item *

The C<test.valgrind> make target now allows tests to be run in parallel.
This target allows Perl's test suite to be run under Valgrind, which detects
certain sorts of C programming errors, though at significant cost in running
time. On suitable hardware, allowing parallel execution claws back a lot of
that additional cost. [perl #121431]

=back

=head1 Platform Support

=head2 Platform-Specific Notes

=over 4

=item Linux

The hints file now looks for C<libgdbm_compat> only if C<libgdbm> itself is
also wanted. The former is never useful without the latter, and in some
circumstances, including it could actually prevent building.

=item Mac OS

The build system now honours an C<ld> setting supplied by the user running
F<Configure>.

=item Win32

Killing a process tree with L<perlfunc/kill> and a negative signal, was broken
starting in 5.18.0. In this bug, C<kill> always returned 0 for a negative
signal even for valid PIDs, and no processes were terminated. This has been
fixed [perl #121230].

=back

=head1 Internal Changes

=over 4

=item *

The Perl core now consistently uses C<av_tindex()> ("the top index of an
array") as a more clearly-named synonym for C<av_len()>.

=item *

The obscure interpreter variable C<PL_timesbuf> is expected to be removed
early in the 5.21.x development series, so that Perl 5.22.0 will not provide
it to XS authors.  While the variable still exists in 5.19.10 (and will
continue to exist in 5.20.0), we hope that this advance warning of the
deprecation will help anyone who is using that variable.

=back

=head1 Selected Bug Fixes

=over 4

=item *

Static builds, as configured with C<-Uusedl> now build
correctly. [perl #121291]

=item *

Regexes with backreferences nested inside subpattern references now behave
more consistently: match variables are dynamically scoped during the
execution of the subpattern call. [perl #121299]

=back

=head1 Acknowledgements

Perl 5.19.10 represents approximately 4 weeks of development since Perl 5.19.9
and contains approximately 13,000 lines of changes across 330 files from 20
authors.

Excluding auto-generated files, documentation and release tools, there were
approximately 8,800 lines of changes to 220 .pm, .t, .c and .h files.

Perl continues to flourish into its third decade thanks to a vibrant community
of users and developers. The following people are known to have contributed the
improvements that became Perl 5.19.10:

Aaron Crane, Andy Dougherty, Aristotle Pagaltzis, Chris 'BinGOs' Williams,
Craig A. Berry, Daniel Dragan, David Mitchell, Father Chrysostomos, H.Merijn
Brand, Jerry D. Hedden, Karl Williamson, Matthew Horsfall, Nicholas Clark, Paul
Johnson, Peter Rabbitson, Ricardo Signes, Steffen Müller, Steve Hay, Tony
Cook, Yves Orton.

The list above is almost certainly incomplete as it is automatically generated
from version control history. In particular, it does not include the names of
the (very much appreciated) contributors who reported issues to the Perl bug
tracker.

Many of the changes included in this version originated in the CPAN modules
included in Perl's core. We're grateful to the entire CPAN community for
helping Perl to flourish.

For a more complete list of all of Perl's historical contributors, please see
the F<AUTHORS> file in the Perl source distribution.

=head1 Reporting Bugs

If you find what you think is a bug, you might check the articles recently
posted to the comp.lang.perl.misc newsgroup and the perl bug database at
https://rt.perl.org/ .  There may also be information at
http://www.perl.org/ , the Perl Home Page.

If you believe you have an unreported bug, please run the L<perlbug> program
included with your release.  Be sure to trim your bug down to a tiny but
sufficient test case.  Your bug report, along with the output of C<perl -V>,
will be sent off to perlbug@perl.org to be analysed by the Perl porting team.

If the bug you are reporting has security implications, which make it
inappropriate to send to a publicly archived mailing list, then please send it
to perl5-security-report@perl.org.  This points to a closed subscription
unarchived mailing list, which includes all the core committers, who will be
able to help assess the impact of issues, figure out a resolution, and help
co-ordinate the release of patches to mitigate or fix the problem across all
platforms on which Perl is supported.  Please only use this address for
security issues in the Perl core, not for modules independently distributed on
CPAN.

=head1 SEE ALSO

The F<Changes> file for an explanation of how to view exhaustive details on
what changed.

The F<INSTALL> file for how to build Perl.

The F<README> file for general stuff.

The F<Artistic> and F<Copying> files for copyright information.

=cut
