perlhack.pod

MSYS在windows下模拟了一个类unix的终端

=item It's easier

Since you don't have to apply the patches yourself, you are sure all
files in the source tree are in the right state.

=item It's more recent

According to Gurusamy Sarathy:

   "... The rsync mirror is automatic and syncs with the repository
    every five minutes.

   "Updating the patch  area  still  requires  manual  intervention
    (with all the goofiness that implies,  which you've noted)  and
    is typically on a daily cycle.   Making this process  automatic
    is on my tuit list, but don't ask me when."

=item It's more reliable

Well, since the patches are updated by hand, I don't have to say any
more ... (see Sarathy's remark).

=back

=head2 Why rsync the patches

=over 4

=item It's easier

If you have more than one machine that you want to keep in track with
bleadperl, it's easier to rsync the patches only once and then apply
them to all the source trees on the different machines.

In case you try to keep in pace on 5 different machines, for which
only one of them has access to the WAN, rsync'ing all the source
trees should than be done 5 times over the NFS. Having
rsync'ed the patches only once, I can apply them to all the source
trees automatically. Need you say more ;-)

=item It's a good reference

If you do not only like to have the most recent development branch,
but also like to B<fix> bugs, or extend features, you want to dive
into the sources. If you are a seasoned perl core diver, you don't
need no manuals, tips, roadmaps, perlguts.pod or other aids to find
your way around. But if you are a starter, the patches may help you
in finding where you should start and how to change the bits that
bug you.

The file B<Changes> is updated on occasions the pumpking sees as his
own little sync points. On those occasions, he releases a tar-ball of
the current source tree (i.e. [e-mail]), which will be an
excellent point to start with when choosing to use the 'rsync the
patches' scheme. Starting with perl@7582, which means a set of source
files on which the latest applied patch is number 7582, you apply all
succeeding patches available from then on (7583, 7584, ...).

You can use the patches later as a kind of search archive.

=over 4

=item Finding a start point

If you want to fix/change the behaviour of function/feature Foo, just
scan the patches for patches that mention Foo either in the subject,
the comments, or the body of the fix. A good chance the patch shows
you the files that are affected by that patch which are very likely
to be the starting point of your journey into the guts of perl.

=item Finding how to fix a bug

If you've found I<where> the function/feature Foo misbehaves, but you
don't know how to fix it (but you do know the change you want to
make), you can, again, peruse the patches for similar changes and
look how others apply the fix.

=item Finding the source of misbehaviour

When you keep in sync with bleadperl, the pumpking would love to
I<see> that the community efforts realy work. So after each of his
sync points, you are to 'make test' to check if everything is still
in working order. If it is, you do 'make ok', which will send an OK
report to [e-mail]. (If you do not have access to a mailer
from the system you just finished successfully 'make test', you can
do 'make okfile', which creates the file C<perl.ok>, which you can
than take to your favourite mailer and mail yourself).

But of course, as always, things will not allways lead to a success
path, and one or more test do not pass the 'make test'. Before
sending in a bug report (using 'make nok' or 'make nokfile'), check
the mailing list if someone else has reported the bug already and if
so, confirm it by replying to that message. If not, you might want to
trace the source of that misbehaviour B<before> sending in the bug,
which will help all the other porters in finding the solution.

Here the saved patches come in very handy. You can check the list of
patches to see which patch changed what file and what change caused
the misbehaviour. If you note that in the bug report, it saves the
one trying to solve it, looking for that point.

=back

If searching the patches is too bothersome, you might consider using
perl's bugtron to find more information about discussions and
ramblings on posted bugs.

=back

If you want to get the best of both worlds, rsync both the source
tree for convenience, reliability and ease and rsync the patches
for reference.

=head2 Submitting patches

Always submit patches to I<[e-mail]>.  This lets other
porters review your patch, which catches a surprising number of errors
in patches.  Either use the diff program (available in source code
form from I<ftp://ftp.gnu.org/pub/gnu/>), or use Johan Vromans'
I<makepatch> (available from I<CPAN/authors/id/JV/>).  Unified diffs
are preferred, but context diffs are accepted.  Do not send RCS-style
diffs or diffs without context lines.  More information is given in
the I<Porting/patching.pod> file in the Perl source distribution.
Please patch against the latest B<development> version (e.g., if
you're fixing a bug in the 5.005 track, patch against the latest
5.005_5x version).  Only patches that survive the heat of the
development branch get applied to maintenance versions.

Your patch should update the documentation and test suite.

To report a bug in Perl, use the program I<perlbug> which comes with
Perl (if you can't get Perl to work, send mail to the address
I<[e-mail]> or I<[e-mail]>).  Reporting bugs through
I<perlbug> feeds into the automated bug-tracking system, access to
which is provided through the web at I<http://bugs.perl.org/>.  It
often pays to check the archives of the perl5-porters mailing list to
see whether the bug you're reporting has been reported before, and if
so whether it was considered a bug.  See above for the location of
the searchable archives.

The CPAN testers (I<http://testers.cpan.org/>) are a group of
volunteers who test CPAN modules on a variety of platforms.  Perl Labs
(I<http://labs.perl.org/>) automatically tests Perl source releases on
platforms and gives feedback to the CPAN testers mailing list.  Both
efforts welcome volunteers.

It's a good idea to read and lurk for a while before chipping in.
That way you'll get to see the dynamic of the conversations, learn the
personalities of the players, and hopefully be better prepared to make
a useful contribution when do you speak up.

If after all this you still think you want to join the perl5-porters
mailing list, send mail to I<[e-mail]>.  To
unsubscribe, send mail to I<[e-mail]>.

To hack on the Perl guts, you'll need to read the following things:

=over 3

=item L<perlguts>

This is of paramount importance, since it's the documentation of what
goes where in the Perl source. Read it over a couple of times and it
might start to make sense - don't worry if it doesn't yet, because the
best way to study it is to read it in conjunction with poking at Perl
source, and we'll do that later on.

You might also want to look at Gisle Aas's illustrated perlguts -
there's no guarantee that this will be absolutely up-to-date with the
latest documentation in the Perl core, but the fundamentals will be
right. (http://gisle.aas.no/perl/illguts/)

=item L<perlxstut> and L<perlxs>

A working knowledge of XSUB programming is incredibly useful for core
hacking; XSUBs use techniques drawn from the PP code, the portion of the
guts that actually executes a Perl program. It's a lot gentler to learn
those techniques from simple examples and explanation than from the core
itself.

=item L<perlapi>

The documentation for the Perl API explains what some of the internal
functions do, as well as the many macros used in the source.

=item F<Porting/pumpkin.pod>

This is a collection of words of wisdom for a Perl porter; some of it is
only useful to the pumpkin holder, but most of it applies to anyone
wanting to go about Perl development.

=item The perl5-porters FAQ

This is posted to perl5-porters at the beginning on every month, and
should be available from http://perlhacker.org/p5p-faq; alternatively,
you can get the FAQ emailed to you by sending mail to
C<[e-mail]>. It contains hints on reading
perl5-porters, information on how perl5-porters works and how Perl
development in general works.

=back

=head2 Finding Your Way Around

Perl maintenance can be split into a number of areas, and certain people
(pumpkins) will have responsibility for each area. These areas sometimes
correspond to files or directories in the source kit. Among the areas are:

=over 3

=item Core modules

Modules shipped as part of the Perl core live in the F<lib/> and F<ext/>
subdirectories: F<lib/> is for the pure-Perl modules, and F<ext/>
contains the core XS modules.

=item Documentation

Documentation maintenance includes looking after everything in the
F<pod/> directory, (as well as contributing new documentation) and
the documentation to the modules in core.

=item Configure

The configure process is the way we make Perl portable across the
myriad of operating systems it supports. Responsibility for the
configure, build and installation process, as well as the overall
portability of the core code rests with the configure pumpkin - others
help out with individual operating systems.

The files involved are the operating system directories, (F<win32/>,
F<os2/>, F<vms/> and so on) the shell scripts which generate F<config.h>
and F<Makefile>, as well as the metaconfig files which generate
F<Configure>. (metaconfig isn't included in the core distribution.)

=item Interpreter

And of course, there's the core of the Perl interpreter itself. Let's
have a look at that in a little more detail.

=back

Before we leave looking at the layout, though, don't forget that
F<MANIFEST> contains not only the file names in the Perl distribution,
but short descriptions of what's in them, too. For an overview of the
important files, try this:

    perl -lne 'print if /^[^\/]+\.[ch]\s+/' MANIFEST

=head2 Elements of the interpreter

The work of the interpreter has two main stages: compiling the code
into the internal representation, or bytecode, and then executing it.
L<perlguts/Compiled code> explains exactly how the compilation stage
happens.

Here is a short breakdown of perl's operation:

=over 3

=item Startup

The action begins in F<perlmain.c>. (or F<miniperlmain.c> for miniperl)
This is very high-level code, enough to fit on a single screen, and it
resembles the code found in L<perlembed>; most of the real action takes
place in F<perl.c>

First, F<perlmain.c> allocates some memory and constructs a Perl
interpreter:

    1 PERL_SYS_INIT3(&argc,&argv,&env);
    2
    3 if (!PL_do_undump) {
    4     my_perl = perl_alloc();
    5     if (!my_perl)
    6         exit(1);
    7     perl_construct(my_perl);
    8     PL_perl_destruct_level = 0;
    9 }

Line 1 is a macro, and its definition is dependent on your operating
system. Line 3 references C<PL_do_undump>, a global variable - all
global variables in Perl start with C<PL_>. This tells you whether the
current running program was created with the C<-u> flag to perl and then
F<undump>, which means it's going to be false in any sane context.

Line 4 calls a function in F<perl.c> to allocate memory for a Perl
interpreter. It's quite a simple function, and the guts of it looks like
this:

    my_perl = (PerlInterpreter*)PerlMem_malloc(sizeof(PerlInterpreter));

Here you see an example of Perl's system abstraction, which we'll see
later: C<PerlMem_malloc> is either your system's C<malloc>, or Perl's
own C<malloc> as defined in F<malloc.c> if you selected that option at
configure time.

Next, in line 7, we construct the interpreter; this sets up all the
special variables that Perl needs, the stacks, and so on.

Now we pass Perl the command line options, and tell it to go:

    exitstatus = perl_parse(my_perl, xs_init, argc, argv, (char **)NULL);
    if (!exitstatus) {
        exitstatus = perl_run(my_perl);
    }


C<perl_parse> is actually a wrapper around C<S_parse_body>, as defined
in F<perl.c>, which processes the command line options, sets up any
statically linked XS modules, opens the program and calls C<yyparse> to
parse it.

=item Parsing

The aim of this stage is to take the Perl source, and turn it into an op
tree. We'll see what one of those looks like later. Strictly speaking,
there's three things going on here.

C<yyparse>, the parser, lives in F<perly.c>, although you're better off
reading the original YACC input in F<perly.y>. (Yes, Virginia, there
B<is> a YACC grammar for Perl!) The job of the parser is to take your
code and `understand' it, splitting it into sentences, deciding which
operands go with which operators and so on.

The parser is nobly assisted by the lexer, which chunks up your input
into tokens, and decides what type of thing each token is: a variable
name, an operator, a bareword, a subroutine, a core function, and so on.
The main point of entry to the lexer is C<yylex>, and that and its
associated routines can be found in F<toke.c>. Perl isn't much like
other computer languages; it's highly context sensitive at times, it can
be tricky to work out what sort of token something is, or where a token
ends. As such, there's a lot of interplay between the tokeniser and the
parser, which can get pretty frightening if you're not used to it.

As the parser understands a Perl program, it builds up a tree of
operations for the interpreter to perform during execution. The routines
which construct and link together the various operations are to be found
in F<op.c>, and will be examined later.

=item Optimization

Now the parsing stage is complete, and the finished tree represents
the operations that the Perl interpreter needs to perform to execute our
program. Next, Perl does a dry run over the tree looking for