# Copyright (C) 2007, The Perl Foundation.
# $Id: /mirror/trunk/docs/project/cage_cleaners_guide.pod 35487 2009-01-12T20:03:00.235999Z infinoid  $

=head1 Cage Cleaner Guide

From F<docs/project/roles_responsibilities.pod>:

 Fixes failing tests, makes sure coding standards are implemented,
 reviews documentation and examples. A class of tickets in the
 tracking system (RT or Trac) has been created for use by this
 group. This is an entry level position, and viewed as a good way
 to get familiar with parrot internals.

=head1 Testing Parrot after making a code cleaning change

To be really I<really> sure you're not breaking anything after doing code
cleaning or attending to the newspaper at the bottom of our Parrot's cage
here are is the process I (ptc) go through before committing a new change:

  make realclean > make_realclean.out 2>&1
  perl Configure.pl > perl_configure.out 2>&1
  make buildtools_tests > buildtools_tests.out 2>&1
  make test > make_test.out 2>&1

Then I diff the C<*.out> files with copies of the C<*.out> files I made on a
previous test run.  If the diffs show nothing nasty is happening, you can be
more sure that you've not broken anything and can commit the change.  Then
rename the C<*.out> files to something like C<*.out.old> so that you
maintain reasonably up to date references for the diffs.

This process should be put into a script and stored somewhere...

=head1 Parrot Cage Cleaners high-level goals

=head2 Smoke testing on many platforms with many compilers

The more platforms we have, the more likely we are to find portability
problems.  Parrot has to be the most portable thing we've created.

More platforms also means more compilers.  Maybe your DEC compiler
is more picky than gcc, and spews more warnings.  Good!  More
opportunities for cleaning!

=head3 icc

C<icc> is the Intel C/C++ Compiler and is available for free for
non-commercial use.  To use C<icc> to build parrot, use the following
arguments to C<Configure.pl>:

  perl Configure.pl --cc=icc --ld=icc

(courtesy of Steve Peters, C<steve at fisharerojo dot org>).

=head2 Compiler pickiness

Use as many compiler warnings as we possibly can.  The more warnings
we enable, the less likely something will pass the watchful eye of
the compiler.

Note that warnings may not just be -W flags.  Some warnings in gcc
only show up when optimization is enabled.

=head2 splint

Splint (L<http://www.splint.org>) is a very very picky lint tool, and
setup and configuration is a pain.  Andy has tried to get Perl 5
running under it nicely, but has met with limited success.  Maybe
the Parrot will be nicer.

=head2 Solaris lint

Sun has made its dev tools freely available at
L<http://developers.sun.com/prodtech/cc/>.  Its lint is the best one
out there, except from Gimpel's FlexeLint
(L<http://www.gimpel.com/html/flex.htm>) which costs many dollars.

=head2 Enforcing coding standards, naming conventions, etc

=over 4

=item * Automatic standards checking

The docs in F<filename here> explains what our code should look
like.  Write something that automatically validates it in a .t file.

=item * C<const> checking

Declaring variables as C<const> wherever possible lets the compiler
do lots of checking that wouldn't normally be possible.  Walk the
source code adding the C<const> qualifier wherever possible.  The
biggest bang is always in passing pointers into functions.

=back

=head2 Why consting is good

In Perl, we have the C<use constant> pragma to define unchanging
values.  The L<Readonly> module extends this to allow arrays and
hashes to be non-modifiable as well.

In C, we have C<const> numbers and pointers, and using them wherever
possible lets us put safety checks in our code, and the compiler
will watch over our shoulders.

=head3 C<const> numbers

The easiest way to use the C<const> qualifier is by flagging numbers
that are set at the top of a block.  For example:

    int max_elements;

    max_elements = nusers * ELEMENTS_PER_USER;

    ...

    array[max_elements++] = n;
    /* but you really meant array[max_elements] = n++; */

Adding a C<const> qualifier means you can't accidentally modify
C<max_elements>.

    const int max_elements = nusers * ELEMENTS_PER_USER;

=head3 C<const> pointers

If a pointer is qualified as const, then its contents cannot be
modified.  This lets the compiler protect you from doing naughty
things to yourself.

Here are two examples for functions you're familiar with:

    int strlen( const char *str );
    void memset( char *ptr, char value, int length );

In the case of C<strlen>, the caller is guaranteed that any string
passed in won't be modified.  How terrible it would be if it was
possible for C<strlen> to modify what gets passed in!

The const on C<strlen>'s parameter also lets the compiler know that
C<strlen> can't be initializing what's passed in.  For example:

    char buffer[ MAX_LEN ];

    int n = strlen( buffer );

The compiler knows that C<buffer> hasn't been initialized, and
that C<strlen> can't be initializing it, so the call to C<strlen>
is on an uninitialized value.

Without the const, the compiler assumes that the contents of any
pointer are getting initialized or modified.

=head3 C<const> arrays

Consting arrays makes all the values in the array non-modifiable.

    const int days_per_month[] =
        { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

You don't want to be able to do C<days_per_month[1] = 4;>, right?
(We'll ignore that about 25% of the time you want C<days_per_month[1]>
to be 29.)

=head3 Mixing C<consts>

Combining C<const>s on a pointer and its contents can get confusing.
It's important to know on which side of the asterisk that the
C<const> lies.

To the left of the asterisk, the characters are constant.  To the
right of the asterisk, the pointer is constant.

Note the difference between a pointer to constant characters:

    /* Pointer to constant characters */
    const char *str = "Don't change me.";
    str++;      /* legal, now points at "o" */
    *str = "x"; /* not legal */

and a constant pointer to characters:

    /* Constant pointer to characters */
    char * const str = buffer;
    str++;      /* not legal */
    *str = 'x'; /* buffer[0] is now 'x' */

Note the difference between which side of the asterisk that the
C<const> is on.

You can also combine the two, with a constant pointer to constant
characters:

    const char * const str = "Don't change me";

or even an array of constant pointers to constant characters:

    const char * const days[] =
        { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };

If you see a declaration you don't understand, use C<cdecl>.  It's
standard in many C compiler suites, and is freely available around
the net.

    $ cdecl
    Type `help' or `?' for help
    cdecl> explain const char * str;
    declare str as pointer to const char
    cdecl> explain char * const str;
    declare str as const pointer to char

=head2 Decreasing the amount of repeated code

PMD (L<http://pmd.sourceforge.net/>) has been used on C code, even
though it's a Java tool.  It looks for repeated strings of tokens
that are candidates for either functions or macros.

=head3 PMD usage

General usage:

  pmd [directory] [report format] [ruleset file]

To generate html output of unused code within parrot use:

  pmd . html rulesets/unusedcode.xml > unused_code.html

Also distributed with PMD is the CPD (Copy/Paste Detector) which finds
duplicate code.  An easy way to get started with this tool is to use the gui
(cpdgui).  Set the root source directory to your parrot working directory,
and choose the C<by extension...> option of the C<Language:> menu.  Then put
C<.c> in the C<Extension:> box and click C<Go>.

=head2 Automated source macros

Perl5 has a lot of good source management techniques that we can use.

=over 4

=item * Macro for interp argument

A macro for declaring the interpreter argument, and maybe a macro
for passing it

BTW, our Perl experience teaches us that somebody is going to want
to make the interpreter a C++ object for Windows environments, and
it wouldn't hurt to make that possible, or at least work in that
direction, as long as clarity doesn't suffer.

=item * Parrot_xxx macros

Automated processing that would make a macro to let us write

    somefunc(interp,a,b,c)

while the linkage is

    Parrot_somefunc(interp,a,b,c)

for namespace cleanup.  This is straight out of F<embed.fnc> and
F<proto.h> in Perl5.

=back

=head2 Automated generation of C headers

This has started significantly with the F<headerizer.pl> program.
Right now, it extracts the function headers correctly, but now I
have to have it create the F<.h> files.

=head2 Creating automated code checking tools

=head2 Documenting function behavior and structure members

=head2 Developing coverage tools

=head2 Automatically running the coverage tools

=head2 Run on many different C compilers

Most of Andy's work right now is with GCC 4.2 on Linux.  We need
many more.

=head2 Run under valgrind

Valgrind (L<http://valgrind.org/>) is a profiler/debugger most notable
for the way it magically monitors memory accesses and management.

To run parrot under Valgrind, the following argument set should be helpful:

  valgrind --num-callers=500 \
     --leak-check=full --leak-resolution=high --show-reachable=yes \
     parrot --leak-test

(adapted from a post to C<parrot-porters> by chromatic).

=head2 IMCC cleanup

From #parrot:

    vsoni: there seems to be some dead code/feature....I had a chat
    with leo and I am going to send and email to p6i for deprecation
    of certain old features

=head2 Help other contributors hack their patches into Parrot-style industrial-strength C code.

From chip's comment at
L<http://www.oreillynet.com/onlamp/blog/2006/07/calling_for_parrot_janitors.html>

    We've just had contributed an improved register allocation
    implementation, but since the contributor is new to Parrot,
    there are some style and coding standards issues that need to
    be worked out. It'd be great if a Cage Cleaner could step up
    and help our new contributor bang the code into Parrotish form.

=head2 Remove usage of deprecated features

F<DEPRECATED.pod> lists features that are deprecated but not yet removed;
An RT ticket will document how this deprecated feature is to be replaced.
Help prepare for the actual removal of the feature by replacing its usage.

=head2 Clean up skipped tests

Parrot has too many skipped tests.  Pick a test file with a skipped test,
disable the skip() line, then make it pass.  The Parrot code may not compile,
or you may have to modify it to bring it up to date.  The test may not even be
useful anymore; we won't know until you try.

If you can make it pass, great!

If you can make it run, great!  Make it a TODO test instead.

If neither, please report your findings so that everyone can decide what to do.

=head1 Handy configuration tips

=head2 Subversion configuration and automatic properties

There is an example C<.subversion/config> file in
F<editor/subversion_config> which is useful in automatically setting the
appropriate Subversion properties relevant to Parrot on addition of new
files.

=head2 Displaying trailing whitespace in vim and emacs

=head3 Vim

Add this to your C<.vimrc>:

    set list
    set listchars=trail:-,tab:\.\ 

B<NOTE>: there is a space character after the last backslash.  It is very 
important!

Contributed by Jerry Gay <jerry dot gay at gmail dot com>.

=head3 Emacs

Add this to your C<.emacs>:

    (setq-default show-trailing-whitespace t)

Emacs 22 users can highlight tabs like this:

    (global-hi-lock-mode 1)
    (highlight-regexp "\t")

Contributed by Eric Hanchrow <offby1 at blarg dot net>.

=head1 AUTHOR

Paul Cochrane a.k.a. ptc; original document by Andy Lester

=head1 SEE ALSO

F<docs/project/roles_responsibilities.pod>, F<RESPONSIBLE_PARTIES>
and the list of Cage items on RT:
L<http://xrl.us/owsd> (Link to rt.perl.org)

=cut
