Project Development

Organization of the Parrot project is lightweight but efficient. It's a meritocracy--people who make valuable contributions are offered more responsibility. Communication is relaxed and informal. As Dan is so fond of saying, "This is far too important to take seriously." It's a bit like a special forces unit--the work gets done not because of tight control from the top, but because the whole team knows the task at hand and does it.

Development Cycles

The cycles in Parrot development center on "point releases." A point release is a version change, such as 0.4.x to 0.5.x. The architect and project manager decide when point releases happen and what features are included. Usually one or two solid new features trigger a point release.

Development proceeds at a steady pace of bug reports, patches submitted, and patches applied. The pace isn't so much a result of careful planning as it is the law of averages--on any given day, someone, somewhere, is working on Parrot. A release is a spike in that activity, but since Parrot tends to follow the "release early, release often" strategy, the spike is relatively small.

Typically, the release manager for the month declares a feature freeze a few days before each release and all development efforts center on bug squashing. This periodic cleanup is one of the most valuable aspects of a release.

Getting Involved

Just like design work, the first step to participating in Parrot development is joining the list. The topics on p2 tend to stick to practical matters: bug reports, patches, notifications of changes committed to the subversion repository, and questions on coding style. Occasionally there are discussions about how to implement a particular feature.

Use the source

The second step to participating in Parrot development is to get a copy of the source code. If you just want to try it out--experiment with a few features and see how it feels--you're probably best off downloading a tarball. For the most stable copy, grab the latest point release from CPAN. The sure way to get the most recent release is at http://search.cpan.org/dist/parrot/ (or search for "parrot" in "Distributions"). If you want something a little more cutting edge than the packaged release, a new snapshot of the subversion repository is created every eight hours. The most recent snapshot is always available at http://cvs.perl.org/snapshots/parrot/parrot-latest.tar.gz.

If you plan to get involved in development, you'll want to check out the source from the subversion repository. Anyone can get anonymous access, committers use their http://auth.perl.org username..

  svn co https://svn.perl.org/parrot/trunk parrot

There's also a web interface for viewing files in the repository at http://svn.perl.org/viewcvs/parrot/.

Now that you've got the source, take a moment to look around. The code changes constantly, so a detailed description of every file is impossible. But a few road signs are helpful starting out.

The most important top-level directory is docs/. The content isn't always up to date, but it is a good place to start. parrot.pod provides a quick overview of what's in each documentation file.

The languages/ directory contains the code that implements various language compilers: Perl 6, Python ("Pynie"), Ruby ("Cardinal"), PHP ("Plumhead"), Python ("Pynie"), Lisp, Lua, Tcl ("ParTcl"), ABC, and WMLScript, as well as Forth, Scheme, Befunge, BASIC, etc. Most are in various stages of partial completion. LANGUAGES.STATUS provides meta information on the included languages, and on languages maintained outside the Parrot repository. If you have a language you're particularly interested to see implemented on Parrot, you might take a peek to see how far along it is.

The lib/ directory contains Perl 5 classes currently used in developing Parrot. The src/pmc/ directory contains the C source code for Parrot classes (PMCs, which you'll read more about in CHP-9Chapter 9). The examples/ directory contains some example Parrot assembler code, as well as benchmarks.

Building Parrot

The first step before you start playing with PASM code is to get a copy of the source code and compile it. There is some information on this in CHP-2-SECT-2.2.1"Use the source" in Chapter 2. For more information and updates, see http://www.parrotcode.org and the documentation in the distributed code.

The basic steps are:Not all operating systems have make. Check the documentation for instructions for systems that aren't Unix-based.

  $ perl Configure.pl
  $ make
  $ make test

Once you've compiled Parrot, create a small test file in the main parrot directory. We'll call it fjord.pasm.

  print "He's pining for the fjords.\n"
  end

.pasm is the standard extension for Parrot assembly language source files. Now you can run this file with:

  $ ./parrot fjord.pasm

And watch the result of the program execution. Instead of executing the program immediately, you could also compile it to bytecode:

  $ ./parrot --output fjord.pbc fjord.pasm

You specify the name of the output bytecode file with the --output (or -o) switch. .pbc is the standard extension for Parrot bytecode. To execute the compiled bytecode, run it through the parrot interpreter:

  $ ./parrot fjord.pbc

That's all there is to it.

Patch submission

Parrot development is a continuous stream of patches. Patches are the currency of exchange in the project--the unit of work. They fix bugs, add features, modify features, remove features, and improve the documentation. Pretty much anything that changes, changes via a patch.

While anyone is free to submit a patch, a small number of people have access to commit changes to the subversion repository. This system works well. It means the project can harness the efforts of a large group, but still keep the same high quality as a small group of experienced developers.

Every submitted patch is automatically forwarded to the p2 list where it's subject to peer review. Patches spark little debate. Patches are typically small modular changes, to make them easy to evaluate. Occasionally an entire language implementation is submitted in a single patch, but these are the exceptions.

Submitting a patch is fairly straightforward. You create a file that lists all your changes and email it to the ticket tracking system at parrotbug@parrotcode.org. But a few common-sense guidelines will make your patches cleaner, better, and less likely to give the pumpking hives.

First off, create your patches from a checked-out subversion repository, not from a tarball, so your diff is running against the latest version of the files. Then, make sure the paths listed in the patch match those in the repository. There are two methods of creating patches that will do this for you. You can make changes directly in your checked-out copy of the subversion repository and then create diffs using svn diff. Or you can make a copy of the repository and then create diffs between the two copies with the diff -u command:

  diff -u parrot/README parrot_changed/README

Either method is fine, and both are equally common on p2. Your working style and the types of changes you make--small and modular versus large and sweeping--will influence which method you choose.

Next, when you're making changes, take some extra time to consider how your patch affects the rest of the system. If your patch adds a new file, patch the main MANIFEST file to include it. If you add a new feature, add a test for it. If you fix a bug, add a test for it. See CHP-9-SECT-13"Writing Tests" in Chapter 9 for more on writing tests for Parrot. Before you submit a patch, always recompile the system with your patch included and run all tests as follows:

  make clean
  perl Configure.pl
  make
  make test

Then consider the people who will review and apply your patch, and try to make their jobs easier. Patch filenames should be as descriptive as possible: fix_readme_aardvark_typo.patch is better than README.patch. An attached file is better than a diff pasted into an email, because it can be applied without manual editing. The conventional extension for patch files is .patch.

In the email message, always start the subject with "[PATCH]", and make the subject as clear as possible: "[PATCH] misspelled aardvark in main README file" is better than "[PATCH] typo". The body of the message should clearly explain what the patch is supposed to do and why you're submitting it. Make a note if you're adding or deleting files so they won't be missed.

Here is a good example of a patch submission using the subversion diff method (an actual patch from p2). It's short, sticks to the point, and clearly expresses the problem and the solution. The patch filename and the subject of the message are both descriptive:

Possible alternates: ticket #23501, #24053 (not from top level)

  Subject: [PATCH] Pointers in List_chunk not initialized
  From: Bruce Gray
  
  On Win32, these tests are segfaulting due to invalid 
  pointers in List_chunk structs:
  t/op/string.t             97-98
  t/pmc/intlist.t           3-4
  t/pmc/pmc.t               80
  
  The problem is caused by list.c/allocate_chunk not 
  initializing the pointers. This patch corrects the problem.
  
  --
  Hope this helps,
  Bruce Gray

With the attached file list_chunk_initialize.patch:

  Index: list.c
  =========================================  
  RCS file: /cvs/public/parrot/list.c,v
  retrieving revision 1.23
  diff -u -r1.23 list.c
  --- list.c        27 Dec 2002 09:33:11 -0000        1.23
  +++ list.c        28 Dec 2002 03:37:35 -0000
  @@ -187,6 +187,10 @@
       Parrot_block_GC(interpreter);
       chunk = (List_chunk *)new_bufferlike_header(interpreter, sizeof(*chunk));
       chunk->items = items;
  +    chunk->n_chunks = 0;
  +    chunk->n_items  = 0;
  +    chunk->next     = NULL;
  +    chunk->prev     = NULL;
       Parrot_allocate_zeroed(interpreter, (Buffer *)chunk, size);
       Parrot_unblock_DOD(interpreter);
       Parrot_unblock_GC(interpreter);

Bug tracking

Bug reports go to the same address as patch submissions (parrotbug@parrotcode.org). Similar conventions apply: make the subject and the message as clear and descriptive as possible. The subject line should start with "[BUG]" to make it immediately obvious what the message is about.

If you want to track a bug or patch you've submitted, the current queue of bugs and patches is publicly viewable at http://rt.perl.org. Bug tracking for Parrot is handled by the Request Tracker (RT) ticket tracking system from Best Practical Solutions.

cpanm Parrot::Op

perl -MCPAN -e shell
install Parrot::Op