++ed by:
ROMANF DROLSKY

2 PAUSE users

MaxMind, Inc.
and 4 contributors

NAME

Stepford - A vaguely Rake/Make/Cake-like thing for Perl - create steps and let a runner run them

VERSION

version 0.003003

SYNOPSIS

    package My::Step::MakeSomething;

    use autodie;
    use Moose;

    has input_file => (
        traits   => ['StepDependency'],
        is       => 'ro',
        required => 1,
    );

    has output_file => (
        traits  => ['StepProduction'],
        is      => 'ro',
        default => '/path/to/file',
    );

    with 'Stepford::Role::Step::FileGenerator';

    sub run {
        my $self = shift;

        open my $input_fh,  '<', $self->input_file();
        open my $output_fh, '>', $self->output_file();
        while (<$input_fh>) {
            chomp;
            print {$output_fh} $_ * 2, "\n";
        }
        close $input_fh;
        close $output_fh;
    }

    package My::Runner;

    use Stepford::Runner;

    my $runner = Stepford::Runner->new(
        step_namespaces => 'My::Step',
        logger          => $log_object,    # optional
        jobs            => 4,              # optional
    );

    # Runs all the steps needed to get to the final_steps.
    $runner->run(
        final_steps => 'My::Step::MakeSomething',
    );

DESCRIPTION

NOTE: This is alpha code. You have been warned!

Stepford provides a framework for running a set of steps that are dependent on other steps. At a high level, this is a lot like Make, Rake, etc. However, the actual implementation is fairly different. Currently, there is no DSL, no Stepfile, etc.

With Stepford, each step is represented by a class you create. That class should consume either the Stepford::Role::Step::FileGenerator role (if it generates files) or the Stepford::Role::Step step (if it doesn't).

Steps declare both their dependencies (required inputs) and productions (outputs) as attributes. These attributes should be given either the StepDependency or StepProduction trait as appropriate.

The Stepford::Runner class analyzes the dependencies and productions for each step to figure out what steps it needs to run in order to satisfy the dependencies of the final steps you specify.

Each step can specify a last_run_time() method (or get one from the Stepford::Role::Step::FileGenerator role). The runner uses this to skip steps that are up to date.

See Stepford::Runner, Stepford::Role::Step, and Stepford::Role::Step::FileGenerator for more details.

CONCEPTS AND DESIGN

In order to understand how Stepford works you must understand a few key concepts.

First off, we have steps. A step is simply a self-contained unit of work, like generating a file, populating a database, etc. There are no restrictions on what steps can do. The only restriction is that they are expected to declare their dependencies and/or productions (more on these below).

Each step is a Moose class. Each step class should represent a concrete action, not a higher-level concept. In other words, the class name should be something like "CopyFooBarFilesToProduction", not "CopyFiles". If you have several steps that all share similar logic, you can use a role to share that logic between classes.

Each step must declare its dependencies and/or productions as regular Moose attributes. These attributes can contain any type of value. They are simply data. Note, however, that if you want to run steps in parallel, then the dependencies (and therefore productions) must be serializable data types (so no DBI handles, etc.).

A dependency is simply a value that a given step expects to get from another step (they can also be supplied to the runner manually).

The flip side of a dependency is a production. This is a value that the step will generate as needed.

Steps are run by a Stepford::Runner object. To create this object, you give it a list of step namespaces and the class(es) of the final step(s) you want to run. The runner looks at the final steps' dependencies and uses this information to figure out what other steps to run. It looks for steps with productions that satisfy these dependencies and adds any matching steps to the execution plan. It does this iteratively for each step it adds to the plan until the dependencies are satisfied for every step.

The runner detects cyclic dependencies (A requires B requires C requires B) and throws an error. It also detects when a step has a dependency that cannot be satisfied by the production of any other step.

Note that the matching of production to dependency is done solely by name. It's up to you to ensure that the output of a production is something that satisfies the dependency (in terms of the value's type, content, etc.).

If multiple classes have a production of the same name, then the first class that Stepford sees "wins". This can be useful if you want to override a step for testing, for example. See the documentation of the Stepford::Runner class's new() method for more details on step namespaces.

It is not possible for a class to have an attribute that is simultaneously a dependency and a production. This would be a natural design for a step that transformed a data value, but it makes dependency resolution impossible. However, nothing stops you from having two attributes that each produce the same value. For example, the attributes could both reference a path on disk and the step's run() method could alter the content of that file in place.

It is not currently possible for a class to have optional dependencies. This may be added in the future if it turns out to be useful.

FUTURE FEATURES

There are several very obvious things that should be added to this framework:

  • Dry runs

VERSIONING POLICY

This module uses semantic versioning as described by http://semver.org/. Version numbers can be read as X.YYYZZZ, where X is the major number, YYY is the minor number, and ZZZ is the patch number.

SUPPORT

Please report all issues with this code using the GitHub issue tracker at https://github.com/maxmind/Stepford/issues.

AUTHOR

Dave Rolsky <drolsky@maxmind.com>

CONTRIBUTORS

  • Greg Oschwald <goschwald@maxmind.com>

  • Olaf Alders <oalders@maxmind.com>

  • Ran Eilam <reilam@maxmind.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2015 by MaxMind, Inc..

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.