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Bug fixes && New Features to the PHP port of Rescue (Workers and Queueing)

tag: v1.1

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README.markdown

php-resque: PHP Resque Worker (and Enqueue)

Resque is a Redis-backed library for creating background jobs, placing those jobs on multiple queues, and processing them later.

Resque was pioneered and is developed by the fine folks at GitHub (yes, I am a kiss-ass), and written in Ruby.

What you're seeing here is an almost direct port of the Resque worker and enqueue system to PHP, which I've thrown together because I'm sure my PHP developers would have a fit if they had to write a line of Ruby.

For more information on Resque, visit the official GitHub project: http://github.com/defunkt/resque/

And for background information, the launch post on the GitHub blog: http://github.com/blog/542-introducing-resque

The PHP port does NOT include its own web interface for viewing queue stats, as the data is stored in the exact same expected format as the Ruby version of Resque.

The PHP port allows for much the same as the Ruby version of Rescue:

  • Workers can be distributed between multiple machines
  • Includes support for priorities (queues)
  • Resilient to memory leaks (fork)
  • Expects failure

In addition, it also:

  • Has the ability to track the status of jobs
  • Will mark a job as failed, if a forked child running a job does not exit with a status code as 0
  • Has built in support for setUp and tearDown methods, called pre and post jobs

Note: php-resque requires at least Redis 2.2.

Jobs

Queueing Jobs

Jobs are queued as follows:

require_once 'lib/Resque.php';

// Required if redis is located elsewhere
Resque::setBackend('localhost', 6379);

$args = array(
    'name' => 'Chris'
);
Resque::enqueue('default', 'My_Job', $args);

Defining Jobs

Each job should be in it's own class, and include a perform method.

class My_Job
{
    public function perform()
    {
        // Work work work
        echo $this->args['name'];
    }
}

When the job is run, the class will be instantiated and any arguments will be set as an array on the instantiated object, and are accessible via $this->args.

Any exception thrown by a job will result in the job failing - be careful here and make sure you handle the exceptions that shouldn't result in a job failing.

Jobs can also have setUp and tearDown methods. If a setUp method is defined, it will be called before the perform method is run. The tearDown method if defined, will be called after the job finishes.

class My_Job
{
    public function setUp()
    {
        // ... Set up environment for this job
    }

    public function perform()
    {
        // .. Run job
    }

    public function tearDown()
    {
        // ... Remove environment for this job
    }
}

Tracking Job Statuses

php-resque has the ability to perform basic status tracking of a queued job. The status information will allow you to check if a job is in the queue, currently being run, has finished, or failed.

To track the status of a job, pass true as the fourth argument to Resque::enqueue. A token used for tracking the job status will be returned:

$token = Resque::enqueue('default', 'My_Job', $args, true);
echo $token;

To fetch the status of a job:

$status = new Resque_Job_Status($token);
echo $status->get(); // Outputs the status

Job statuses are defined as constants in the Resque_Job_Status class. Valid statuses include:

  • Resque_Job_Status::STATUS_WAITING - Job is still queued
  • Resque_Job_Status::STATUS_RUNNING - Job is currently running
  • Resque_Job_Status::STATUS_FAILED - Job has failed
  • Resque_Job_Status::STATUS_COMPLETE - Job is complete
  • false - Failed to fetch the status - is the token valid?

Statuses are available for up to 24 hours after a job has completed or failed, and are then automatically expired. A status can also forcefully be expired by calling the stop() method on a status class.

Workers

Workers work in the exact same way as the Ruby workers. For complete documentation on workers, see the original documentation.

A basic "up-and-running" resque.php file is included that sets up a running worker environment is included in the root directory.

The exception to the similarities with the Ruby version of resque is how a worker is initially setup. To work under all environments, not having a single environment such as with Ruby, the PHP port makes no assumptions about your setup.

To start a worker, it's very similar to the Ruby version:

$ QUEUE=file_serve php resque.php

It's your responsibility to tell the worker which file to include to get your application underway. You do so by setting the APP_INCLUDE environment variable:

$ QUEUE=file_serve APP_INCLUDE=../application/init.php php resque.php

Getting your application underway also includes telling the worker your job classes, by means of either an autoloader or including them.

Logging

The port supports the same environment variables for logging to STDOUT. Setting VERBOSE will print basic debugging information and VVERBOSE will print detailed information.

$ VERBOSE QUEUE=file_serve php resque.php
$ VVERBOSE QUEUE=file_serve php resque.php

Priorities and Queue Lists

Similarly, priority and queue list functionality works exactly the same as the Ruby workers. Multiple queues should be separated with a comma, and the order that they're supplied in is the order that they're checked in.

As per the original example:

$ QUEUE=file_serve,warm_cache php resque.php

The file_serve queue will always be checked for new jobs on each iteration before the warm_cache queue is checked.

Running All Queues

All queues are supported in the same manner and processed in alphabetical order:

$ QUEUE=* php resque.php

Running Multiple Workers

Multiple workers ca be launched and automatically worked by supplying the COUNT environment variable:

$ COUNT=5 php resque.php

Forking

Similarly to the Ruby versions, supported platforms will immediately fork after picking up a job. The forked child will exit as soon as the job finishes.

The difference with php-resque is that if a forked child does not exit nicely (PHP error or such), php-resque will automatically fail the job.

Signals

Signals also work on supported platforms exactly as in the Ruby version of Resque:

  • QUIT - Wait for child to finish processing then exit
  • TERM / INT - Immediately kill child then exit
  • USR1 - Immediately kill child but don't exit
  • USR2 - Pause worker, no new jobs will be processed
  • CONT - Resume worker.

Process Titles/Statuses

The Ruby version of Resque has a nifty feature whereby the process title of the worker is updated to indicate what the worker is doing, and any forked children also set their process title with the job being run. This helps identify running processes on the server and their resque status.

PHP does not have this functionality by default.

A PECL module (http://pecl.php.net/package/proctitle) exists that adds this funcitonality to PHP, so if you'd like process titles updated, install the PECL module as well. php-resque will detect and use it.

Event/Hook System

php-resque has a basic event system that can be used by your application to customize how some of the php-resque internals behave.

You listen in on events (as listed below) by registering with Resque_Event and supplying a callback that you would like triggered when the event is raised:

Resque_Event::listen('eventName', [callback]);

[callback] may be anything in PHP that is callable by call_user_func_array:

  • A string with the name of a function
  • An array containing an object and method to call
  • An array containing an object and a static method to call
  • A closure (PHP 5.3)

Events may pass arguments (documented below), so your callback should accept these arguments.

You can stop listening to an event by calling Resque_Event::stopListening with the same arguments supplied to Resque_Event::listen.

It is up to your application to register event listeners. When enqueuing events in your application, it should be as easy as making sure php-resque is loaded and calling Resque_Event::listen.

When running workers, if you run workers via the default resque.php script, your APP_INCLUDE script should initialize and register any listeners required for operation. If you have rolled your own worker manager, then it is again your responsibility to register listeners.

A sample plugin is included in the extras directory.

Events

beforeFirstFork

Called once, as a worker initializes. Argument passed is the instance of Resque_Worker that was just initialized.

beforeFork

Called before php-resque forks to run a job. Argument passed contains the instance of Resque_Job for the job about to be run.

beforeFork is triggered in the parent process. Any changes made will be permanent for as long as the worker lives.

afterFork

Called after php-resque forks to run a job (but before the job is run). Argument passed contains the instance of Resque_Job for the job about to be run.

afterFork is triggered in the child process after forking out to complete a job. Any changes made will only live as long as the job is being processed.

beforePerform

Called before the setUp and perform methods on a job are run. Argument passed contains the instance of Resque_Job about for the job about to be run.

You can prevent execution of the job by throwing an exception of Resque_Job_DontPerform. Any other exceptions thrown will be treated as if they were thrown in a job, causing the job to fail.

afterPerform

Called after the perform and tearDown methods on a job are run. Argument passed contains the instance of Resque_Job that was just run.

Any exceptions thrown will be treated as if they were thrown in a job, causing the job to be marked as having failed.

onFailure

Called whenever a job fails. Arguments passed (in this order) include:

  • Exception - The exception that was thrown when the job failed
  • Resque_Job - The job that failed

afterEnqueue

Called after a job has been queued using the Resque::enqueue method. Arguments passed (in this order) include:

  • Class - string containing the name of the class the job was scheduled in
  • Arguments - array of arguments supplied to the job

Contributors

  • chrisboulton
  • thedotedge
  • hobodave
  • scraton
  • KevBurnsJr
  • jmathai
  • dceballos
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