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Flowpack.JobQueue.Common

Neos Flow package that allows for asynchronous and distributed execution of tasks.

Table of contents

• Quickstart
• Introduction
• Message Queue
• Job Queue
• Command Line Interface
• Signals & Slots
• License
• Contributions

Quickstart (TL;DR)

1. Install this package using composer:

   (or by adding the dependency to the composer manifest of an installed package)

2. Configure a basic queue by adding the following to your Settings.yaml:

3. Initialize the queue (if required)

   With

   you can setup the queue and/or verify its configuration. In the case of the FakeQueue that step is not required.

   Note: The queue:setup command won't remove any existing messages, there is no harm in calling it multiple times

4. Annotate any public method you want to be executed asynchronously:

   or use attributes instead of annotations (PHP 8.0 and later):

   Note: The method needs to be public and it must not return anything

5. Start the worker (if required)

   With the above code in place, whenever the method SomeClass::sendEmail() is about to be called that method call is converted into a job that is executed asynchronously[1].

   Unless you use the FakeQueue like in the example, a so called worker has to be started, to listen for new jobs and execute them::

Introduction

To get started let's first define some terms:

Message

A piece of information passed between programs or systems, sometimes also referred to as "Event".
In the JobQueue packages we use messages to transmit `Jobs`.

Message Queue

According to Wikipedia "message queues [...] are software-engineering components used for inter-process communication (IPC), or for inter-thread communication within the same process".
In the context of the JobQueue packages we refer to "Message Queue" as a FIFO buffer that distributes messages to one or more consumers, so that every message is only processed once.

Job

A unit of work to be executed (asynchronously).
In the JobQueue packages we use the Message Queue to store serialized jobs, so it acts as a "Job stream".

Job Manager

Central authority allowing adding and fetching jobs to/from the Message Queue.

Worker

The worker watches a queue and triggers the job execution.
This package comes with a `job:work` command that does this (see below)

submit

New messages are *submitted* to a queue to be processed by a worker

reserve

Before a message can be processed it has to be *reserved*.
The queue guarantees that a single message can never be reserved by two workers (unless it has been released again)

release

A reserved message can be *released* to the queue to be processed at a later time.
The *JobManager* does this if Job execution failed and the `maximumNumberOfReleases` setting for the queue is greater than zero

abort

If a message could not be processed successfully it is *aborted* marking it *failed* in the respective queue so that it can't be reserved again.
The *JobManager* aborts a message if Job execution failed and the message can't be released (again)

finish

If a message was processed successfully it is marked *finished*.
The *JobManager* finishes a message if Job execution succeeded.

Message Queue

The Flowpack.JobQueue.Common package comes with a very basic Message Queue implementation Flowpack\JobQueue\Common\Queue\FakeQueue that allows for execution of Jobs using sub requests. It doesn't need any 3rd party tools or server loops and works for basic scenarios. But it has a couple of limitations to be aware of:

1. It is not actually a queue, but dispatches jobs immediately as they are queued. So it's not possible to distribute the work to multiple workers

2. The JobManager is not involved in processing of jobs so the jobs need to take care of error handling themselves.

3. For the same reason Signals are not emitted for the FakeQueue.

4. With Flow 3.3+ The FakeQueue supports a flag async. Without that flag set, executing jobs block the main thread!

For advanced usage it is recommended to use one of the implementing packages like one of the following:

• Flowpack.JobQueue.Doctrine
• Flowpack.JobQueue.Beanstalkd
• Flowpack.JobQueue.Redis

Configuration

This is the simplest configuration for a queue:

With this a queue named test will be available.

Note: For reusable packages you should consider adding a vendor specific prefixes to avoid collisions. We recommend to use a classname or the package name with the function name (e.g. Flowpack.ElasticSearch.ContentRepositoryQueueIndexer.

Queue parameters

The following parameters are supported by all queues:

A more complex example could look something like:

As you can see, you can have multiple queues in one installations. That allows you to use different backends/options for queues depending on the requirements.

Presets

If multiple queries share common configuration presets can be used to ease readability and maintainability:

This will configure two DoctrineQueues "email" and "log" with some common options but different table names and poll intervals.

Job Queue

The job is an arbitrary class implementing Flowpack\JobQueue\Common\Job\JobInterface. This package comes with one implementation StaticMethodCallJob that allows for invoking a public method (see Quickstart) but often it makes sense to create a custom Job:

Note: It's crucial that the execute() method returns TRUE on success, otherwise the corresponding message will be released again and/or marked failed.

With that in place, the new job can be added to a queue like this:

Command Line Interface

Use the flowpack.jobqueue.common:queue:* and flowpack.jobqueue.common:job:* commands to interact with the job queues:

Signal & Slots

When working with JobQueues proper monitoring is crucial as failures might not be visible immediately. The JobManager emits signals for all relevant events, namely:

• messageSubmitted
• messageTimeout
• messageReserved
• messageFinished
• messageReleased
• messageFailed

Those can be used to implement some more sophisticated logging for example:

This would log every failed message to the system log.

License

This package is licensed under the MIT license

Contributions

Pull-Requests are more than welcome. Make sure to read the Code Of Conduct.

[1] The FakeQueue actually executes Jobs synchronously unless the async flag is set (requires Flow 3.3+)