[<img src='https://i.imgur.com/Eec71eh.png' alt='Que' width='200px' />][docs]
=============================================================================
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> Simple Background Job Processing in Elixir :zap:
Que is a job processing library backed by [`Mnesia`][mnesia], a distributed
real-time database that comes with Erlang / Elixir. That means it doesn't
depend on any external services like `Redis` for persisting job state. This
makes it really easy to use since you don't need to install anything other
than Que itself.
See the [Documentation][docs].
<br>
## Installation
Add `que` to your project dependencies in `mix.exs`:
```elixir
def deps do
[{:que, "~> 0.10.1"}]
end
```
and then add it to your list of `applications`:
```elixir
def application do
[applications: [:que]]
end
```
### Mnesia Setup
Que runs out of the box, but by default all jobs are stored in-memory.
To persist jobs across application restarts, specify the DB path in
your `config.exs`:
```elixir
config :mnesia, dir: 'mnesia/#{Mix.env}/#{node()}' # Notice the single quotes
```
And run the following mix task:
```bash
$ mix que.setup
```
This will create the Mnesia schema and job database for you. For a
detailed guide, see the [Mix Task Documentation][docs-mix]. For
compiled releases where `Mix` is not available
[see this][docs-setup-prod].
<br>
## Usage
Que is very similar to other job processing libraries such as Ku and
Toniq. Start by defining a [`Worker`][docs-worker] with a `perform/1`
callback to process your jobs:
```elixir
defmodule App.Workers.ImageConverter do
use Que.Worker
def perform(image) do
ImageTool.save_resized_copy!(image, :thumbnail)
ImageTool.save_resized_copy!(image, :medium)
end
end
```
You can now add jobs to be processed by the worker:
```elixir
Que.add(App.Workers.ImageConverter, some_image)
#=> {:ok, %Que.Job{...}}
```
### Pattern Matching
The argument here can be any term from a Tuple to a Keyword List
or a Struct. You can also pattern match and use guard clauses like
any other method:
```elixir
defmodule App.Workers.NotificationSender do
use Que.Worker
def perform(type: :like, to: user, count: count) do
User.notify(user, "You have #{count} new likes on your posts")
end
def perform(type: :message, to: user, from: sender) do
User.notify(user, "You received a new message from #{sender.name}")
end
def perform(to: user) do
User.notify(user, "New activity on your profile")
end
end
```
### Concurrency
By default, all workers process one Job at a time, but you can
customize that by passing the `concurrency` option:
```elixir
defmodule App.Workers.SignupMailer do
use Que.Worker, concurrency: 4
def perform(email) do
Mailer.send_email(to: email, message: "Thank you for signing up!")
end
end
```
### Job Success / Failure Callbacks
The worker can also export optional `on_success/1` and `on_failure/2`
callbacks that handle appropriate cases.
```elixir
defmodule App.Workers.ReportBuilder do
use Que.Worker
def perform({user, report}) do
report.data
|> PDFGenerator.generate!
|> File.write!("reports/#{user.id}/report-#{report.id}.pdf")
end
def on_success({user, _}) do
Mailer.send_email(to: user.email, subject: "Your Report is ready!")
end
def on_failure({user, report}, error) do
Mailer.send_email(to: user.email, subject: "There was a problem generating your report")
Logger.error("Could not generate report #{report.id}. Reason: #{inspect(error)}")
end
end
```
### Setup and Teardown
You can similarly export optional `on_setup/1` and `on_teardown/1` callbacks
that are respectively run before and after the job is performed (successfully
or not). But instead of the job arguments, they pass the job struct as an
argument which holds a lot more internal details that can be useful for custom
features such as logging, metrics, requeuing and more.
```elixir
defmodule MyApp.Workers.VideoProcessor do
use Que.Worker
def on_setup(%Que.Job{} = job) do
VideoMetrics.record(job.id, :start, process: job.pid, status: :starting)
end
def perform({user, video, options}) do
User.notify(user, "Your video is processing, check back later.")
FFMPEG.process(video.path, options)
end
def on_teardown(%Que.Job{} = job) do
{user, video, _options} = job.arguments
link = MyApp.Router.video_path(user.id, video.id)
VideoMetrics.record(job.id, :end, status: job.status)
User.notify(user, "We've finished processing your video. See the results.", link)
end
end
```
Head over to Hexdocs for detailed [`Worker` documentation][docs-worker].
<br>
## Roadmap
- [x] Write Documentation
- [x] Write Tests
- [x] Persist Job State to Disk
- [x] Provide an API to interact with Jobs
- [x] Add Concurrency Support
- [x] Make jobs work in Parallel
- [x] Allow customizing the number of concurrent jobs
- [x] Success/Failure Callbacks
- [x] Find a more reliable replacement for Amnesia
- [ ] Delayed Jobs
- [ ] Allow job cancellation
- [ ] Job Priority
- [ ] Support running in a multi-node enviroment
- [ ] Recover from node failures
- [ ] Support for more Persistence Adapters
- [ ] Redis
- [ ] Postgres
- [x] Mix Task for creating Mnesia Database
- [ ] Better Job Failures
- [ ] Option to set timeout on workers
- [ ] Add strategies to automatically retry failed jobs
- [ ] Web UI
<br>
## Contributing
- [Fork][github-fork], Enhance, Send PR
- Lock issues with any bugs or feature requests
- Implement something from Roadmap
- Spread the word :heart:
<br>
## License
This package is available as open source under the terms of the [MIT License][license].
<br>
[logo]: https://i.imgur.com/Eec71eh.png
[shield-version]: https://img.shields.io/hexpm/v/que.svg
[shield-license]: https://img.shields.io/hexpm/l/que.svg
[shield-downloads]: https://img.shields.io/hexpm/dt/que.svg
[shield-travis]: https://img.shields.io/travis/sheharyarn/que/master.svg
[shield-inch]: https://inch-ci.org/github/sheharyarn/que.svg?branch=master
[travis-ci]: https://travis-ci.org/sheharyarn/que
[inch-ci]: https://inch-ci.org/github/sheharyarn/que
[license]: https://opensource.org/licenses/MIT
[mnesia]: http://erlang.org/doc/man/mnesia.html
[hexpm]: https://hex.pm/packages/que
[docs]: https://hexdocs.pm/que
[docs-worker]: https://hexdocs.pm/que/Que.Worker.html
[docs-mix]: https://hexdocs.pm/que/Mix.Tasks.Que.Setup.html
[docs-setup-prod]: https://hexdocs.pm/que/Que.Persistence.Mnesia.html#setup!/0
[github-fork]: https://github.com/sheharyarn/que/fork
