---
Authors:
  - Ayaz Akram
---

# Tasks

## Introduction
The actual gem5 experiment is executed with the help of [Celery](http://www.celeryproject.org/).
Celery server can run many gem5 tasks asynchronously. Once a user creates a gem5Run object (discussed previously) while using gem5art, this object needs to be passed to a method run_gem5_instance() registered with Celery app, which is responsible for starting a Celery task to run gem5. The other argument needed by the run_gem5_instance() is the current working directory. Fundamentally, celery is not required to run gem5 jobs with gem5art and a job can be directly launched by calling run() function of gem5Run object. However, celery can do a better job of managing multiple runs.

Celery server can be started with the following command:

```sh
celery -E -A gem5art.tasks.celery worker --autoscale=[number of workers],0
```

This will start a server with events enabled that will accept gem5 tasks as defined in gem5art.
It will autoscale from 0 to desired number of workers.

<!--Then, you can write a script (e.g., `launch_tests.py`) which will first create all of the required artifacts and will call the `run` task defined in gem5art.-->

Celery relies on a message broker `RabbitMQ` for communication between the client and workers.
If not already installed, you need to install `RabbitMQ` on your system (before running celery) using:

```sh
apt-get install rabbitmq-server
```

## Monitoring Celery
Celery does not explicitly show the status of the runs by default. 
[flower](https://flower.readthedocs.io/en/latest/), a Python package, is a web-based tool for monitoring and administrating Celery.  

To install the flower package, 
```sh
pip install flower
```

You can monitor the celery cluster doing the following:

```sh
flower -A gem5art.tasks.celery --port=5555
```
This will start a webserver on port 5555.

## Removing all tasks

```sh
celery -A gem5art.tasks.celery purge
```

## Viewing state of all jobs in celery

```sh
celery -A gem5art.tasks.celery events
```

## Tasks API Documentation
```eval_rst
Task
----

.. automodule:: gem5art.tasks.tasks
    :members:
    :undoc-members:

.. automodule:: gem5art.tasks.celery
    :members:
    :undoc-members:
```