Quickstart: Background Tasks

If you need to run a process that takes a long time, you want your app to carry on running while it executes.

Follow this quickstart to trigger an artificially slow-running HTTP request in the background, and return control to your main app while it executes.

Create an app

Log in to Anvil and click ‘Blank App’. Choose the Material Design theme.

Add a Server Module

In the App Browser, click “+ Add Server Module” next to Server Code to add a new Server Module.

A new tab will open with a code editor with an orange background.

In the App Browser, click the + next to Server Code to add a new Server Module.

You will see a code editor with a yellow background.

Write a Background Task

Start by importing the anvil.http library.

import anvil.http

Write this function into the Server Module

@anvil.server.background_task
def make_slow_request():
  response = anvil.http.request("https://httpstat.us/200?sleep=5000")  # An API that provides slow responses
  print(response)

The @anvil.server.background_task decorator means that this function can be run in the background.

Launch the Background Task

Still in the server module, write a function that launches the Background Task

@anvil.server.callable
def launch_slow_request_task():
  task = anvil.server.launch_background_task('make_slow_request')
  return task

The @anvil.server.callable decorator means this function can be called from the client code.

Go to the code for Form1. It looks like this:

At the end of the __init__ method, write these lines:

    self.task = anvil.server.call('launch_slow_request_task')

This means your function will run when the app starts, and the task object will be stored. The task object holds all available information about the task.

Run your app

Now click the ‘Run’ button at the top of the screen.

The App Console at the bottom will show your Background Task running:

The bottom of the Output Panel will show your Background Task running:

Check the output

To check the output, open the app’s Logs in the Sidebar Menu. Then select Background Tasks. You’ll see a table showing all the Background Tasks that this app has ever run:

Click on View Logs. You’ll be taken to the App Logs entry for that Task:

Click on Background Tasks in the Gear Menu :

You’ll see a table showing all the Background Tasks that this app has ever run:

Click on View Logs. You’ll be taken to the App Logs entry for that Task:

You can see the output from the Background Task. As expected, the Task printed the response from the test HTTP endpoint.

(It’s a Media object with a length of 0 bytes and no content - that’s because the test server (https://httpstat.us) returns empty responses.)

Copy the example app

Click on the button below to clone a finished version of this app into your account.

Next up

Want more depth on this subject?

You can pass data from a Background Task into the main app, access a task’s state, and terminate it programmatically.

You can also get a list of all the Background Tasks your app has.

Read more about Background Tasks to find out how.

Want another quickstart?

Every quickstart is on the Quickstarts page.

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