Async Counter App

In the previous counter app, we had a purely sequential blocking application. There are times when you may be interested in running IO operations or compute asynchronously.

For this tutorial, we will build a single file version of an async TUI using tokio. This tutorial section is a simplified version of the async ratatui counter app.

Installation

Here’s an example of the Cargo.toml file required for this tutorial:

[package]
name = "ratatui-counter-async-app"
version = "0.1.0"
edition = "2021"

[dependencies]
color-eyre = "0.6.2"
crossterm = { version = "0.27.0", features = ["event-stream"] }
ratatui = "0.24.0"
tokio = { version = "1.32.0", features = ["full"] }
tokio-util = "0.7.9"
futures = "0.3.28"

If you were already using crossterm before, note that now you’ll need to add features = ["event-stream"] to use crossterm’s async features.

You can use cargo add from the command line to add the above dependencies in one go:

cargo add ratatui crossterm color-eyre tokio tokio-util futures --features tokio/full,crossterm/event-stream

Setup

Let’s take the single file multiple function example from the counter app from earlier:

fn main() -> Result<()> {
  // setup terminal
  startup()?;

  let result = run();

  // teardown terminal before unwrapping Result of app run
  shutdown()?;

  result?;

  Ok(())
}

Tokio is an asynchronous runtime for the Rust programming language. It provides the building blocks needed for writing network applications. We recommend you read the Tokio documentation to learn more.

For the setup for this section of the tutorial, we are going to make just one change. We are going to make our main function a tokio entry point.

#[tokio::main]
async fn main() -> Result<()> {
  // setup terminal
  startup()?;

  let result = run();

  // teardown terminal before unwrapping Result of app run
  shutdown()?;

  result?;

  Ok(())
}

Adding this #[tokio::main] macro allows us to spawn tokio tasks within main. At the moment, there are no async functions other than main and we are not using .await anywhere yet. We will change that in the following sections. But first, we let us introduce the Action enum.