What is Runtime in Rust?

Question

I've read a blog. It says Rust doesn't not have built-in runtime. And I read a sentence in that blog:

A runtime of your choosing, such as Tokio, async_std, smol, etc.

So what is the runtime in Rust?

Answer 1

There is no "the runtime" in Rust.

A runtime, in the context of your quote, is something which can execute asynchronous tasks / futures (an executor), usually bundled with utilities for synchronisation, IO, ...: while the Rust standard library contains the building blocks for asynchronous execution (a few traits and the async and await keywords) it provides no actual way to create, synchronise, or execute asynchronous tasks.