Tokio (software)

Last updated
Tokio
Original author(s) Carl Lerche
Initial releaseDecember 23, 2020;4 years ago (2020-12-23)
Stable release
1.47.1 [1]   OOjs UI icon edit-ltr-progressive.svg
Repository
Written in Rust
Operating system macOS, Windows, Linux, FreeBSD, WebAssembly
Type Asynchronous runtime
License MIT License
Website tokio.rs

Tokio is a software library for the Rust programming language. It provides a runtime and functions that enable the use of asynchronous I/O, allowing for concurrency in regards to task completion. [2] [3] [4]

Contents

Tokio was released in August 2016 for Rust, a general-purpose programming language. Developed by Carl Lerche, Tokio began as a network application framework and supports features such as socket listening and broadcasting, allowing messages to be transferred between computers.

History

Tokio began in August 2016 by Carl Lerche as a network application framework for Rust built on futures, allowing for network-based middleware and a non-blocking, or asynchronous, implementation of readiness interest to the reactor. Tokio was inspired by Finagle, a Scala-based asynchronous remote procedure call (RPC) system developed at Twitter for Java virtual machines (JVM), allowing distributed systems to communicate within a JVM. Tokio utilizes the lower-level Rust crate mio, itself using system calls such as epoll (Linux), kqueue (FreeBSD), and the input/output completion port (IOCP) API (Windows). For Linux it can also use io_uring via tokio-uring. [5] [6] [7] The name "Tokio" is derived from Tokyo and mio, and the Tokio logo vaguely resembles the city emblem of Tokyo. [8] The preliminary version of Tokio was released in January 2017, [9] followed by a full release in December 2020. [10] [11] In 2017, Tokio received a grant from the Mozilla Open Source Support fund. [12] In April 2021, Tokio funded its first paid contributor, Alice Ryhl, for her work both developing the project and assisting its users. [13] [14]

While Rust has supported asynchronous functions since version 1.39, released in November 2019, [15] it provides no facilities to execute them, requiring an external runtime for that purpose. [16] Tokio provides a runtime that uses a multi-threaded work stealing scheduler. [10] Rust's futures are lazily evaluated, requiring functions to call .await before they do any work. [17] When .await is invoked, Tokio's runtime may pause the original future until its I/O completes, and unpauses a different task that is ready for further processing. [18]

Users of Tokio include the development teams behind Discord and AWS Lambda. [10] The JavaScript and TypeScript runtime Deno uses Tokio under the hood, in comparison to the JavaScript runtime Node.js, which uses the libuv library. [19]

Features

Runtime

Tokio allows for the execution of asynchronous functions in Rust through its built-in runtime, which may be initialized via the #[tokio::main] macro. [18] For example:

usestd::error::Error;#[tokio::main]asyncfnmain()->Result<(),Box<dynError>>{leturl="https://en.wikipedia.org/";lettext=reqwest::get(url).await?.text().await?;println!("{}",text);Ok(())}

Here, the reqwest crate is used to request the HyperText Markup Language (HTML) for English Wikipedia. After reqwest::get is called to initialize the asynchronous request, .await will hand over control to the runtime, which then drives all the I/O operations of the request to completion before resuming the main function after the .await.

A simple example of a TCP echo server is as follows:

usestd::error::Error;usetokio::io::{AsyncBufReadExt,AsyncWriteExt,BufReader};usetokio::net::TcpListener;#[tokio::main]asyncfnmain()->Result<(),Box<dynError>>{// Run a server on port 8080.letlistener=TcpListener::bind("localhost:8080").await?;loop{// Wait for a new connection from a client.let(mutstream,_remote_addr)=listener.accept().await?;// Spawn a new asynchronous task to handle the connection.tokio::spawn(asyncmove{let(reader,mutwriter)=stream.split();letmutreader=BufReader::new(reader);// While there is data to be read from the stream…while!reader.fill_buf().await.unwrap().is_empty(){// Write the data back.writer.write_all(reader.buffer()).await.unwrap();}});}}

This code makes use of the tokio::spawn function to create an asynchronous task (implemented as a stackless coroutine), allowing each connection to be handled separately in the same process, as the runtime ensures that tasks run in the background automatically. [20] Importantly however, the runtime multiplexes the tasks’ execution on a single thread pool (whose size is by default equal to the number of processors on the system), and so in comparison to the approach of spawning a separate thread for each task, fewer resources are consumed.

Asynchronous I/O and timers

Tokio provides several I/O and timing primitives that work natively inside its runtime. The TcpListener structure used above contains a Transmission Control Protocol (TCP) socket listener that is registered with the runtime, allowing it to be used asynchronously; similarly, the tokio::time::sleep function can be used to suspend a task’s execution for a certain duration of time, and again this is implemented by registration with the runtime. [21]

Synchronization primitives

Tokio also provides several generic synchronization primitives suitable for use in an asynchronous context, including locks, semaphores, barriers and channels. [22] Unlike the I/O and timer primitives, these work even outside of the runtime context. [23]

Blocking thread pool

To facilitate interopability with traditional synchronous code, Tokio provides as part of its runtime a thread pool on which synchronous I/O operations may run. [24] In particular, tokio::task::spawn_blocking creates a task which runs in this pool, and is allowed to perform blocking operations—this is unlike tokio::spawn, which may only run asynchronous code. [25] For example, this is used to implement filesystem operations, as many platforms do not provide native asynchronous filesystem APIs (an exception to this is Linux’s io_uring, however support for this exists only in the external tokio_uring library and is not yet built in). [26]

References

  1. ↑ "Release 1.47.1". 1 August 2025. Retrieved 14 August 2025.
  2. ↑ Chanda, Abhishek (2018). Network Programming with Rust: Build fast and resilient network servers and clients by leveraging Rust's memory-safety and concurrency features. Birmingham: Packt Publishing. ISBN   978-1-78862-171-7. OCLC   1028194311.
  3. ↑ Sharma, Rahul (2019). Mastering Rust : learn about memory safety, type system, concurrency, and the new features of Rust 2018 edition. Vesa Kaihlavirta (Second ed.). Birmingham, UK. ISBN   978-1-78934-118-8. OCLC   1090681119.{{cite book}}: CS1 maint: location missing publisher (link)
  4. ↑ De Simone, Sergio (2021-01-06). "Rust Asynchronous Runtime Tokio Reaches 1.0". InfoQ. Retrieved 2021-11-21.
  5. ↑ Lerche, Carl (August 3, 2016). "Announcing Tokio" . Retrieved December 11, 2022.
  6. ↑ "Finagle: A Protocol-Agnostic RPC System". August 19, 2011. Retrieved December 11, 2022.
  7. ↑ Gomez, Guillaume; Boucher, Antoni (2018). Rust Programming By Example: Enter the World of Rust by Building Engaging, Concurrent, Reactive, and Robust Applications. Birmingham: Packt Publishing. ISBN   9781788470308.
  8. ↑ Lerche, Carl (August 3, 2016). "I enjoyed visiting Tokio (Tokyo) the city and I liked the "io" suffix and how it plays w/ Mio as well. I don't know... naming is hard so I didn't spend too much time thinking about it". Reddit . Retrieved December 11, 2022.
  9. ↑ Lerche, Carl; Crichton, Alex; Turon, Aaron. "Announcing Tokio 0.1" . Retrieved December 11, 2022.
  10. 1 2 3 Krill, Paul (2021-01-08). "Tokio Rust runtime reaches 1.0 status". InfoWorld . Retrieved 2021-09-03.
  11. ↑ Lerche, Carl. "Announcing Tokio 1.0" . Retrieved December 11, 2022.
  12. ↑ "Mozilla Awards $365,000 to Open Source Projects as part of MOSS". LWN.net. Retrieved 2021-11-21.
  13. ↑ "Welcoming Alice Ryhl as the first paid Tokio contributor". Tokio. Retrieved 2021-11-28.
  14. ↑ Allen Wyma (12 November 2021). "Tokio Ecosystem with Alice Ryhl". Rustacean Station (Podcast). Retrieved 2021-11-26.
  15. ↑ "Rust Gets Zero-Cost Async/Await Support in Rust 1.39". InfoQ. Retrieved 2021-11-28.
  16. ↑ "The Async Ecosystem". Asynchronous Programming in Rust. Retrieved 2021-11-28.
  17. ↑ Matsakis, Niko (2019-11-07). "Async-await on stable Rust!". Rust Blog. Retrieved 2021-11-28.
  18. 1 2 "Hello Tokio". Tokio. Retrieved 2021-11-28.
  19. ↑ Rappl Moraza, Florian (2022). Modern Frontend Development with Node.js: A Compendium for Modern JavaScript Web Development Within the Node.js Ecosystem. Birmingham, UK. ISBN   9781804617380.{{cite book}}: CS1 maint: location missing publisher (link)
  20. ↑ Tokio Contributors (2025-07-04). "Module task" . Retrieved 2025-07-18.
  21. ↑ Lerche, Carl (2018-03-30). "New Timer implementation" . Retrieved 2025-07-18.
  22. ↑ Tokio Contributors (2025-07-04). "Module sync" . Retrieved 2025-07-18.
  23. ↑ Lerche, Carl (2020-04-01). "Reducing tail latencies with automatic cooperative task yielding" . Retrieved 2025-07-18.
  24. ↑ Tokio Contributors (2025-07-04). "Function spawn_blocking" . Retrieved 2025-07-18.
  25. ↑ Ryhl, Alice (2020-12-21). "Async: What is blocking?" . Retrieved 2025-07-18.
  26. ↑ Tokio Contributors (2025-07-04). "Module fs" . Retrieved 2025-07-18.
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