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]
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:
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.
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]
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]
^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. ISBN978-1-78862-171-7. OCLC1028194311.
^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. ISBN978-1-78934-118-8. OCLC1090681119.{{cite book}}: CS1 maint: location missing publisher (link)
