chore: prepare v0.6.21 release

This removes the `=` dependency on an older `cfg-if` version.
3 files changed
tree: 6decd2f285d895266ce261779ddd4cd811e5df7c
  1. benches/
  2. ci/
  3. src/
  4. test/
  5. .cirrus.yml
  6. .gitignore
  7. azure-pipelines.yml
  8. Cargo.toml

Mio – Metal IO

Mio is a lightweight I/O library for Rust with a focus on adding as little overhead as possible over the OS abstractions. MIT licensed Build Status Build Status

API documentation

This is a low level library, if you are looking for something easier to get started with, see Tokio.


To use mio, first add this to your Cargo.toml:

mio = "0.6"

Then, add this to your crate root:

extern crate mio;


  • Non-blocking TCP, UDP.
  • I/O event notification queue backed by epoll, kqueue, and IOCP.
  • Zero allocations at runtime
  • Platform specific extensions.


The following are specifically omitted from Mio and are left to the user or higher-level libraries.

  • File operations
  • Thread pools / multi-threaded event loop
  • Timers


Currently supported platforms:

  • Linux
  • OS X
  • Windows
  • FreeBSD
  • NetBSD
  • Solaris
  • Android
  • iOS

There are potentially others. If you find that Mio works on another platform, submit a PR to update the list!


A group of Mio users hang out in the #mio channel on the Mozilla IRC server ( This can be a good place to go for questions.


Interested in getting involved? We would love to help you! For simple bug fixes, just submit a PR with the fix and we can discuss the fix directly in the PR. If the fix is more complex, start with an issue.

If you want to propose an API change, create an issue to start a discussion with the community. Also, feel free to talk with us in the IRC channel.

Finally, be kind. We support the Rust Code of Conduct.