Metal IO library for Rust
Rust Shell
Latest commit 43a69f2 Feb 5, 2017 @carllerche Rewrite the readiness queue
The current readiness queue implication has some concurrency bugs. So,
instead of fixing the bug, let's rewrite everything! :)

But more seriously, the current implication has some problems (besides
having bugs):

* It's complicated
* It is not fair when using level-triggered notifications
* It is !Sync

This implication will hopefully resolve the bugs, as well as simplifying
the implementation by reducing all the critical concurrent state for a
given node to a single atomic variable. It also changes the queueing
strategy from a stack to an actual queue based on the 1024cores MPSC
queue. However, this queue is able to reuse the nodes.

The last step in making `Poll` fully `Sync` is to coordinate calls to
`poll`. There can only be one single concurrent call to `poll`.

In order to respect the timeout argument to `poll`, Mutex cannot be used
for coordination. This is due to the lack of a `lock_timeout` function.
Instead, we use a combination of an atomic, a mutex, and a condvar. The
atomic enables a fast path when `Poll` is used on a single thread. In
the event of concurrent calls to `poll`, extra threads block using the
condvar until they are granted access.

MIO - Metal IO

MIO is a lightweight IO library for Rust with a focus on adding as little overhead as possible over the OS abstractions. Build Status Build status

Getting started guide

Currently a work in progress: Getting Started. Feedback can be posted on the PR.

API documentation


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

mio = "0.6"

Then, add this to your crate root:

extern crate mio;


  • Event loop backed by epoll, kqueue.
  • Zero allocations at runtime
  • Non-blocking TCP, UDP and Unix domain sockets
  • High performance timer system
  • Thread safe message channel for cross thread communication

Non goals

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


Currently supported platforms:

  • Linux
  • OS X
  • Windows
  • Android
  • NetBSD

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


Please submit PRs containing links to MIO resources.


  • tokio-core - Underlying event loop for the Tokio project.
  • mioco - Mio COroutines
  • simplesched - Coroutine I/O with a simple scheduler
  • coio-rs - Coroutine I/O with work-stealing scheduler
  • rotor - A wrapper that allows to create composable I/O libraries on top of mio
  • ws-rs - WebSockets based on Mio


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.