Fix assumption about queue order. Fixes #216 .

The mpmc queue can fill slots out of order if a context switch occurs
between "reserving" a slot and marking that slot as filled.

So, insertion into slot 2 can look successful (and cause mio to
increment its own queue length counts) before an insertion into slot 1
is fully committed.

So, then when mio actually reads the queue, it gets None, because
slot 1, the "next" slot, isn't completely done yet.  Yielding the
scheduler to other threads will allow the partially-committed slot
to finish committing, and the queue will eventually be seen as having
both elements, slots 1 and 2.
1 file changed
tree: 1d34dfa4069ba796f43fa2bceda7bc494f3bd8c4
  1. .gitignore
  2. .travis.yml
  4. Cargo.toml
  7. src/
  8. test/

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


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

mio = "0.3.0"

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


  • Signal handling
  • Windows support

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, MIO only supports Linux and Darwin. The goal is to support all platforms that support Rust and the readiness IO model.


Please submit PRs containing links to MIO resources.


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.