XNIO Concepts

Internal

• XNIO
• Undertow Concepts

Overview

XNIO is a simplified low-level I/O layer, built in top of Java NIO. It has an API for combining blocking and non-blocking operations, even on the same channel.

NIO Concepts

• NIO ByteBuffer

XNIO Worker

• https://docs.jboss.org/author/display/XNIO/Workers
• http://docs.jboss.org/xnio/3.1/api/index.html?org/xnio/XnioWorker.html

An XNIO worker is the central point of coordination for a network application. It manages several kind of threads, and the threads created by the worker are tagged with the worker name. A worker has two different types of thread pools:

I/O Thread

The I/O threads run non-blocking handlers. They run in a loop, which does three things:

1. runs any tasks that have been scheduled for execution by the I/O thread
2. runs any scheduled tasks that have hit their timeout
3. call Selector.start() and then invoke any callbacks for the selected keys.

The I/O must never perform blocking operations because they are responsible for multiple connections, so while the operation is blocking, the other connections will essentially hang.

The I/O threads come in two types:

• Read threads that can handle callbacks for read events.
• Write threads that can handle callback for write events.

Worker Thread

Worker threads are used for blocking tasks (such as servlet invocations). The worker threads are managed by a standard Executor-based thread pool.

Channel

XNIO provides a channel abstraction that hides the underlying transport. Channels are notified of events using the ChannelListener API. Upon creation, channels are assigned an I/O Thread, which will be used to execute all ChannelListener invocations for the channel.