XNIO Concepts

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Internal

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

XNIO Worker

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.

For details on how to configure I/O Threads see XNIO Configuration.

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.

For details on how to configure worker threads see XNIO Configuration.

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.

Also see NIO Channel.

ChannelListener

A ChannelListener is a listener for Channel events, such as: channel readable, channel writable, channel opened, channel closed, channel bound, channel unbound.