Netty Loom Experiment

This repository contains Project Loom and Netty related test code.

Contents / Goals

I created these examples since I was curious about Project Loom and what it would mean for my Netty based Vert.x projects.

Netty

In my first test I created a regular netty server which makes use of the NioEventLoopGroup. A custom thread factory is used to enable Netty to use VirtualThreads instead of platform threads.

I went further down the rabbit hole since I wanted to check whether it would be possible to use on-demand virtual threads instead of pooling virtual threads. I thus created the LoomNioEventLoopGroup. Unfortunatly my knowledge of selector based IO is very limited and I did not yet find a way to change the request handling.

For comparison I also created the #testPlatformThreads variant which uses regular platform threads.

NIO

In order to further experiment with NIO Server handling I created a few additional testcases to check whether there are other potential ways to make use of virtualthreads.

The SimpleAsyncSocketServerTest contains a basic NIO server which only uses platform threads. I started from here to learn more about AsynchronousServerSocketChannel.

In the NioServerExampleTest I use virtual threads to handle previously accepted connections. Actually I'm a bit surprised that this example even works since the selector in the thread is registered after the connection has been accepted.

Next I had the idea to use the AsynchronousServerSocketChannel which has the benefit that it can accept callbacks for request handling. The #testServerWithFork test forks a dedicated virtual thread in the accept handler for each connection. The #testServerWithGroup uses the option to setup a AsynchronousChannelGroup to handle threading internally. This is similar to Netty as it works with a dedicated thread pool.

Loom

During my testing I noticed that Netty would not be able to process requests when I configured a thread pool size of 500+. I created the LoomThreadTest to replicate this issue and found that the JVM would not run / start a virtual thread of 400+ previous threads were calling new Selector().select(). I'm not yet sure why this is the case.

Used Versions:

• Netty Version: 4.1.70.Final-SNAPSHOT@77b7c1a56dcd4fc964137f21caf321a1ca19c0ed
• JVM / JDK - Loom EA Build:

openjdk version "18-loom" 2022-03-15
OpenJDK Runtime Environment (build 18-loom+5-274)
OpenJDK 64-Bit Server VM (build 18-loom+5-274, mixed mode, sharing)