ModernUO/README.md at 6aedbbe2efa4749cb3532b46832e4a905fb3b8ef

perf(core): sleep the event loop when idle

The loop span through its body regardless of whether there was anything
to do -- ~10% of a desktop core for an empty shard, ~70% of a small VPS
core, and a process that never idles is exactly what burstable vCPU
plans throttle.

The loop now blocks in NetState.WaitForCompletion whenever every queue
it drains is empty, waking on the next timer tick or the moment work
arrives. Receive completions, new connections, and cross-thread
LoopContext.Post (via IORingGroup 1.0.10's sticky Wake) are all in the
wait set, so sleeping adds no latency to any of them; only timer-driven
logic sees wheel lag, bounded by server.eventLoopIdleWaitMs (default
2ms, 0 = never sleep).

Measured on a real world of 190k items / 33k mobiles: 10.4% of a core
to 0.8-1.0%, with peak tick lag unchanged. Spin mode independently
gained 7x the iterations per core from the ring's AcceptEx rework.
Sleeping also gives the GC natural pause points, which the old spin
loop denied it -- memory no longer climbs until a save forces a
collection.

A sleep is bounded by the next wheel turn, so a correctly honoured
sleep can never miss a deadline; the only way sleeping harms the wheel
is the host returning the wait late. That overshoot is measured on
every sleep, and an escalating backoff (server.lateWakeThreshold)
suspends sleeping when it persists -- server work like saves or heavy
commands cannot trip it by construction. Hosts without high-resolution
waits are detected once at startup and spin instead. The admin gump
shows the verdict instead of the now-meaningless CPS figure, which is
removed.

Time accounting for diagnosis is compiled out of normal builds: build
with -p:EventLoopProfiling=true to enable EventLoopProfiler (per-phase
wall time, sleep overshoot, GC pauses, stolen-time residual, ~15min
ring buffer) and the [LoopStats command with CSV dump. See
dev-docs/debugging-event-loop.md for the diagnosis funnel.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

2026-08-09 12:53:48 -07:00

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Ultima Online Server Emulator for the modern era!

Requirements

Supported Operating Systems

Required Frameworks

All Operating Systems

Windows

Hardware

Use	vCPU	RAM	Storage
Development / test	2 dedicated	2 GB	SSD
Small live shard (< 50 concurrent)	4 dedicated	4 GB	NVMe
Medium (50–200)	4–8	8 GB	NVMe
Large (200+)	8+, high clock	16 GB+	NVMe

Game logic is single-threaded, so single-core clock speed matters more than core count, and dedicated vCPU matters more than either — burstable or shared plans throttle once credits run out, which is the most common cause of unexplained lag spikes. Save size drives RAM more than player count does.

See dev-docs/server-requirements.md for the reasoning and tuning options.

Development

Supported IDEs

Getting Started

Install prerequisite requirements
Clone this repository (or download the latest):
- git clone https://github.com/modernuo/ModernUO.git
Open ModernUO.sln to start developing

Building/Publishing

Interactive Mode (Recommended for new users)

Run ./publish.cmd (Windows) or ./publish.sh (Linux/macOS) with no arguments to launch the guided build tool. It will:

Check prerequisites (.NET SDK, native libraries)
Walk you through configuration and platform selection
Build and publish the server to the Distribution directory
Show deployment instructions for cross-compiled builds

Command Line

./publish.cmd [release|debug] [os] [arch]

os - Supported operating systems
- win - Windows
- osx - macOS
- linux - Linux
arch
- x64 - Intel/AMD 64-bit
- arm64 - ARM 64-bit

Linux Prerequisites

Fedora, CentOS, RHEL, AlmaLinux, Rocky, etc

dnf upgrade --refresh -y
# RHEL-family distributions (CentOS Stream, AlmaLinux, Rocky, RHEL) need CRB and EPEL enabled.
# Fedora skips this block.
dnf install -y dnf-plugins-core
dnf config-manager --set-enabled crb
dnf install -y epel-release
# Prerequisites
dnf install -y findutils libicu libdeflate libargon2 tzdata

Ubuntu, Debian, etc

apt-get update -y
# The ICU runtime package carries the ABI version in its name (libicu74, libicu76, …) and has no
# stable alias, so match it by pattern rather than pinning a release-specific name.
apt-get install -y '^libicu[0-9]+$' libdeflate0 libargon2-1 tzdata

Only the runtime libraries are needed — the -dev/-devel packages are not. Run ./build-tool --check-prereqs to check the current machine and print the exact packages your release needs.

zstd is not listed because ZstdNet bundles libzstd for every platform, and liburing is not listed because IORingGroup issues io_uring syscalls directly.

If the shard's configured time zone is a legacy alias such as US/Eastern, Debian 12 and Ubuntu 24.04 also need tzdata-legacy. See Platform Prerequisites for what each dependency is for and what breaks without it.

OSX Requirements

brew install icu4c libdeflate argon2

Running the Server

Follow the publish instructions
The Distribution directory is portable — copy it to your production server for deployment
Run ModernUO.exe or dotnet ModernUO.dll from the Distribution directory
On first run, the server will prompt you to configure game data file locations

Troubleshooting / FAQ

See FAQ

Thank you for supporting us! You can find out how by visiting the sponsors page.

Collaborators

Thanks

RunUO Team & Community
Voxpire, the ServUO Team & Community
Karasho, Jaedan and the ClassicUO Community

Development Tools & Plugins provided with ♥ by

Code Signing Policy

Free code signing provided by SignPath.io, certificate by SignPath Foundation.

This program will not transfer any information to other networked systems unless specifically requested by the user or the person installing or operating it

Teams & Roles

Approvers & Committers: Development Team

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ModernUO