Highly Performant & Scalable Ultima Online Server Emulator
https://www.modernuo.com
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Reclaiming lapsed holds was O(entries held). Every cap-triggered reclaim during a flood, and every periodic sweep, walked the whole dictionary to find the few that had expired. That is what forced the cap to be sized for the scan rather than for the flood. A hold is now never refreshed: the first detection sets the expiry and later ones leave it alone. That makes insertion order equal to expiry order, so a ring of the same keys is sorted by construction and retiring lapsed entries stops at the first live record -- the cost is the number expiring, not the number held. Nothing is lost by dropping the refresh: the rate limiter runs ahead of the connection filters (NetState.Network.cs) and reports to the ban channel, so a flooder whose hold lapses is re-held on its next attempt. Because the ring carries the expiry, the dictionary only had to answer membership, so it is a HashSet now: 36 bytes a slot against 52. The ring is parallel UInt128[]/long[] rather than an array of structs -- UInt128 forces 16-byte alignment, so a packed pair would cost 32 bytes where these cost 24, and the drain reads only the long[]. Measured, standalone copies of both designs head to head at the shipped 324,449 cap: accept path, nothing held 9.1ns -> 6.1ns per call sustained flood at cap 26.7ms -> 9.3ms over 60k rejected addresses flood end, realistic spread 9.49ms -> 0.05ms worst single call flood end, all at one instant 8.85ms -> 10.69ms The third line is the point: the on-loop stall drops 190x because the work is spread across the calls that were happening anyway. Two honest costs. Total work over that spread rises 1.9x (sequential dictionary scan beats random-access set removes on cache), and the synthetic case where every entry shares one expiry millisecond is 21% worse. Peak latency is the currency for a game loop, and reaching that synthetic case needs an entire flood to land inside one millisecond. The SweepThrottleMs added earlier goes away with the scan it was throttling. The periodic timer stays, now O(expiring), purely to reclaim memory on a shard that goes quiet after a flood. Release now purges the ring record too. Nothing records that a key was released, so a re-detection before the old record lapsed would otherwise be retired early by it. O(n), on an operator retraction. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
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| AGENTS.md | ||
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| FAQ.md | ||
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| global.json | ||
| LICENSE | ||
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| publish.sh | ||
| README.md | ||
| rider-settings.zip | ||
| Rules.ruleset | ||
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ModernUO 
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.slnto 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
Distributiondirectory - Show deployment instructions for cross-compiled builds
Command Line
./publish.cmd [release|debug] [os] [arch]
os- Supported operating systemsarchx64- Intel/AMD 64-bitarm64- 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
Distributiondirectory is portable — copy it to your production server for deployment - Run
ModernUO.exeordotnet ModernUO.dllfrom theDistributiondirectory - On first run, the server will prompt you to configure game data file locations
Troubleshooting / FAQ
- See FAQ
Want to sponsor?
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