Highly Performant & Scalable Ultima Online Server Emulator
https://www.modernuo.com
c-sharpcsharpcsharp-coredotnetdotnet-coreemulatorgplgplv3mmommo-enginemmorpgmmorpg-serveronlinerpgrunuoserverservuoultimaultima-onlineuo
294dcd94a0
## Summary Two related fixes on the outbound path: 1. Consume **IORingGroup 1.0.8**, which allows more than one send in flight per socket, and expose the two settings that go with it. 2. Stop `NetState.Send` silently discarding packets when the send buffer fills — including an out-of-bounds write reachable in that state. ## 1. Send-path stall (RIO) RIO reports send completion on **acknowledgement**, not on copy, so a completion cannot arrive sooner than one round trip. With one send in flight, `PostSend` refused to post again until the previous completion arrived — capping a connection at **one send per RTT** whenever it had data queued. Measured on a 50ms-RTT production shard: | | before | after | |---|---|---| | in-game latency, data flowing | **101–146 ms** | **48–51 ms** | | p95 | ~135 ms | 52.8 ms | | samples > 70 ms | 20 | **0** | The control that confirms the mechanism: server-side post→completion was **unchanged** at median 92ms across both runs. The ACK-binding is inherent to RIO and did not move; only its propagation into application latency did. Two things worth recording, because they explain why this went unnoticed: - As little as **6 bytes** of queued data held the gate shut, so it reproduced in empty areas, not just crowded ones. - The same measurement at loopback RTT is **microseconds**, so local testing could never surface it. New settings, both restart-time: - **`network.maxOutstandingSends`** (default 32) — sends in flight per connection. Honoured by RIO only; other backends complete sends on copy and report 1. Costs a request-queue and completion-queue slot per send, **not another buffer**, since every outstanding send addresses a different range of the same registered buffer. Worst-case added latency is roughly `completion RTT / value`. - **`network.sendBufferSize`** (default 256KB) — per-connection send buffer, coerced to a power of two of at least the platform allocation granularity. This is the lever for the disconnects below, and the per-connection memory ceiling. ## 2. Send buffer full `NetState.Send` had three failure modes once the buffer filled, none of them visible: | writable | behaviour | |---|---| | `0` | `GetSendBuffer` returned false → **packet dropped**, no log, no disconnect | | `4 … needed-1` | `Compress` returned 0 → `CommitWrite(0)` → **packet dropped** the same way | | `1 … 3` | `safeOutputLength = (nuint)output.Length - 4` **underflows** → hot-loop bounds check never trips → **writes past the span** | The first two leave a client connected while quietly missing game state, which is undiagnosable from either end. The third corrupts the in-flight region of the ring buffer, and is reachable precisely when a connection is congested, since callers only check for non-zero space. `Compress` now refuses an output too small to bound, and `Send` reports exhaustion instead of dropping — logging and disconnecting with **needed / writable / unacked / capacity**. Those numbers separate a slow client holding the buffer from a buffer genuinely too small for the shard, which is the case that warrants raising `network.sendBufferSize`. ## Testing `NetworkCompressionBoundsTests` covers the underflow using sentinel bytes around the output window. **Verified to fail without the guard** (4 failures from overwritten sentinels), confirming the out-of-bounds writes were real rather than theoretical. Full suites green: **788 Server.Tests**, **597 UOContent.Tests**, Release build clean against the published 1.0.8. ## Notes for reviewers - Upstream change: modernuo/IORingGroup#9. - The buffer-full path is now *loud* where it used to be silent. If a shard has been quietly dropping packets under load, this will surface as disconnects — that is the intended outcome, and the log line says which setting to raise. - Follow-up under discussion: promoting a connection to a larger buffer instead of disconnecting, which looks feasible on a live connection since buffers are referenced per-operation rather than bound to the request queue. |
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| LICENSE | ||
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| README.md | ||
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ModernUO 
Ultima Online Server Emulator for the modern era!
Requirements
Supported Operating Systems
Required Frameworks
All Operating Systems
Windows
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-devel zstd libargon2-devel liburing-devel
Ubuntu, Debian, etc
apt-get update -y
apt-get install -y libicu-dev libdeflate-dev zstd libargon2-dev liburing-dev
OSX Requirements
brew install icu4c libdeflate zstd 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