## Problem
`RunEventLoop` span through its body regardless of whether there was anything to do — ~10% of a desktop core for an empty shard, and ~70% of a core on a 3 vCPU VPS. A process that never idles is exactly what burstable vCPU plans throttle, which is how this surfaced: lag spikes that went away when the operator bought more cores. The spin also denied the GC its natural pause points, so memory climbed until a world save forced a collection — alarming in task manager, harmless in practice, and a recurring source of "is my server leaking?" reports.
## Result
Windows desktop, real world of **190,728 items / 33,158 mobiles**, no players, saves and prebake off, three consecutive runs:
| | Legacy spin | Idle sleeping |
|---|---|---|
| **CPU** | 10.42 – 10.50% of one core | **0.78 – 1.00%** |
| **Tick lag** (peak/15s) | 4–10 ms | 5–11 ms |
**~10× less CPU with tick lag unchanged** — the CPU came free rather than being traded for latency. Slower hosts gain proportionally more. Spin mode (`server.eventLoopIdleWaitMs=0`) independently gained **7× the iterations per core** (1.19M → 8.3M cycles/sec) from the ring's AcceptEx rework.
## How
The loop blocks in `NetState.WaitForCompletion` whenever every queue it drains is empty (all the drains are bounded, so leftovers keep it awake). Receive completions, new connections, and cross-thread `LoopContext.Post` (via the ring'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 the idle wait.
**Health is measured at the only place sleeping can cause harm.** A sleep is bounded by the time to the next wheel turn, so a correctly honoured sleep can never miss a deadline — the only failure mode is the host returning the wait late. That overshoot is measured on every sleep (one extra timestamp read; production's entire accounting cost), and an escalating backoff suspends sleeping when it persists. By construction, server work — saves, heavy staff commands, deep timer callbacks — cannot trip it, so the warning means exactly one thing: *the host is not scheduling the process promptly*, with two known remedies (dedicated CPU, or `=0`). Hosts with no high-resolution wait mechanism at all are detected once at startup and spin instead.
**CPS is removed.** `Core.CyclesPerSecond`/`AverageCPS` measured nothing actionable before and became actively misleading once the loop sleeps (the rate is set by the sleep, not by shard health). The admin gump's Performance page now shows the verdict instead: `Healthy` / `Sleep suspended (host)` / `Spinning (configured)`.
## Configuration
| Setting | Default | Meaning |
|---|---|---|
| `server.eventLoopIdleWaitMs` | `2` | Longest idle block. Measured across 1/2/4/8 ms, 2 is where the trade stops being free. `0` = never sleep: ~98% of a core, zero scheduling overhead — for large shards on dedicated CPU. |
| `server.lateWakeThreshold` | `1` | Idle waits the host may return a full tick late, per second, before sleeping backs off. Raise for jittery hosts; very high disables the backoff. |
## Diagnostics (compiled out by default)
`dotnet build -p:EventLoopProfiling=true` compiles in `EventLoopProfiler` — every hook is `[Conditional("EVENT_LOOP_PROFILING")]`, so normal builds contain zero profiling IL. The profiling build decomposes each second of wall time into **work (per loop phase) / sleep / GC pause / stolen residual**, keeps ~15 minutes of history in a ring buffer, and the `[LoopStats` command prints the last minute and dumps the full history to CSV. `dev-docs/debugging-event-loop.md` is the diagnosis guide (for humans and AI): what production already tells you, when to flip the profiling build, the signature table for host-steal vs deep-processing vs GC vs wake bugs, why dotnet-trace comes last, and the GC/RAM "leak" misconception.
## Verification
- 815 Server.Tests green; both build configurations compile.
- Docker echo harness green on epoll and io_uring (ping-pong mode); kqueue verified manually on an M1 Max.
- A/B measurements and per-change numbers: `measure/event-loop` branch.
## Notes
The full measurement harness and vendored ring sources used to develop this live on the [`measure/event-loop`](https://github.com/modernuo/ModernUO/tree/measure/event-loop) branch, kept for future loop work.
**Only one functional change**
* Fixes a bug in LogFactory where `Warning` is being logged as `Information`
Non-functional changes:
* Updates/Fixes copyright headers
* Removes namespace scopes for core files.
View with [whitespace off](https://github.com/modernuo/ModernUO/pull/1187/files?w=1).
### Changes/Fixes:
* Adds timer pooling.
* Allows pool to be configurable in ModernUO.json
* Pool replenishes itself asynchronously if depleted.
* Fixes an issue with barkeeps and town criers
* Fixes an issue with incognito buff icons not being removed
* Fixes an issue with polymorph name mod not being removed
* Fixes several places where timers go on forever even after an object is deleted, keeping a reference (memory leak)
* Eliminates the timer for MiningCart altogether.
* Deletes `AcidSlime` since it is a duplicate of `PoolOfAcid`
* Fixes HonorableExecution and standardizes the code for other Bushido moves.
## Changes to the Timer API:
```cs
public class Timer
{
// Creates a timer that will be returned to the pool once execution stops.
public static void StartTimer(Action callback);
public static void StartTimer(TimeSpan delay, Action callback);
public static void StartTimer(TimeSpan delay, TimeSpan interval, Action callback);
public static void StartTimer(TimeSpan interval, int count, Action callback);
public static void StartTimer(TimeSpan delay, TimeSpan interval, int count, Action callback);
// Creates a timer and returns a token for more control. Requires manual cancellation in order for the timer to be returned to the pool.
// If the token is dereferenced, the timer will be dereferenced too. While not returning a timer to the pool is not considered hazardous, it does defeat the purpose of pooled timers.
public static void StartTimer(Action callback, out TimerExecutionToken token);
public static void StartTimer(TimeSpan delay, Action callback, out TimerExecutionToken token);
public static void StartTimer(TimeSpan delay, TimeSpan interval, Action callback, out TimerExecutionToken token);
public static void StartTimer(TimeSpan interval, int count, Action callback, out TimerExecutionToken token);
public static void StartTimer(TimeSpan delay, TimeSpan interval, int count, Action callback, out TimerExecutionToken token);
// If you aren't sure how to use the API above, or you don't care about performance, then you can use the old RunUO Timer.DelayCall
public static DelayCallTimer DelayCall(Action callback);
public static DelayCallTimer DelayCall(TimeSpan delay, Action callback);
public static DelayCallTimer DelayCall(TimeSpan delay, TimeSpan interval, Action callback);
public static DelayCallTimer DelayCall(TimeSpan interval, int count, Action callback);
public static DelayCallTimer DelayCall(TimeSpan delay, TimeSpan interval, int count, Action callback);
}
public struct TimerExecutionToken
{
public bool Running { get; }
public int Index { get; }
public int RemainingCount { get; }
public DateTime Next { get; }
}
```
## When to use `TimerExecutionToken`?
Use tokens when you want to gain the performance benefit of using a pooled timer, but you need one of the following:
* Access to the next time the timer will tick:`token.Next`
* Access to which interval, how many intervals there are, or how many are remaining: `token.Index`, `token.Count`, and `token.RemainingCount`
* Stop a timer manually.
* Determine if the timer is running: `timer.Running`
* See notes below about requirements for using tokens!
## Notes about using the TimerExecutionToken:
When you opt-in to receive a token, you must call `Cancel()` to return the timer. This can be done inside of the callback, or outside of the callback at any time.
If this is not called and your timer is an infinite interval, then you will create a potential memory leak, or null pointer exception in your callback.
If the timer ends and is stopped, but cancel is not called, then the timer will never return to the pool and stay referenced until the token is deleted or cancel is called. (Memory leak)
## Is this thread safe?
No. The ModernUO timer system is not thread safe at all. If you require a thread safe timer system, contact me and I'll help adapt this system. Keep in mind that there is a massive performance hit to make this thread safe when there are literally no use cases for it.
If you need to synchronize execution, meaning you want to execute code from another thread on the core thread. Let's say you have a discord bot that is pushing commands to the game server. Then use `EventLoopContext.Post(SendOrPostCallback callback, object state);`.
- [X] Cleans up gump packets
- [X] Adds event loop task synchronization
- [X] Moves timer pause and cleans up the delay task timer class
- [X] Cleans up the conserve cpu
- [X] Renames variables to make them consistent with the new style
- [X] Removes process delta recursion checking.
- [X] Properly diposes net states. This fixes edge cases that may cause hanging connections to stay open longer than they should.
- [X] Fixes an issue with gump items not compiling properly
Users can now utilize `Timer.Pause()` since the code will be executed on the proper thread.
```cs
public void async void Talk()
{
_canTalk = false;
await Timer.Pause(Utility.RandomMinMax(5000, 8000)); // Talk after 5-8 seconds
DoTalk();
await Timer.Pause(Utility.RandomMinMax(12000, 25000)); // Reset ability to talk after 12-25 seconds
_canTalk = true;
}
```
