6aedbbe2ef
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>
69 lines
1.7 KiB
C#
69 lines
1.7 KiB
C#
using Xunit;
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namespace Server.Tests;
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/// <summary>
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/// The event loop only sleeps when every queue it drains is empty. These drains are deliberately
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/// bounded -- ExecuteTasks stops at its per-frame cap -- so leftover work is normal and must keep
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/// the loop awake. Getting this wrong strands queued work for the length of a sleep.
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/// </summary>
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[Collection("Sequential Server Tests")]
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public class EventLoopIdleTests
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{
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[Fact]
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public void FreshContextIsEmpty()
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{
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var context = new EventLoopContext();
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Assert.True(context.IsEmpty);
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}
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[Fact]
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public void PostedWorkMakesContextNonEmpty()
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{
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var context = new EventLoopContext();
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context.Post(() => { });
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Assert.False(context.IsEmpty);
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}
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[Fact]
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public void PriorityWorkMakesContextNonEmpty()
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{
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var context = new EventLoopContext();
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context.Post(() => { }, EventLoopContext.Priority.High);
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Assert.False(context.IsEmpty);
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}
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[Fact]
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public void ContextIsEmptyAgainOnceDrained()
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{
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var context = new EventLoopContext();
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context.Post(() => { });
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context.ExecuteTasks();
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Assert.True(context.IsEmpty);
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}
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[Fact]
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public void WorkBeyondThePerFrameCapKeepsContextNonEmpty()
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{
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// The cap is what makes IsEmpty necessary: a single ExecuteTasks pass cannot be assumed
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// to have drained everything, so the loop must not treat "I just ran tasks" as "idle".
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const int perFrameCap = 128;
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var context = new EventLoopContext(perFrameCap);
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for (var i = 0; i < perFrameCap + 10; i++)
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{
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context.Post(() => { });
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}
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context.ExecuteTasks();
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Assert.False(context.IsEmpty);
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}
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}
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