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Reduce FSM<TState, TData> allocations - #6145
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* Made `Event` a `readonly struct` * Eliminated unnecessary `List<object>` allocations * Cleaned up XML-DOC comments
Aaronontheweb
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Aaronontheweb
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Described API and memory allocation changes.
| public override string ToString() { } | ||
| } | ||
| public sealed class Event<TD> : Akka.Actor.INoSerializationVerificationNeeded | ||
| public struct Event<TD> : Akka.Actor.INoSerializationVerificationNeeded |
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Technically a binary breaking change maybe, but it's source compatible.
| public static Akka.Actor.FSMBase.StateTimeout Instance { get; } | ||
| } | ||
| public class State<TS, TD> : System.IEquatable<Akka.Actor.FSMBase.State<TS, TD>> | ||
| public sealed class State<TS, TD> : System.IEquatable<Akka.Actor.FSMBase.State<TS, TD>> |
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sealed the State class for better perf.
| public State(TS stateName, TD stateData, TimeSpan? timeout = null, Reason stopReason = null, IReadOnlyList<object> replies = null, bool notifies = true) | ||
| { | ||
| Replies = replies ?? new List<object>(); | ||
| Replies = replies ?? Array.Empty<object>(); |
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Eliminated unnecessary List<object> allocation.
| internal State<TS, TD> WithNotification(bool notifies) | ||
| { | ||
| // don't bother allocating even a stack type if the notifies value is identical. | ||
| if (Notifies == notifies) |
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Don't return a new copy of this object if the current Notifies value matches the new one (it usually does.)
| /// </summary> | ||
| /// <typeparam name="TD">The state data for this event</typeparam> | ||
| public sealed class Event<TD> : INoSerializationVerificationNeeded | ||
| public readonly struct Event<TD> : INoSerializationVerificationNeeded |
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We allocate one of these for every message we process, so changing to a readonly struct here greatly reduces Gen 0 / 1 GC.
| public State<TState, TData> Stay() | ||
| { | ||
| return GoTo(_currentState.StateName).WithNotification(false); | ||
| return _currentState.WithNotification(false); |
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Biggest memory savings - don't allocate a new State object each time we call Stay. Re-use the same value.
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FWIW, there's no benefit to copying the same state over and over again here. The Reason, Replies properties et al don't have any effects when used here in combination with WithNotification(false).
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Looked at making |
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Looks like this change definitely caused an issue with the |
Spec could also be racy - worked on my machine. |
Nope, definitely an error related to my changes. Will investigate. |
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Benchmarks based on latest changes. BenchmarkDotNet=v0.13.1, OS=Windows 10.0.19044.2006 (21H2)
AMD Ryzen 7 1700, 1 CPU, 16 logical and 8 physical cores
.NET SDK=6.0.201
[Host] : .NET 6.0.3 (6.0.322.12309), X64 RyuJIT
DefaultJob : .NET 6.0.3 (6.0.322.12309), X64 RyuJIT
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* close akkadotnet#2560 - added performance benchmarks for FSM * Improved FSM memory consumption * Made `Event` a `readonly struct` * Eliminated unnecessary `List<object>` allocations * Cleaned up XML-DOC comments * don't return new `State<TState, TData>` during `Stay()` * API approvals * fixed `State<TS.,TD>` errors
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Changes
Reduced some unnecessary allocations inside the
FSM<TState, TData>class.Checklist
For significant changes, please ensure that the following have been completed (delete if not relevant):
Latest
v1.4BenchmarksThis PR's Benchmarks
48% memory reduction, 14% throughput improvement