Akka.Streams: build island-boundary subscribers without runtime generics (Native AOT) by Aaronontheweb · Pull Request #8732 · akkadotnet/akka.net

Aaronontheweb · 2026-10-02T21:18:20Z

Akka.Streams built the types on every island boundary (BoundarySubscriber<T>, BoundaryPublisher<T>, ActorOutputBoundary<T>, the untyped wrappers, and a few more) with MakeGenericType + Activator. Native AOT trims those constructors, so any stream that crosses an island boundary failed with MissingMethodException. This PR builds each of them from code that already knows T, so AOT apps need no trimmer roots.

Changes

Inlet<T>/Outlet<T> get internal factories for BoundarySubscriber<T>, BoundaryPublisher<T>, ActorOutputBoundary<T> and MaterializedValueSource<T>; the materializer, GraphInterpreterShell.Init and Fusing call them instead of reflecting on the port type.
UntypedSubscriber/UntypedPublisher drop their reflective FromTyped(object) and gain typed operations for sink subscribers, the materialization-panic path (ErrorPublisher<T>/CancellingSubscriber<T>) and ActorSubscription.Create; ProcessorModule wraps its processor with its own TIn/TOut. Panic clean-up is now best effort, so the original materialization failure always surfaces.
The old reflective path stays only for port/publisher/subscriber types implemented outside Akka.Streams, gated on Akka.DynamicTypeLoading (RuntimeGenerics); with the switch off it throws NotSupportedException naming the switch.
SubscriberManagement's TStreamBuffer gets [DynamicallyAccessedMembers(PublicConstructors)], so Sink.AsPublisher(fanout: true) keeps its buffer constructor.
Hosting AOT canary: new StreamsScenarios.cs runs .Async(), AsPublisher→FromPublisher, fan-out, Source.ActorPublisher and a materialized-value graph, each with int and string. Docs: new "Akka.Streams Under Native AOT" section in native-aot.md; the stream-ref error now points to Stream refs under Native AOT: source-generated ISourceRef<T>/ISinkRef<T> fields (no element-type reflection) #8673.

Testing

Hosting AOT canary (linux-x64, no TrimmerRootDescriptor): on dev it fails with MissingMethodException on BoundarySubscriber<Int32> and emits 8 Akka.Streams IL warnings; with this PR it prints [canary-hosting] OK with 0 warnings (baseline stays empty).
Full Akka.Streams.Tests and Akka.API.Tests; new MaterializerSessionSpec covers the sink-subscriber and panic paths and the switch-off NotSupportedException.
Once this merges, the StreamsRoots.xml trimmer-root workaround in Persistence: register plugins in code through Akka.Persistence.Hosting (AOT) #8730's persistence canary (and the Embedded plugin canary) can be deleted.

Breaking changes

Obsoleted (not removed): Construct.Instantiate, TypeExtensions.GetSubscribedType/GetPublishedType.
Otherwise none expected; all other new members are internal.

Closes #8731

…ics (Native AOT) The materializer built BoundarySubscriber<T>, BoundaryPublisher<T>, ActorOutputBoundary<T>, MaterializedValueSource<T>, ActorSubscription<T> and the UntypedSubscriberImpl<T>/UntypedPublisherImpl<T> wrappers with MakeGenericType + Activator. Native AOT trims those constructors, so any stream crossing an island boundary failed with MissingMethodException. Every one of these types is now built by code that already knows T: Inlet<T>/Outlet<T> (internal factories), the typed untyped-wrappers (sink subscribers, panic-path ErrorPublisher/CancellingSubscriber, ActorSubscription) and ProcessorModule. The old reflective path only remains for port/publisher/subscriber types implemented outside Akka.Streams, behind Akka.DynamicTypeLoading. SubscriberManagement's stream-buffer type parameter gets [DynamicallyAccessedMembers] so the fan-out publisher's buffer constructor survives trimming. The Hosting AOT canary now runs streams across island boundaries (value and reference element types) with no trimmer roots. Closes akkadotnet#8731

The persistence canary now registers a journal, a snapshot store and a stash overflow configurator that Akka.Persistence does not ship and runs them with Akka.DynamicTypeLoading off, next to the built-in inmem plugins. The comment that called two sends a burst now says what the actor does. Tests: add the unregistered snapshot store guard, switch-on tests for a registered snapshot store, event adapter, binding and stash configurator, and a run of PersistencePluginProxy with the switch off. Fold the exact-message event adapter test into the existing one, keep Merge in its own test, and make the read journal switch-on test assert the default config injection. Docs: show how to add a read journal's default HOCON with the switch off, and note in the baseline that Streams joins the gate once akkadotnet#8732 merges.

Aaronontheweb

Self-review: what each change and test is for. Inline comments have the detail.

What this PR does

Builds every island-boundary type from code that already knows T: Inlet<T>/Outlet<T> factories, typed methods on the untyped wrappers, and ProcessorModule. Native AOT never compiles a closed generic type that only MakeGenericType asks for.
Keeps the reflective path only for port, publisher and subscriber types implemented outside Akka.Streams, gated on Akka.DynamicTypeLoading.
Reproduced on 87fd339: the Hosting AOT canary publishes with 0 IL warnings and prints OK.

Overlap

The two MaterializerSessionSpec panic tests differ only by element type (matters under AOT, not on the JIT).
The Source.Queue canary scenario covers nothing the first .Async() scenario doesn't.

Not covered

The NotSupportedException path with the switch off (custom Inlet/Outlet subclass, foreign IUntypedPublisher/IUntypedSubscriber).
ActorSubscription.Create's typed path (only the legacy FanIn<T>/FanOut<T> actors reach it).
The IUntypedVirtualPublisher branches (nothing constructs VirtualPublisher<T>).

A cleanup pass addressing these is in progress.

Aaronontheweb · 2026-10-02T21:34:01Z

        /// <returns>TBD</returns>
        public override Inlet CarbonCopy() => new Inlet<T>(Name);
+
+        internal override IUntypedSubscriber CreateBoundarySubscriber(IActorRef parent, GraphInterpreterShell shell, int id)


We build BoundarySubscriber<T> here because Inlet<T> knows T at compile time, so ILC compiles it for every element type the app uses. This replaces inlet.GetType().GetGenericArguments().First() + Instantiate in the materializer, the MissingMethodException from #8731.

Aaronontheweb · 2026-10-02T21:34:01Z

        public abstract Outlet CarbonCopy();

-
+        // INTERNAL API. The three factories below build the types that need this port's element type.


We give Outlet the same pattern for the three other types the materializer and fuser built by reflection: BoundaryPublisher<T>, ActorOutputBoundary<T> and MaterializedValueSource<T>. The base versions are the gated fallback; Outlet<T> overrides all three.

Aaronontheweb · 2026-10-02T21:34:01Z

        /// <returns>TBD</returns>
        public override Outlet CarbonCopy() => new Outlet<T>(Name);
+
+        internal override IUntypedPublisher CreateBoundaryPublisher(IActorRef parent, GraphInterpreterShell shell, int id, out IActorPublisher actorPublisher)


We return the BoundaryPublisher<T> inside an UntypedPublisherImpl<T> and hand the raw publisher back through out for ExposedPublisher. Behavior change: the materializer's port-to-publisher map used to hold the BoundaryPublisher<T> itself (it implements IUntypedPublisher through ActorPublisher<T>); it now holds the wrapper, so DoSubscribe and the panic path can use the typed UntypedPublisher methods. Cost: one extra allocation per island outlet per materialization.

Aaronontheweb · 2026-10-02T21:34:01Z

-                        var t = module.CreateProcessor();
-                        var processor = t.Item1;
-                        var materialized = t.Item2;
+                        var (subscriber, publisher, materialized) = module.CreateUntypedProcessor();


We let ProcessorModule wrap its processor with its own TIn/TOut, because the old FromTyped(object) read the element types off the runtime type with GetInterfaces + MakeGenericType. The unused ProcessorForMethod lookup is also removed. Public ProcessorModule.CreateProcessor() stays for API compatibility, but nothing in the repo calls it now.

Aaronontheweb · 2026-10-02T21:34:02Z

+                .RunWith(Sink.Seq<int>(), mat),
+            Enumerable.Range(1, 5), "fan-out AsPublisher (int)");
+
+        // Source.ActorPublisher is what the persistence query read journals are built on.


We run Source.ActorPublisher because it proves the persistence-query shape from #8730 (a source module feeding a graph-stage island) via the same BoundarySubscriber<T> that failed there.

Aaronontheweb · 2026-10-02T21:34:02Z

+        queue.Complete();
+        await ExpectAsync(done, new[] { 1, 2, 3 }, "Source.Queue (int)");
+
+        // A graph that reads its own materialized value (an int) back as a stream element:


We read the materialized value back as an element because it proves auto-fusing rebuilds MaterializedValueSource<T> via Outlet<T>.CreateMaterializedValueSource; int only.

Aaronontheweb · 2026-10-02T21:34:02Z

 #
-# Empty since #8671 put the Akka.Streams stream-ref reflection behind Akka.DynamicTypeLoading. Any
+# Empty since #8671 put the Akka.Streams stream-ref reflection behind Akka.DynamicTypeLoading, and
+# #8731 stopped the materializer building island-boundary types with MakeGenericType. Any


We keep the baseline empty because the publish now emits no Akka.Streams IL warnings. Reproduced on 87fd339 (dotnet publish -r linux-x64 -c Release): 0 IL warnings in total, canary prints [canary-hosting] OK.

- Materialization panic clean-up is best effort: a failing step (e.g. a foreign IUntypedSubscriber with Akka.DynamicTypeLoading off) no longer replaces the original exception or skips the remaining ports. - Obsolete Construct.Instantiate (now [RequiresDynamicCode] and [RequiresUnreferencedCode]) and TypeExtensions.GetSubscribedType / GetPublishedType (now [DynamicallyAccessedMembers(Interfaces)]); API approvals updated. - MaterializerSessionSpec: switch-off NotSupportedException specs for a non-generic Inlet/Outlet and a foreign IUntypedPublisher, a panic spec proving the original failure surfaces; int/string duplicate collapsed. - Hosting AOT canary: every streams scenario runs with int and string, Source.Queue dropped, fan-out comment corrected. - Stream-ref error message and docs point to akkadotnet#8673. - docs: "Akka.Streams Under Native AOT" section in native-aot.md.

PersistenceSetup.Create().WithEmbeddedPersistence() registers the journal, snapshot store and read journal by plugin id, each with its reference configuration, so a user writes no class names and no WithFallback. WithEmbeddedJournal, WithEmbeddedSnapshotStore and WithEmbeddedReadJournal take a plugin id; the journal takes event adapters. The read journal provider gets its plugin id from the registration. The AOT canary uses the new API and now also runs an event adapter, a Both-mode database with a delete, and keeps StreamsRoots.xml until akkadotnet#8732 has merged.

Aaronontheweb

LGTM - enables support for custom ISubscriber<T> and IPublisher<T> types to the extent that it's possible. Needed to make .Async() work in a number of cases.

Aaronontheweb · 2026-10-03T01:07:44Z

+        // .Async() splits the graph into islands: BoundarySubscriber, BoundaryPublisher and
+        // ActorOutputBoundary on every edge between them.
+        await ExpectAsync(
+            Source.From(Enumerable.Range(1, 10)).Async().Select(x => x * 2).Async().RunWith(Sink.Seq<int>(), mat),


Exercises the .Async() path inside the AOT system.

…land-boundaries

…ings #8732 builds island-boundary subscribers without runtime generics, so the canary's queries run without StreamsRoots.xml. Delete it with its csproj item and README section, and add src/core/Akka.Streams/ to the canary's gated warning scope. The publish shows no Akka.Streams warnings.

Aaronontheweb added this to the 1.6.0 milestone Oct 2, 2026

Aaronontheweb added akka-streams AOT Ahead-of-Time (AOT) Compilation labels Oct 2, 2026

Aaronontheweb commented Oct 2, 2026

View reviewed changes

Aaronontheweb mentioned this pull request Oct 2, 2026

Persistence: register plugins in code through Akka.Persistence.Hosting (AOT) #8730

Closed

Aaronontheweb mentioned this pull request Oct 2, 2026

Akka.Persistence.Embedded: SQLite journal, snapshot store and read journal (AOT-compatible) #8733

Closed

Aaronontheweb commented Oct 3, 2026

View reviewed changes

Merge remote-tracking branch 'akkadotnet/dev' into fix/streams-aot-is…

dae745a

…land-boundaries

Aaronontheweb merged commit 0ad59d3 into akkadotnet:dev Oct 3, 2026
16 checks passed

This was referenced Oct 7, 2026

Bump Akka from 1.6.0-beta1 to 1.6.0-beta3 Aaronontheweb/link-validator#194

Closed

Bump Akka.TestKit.Xunit2 from 1.6.0-beta1 to 1.6.0-beta3 Aaronontheweb/link-validator#195

Merged

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Akka.Streams: build island-boundary subscribers without runtime generics (Native AOT) - #8732

Akka.Streams: build island-boundary subscribers without runtime generics (Native AOT)#8732
Aaronontheweb merged 3 commits into
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Aaronontheweb:fix/streams-aot-island-boundaries

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		public abstract Outlet CarbonCopy();


		// INTERNAL API. The three factories below build the types that need this port's element type.

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