Mantle window helping

- A caller whose submission window is full runs the next component itself instead of parking
- Pass barriers run still-queued component tasks in reverse order before waiting
- Queued component tasks reopen the submitting generation's runtime scope on whichever thread runs them
- Helpers only run queued tasks bound to their own runtime or when they hold none
- A finished submission no longer reports a task as dropped once a helper started it
- Burst worker scope test keeps one stage on a worker while the caller helps

core/src/main/java/art/arcane/iris/generation/mantle/MatterGenerator.java

@@ -3,6 +3,7 @@ package art.arcane.iris.generation.mantle;
 import art.arcane.iris.generation.runtime.IrisComplex;
 import art.arcane.iris.generation.runtime.Engine;
 import art.arcane.iris.generation.runtime.EnginePlatformHooks;
+import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.spi.IrisLogging;
 import art.arcane.iris.generation.concurrent.MultiBurst;
 import art.arcane.iris.generation.context.ChunkContext;
@@ -106,6 +107,7 @@ public interface MatterGenerator {
             // write into released chunks.
             List<MatterComponentTask> outstandingTasks = null;
             List<DeferredComponent> deferredComponents = null;
+            IrisEngine.GenerationRuntimeBinding generationRuntime = scopedGenerationRuntime();
             SubmissionWindow submissions = multicore && !DISPATCHER.ownsCurrentThread()
                     ? new SubmissionWindow()
                     : null;
@@ -231,7 +233,8 @@ public interface MatterGenerator {
                                 for (int componentIndex = 0; componentIndex < eligibleComponentCount; componentIndex++) {
                                     MantleComponent component = eligibleComponents[componentIndex];
                                     outstandingTasks.add(runComponentAsync(
-                                            chunk, component, writer, finalPassX, finalPassZ, context, submissions));
+                                            chunk, component, writer, finalPassX, finalPassZ, context, submissions,
+                                            generationRuntime));
                                 }
                             } else {
                                 for (int componentIndex = 0; componentIndex < eligibleComponentCount; componentIndex++) {
@@ -248,6 +251,7 @@ public interface MatterGenerator {
                     }
 
                     if (asyncComponents) {
+                        runQueuedComponentTasks(outstandingTasks, generationRuntime);
                         awaitComponentTasks(outstandingTasks);
                     } else if (deferredComponents != null) {
                         runDeferredComponents(deferredComponents, writer, context);
@@ -382,6 +386,19 @@ public interface MatterGenerator {
         return true;
     }
 
+    private IrisEngine.GenerationRuntimeBinding scopedGenerationRuntime() {
+        return getEngine() instanceof IrisEngine irisEngine && irisEngine.hasGenerationRuntimeScope()
+                ? irisEngine.captureGenerationRuntimeBinding()
+                : null;
+    }
+
+    private IrisEngine.GenerationRuntimeScope openGenerationRuntime(IrisEngine.GenerationRuntimeBinding binding) {
+        if (binding == null || !(getEngine() instanceof IrisEngine irisEngine)) {
+            return null;
+        }
+        return irisEngine.openGenerationRuntimeScope(binding);
+    }
+
     private boolean shouldGenerateComponent(MantleComponent component) {
         if (!component.isEnabled()) {
             return false;
@@ -398,7 +415,8 @@ public interface MatterGenerator {
             int chunkX,
             int chunkZ,
             ChunkContext context,
-            SubmissionWindow submissions
+            SubmissionWindow submissions,
+            IrisEngine.GenerationRuntimeBinding generationRuntime
     ) {
         MantleFlag flag = component.getFlag();
         MatterTaskKey key = new MatterTaskKey(getMantle(), chunkX, chunkZ, flag);
@@ -428,24 +446,25 @@ public interface MatterGenerator {
         if (running != null) {
             return running;
         }
-        submissions.acquire();
+        boolean submit = submissions.reserve();
         MatterComponentTask existing = IN_FLIGHT_COMPONENTS.putIfAbsent(key, task);
         if (existing != null) {
-            submissions.release();
+            if (submit) {
+                submissions.release();
+            }
             return existing;
         }
         try {
+            if (!submit) {
+                completeComponentTask(task, chunk, component, writer, chunkX, chunkZ, context, null);
+                return task;
+            }
             IrisContext callerContext = IrisContext.get();
             submissions.track(task);
-            task.setSubmission(DISPATCHER.submit(() -> completeComponentTask(
-                    task,
-                    chunk,
-                    component,
-                    writer,
-                    chunkX,
-                    chunkZ,
-                    context,
-                    callerContext)));
+            Runnable work = () -> runComponentTask(
+                    task, chunk, component, writer, chunkX, chunkZ, context, callerContext, generationRuntime);
+            task.queue(work, generationRuntime);
+            task.setSubmission(DISPATCHER.submit(work));
             return task;
         } catch (Throwable throwable) {
             task.cancel(throwable);
@@ -489,6 +508,20 @@ public interface MatterGenerator {
         deferredComponents.clear();
     }
 
+    private static void runQueuedComponentTasks(List<MatterComponentTask> tasks,
+                                                IrisEngine.GenerationRuntimeBinding helperRuntime) {
+        boolean interrupted = Thread.interrupted();
+        try {
+            for (int index = tasks.size() - 1; index >= 0; index--) {
+                tasks.get(index).runIfQueued(helperRuntime);
+            }
+        } finally {
+            if (interrupted) {
+                Thread.currentThread().interrupt();
+            }
+        }
+    }
+
     /**
      * Pass barrier. Waits for every launched task, even if one of them failed, so that no task is
      * still writing through the writer once this returns. The first failure is rethrown.
@@ -592,19 +625,42 @@ public interface MatterGenerator {
             int chunkZ,
             ChunkContext context,
             IrisContext callerContext
+    ) {
+        Throwable failure = runComponentTask(task, chunk, component, writer, chunkX, chunkZ, context, callerContext, null);
+        if (failure instanceof RuntimeException runtime) {
+            throw runtime;
+        }
+        if (failure instanceof Error error) {
+            throw error;
+        }
+        if (failure != null) {
+            throw new CompletionException(failure);
+        }
+    }
+
+    private Throwable runComponentTask(
+            MatterComponentTask task,
+            MantleChunk<Matter> chunk,
+            MantleComponent component,
+            MantleWriter writer,
+            int chunkX,
+            int chunkZ,
+            ChunkContext context,
+            IrisContext callerContext,
+            IrisEngine.GenerationRuntimeBinding generationRuntime
     ) {
         if (!task.start()) {
-            return;
+            return null;
         }
         Throwable failure = null;
         try {
-            runComponentWithContext(chunk, component, writer, chunkX, chunkZ, context, callerContext);
+            runComponentWithContext(chunk, component, writer, chunkX, chunkZ, context, callerContext, generationRuntime);
         } catch (Throwable throwable) {
             failure = throwable;
-            throw throwable;
         } finally {
             task.finish(failure);
         }
+        return failure;
     }
 
     private void runComponentWithContext(
@@ -614,17 +670,19 @@ public interface MatterGenerator {
             int chunkX,
             int chunkZ,
             ChunkContext context,
-            IrisContext callerContext
+            IrisContext callerContext,
+            IrisEngine.GenerationRuntimeBinding generationRuntime
     ) {
-        if (callerContext == null) {
+        if (callerContext == null && generationRuntime == null) {
             runComponentInline(chunk, component, writer, chunkX, chunkZ, context);
             return;
         }
 
-        try (IrisContext.Scope ignored = IrisContext.open(
-                callerContext.getEngine(),
-                callerContext.getGenerationSessionId(),
-                callerContext.getChunkContext())) {
+        try (IrisEngine.GenerationRuntimeScope runtimeScope = openGenerationRuntime(generationRuntime);
+             IrisContext.Scope contextScope = callerContext == null ? null : IrisContext.open(
+                     callerContext.getEngine(),
+                     callerContext.getGenerationSessionId(),
+                     callerContext.getChunkContext())) {
             runComponentInline(chunk, component, writer, chunkX, chunkZ, context);
         }
     }
@@ -647,6 +705,8 @@ public interface MatterGenerator {
         private final MatterTaskKey key;
         private final CompletableFuture<Void> future = new CompletableFuture<>();
         private volatile Future<?> submission;
+        private volatile Runnable queuedWork;
+        private volatile IrisEngine.GenerationRuntimeBinding queuedRuntime;
         private volatile Throwable failure;
         private boolean started;
         private boolean slowWarningIssued;
@@ -667,6 +727,22 @@ public interface MatterGenerator {
             return true;
         }
 
+        synchronized boolean isStarted() {
+            return started;
+        }
+
+        void queue(Runnable work, IrisEngine.GenerationRuntimeBinding runtime) {
+            queuedRuntime = runtime;
+            queuedWork = work;
+        }
+
+        void runIfQueued(IrisEngine.GenerationRuntimeBinding helperRuntime) {
+            Runnable work = queuedWork;
+            if (work != null && !future.isDone() && (helperRuntime == null || helperRuntime == queuedRuntime)) {
+                work.run();
+            }
+        }
+
         synchronized void setSubmission(Future<?> submission) {
             this.submission = submission;
             if (failure != null) {
@@ -720,7 +796,7 @@ public interface MatterGenerator {
                             continue;
                         }
                         Future<?> submitted = submission;
-                        boolean dropped = submitted != null && submitted.isDone();
+                        boolean dropped = submitted != null && submitted.isDone() && !isStarted();
                         long waited = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
                         if (dropped) {
                             IllegalStateException dispatchFailure = new IllegalStateException(
@@ -775,13 +851,20 @@ public interface MatterGenerator {
         private final Semaphore slots = new Semaphore(COMPONENT_SUBMISSION_LIMIT);
         private volatile Throwable failure;
 
-        void acquire() {
-            slots.acquireUninterruptibly();
+        boolean reserve() {
             Throwable observed = failure;
+            if (observed != null) {
+                throw new CompletionException(observed);
+            }
+            if (!slots.tryAcquire()) {
+                return false;
+            }
+            observed = failure;
             if (observed != null) {
                 slots.release();
                 throw new CompletionException(observed);
             }
+            return true;
         }
 
         void release() {

core/src/test/java/art/arcane/iris/generation/mantle/MatterGeneratorConcurrencyTest.java

@@ -2,6 +2,7 @@ package art.arcane.iris.generation.mantle;
 
 import art.arcane.iris.configuration.IrisSettings;
 import art.arcane.iris.generation.runtime.Engine;
+import art.arcane.iris.generation.runtime.IrisEngine;
 import art.arcane.iris.generation.terrain.IrisDimension;
 import art.arcane.iris.testsupport.Await;
 import art.arcane.iris.testsupport.PlatformBinding;
@@ -76,11 +77,13 @@ public class MatterGeneratorConcurrencyTest {
     @Test
     public void externalWindowsBoundManagedBlockedComponentSubmissions() throws Exception {
         GeneratorFixture fixture = new GeneratorFixture(true);
-        int maximum = 2 * MatterGenerator.COMPONENT_SUBMISSION_LIMIT;
+        int pooled = 2 * MatterGenerator.COMPONENT_SUBMISSION_LIMIT;
+        int maximum = pooled + 2;
         CountDownLatch admitted = new CountDownLatch(maximum);
         CountDownLatch excess = new CountDownLatch(1);
         CountDownLatch release = new CountDownLatch(1);
         AtomicInteger started = new AtomicInteger();
+        AtomicInteger startedOnDispatcher = new AtomicInteger();
         AtomicInteger completed = new AtomicInteger();
         RecordingComponent component = new RecordingComponent(ReservedFlag.OBJECT, 0, 64) {
             @Override
@@ -88,6 +91,9 @@ public class MatterGeneratorConcurrencyTest {
                 if (started.incrementAndGet() > maximum) {
                     excess.countDown();
                 }
+                if (MatterGenerator.DISPATCHER.ownsCurrentThread()) {
+                    startedOnDispatcher.incrementAndGet();
+                }
                 admitted.countDown();
                 awaitManaged(release);
                 completed.incrementAndGet();
@@ -102,6 +108,7 @@ public class MatterGeneratorConcurrencyTest {
             await(admitted);
             assertFalse(excess.await(300L, TimeUnit.MILLISECONDS));
             assertEquals(maximum, started.get());
+            assertEquals(pooled, startedOnDispatcher.get());
             assertEquals(maximum, activeClaims(fixture, 0, 4) + activeClaims(fixture, 32, 4));
             verify(fixture.mantle.getChunk(-4, -4), never()).release();
         } finally {
@@ -358,14 +365,23 @@ public class MatterGeneratorConcurrencyTest {
     }
 
     @Test
-    public void multicoreComponentRunsOnTheDispatcher() {
+    public void multicoreComponentsSpreadAcrossTheDispatcherWhileTheCallerHelps() {
         GeneratorFixture fixture = new GeneratorFixture();
         Thread caller = Thread.currentThread();
-        Set<Thread> threads = ConcurrentHashMap.newKeySet();
+        AtomicInteger dispatcherRuns = new AtomicInteger();
+        AtomicInteger completed = new AtomicInteger();
+        CountDownLatch dispatched = new CountDownLatch(1);
         RecordingComponent ordinary = new RecordingComponent(ReservedFlag.OBJECT, 0, 16) {
             @Override
             public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
-                threads.add(Thread.currentThread());
+                if (Thread.currentThread() == caller) {
+                    await(dispatched);
+                } else {
+                    assertTrue(MatterGenerator.DISPATCHER.ownsCurrentThread());
+                    dispatcherRuns.incrementAndGet();
+                    dispatched.countDown();
+                }
+                completed.incrementAndGet();
             }
         };
         TestMatterGenerator generator = fixture.generator(List.of(
@@ -374,41 +390,157 @@ public class MatterGeneratorConcurrencyTest {
 
         generator.generateMatter(0, 0, true, fixture.context);
 
-        assertFalse(threads.isEmpty());
-        assertFalse(threads.contains(caller));
+        assertEquals(9, completed.get());
+        assertTrue(dispatcherRuns.get() > 0);
     }
 
     @Test
-    public void asyncComponentReceivesCallerContextAndCallerScopeIsRestored() {
+    public void componentsReceiveTheCallerContextOnEveryThreadAndCallerScopeIsRestored() {
         GeneratorFixture fixture = new GeneratorFixture();
-        AtomicReference<IrisContext> observed = new AtomicReference<>();
-        AtomicReference<Thread> observedThread = new AtomicReference<>();
-        RecordingComponent concurrent = new RecordingComponent(ReservedFlag.CARVED, 0, 0) {
+        Thread callerThread = Thread.currentThread();
+        Set<IrisContext> observed = ConcurrentHashMap.newKeySet();
+        AtomicInteger dispatcherRuns = new AtomicInteger();
+        CountDownLatch dispatched = new CountDownLatch(1);
+        RecordingComponent concurrent = new RecordingComponent(ReservedFlag.CARVED, 0, 16) {
             @Override
             public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
-                observed.set(IrisContext.require());
-                observedThread.set(Thread.currentThread());
+                observed.add(IrisContext.require());
+                if (Thread.currentThread() == callerThread) {
+                    await(dispatched);
+                } else {
+                    assertTrue(MatterGenerator.DISPATCHER.ownsCurrentThread());
+                    dispatcherRuns.incrementAndGet();
+                    dispatched.countDown();
+                }
             }
         };
         TestMatterGenerator generator = fixture.generator(List.of(
-                new MantlePass(List.of(concurrent), 0, 0)
+                new MantlePass(List.of(concurrent), 1, 0)
         ));
 
         assertNull(IrisContext.get());
         try (IrisContext.Scope ignored = IrisContext.open(fixture.engine, 91L, fixture.context)) {
             IrisContext caller = IrisContext.require();
-            Thread callerThread = Thread.currentThread();
             generator.generateMatter(0, 0, true, fixture.context);
 
-            assertNotSame(callerThread, observedThread.get());
-            assertSame(fixture.engine, observed.get().getEngine());
-            assertSame(fixture.context, observed.get().getChunkContext());
-            assertEquals(91L, observed.get().getGenerationSessionId());
+            assertTrue(dispatcherRuns.get() > 0);
+            for (IrisContext context : observed) {
+                assertSame(fixture.engine, context.getEngine());
+                assertSame(fixture.context, context.getChunkContext());
+                assertEquals(91L, context.getGenerationSessionId());
+            }
             assertSame(caller, IrisContext.require());
         }
         assertNull(IrisContext.get());
     }
 
+    @Test
+    public void externalBarrierRunsItsQueuedComponentsWhileTheDispatcherIsBusy() throws Exception {
+        GeneratorFixture fixture = new GeneratorFixture(true);
+        CountDownLatch releaseDispatcher = new CountDownLatch(1);
+        List<Future<?>> blockers = occupyDispatcher(releaseDispatcher);
+        AtomicReference<Thread> generationThread = new AtomicReference<>();
+        Set<Thread> threads = ConcurrentHashMap.newKeySet();
+        AtomicInteger completed = new AtomicInteger();
+        RecordingComponent component = new RecordingComponent(ReservedFlag.OBJECT, 0, 16) {
+            @Override
+            public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
+                threads.add(Thread.currentThread());
+                completed.incrementAndGet();
+            }
+        };
+        TestMatterGenerator generator = fixture.generator(List.of(new MantlePass(List.of(component), 1, 0)));
+        try {
+            CompletableFuture<Void> generation = CompletableFuture.runAsync(() -> {
+                generationThread.set(Thread.currentThread());
+                generator.generateMatter(0, 0, true, fixture.context);
+            });
+            generation.get(5L, TimeUnit.SECONDS);
+            assertEquals(9, completed.get());
+            assertEquals(Set.of(generationThread.get()), threads);
+            assertEquals(0, activeClaims(fixture, 0, 1));
+        } finally {
+            releaseDispatcher.countDown();
+            for (Future<?> blocker : blockers) {
+                blocker.get(10L, TimeUnit.SECONDS);
+            }
+        }
+    }
+
+    @Test
+    public void dispatcherComponentsRunInsideTheCallersGenerationRuntime() {
+        GeneratorFixture fixture = new GeneratorFixture(true, true);
+        Thread caller = Thread.currentThread();
+        fixture.bindRuntime(caller);
+        IrisEngine engine = (IrisEngine) fixture.engine;
+        AtomicInteger dispatcherRuns = new AtomicInteger();
+        AtomicInteger unscopedRuns = new AtomicInteger();
+        AtomicInteger completed = new AtomicInteger();
+        CountDownLatch dispatched = new CountDownLatch(1);
+        RecordingComponent component = new RecordingComponent(ReservedFlag.OBJECT, 0, 64) {
+            @Override
+            public void generateLayer(MantleWriter writer, int x, int z, ChunkContext context) {
+                if (!engine.hasGenerationRuntimeScope() || engine.captureGenerationRuntimeBinding() != fixture.runtime) {
+                    unscopedRuns.incrementAndGet();
+                }
+                if (Thread.currentThread() == caller) {
+                    await(dispatched);
+                } else {
+                    dispatcherRuns.incrementAndGet();
+                    dispatched.countDown();
+                }
+                completed.incrementAndGet();
+            }
+        };
+        TestMatterGenerator generator = fixture.generator(List.of(new MantlePass(List.of(component), 4, 0)));
+
+        generator.generateMatter(0, 0, true, fixture.context);
+
+        assertEquals(81, completed.get());
+        assertEquals(0, unscopedRuns.get());
+        assertTrue(dispatcherRuns.get() > 0);
+        assertEquals(fixture.openedRuntimes.get(), fixture.closedRuntimes.get());
+        assertTrue(fixture.openedRuntimes.get() >= dispatcherRuns.get());
+    }
+
+    @Test
+    public void helpersOnlyRunQueuedComponentsBoundToTheirOwnRuntime() {
+        GeneratorFixture fixture = new GeneratorFixture();
+        IrisEngine.GenerationRuntimeBinding own = mock(IrisEngine.GenerationRuntimeBinding.class);
+        IrisEngine.GenerationRuntimeBinding foreign = mock(IrisEngine.GenerationRuntimeBinding.class);
+        AtomicInteger runs = new AtomicInteger();
+        MatterGenerator.MatterComponentTask bound = new MatterGenerator.MatterComponentTask(
+                new MatterGenerator.MatterTaskKey(fixture.mantle, 0, 0, ReservedFlag.OBJECT));
+        bound.queue(runs::incrementAndGet, own);
+        MatterGenerator.MatterComponentTask unbound = new MatterGenerator.MatterComponentTask(
+                new MatterGenerator.MatterTaskKey(fixture.mantle, 1, 0, ReservedFlag.OBJECT));
+        unbound.queue(runs::incrementAndGet, null);
+
+        bound.runIfQueued(foreign);
+        unbound.runIfQueued(foreign);
+        assertEquals(0, runs.get());
+        bound.runIfQueued(own);
+        unbound.runIfQueued(null);
+        bound.runIfQueued(null);
+        assertEquals(3, runs.get());
+    }
+
+    private static List<Future<?>> occupyDispatcher(CountDownLatch release) {
+        int blockers = Math.max(1, MultiBurst.burst.parallelism()) * 4;
+        List<Future<?>> futures = new ArrayList<>(blockers);
+        for (int index = 0; index < blockers; index++) {
+            futures.add(MultiBurst.burst.submit(() -> {
+                try {
+                    assertTrue(release.await(30L, TimeUnit.SECONDS));
+                } catch (InterruptedException interruption) {
+                    Thread.currentThread().interrupt();
+                }
+            }));
+        }
+        return futures;
+    }
+
+
     @Test
     public void terrainPhasePreparesContentReachWithoutPublishingPlanned() {
         GeneratorFixture fixture = new GeneratorFixture(true);
@@ -701,6 +833,42 @@ public class MatterGeneratorConcurrencyTest {
         assertFalse(MatterGenerator.IN_FLIGHT_COMPONENTS.containsKey(key));
     }
 
+    @Test
+    public void componentStartedByAHelperIsNotDroppedWhenItsSubmissionFinishesFirst() throws Exception {
+        GeneratorFixture fixture = new GeneratorFixture();
+        MatterGenerator.MatterTaskKey key = new MatterGenerator.MatterTaskKey(fixture.mantle, 3, 0, ReservedFlag.OBJECT);
+        MatterGenerator.MatterComponentTask task = new MatterGenerator.MatterComponentTask(key);
+        CountDownLatch running = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        CountDownLatch polls = new CountDownLatch(2);
+        task.queue(() -> {
+            if (task.start()) {
+                running.countDown();
+                await(release);
+                task.finish(null);
+            }
+        }, null);
+        Future<?> submission = mock(Future.class);
+        when(submission.isDone()).thenAnswer(invocation -> {
+            polls.countDown();
+            return true;
+        });
+        task.setSubmission(submission);
+        CompletableFuture<Void> helper = CompletableFuture.runAsync(() -> task.runIfQueued(null));
+        await(running);
+        CompletableFuture<Void> waiter = CompletableFuture.runAsync(
+                () -> task.await(MatterGenerator.COMPONENT_TASK_TIMEOUT_MS));
+        try {
+            await(polls);
+            assertFalse(waiter.isDone());
+        } finally {
+            release.countDown();
+        }
+        helper.get(5L, TimeUnit.SECONDS);
+        waiter.get(5L, TimeUnit.SECONDS);
+        verify(submission, never()).cancel(anyBoolean());
+    }
+
     @Test
     public void interruptedWaiterDrainsRunningTaskAndRestoresInterrupt() throws Exception {
         GeneratorFixture fixture = new GeneratorFixture();
@@ -814,22 +982,49 @@ public class MatterGeneratorConcurrencyTest {
         private final Engine engine;
         private final Mantle<Matter> mantle;
         private final ChunkContext context;
+        private final IrisEngine.GenerationRuntimeBinding runtime = mock(IrisEngine.GenerationRuntimeBinding.class);
+        private final ThreadLocal<Integer> runtimeDepth = ThreadLocal.withInitial(() -> 0);
+        private final AtomicInteger openedRuntimes = new AtomicInteger();
+        private final AtomicInteger closedRuntimes = new AtomicInteger();
+        private volatile Thread boundThread;
 
         private GeneratorFixture() {
             this(false);
         }
 
+        private GeneratorFixture(boolean lockingChunks) {
+            this(lockingChunks, false);
+        }
+
         /**
          * @param lockingChunks true to give every chunk a real per-flag lock and flag state, so a
          *                      generation that reaches a chunk another generation is working on
          *                      blocks exactly like production
          */
         @SuppressWarnings("unchecked")
-        private GeneratorFixture(boolean lockingChunks) {
+        private GeneratorFixture(boolean lockingChunks, boolean runtimeBoundCaller) {
             IrisDimension dimension = mock(IrisDimension.class);
             when(dimension.isUseMantle()).thenReturn(true);
             EngineMantle engineMantle = mock(EngineMantle.class);
-            engine = mock(Engine.class);
+            if (runtimeBoundCaller) {
+                IrisEngine irisEngine = mock(IrisEngine.class);
+                when(irisEngine.hasGenerationRuntimeScope()).thenAnswer(invocation -> runtimeBound());
+                when(irisEngine.captureGenerationRuntimeBinding()).thenAnswer(invocation -> runtimeBound() ? runtime : null);
+                when(irisEngine.openGenerationRuntimeScope(runtime)).thenAnswer(invocation -> {
+                    openedRuntimes.incrementAndGet();
+                    runtimeDepth.set(runtimeDepth.get() + 1);
+                    IrisEngine.GenerationRuntimeScope scope = mock(IrisEngine.GenerationRuntimeScope.class);
+                    doAnswer(close -> {
+                        runtimeDepth.set(runtimeDepth.get() - 1);
+                        closedRuntimes.incrementAndGet();
+                        return null;
+                    }).when(scope).close();
+                    return scope;
+                });
+                engine = irisEngine;
+            } else {
+                engine = mock(Engine.class);
+            }
             when(engine.getDimension()).thenReturn(dimension);
             when(engine.getMantle()).thenReturn(engineMantle);
             mantle = mock(Mantle.class);
@@ -846,6 +1041,14 @@ public class MatterGeneratorConcurrencyTest {
             when(context.getGenerationSessionId()).thenReturn(91L);
         }
 
+        private void bindRuntime(Thread thread) {
+            boundThread = thread;
+        }
+
+        private boolean runtimeBound() {
+            return Thread.currentThread() == boundThread || runtimeDepth.get() > 0;
+        }
+
         private TestMatterGenerator generator(List<MantlePass> passes) {
             return new TestMatterGenerator(engine, mantle, passes);
         }

core/src/test/java/art/arcane/iris/generation/runtime/IrisEngineGenerationRuntimeScopeTest.java

@@ -42,6 +42,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CopyOnWriteArraySet;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -431,25 +432,36 @@ public class IrisEngineGenerationRuntimeScopeTest {
         };
         MultiBurst workerPool = new MultiBurst("Generation Runtime Scope Test", Thread.NORM_PRIORITY, () -> 2);
         when(detached.target.getBurster()).thenReturn(workerPool);
-        AtomicReference<EngineTarget> observedTarget = new AtomicReference<>();
-        AtomicReference<Thread> observedThread = new AtomicReference<>();
+        Set<EngineTarget> observedTargets = new CopyOnWriteArraySet<>();
+        Set<Thread> workerThreads = new CopyOnWriteArraySet<>();
+        CountDownLatch workerRan = new CountDownLatch(1);
+        Thread caller = Thread.currentThread();
         EngineStage stage = (x, z, blocks, biomes, multicore, context) -> {
-            observedTarget.set(engine.getTarget());
-            observedThread.set(Thread.currentThread());
+            observedTargets.add(engine.getTarget());
+            if (Thread.currentThread() == caller) {
+                try {
+                    assertTrue(workerRan.await(5L, TimeUnit.SECONDS));
+                } catch (InterruptedException interruption) {
+                    Thread.currentThread().interrupt();
+                    throw new AssertionError(interruption);
+                }
+                return;
+            }
+            workerThreads.add(Thread.currentThread());
+            workerRan.countDown();
         };
         ChunkContext context = mock(ChunkContext.class);
         when(context.getGenerationSessionId()).thenReturn(17L);
-        Thread caller = Thread.currentThread();
 
         try (IrisEngine.GenerationRuntimeScope ignored = engine.openGenerationRuntimeScope(binding)) {
-            mode.burst(stage).generate(0, 0, null, null, true, context);
+            mode.burst(stage, stage).generate(0, 0, null, null, true, context);
         } finally {
             mode.close();
             workerPool.close();
         }
 
-        assertSame(detached.target, observedTarget.get());
-        assertNotSame(caller, observedThread.get());
+        assertEquals(Set.of(detached.target), observedTargets);
+        assertTrue(!workerThreads.isEmpty() && !workerThreads.contains(caller));
     }
 
     @Test