Merged terrain sampling

- Concurrent fallback queries share pending terrain samples
- Pure height generators reuse noise contexts across batches
- Storage allocation tests account for the configured heap budget

core/src/main/java/art/arcane/iris/generation/hydrology/HydrologyBasisCache.java

@@ -1,8 +1,15 @@
 package art.arcane.iris.generation.hydrology;
 
+import art.arcane.iris.generation.stream.ProvisionalSampling;
 import art.arcane.volmlib.util.cache.CacheKey;
 import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
 import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+
+import java.util.Objects;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.RejectedExecutionException;
 
 final class HydrologyBasisCache {
     private static final int MAXIMUM_ENTRIES = 32_768;
@@ -39,23 +46,74 @@ final class HydrologyBasisCache {
         seed(samples, full);
     }
 
-    boolean findWithoutSlope(long packed, HydrologyTerrainSample[] samples, int index) {
-        Stripe stripe = stripe(withoutSlope, packed);
-        synchronized (stripe) {
-            samples[index] = stripe.samples.getAndMoveToFirst(packed);
-            return samples[index] != null || stripe.samples.containsKey(packed);
+    HydrologyTerrainSample[] sampleWithoutSlopeBatch(long[] coordinates, int count,
+                                                    HydrologyNaturalTerrainSampler sampler) {
+        Objects.checkFromIndexSize(0, count, coordinates.length);
+        if (count > HydrologyTerrainSampler.MAXIMUM_BATCH_SIZE) {
+            throw new IllegalArgumentException("Terrain basis batch exceeds its sample limit");
         }
-    }
-
-    HydrologyTerrainSample rememberWithoutSlope(long packed, HydrologyTerrainSample sample) {
-        Stripe stripe = stripe(withoutSlope, packed);
-        synchronized (stripe) {
-            if (stripe.samples.containsKey(packed)) {
-                return stripe.samples.getAndMoveToFirst(packed);
+        HydrologyTerrainSample[] samples = new HydrologyTerrainSample[count];
+        Pending[] pending = new Pending[count];
+        long[] ownedCoordinates = new long[count];
+        Pending[] owned = new Pending[count];
+        int ownedCount = count;
+        Completion completion = new Completion();
+        int[] next = new int[count];
+        int[] heads = groupByStripe(coordinates, count, next);
+        try {
+            for (int stripeIndex = 0; stripeIndex < withoutSlope.length; stripeIndex++) {
+                if (heads[stripeIndex] == 0) {
+                    continue;
+                }
+                Stripe stripe = withoutSlope[stripeIndex];
+                synchronized (stripe) {
+                    for (int position = heads[stripeIndex]; position != 0; position = next[position - 1]) {
+                        int index = position - 1;
+                        long packed = coordinates[index];
+                        HydrologyTerrainSample cached = stripe.samples.getAndMoveToFirst(packed);
+                        if (cached != null || stripe.samples.containsKey(packed)) {
+                            samples[index] = cached;
+                            continue;
+                        }
+                        Pending loading = stripe.pending.get(packed);
+                        if (loading == null) {
+                            loading = new Pending(completion);
+                            stripe.pending.put(packed, loading);
+                            ownedCoordinates[index] = packed;
+                            owned[index] = loading;
+                        }
+                        pending[index] = loading;
+                    }
+                }
             }
-            stripe.put(packed, sample);
-            return sample;
+            int claimed = 0;
+            for (int index = 0; index < count; index++) {
+                if (owned[index] != null) {
+                    ownedCoordinates[claimed] = ownedCoordinates[index];
+                    owned[claimed++] = owned[index];
+                }
+            }
+            ownedCount = claimed;
+            if (ownedCount > 0) {
+                loadBatch(ownedCoordinates, owned, ownedCount, sampler);
+            }
+        } catch (RuntimeException | Error failure) {
+            for (int index = 0; index < ownedCount; index++) {
+                if (owned[index] != null) {
+                    fail(withoutSlope, ownedCoordinates[index], owned[index], failure);
+                }
+            }
+            completion.failure = failure;
+            throw failure;
+        } finally {
+            completion.complete.countDown();
         }
+        for (int index = 0; index < count; index++) {
+            if (pending[index] != null) {
+                samples[index] = pending[index].await();
+            }
+        }
+        return samples;
     }
 
     void seedWithoutSlope(Long2ObjectMap<HydrologyTerrainSample> samples) {
@@ -64,15 +122,104 @@ final class HydrologyBasisCache {
 
     private HydrologyTerrainSample sample(int x, int z, HydrologyNaturalTerrainSampler sampler, boolean omitSlope) {
         long packed = RiverFootprint.pack(x, z);
-        Stripe stripe = stripe(omitSlope ? withoutSlope : full, packed);
+        Stripe[] stripes = omitSlope ? withoutSlope : full;
+        Stripe stripe = stripe(stripes, packed);
+        Pending loading;
+        boolean owner = false;
         synchronized (stripe) {
             HydrologyTerrainSample cached = stripe.samples.getAndMoveToFirst(packed);
             if (cached != null || stripe.samples.containsKey(packed)) {
                 return cached;
             }
-            HydrologyTerrainSample sampled = omitSlope ? sampler.sampleBasisWithoutSlope(x, z) : sampler.sampleBasis(x, z);
-            stripe.put(packed, sampled);
-            return sampled;
+            loading = stripe.pending.get(packed);
+            if (loading == null) {
+                loading = new Pending(new Completion());
+                stripe.pending.put(packed, loading);
+                owner = true;
+            }
+        }
+        if (owner) {
+            try {
+                HydrologyTerrainSample sampled = ProvisionalSampling.memoizable(() -> omitSlope
+                        ? sampler.sampleBasisWithoutSlope(x, z) : sampler.sampleBasis(x, z));
+                complete(stripes, packed, loading, sampled, false);
+            } catch (ProvisionalSampling.Unmemoizable provisional) {
+                complete(stripes, packed, loading, provisional.value(), true);
+            } catch (RuntimeException | Error failure) {
+                fail(stripes, packed, loading, failure);
+                throw failure;
+            } finally {
+                loading.completion.complete.countDown();
+            }
+        }
+        return loading.await();
+    }
+
+    private void loadBatch(long[] coordinates, Pending[] pending, int count, HydrologyNaturalTerrainSampler sampler) {
+        HydrologyTerrainSample[] samples;
+        boolean provisional = false;
+        try {
+            samples = ProvisionalSampling.memoizable(() -> sampler.sampleBasisWithoutSlopeBatch(coordinates, count));
+        } catch (ProvisionalSampling.Unmemoizable value) {
+            samples = value.value();
+            provisional = true;
+        }
+        if (samples.length < count) {
+            throw new IllegalStateException("Terrain basis batch returned too few samples");
+        }
+        int[] next = new int[count];
+        int[] heads = groupByStripe(coordinates, count, next);
+        for (int stripeIndex = 0; stripeIndex < withoutSlope.length; stripeIndex++) {
+            if (heads[stripeIndex] == 0) {
+                continue;
+            }
+            Stripe stripe = withoutSlope[stripeIndex];
+            synchronized (stripe) {
+                for (int position = heads[stripeIndex]; position != 0; position = next[position - 1]) {
+                    int index = position - 1;
+                    complete(stripe, coordinates[index], pending[index], samples[index], provisional);
+                }
+            }
+        }
+    }
+
+    private int[] groupByStripe(long[] coordinates, int count, int[] next) {
+        int[] heads = new int[withoutSlope.length];
+        for (int index = count - 1; index >= 0; index--) {
+            int stripeIndex = (int) CacheKey.mix(coordinates[index]) & (withoutSlope.length - 1);
+            next[index] = heads[stripeIndex];
+            heads[stripeIndex] = index + 1;
+        }
+        return heads;
+    }
+
+    private void complete(Stripe[] stripes, long packed, Pending pending, HydrologyTerrainSample sample,
+                          boolean provisional) {
+        Stripe stripe = stripe(stripes, packed);
+        synchronized (stripe) {
+            complete(stripe, packed, pending, sample, provisional);
+        }
+    }
+
+    private void complete(Stripe stripe, long packed, Pending pending, HydrologyTerrainSample sample,
+                          boolean provisional) {
+        if (stripe.samples.containsKey(packed)) {
+            sample = stripe.samples.getAndMoveToFirst(packed);
+            provisional = false;
+        } else if (!provisional) {
+            stripe.put(packed, sample);
+        }
+        stripe.pending.remove(packed);
+        pending.sample = sample;
+        pending.provisional = provisional;
+    }
+
+    private void fail(Stripe[] stripes, long packed, Pending pending, Throwable failure) {
+        Stripe stripe = stripe(stripes, packed);
+        synchronized (stripe) {
+            if (stripe.pending.remove(packed, pending)) {
+                pending.completion.failure = failure;
+            }
         }
     }
 
@@ -92,6 +239,7 @@ final class HydrologyBasisCache {
     private static final class Stripe {
         private final int maximumEntries;
         private final Long2ObjectLinkedOpenHashMap<HydrologyTerrainSample> samples;
+        private final Long2ObjectOpenHashMap<Pending> pending = new Long2ObjectOpenHashMap<>();
 
         private Stripe(int maximumEntries) {
             this.maximumEntries = maximumEntries;
@@ -105,4 +253,73 @@ final class HydrologyBasisCache {
             samples.putAndMoveToFirst(packed, value);
         }
     }
+
+    private static final class Pending {
+        private final Completion completion;
+        private HydrologyTerrainSample sample;
+        private boolean provisional;
+
+        private Pending(Completion completion) {
+            this.completion = completion;
+        }
+
+        private HydrologyTerrainSample await() {
+            completion.await();
+            if (provisional) {
+                ProvisionalSampling.mark();
+            }
+            return sample;
+        }
+    }
+
+    private static final class Completion implements ForkJoinPool.ManagedBlocker {
+        private final Thread owner = Thread.currentThread();
+        private final CountDownLatch complete = new CountDownLatch(1);
+        private Throwable failure;
+
+        private void await() {
+            if (!isReleasable() && owner == Thread.currentThread()) {
+                throw new IllegalStateException("Recursive terrain basis sampling");
+            }
+            boolean interrupted = false;
+            boolean managed = true;
+            try {
+                while (!isReleasable()) {
+                    try {
+                        if (managed) {
+                            ForkJoinPool.managedBlock(this);
+                        } else {
+                            complete.await();
+                        }
+                    } catch (InterruptedException interruption) {
+                        interrupted = true;
+                        managed = false;
+                    } catch (RejectedExecutionException unavailable) {
+                        managed = false;
+                    }
+                }
+            } finally {
+                if (interrupted) {
+                    Thread.currentThread().interrupt();
+                }
+            }
+            if (failure instanceof Error error) {
+                throw error;
+            }
+            if (failure instanceof RuntimeException runtime) {
+                throw runtime;
+            }
+        }
+
+        @Override
+        public boolean block() throws InterruptedException {
+            complete.await();
+            return true;
+        }
+
+        @Override
+        public boolean isReleasable() {
+            return complete.getCount() == 0;
+        }
+    }
 }

core/src/main/java/art/arcane/iris/generation/hydrology/HydrologyFootprintCompiler.java

@@ -946,8 +946,6 @@ final class HydrologyFootprintCompiler {
             HydrologyTerrainSample cached = terrainBases.get(key);
             if (cached != null) {
                 samples[index] = cached;
-            } else if (sharedBasis != null && sharedBasis.findWithoutSlope(key, samples, index)) {
-                continue;
             } else if (naturalSampler == null) {
                 samples[index] = sampleTerrainBasis(RiverFootprint.unpackX(key), RiverFootprint.unpackZ(key));
             } else {
@@ -956,10 +954,11 @@ final class HydrologyFootprintCompiler {
             }
         }
         if (missingCount > 0) {
-            HydrologyTerrainSample[] loaded = naturalSampler.sampleBasisWithoutSlopeBatch(missing, missingCount);
+            HydrologyTerrainSample[] loaded = sharedBasis == null
+                    ? naturalSampler.sampleBasisWithoutSlopeBatch(missing, missingCount)
+                    : sharedBasis.sampleWithoutSlopeBatch(missing, missingCount, naturalSampler);
             for (int index = 0; index < missingCount; index++) {
-                samples[positions[index]] = sharedBasis == null ? loaded[index]
-                        : sharedBasis.rememberWithoutSlope(missing[index], loaded[index]);
+                samples[positions[index]] = loaded[index];
             }
         }
         for (int index = 0; index < count; index++) {

core/src/main/java/art/arcane/iris/generation/hydrology/HydrologyForkJoin.java

@@ -1,5 +1,7 @@
 package art.arcane.iris.generation.hydrology;
 
+import art.arcane.iris.generation.stream.ProvisionalSampling;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
@@ -91,6 +93,7 @@ public final class HydrologyForkJoin {
         private final CountDownLatch complete = new CountDownLatch(1);
         private T result;
         private Throwable failure;
+        private boolean provisional;
 
         Task(Callable<T> work) {
             this.work = Objects.requireNonNull(work);
@@ -136,6 +139,9 @@ public final class HydrologyForkJoin {
             if (failure != null) {
                 throw unwrap(failure);
             }
+            if (provisional) {
+                ProvisionalSampling.mark();
+            }
             return result;
         }
 
@@ -156,7 +162,10 @@ public final class HydrologyForkJoin {
                 return;
             }
             try {
-                result = call(work);
+                result = ProvisionalSampling.memoizable(() -> call(work));
+            } catch (ProvisionalSampling.Unmemoizable value) {
+                result = value.value();
+                provisional = true;
             } catch (RuntimeException | Error failed) {
                 failure = failed;
             } finally {

core/src/main/java/art/arcane/iris/generation/hydrology/runtime/IrisHydrologyNaturalHeightProvider.java

@@ -1,6 +1,18 @@
 package art.arcane.iris.generation.hydrology.runtime;
 
+import art.arcane.iris.generation.hydrology.RiverFootprint;
+
 @FunctionalInterface
 public interface IrisHydrologyNaturalHeightProvider {
     double sample(int blockX, int blockZ);
+
+    default boolean supportsBatch() {
+        return false;
+    }
+
+    default void sampleBatch(long[] coordinates, int count, double[] heights) {
+        for (int index = 0; index < count; index++) {
+            heights[index] = sample(RiverFootprint.unpackX(coordinates[index]), RiverFootprint.unpackZ(coordinates[index]));
+        }
+    }
 }

core/src/main/java/art/arcane/iris/generation/hydrology/runtime/IrisHydrologyRoutingTerrainSampler.java

@@ -10,6 +10,8 @@ import art.arcane.iris.generation.hydrology.RiverFootprint;
 import art.arcane.volmlib.nativelib.terrain.NativeGenerationScope;
 import art.arcane.iris.generation.hydrology.HydrologyForkJoin;
 import art.arcane.iris.generation.concurrent.MultiBurst;
+import art.arcane.iris.generation.stream.ProvisionalSampling;
+import it.unimi.dsi.fastutil.longs.Long2IntOpenHashMap;
 import it.unimi.dsi.fastutil.longs.Long2DoubleLinkedOpenHashMap;
 import it.unimi.dsi.fastutil.longs.Long2ObjectLinkedOpenHashMap;
 
@@ -98,15 +100,10 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
                 return cached;
             }
         }
-        NaturalClassification sampled = NaturalClassification.LAND;
-        if (oceanClassifier.isOcean(blockX, blockZ)) {
-            double height = naturalHeight(stripe, packed, blockX, blockZ);
-            if (!Double.isFinite(height)) {
-                return NaturalClassification.UNAVAILABLE;
-            }
-            if (physicalOcean(true, height, seaLevel)) {
-                sampled = NaturalClassification.OCEAN;
-            }
+        long revision = ProvisionalSampling.revision();
+        NaturalClassification sampled = classifyNatural(stripe, packed, blockX, blockZ);
+        if (sampled == NaturalClassification.UNAVAILABLE || revision != ProvisionalSampling.revision()) {
+            return sampled;
         }
         synchronized (stripe) {
             TerrainBasis basis = stripe.bases.getAndMoveToLast(packed);
@@ -123,6 +120,17 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
         return sampled;
     }
 
+    private NaturalClassification classifyNatural(CacheStripe stripe, long packed, int blockX, int blockZ) {
+        if (!oceanClassifier.isOcean(blockX, blockZ)) {
+            return NaturalClassification.LAND;
+        }
+        double height = naturalHeight(stripe, packed, blockX, blockZ);
+        if (!Double.isFinite(height)) {
+            return NaturalClassification.UNAVAILABLE;
+        }
+        return physicalOcean(true, height, seaLevel) ? NaturalClassification.OCEAN : NaturalClassification.LAND;
+    }
+
     @Override
     public HydrologyTerrainSample sampleBasis(int blockX, int blockZ) {
         // Point samples carry the forward slope; the aligned grid derives its own from neighbouring bases.
@@ -144,10 +152,15 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
         int workers = Math.min(Math.min(samplingOptions.maximumWorkers(), Runtime.getRuntime().availableProcessors()),
                 Math.ceilDiv(count, MINIMUM_PARALLEL_BASIS_SAMPLES));
         Supplier<NativeGenerationScope> scope = workers > 1 ? samplingOptions.batchScopes().capture() : null;
-        if (scope == null) {
-            return HydrologyNaturalTerrainSampler.super.sampleBasisWithoutSlopeBatch(coordinates, count);
-        }
         HydrologyTerrainSample[] samples = new HydrologyTerrainSample[count];
+        if (scope == null) {
+            TerrainBasis[] bases = new TerrainBasis[count];
+            fillBasisBatch(coordinates, count, bases, 0);
+            for (int index = 0; index < count; index++) {
+                samples[index] = bases[index].terrain();
+            }
+            return samples;
+        }
         int perWorker = Math.ceilDiv(count, workers);
         ArrayList<Callable<Void>> tasks = new ArrayList<>(workers);
         for (int worker = 0; worker < workers; worker++) {
@@ -158,12 +171,12 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
             }
             tasks.add(() -> {
                 try (NativeGenerationScope ignored = scope.get()) {
+                    long[] slice = new long[end - start];
+                    System.arraycopy(coordinates, start, slice, 0, slice.length);
+                    TerrainBasis[] bases = new TerrainBasis[slice.length];
+                    fillBasisBatch(slice, slice.length, bases, 0);
                     for (int index = start; index < end; index++) {
-                        if (Thread.currentThread().isInterrupted()) {
-                            throw new CancellationException("Terrain basis sampling interrupted");
-                        }
-                        samples[index] = sampleBasisWithoutSlope(RiverFootprint.unpackX(coordinates[index]),
-                                RiverFootprint.unpackZ(coordinates[index]));
+                        samples[index] = bases[index - start].terrain();
                     }
                 }
                 return null;
@@ -183,9 +196,12 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
                 return cached.terrain().ocean() ? Double.NaN : cached.terrain().naturalHeight();
             }
         }
+        long revision = ProvisionalSampling.revision();
         double naturalHeight = naturalHeight(stripe, packed, blockX, blockZ);
+        boolean memoizable = revision == ProvisionalSampling.revision();
         if (!Double.isFinite(naturalHeight)) {
-            TerrainBasis basis = loadBasis(blockX, blockZ, stripe, packed, naturalHeight);
+            TerrainBasis basis = memoizable ? loadBasis(blockX, blockZ, stripe, packed, naturalHeight)
+                    : sampleBasis(blockX, blockZ, naturalHeight);
             return basis.terrain().ocean() ? Double.NaN : basis.terrain().naturalHeight();
         }
         long roundedHeight = StrictMath.round(naturalHeight);
@@ -194,7 +210,8 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
         }
         NaturalClassification classification = classifyNatural(blockX, blockZ);
         if (classification == NaturalClassification.UNAVAILABLE) {
-            TerrainBasis basis = loadBasis(blockX, blockZ, stripe, packed, naturalHeight);
+            TerrainBasis basis = memoizable ? loadBasis(blockX, blockZ, stripe, packed, naturalHeight)
+                    : sampleBasis(blockX, blockZ, naturalHeight);
             return basis.terrain().ocean() ? Double.NaN : basis.terrain().naturalHeight();
         }
         return classification == NaturalClassification.OCEAN ? Double.NaN : (int) roundedHeight;
@@ -209,16 +226,28 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
                 return cached;
             }
         }
-        return loadBasis(blockX, blockZ, stripe, packed, naturalHeight(stripe, packed, blockX, blockZ));
+        long revision = ProvisionalSampling.revision();
+        TerrainBasis sampled = sampleBasis(blockX, blockZ, naturalHeight(stripe, packed, blockX, blockZ));
+        return revision == ProvisionalSampling.revision() ? publishBasis(stripe, packed, sampled) : sampled;
     }
 
     private TerrainBasis loadBasis(int blockX, int blockZ, CacheStripe stripe, long packed, double naturalHeight) {
+        long revision = ProvisionalSampling.revision();
+        TerrainBasis sampled = sampleBasis(blockX, blockZ, naturalHeight);
+        return revision == ProvisionalSampling.revision() ? publishBasis(stripe, packed, sampled) : sampled;
+    }
+
+    private TerrainBasis sampleBasis(int blockX, int blockZ, double naturalHeight) {
         TerrainBasis sampled = basisProvider.sample(blockX, blockZ, naturalHeight);
         if (sampled == null) {
             throw new NullPointerException(
                     "Hydrology terrain basis provider returned null at " + blockX + "," + blockZ
             );
         }
+        return sampled;
+    }
+
+    private TerrainBasis publishBasis(CacheStripe stripe, long packed, TerrainBasis sampled) {
         synchronized (stripe) {
             TerrainBasis existing = stripe.bases.getAndMoveToLast(packed);
             if (existing != null) {
@@ -349,14 +378,108 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
             int minimumRow,
             int maximumRow
     ) {
+        int capacity = Math.min(HydrologyTerrainSampler.MAXIMUM_BATCH_SIZE,
+                Math.multiplyExact(maximumRow - minimumRow, planeWidth));
+        long[] coordinates = new long[capacity];
+        int count = 0;
+        int destination = minimumRow * planeWidth;
         for (int gridZ = minimumRow; gridZ < maximumRow; gridZ++) {
             int z = Math.toIntExact((long) minimumZ + (long) gridZ * spacing);
-            int planeIndex = gridZ * planeWidth;
             for (int gridX = 0; gridX < planeWidth; gridX++) {
                 int x = Math.toIntExact((long) minimumX + (long) gridX * spacing);
-                plane[planeIndex++] = basis(x, z);
+                coordinates[count++] = RiverFootprint.pack(x, z);
+                if (count == coordinates.length) {
+                    fillBasisBatch(coordinates, count, plane, destination);
+                    destination += count;
+                    count = 0;
+                }
             }
         }
+        if (count > 0) {
+            fillBasisBatch(coordinates, count, plane, destination);
+        }
+    }
+
+    private void fillBasisBatch(long[] coordinates, int count, TerrainBasis[] target, int offset) {
+        if (!heightProvider.supportsBatch()) {
+            for (int index = 0; index < count; index++) {
+                if (Thread.currentThread().isInterrupted()) {
+                    throw new CancellationException("Terrain basis sampling interrupted");
+                }
+                target[offset + index] = basis(RiverFootprint.unpackX(coordinates[index]),
+                        RiverFootprint.unpackZ(coordinates[index]));
+            }
+            return;
+        }
+        long[] missing = new long[count];
+        int[] slots = new int[count];
+        double[] heights = new double[count];
+        Long2IntOpenHashMap indices = new Long2IntOpenHashMap(count);
+        indices.defaultReturnValue(-1);
+        int missingCount = 0;
+        for (int index = 0; index < count; index++) {
+            int x = RiverFootprint.unpackX(coordinates[index]);
+            int z = RiverFootprint.unpackZ(coordinates[index]);
+            long packed = pack(x, z);
+            CacheStripe stripe = stripe(packed);
+            synchronized (stripe) {
+                TerrainBasis basis = stripe.bases.getAndMoveToLast(packed);
+                if (basis != null) {
+                    target[offset + index] = basis;
+                    slots[index] = -1;
+                    continue;
+                }
+                heights[index] = stripe.naturalHeights.getAndMoveToLast(packed);
+            }
+            if (!Double.isNaN(heights[index])) {
+                slots[index] = -1;
+                continue;
+            }
+            int slot = indices.get(coordinates[index]);
+            if (slot < 0) {
+                slot = missingCount++;
+                indices.put(coordinates[index], slot);
+                missing[slot] = coordinates[index];
+            }
+            slots[index] = slot;
+        }
+        double[] sampled = new double[missingCount];
+        boolean memoizable = true;
+        if (missingCount > 0) {
+            if (Thread.currentThread().isInterrupted()) {
+                throw new CancellationException("Terrain basis sampling interrupted");
+            }
+            long revision = ProvisionalSampling.revision();
+            heightProvider.sampleBatch(missing, missingCount, sampled);
+            memoizable = revision == ProvisionalSampling.revision();
+            for (int index = 0; memoizable && index < missingCount; index++) {
+                if (!Double.isFinite(sampled[index])) {
+                    continue;
+                }
+                long packed = pack(RiverFootprint.unpackX(missing[index]), RiverFootprint.unpackZ(missing[index]));
+                CacheStripe stripe = stripe(packed);
+                synchronized (stripe) {
+                    double existing = stripe.naturalHeights.getAndMoveToLast(packed);
+                    if (Double.isNaN(existing)) {
+                        stripe.naturalHeights.putAndMoveToLast(packed, sampled[index]);
+                        stripe.evictOldest(stripe.naturalHeights);
+                    } else {
+                        sampled[index] = existing;
+                    }
+                }
+            }
+        }
+        for (int index = 0; index < count; index++) {
+            if (target[offset + index] != null) {
+                continue;
+            }
+            int x = RiverFootprint.unpackX(coordinates[index]);
+            int z = RiverFootprint.unpackZ(coordinates[index]);
+            long packed = pack(x, z);
+            double height = slots[index] < 0 ? heights[index] : sampled[slots[index]];
+            target[offset + index] = memoizable ? loadBasis(x, z, stripe(packed), packed, height)
+                    : sampleBasis(x, z, height);
+        }
     }
 
     private int gridWorkerCount(int planeWidth, int planeSize) {
@@ -384,8 +507,9 @@ final class IrisHydrologyRoutingTerrainSampler implements HydrologyNaturalTerrai
                 return cachedBasis.naturalHeight();
             }
         }
+        long revision = ProvisionalSampling.revision();
         double sampled = heightProvider.sample(blockX, blockZ);
-        if (!Double.isFinite(sampled)) {
+        if (!Double.isFinite(sampled) || revision != ProvisionalSampling.revision()) {
             // Never memoize a broken sample: the basis provider rejects it with a diagnostic and a
             // later sample of the same column gets a fresh chance instead of the cached failure.
             return sampled;

core/src/main/java/art/arcane/iris/generation/hydrology/runtime/IrisHydrologyRuntime.java

@@ -100,7 +100,7 @@ public final class IrisHydrologyRuntime implements AutoCloseable {
         HydrologyGeometrySampler geometrySampler = geometrySampler(context, hydrology);
         IrisHydrologyRoutingTerrainSampler.Sources terrainSources = new IrisHydrologyRoutingTerrainSampler.Sources(
                 this::createTerrainBasis,
-                (int x, int z) -> context.naturalHeightProvider().sample(x, z),
+                context.naturalHeightProvider(),
                 (int x, int z) -> context.naturalOceanClassifier().isOcean(x, z),
                 settings.seaLevel()
         );

core/src/main/java/art/arcane/iris/generation/noise/IrisGenerator.java

@@ -41,7 +41,10 @@ import lombok.Getter;
 import lombok.Setter;
 import lombok.experimental.Accessors;
 
+import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
+import java.util.function.DoubleBinaryOperator;
 
 @Accessors(chain = true)
 @NoArgsConstructor
@@ -208,26 +211,106 @@ public class IrisGenerator extends IrisRegistrant {
         if (surfaceDetail == 1D) {
             return sampleHeight(rx, rz, superSeed, data, engine);
         }
+        return surfaceHeight(rx, rz, superSeed, data, engine, null);
+    }
+
+    public boolean supportsBatch() {
+        if (getClass() != IrisGenerator.class || !Double.isFinite(surfaceDetail)
+                || surfaceDetail < 0D || surfaceDetail > 1D) {
+            return false;
+        }
+        for (IrisNoiseGenerator layer : composite) {
+            if (!layer.supportsBatch()) {
+                return false;
+            }
+        }
+        return !hasCliffs() || cliffHeightGenerator.supportsBatch();
+    }
+
+    public void getHeights(double[] xs, double[] zs, long superSeed, double[] target, int count) {
+        Objects.checkFromIndexSize(0, count, xs.length);
+        Objects.checkFromIndexSize(0, count, zs.length);
+        Objects.checkFromIndexSize(0, count, target.length);
+        if (count > 4096) {
+            throw new IllegalArgumentException("Generator batch exceeds 4096 samples");
+        }
+        if (count < 8 || !supportsBatch()) {
+            for (int index = 0; index < count; index++) {
+                target[index] = getHeight(xs[index], zs[index], superSeed);
+            }
+            return;
+        }
+        if (composite.isEmpty()) {
+            Arrays.fill(target, 0, count, 0D);
+            return;
+        }
+        IrisData data = getLoader();
+        Engine engine = data == null ? null : data.getEngine();
+        DoubleBinaryOperator prepared = prepareHeight(superSeed, data, engine);
+        for (int index = 0; index < count; index++) {
+            target[index] = surfaceDetail == 1D ? prepared.applyAsDouble(xs[index], zs[index])
+                    : surfaceHeight(xs[index], zs[index], superSeed, data, engine, prepared);
+        }
+    }
+
+    private DoubleBinaryOperator prepareHeight(long superSeed, IrisData data, Engine engine) {
+        int hc = (int) ((cliffHeightMin * 10) + 10 + cliffHeightMax * getSeed() + offsetX + offsetZ);
+        DoubleBinaryOperator[] layers = new DoubleBinaryOperator[composite.size()];
+        double totalOpacity = 0D;
+        for (int index = 0; index < layers.length; index++) {
+            IrisNoiseGenerator layer = composite.get(index);
+            layers[index] = layer.prepareBatch(getSeed() + superSeed + hc, data, engine);
+            if (!multiplicitive) {
+                totalOpacity += layer.getOpacity();
+            }
+        }
+        double sumOpacity = totalOpacity;
+        double cliffSeed = (double) (superSeed + 294596 + hc) - 34857;
+        DoubleBinaryOperator cliffs = hasCliffs() ? cliffHeightGenerator.prepareBatch(
+                (long) (getSeed() + cliffSeed + hc), data, engine) : null;
+        return (rx, rz) -> {
+            double sampleX = (rx + offsetX) / zoom;
+            double sampleZ = (rz + offsetZ) / zoom;
+            double h = multiplicitive ? 1D : 0D;
+            for (DoubleBinaryOperator layer : layers) {
+                double sampled = layer.applyAsDouble(sampleX, sampleZ);
+                h = multiplicitive ? h * sampled : h + sampled;
+            }
+            double value = multiplicitive ? h * opacity : (h / sumOpacity) * opacity;
+            if (Double.isNaN(value)) {
+                value = 0D;
+            }
+            if (cliffs != null) {
+                double height = IrisInterpolation.lerp(cliffHeightMin, cliffHeightMax,
+                        cliffs.applyAsDouble(sampleX, sampleZ));
+                value = (Math.round((value * 255D) / height) * height) / 255D;
+            }
+            return hasCellCracks() ? cell(rx, rz, value, superSeed + 48622 + hc) : value;
+        };
+    }
+
+    private double surfaceHeight(double rx, double rz, long superSeed, IrisData data, Engine engine,
+                                 DoubleBinaryOperator prepared) {
         SurfaceCacheStripe[] stripes = surfaceCache(data, engine).stripes();
         double lowerX = Math.floor(rx / SURFACE_GRID) * SURFACE_GRID;
         double lowerZ = Math.floor(rz / SURFACE_GRID) * SURFACE_GRID;
         double dx = (rx - lowerX) / SURFACE_GRID;
         double dz = (rz - lowerZ) / SURFACE_GRID;
-        double northWest = cachedSurfaceHeight(lowerX, lowerZ, superSeed, stripes, data, engine);
+        double northWest = cachedSurfaceHeight(lowerX, lowerZ, superSeed, stripes, data, engine, prepared);
         if (dx == 0D && dz == 0D) {
             return northWest;
         }
         double north = dx == 0D ? northWest : IrisInterpolation.lerp(northWest,
-                cachedSurfaceHeight(lowerX + SURFACE_GRID, lowerZ, superSeed, stripes, data, engine), dx);
+                cachedSurfaceHeight(lowerX + SURFACE_GRID, lowerZ, superSeed, stripes, data, engine, prepared), dx);
         double smooth = north;
         if (dz != 0D) {
-            double southWest = cachedSurfaceHeight(lowerX, lowerZ + SURFACE_GRID, superSeed, stripes, data, engine);
+            double southWest = cachedSurfaceHeight(lowerX, lowerZ + SURFACE_GRID, superSeed, stripes, data, engine, prepared);
             double south = dx == 0D ? southWest : IrisInterpolation.lerp(southWest,
-                    cachedSurfaceHeight(lowerX + SURFACE_GRID, lowerZ + SURFACE_GRID, superSeed, stripes, data, engine), dx);
+                    cachedSurfaceHeight(lowerX + SURFACE_GRID, lowerZ + SURFACE_GRID, superSeed, stripes, data, engine, prepared), dx);
             smooth = IrisInterpolation.lerp(north, south, dz);
         }
         return surfaceDetail == 0D ? smooth
-                : smooth + (sampleHeight(rx, rz, superSeed, data, engine) - smooth) * surfaceDetail;
+                : smooth + ((prepared == null ? sampleHeight(rx, rz, superSeed, data, engine) : prepared.applyAsDouble(rx, rz)) - smooth) * surfaceDetail;
     }
 
     private double sampleHeight(double rx, double rz, long superSeed, IrisData data, Engine engine) {
@@ -267,9 +350,9 @@ public class IrisGenerator extends IrisRegistrant {
         return v;
     }
 
-    private double cachedSurfaceHeight(double x, double z, long superSeed, SurfaceCacheStripe[] stripes, IrisData data, Engine engine) {
+    private double cachedSurfaceHeight(double x, double z, long superSeed, SurfaceCacheStripe[] stripes, IrisData data, Engine engine, DoubleBinaryOperator prepared) {
         if (x != (int) x || z != (int) z) {
-            return sampleHeight(x, z, superSeed, data, engine);
+            return prepared == null ? sampleHeight(x, z, superSeed, data, engine) : prepared.applyAsDouble(x, z);
         }
         long key = ((long) (int) x << 32) | ((int) z & 0xffffffffL);
         long mixed = key ^ (key >>> 33);
@@ -281,7 +364,7 @@ public class IrisGenerator extends IrisRegistrant {
         if (cached != null) {
             return cached.height();
         }
-        double height = sampleHeight(x, z, superSeed, data, engine);
+        double height = prepared == null ? sampleHeight(x, z, superSeed, data, engine) : prepared.applyAsDouble(x, z);
         stripe.put(slot, new SurfaceSample(key, superSeed, height));
         return height;
     }

core/src/main/java/art/arcane/iris/generation/noise/IrisNoiseGenerator.java

@@ -48,6 +48,7 @@ import lombok.Setter;
 import lombok.experimental.Accessors;
 
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.DoubleBinaryOperator;
 
 @Snippet("generator")
 @Accessors(chain = true)
@@ -176,6 +177,67 @@ public class IrisNoiseGenerator {
         return sample(getGenerator(superSeed, data, engine), x, z);
     }
 
+    boolean supportsBatch() {
+        if (getClass() != IrisNoiseGenerator.class) {
+            return false;
+        }
+        if (!enabled) {
+            return true;
+        }
+        for (IrisGeneratorStyle current = style; current != null; current = current.getFracture()) {
+            if (current.getClass() != IrisGeneratorStyle.class || current.getExpression() != null
+                    || current.getImageMap() != null) {
+                return false;
+            }
+        }
+        for (IrisNoiseGenerator child : fracture) {
+            if (!child.supportsBatch()) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    DoubleBinaryOperator prepareBatch(long superSeed, IrisData data, Engine engine) {
+        if (!enabled) {
+            double value = offsetY;
+            return (x, z) -> value;
+        }
+        if (hasDeepFracture()) {
+            FractureSamples samples = new FractureSamples();
+            if (samples.prepare(this, superSeed, data, engine)) {
+                return samples::sample;
+            }
+        }
+        DoubleBinaryOperator[] children = new DoubleBinaryOperator[fracture.size()];
+        double[] offsets = new double[fracture.size()];
+        int salt = 33;
+        for (int index = 0; index < children.length; index++) {
+            IrisNoiseGenerator child = fracture.get(index);
+            if (child.isEnabled()) {
+                children[index] = child.prepareBatch(superSeed + seed + salt, data, engine);
+                offsets[index] = child.getOpacity() / 2D;
+            }
+            salt += 819;
+        }
+        CNG generator = getGenerator(superSeed, data, engine);
+        return (x, z) -> samplePrepared(generator, children, offsets, x, z);
+    }
+
+    private double samplePrepared(CNG generator, DoubleBinaryOperator[] children, double[] offsets,
+                                  double xv, double zv) {
+        double x = xv;
+        double z = zv;
+        for (int index = 0; index < children.length; index++) {
+            DoubleBinaryOperator child = children[index];
+            if (child != null) {
+                x += child.applyAsDouble(xv, zv) - offsets[index];
+                z += child.applyAsDouble(zv, xv) - offsets[index];
+            }
+        }
+        return sample(generator, x, z);
+    }
+
     public KList<IrisNoiseGenerator> getAllComposites() {
         KList<IrisNoiseGenerator> g = new KList<>();
 

core/src/main/java/art/arcane/iris/generation/runtime/IrisComplex.java

@@ -39,6 +39,8 @@ import art.arcane.iris.generation.hydrology.HydrologyColumnSample;
 import art.arcane.iris.generation.hydrology.HydrologyColumnSnapshot;
 import art.arcane.iris.generation.hydrology.HydrologyFeatureType;
 import art.arcane.iris.generation.hydrology.runtime.IrisHydrologyNaturalSample;
+import art.arcane.iris.generation.hydrology.runtime.IrisHydrologyNaturalHeightProvider;
+import art.arcane.iris.generation.hydrology.RiverFootprint;
 import art.arcane.iris.generation.hydrology.runtime.IrisHydrologyRuntime;
 import art.arcane.iris.generation.hydrology.runtime.IrisHydrologyRuntimeContext;
 import art.arcane.iris.generation.image.IrisImageMapApplication;
@@ -454,7 +456,7 @@ public class IrisComplex implements DataProvider {
                     engine.getDimension(),
                     data,
                     (x, z, naturalHeight) -> sampleHydrologyNatural(engine, x, z, naturalHeight),
-                    (x, z) -> naturalHeightStream.getDouble(x, z),
+                    new HydrologyHeightProvider(),
                     (x, z) -> describeNaturalHeight(engine, x, z),
                     this::sampleNaturalOcean,
                     footprint -> new MantleHydrologyCaveVoxelView(engine, this, footprint),
@@ -791,6 +793,154 @@ public class IrisComplex implements DataProvider {
         return column == null ? getHeightStream().getDouble(x, z) : column.nearestSurfaceY(surfaceY);
     }
 
+    private boolean supportsHeightBatch() {
+        if (terrainEngine.getDimension().getTerrainSamplingStep() != 1 || !biomeBuffetGenerators.isEmpty()
+                || !reuseNaturalBaseBiome) {
+            return false;
+        }
+        for (IrisGenerator[] group : frozenGenerators) {
+            for (IrisGenerator generator : group) {
+                if (!generator.supportsBatch()) {
+                    return false;
+                }
+            }
+        }
+        for (IrisShapedGeneratorStyle overlay : terrainEngine.getDimension().getOverlayNoise()) {
+            if (overlay.getClass() != IrisShapedGeneratorStyle.class) {
+                return false;
+            }
+            for (IrisGeneratorStyle style = overlay.getGenerator(); style != null; style = style.getFracture()) {
+                if (style.getClass() != IrisGeneratorStyle.class || style.getExpression() != null) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    private void sampleBaseHeightBatch(long[] coordinates, int count, double[] target) {
+        ((CachedDoubleStream2D) baseTerrainHeightStream).getBatch(coordinates, count, target, this::resolveBaseHeightBatch);
+    }
+
+    private void resolveBaseHeightBatch(long[] missing, int size, double[] values) {
+        double[] xs = new double[size];
+        double[] zs = new double[size];
+        double[] lows = new double[size];
+        double[] highs = new double[size];
+        double[] activeXs = new double[size];
+        double[] activeZs = new double[size];
+        double[] noise = new double[size];
+        double[] groupHeights = new double[size];
+        int[] active = new int[size];
+        for (int index = 0; index < size; index++) {
+            xs[index] = RiverFootprint.unpackX(missing[index]);
+            zs[index] = RiverFootprint.unpackZ(missing[index]);
+        }
+        long seed = terrainEngine.getSeedManager().getHeight() + 239945;
+        for (int group = 0; group < frozenInterpolators.length; group++) {
+            IrisGenerator[] generators = frozenGenerators[group];
+            if (generators.length == 0) {
+                continue;
+            }
+            int activeCount = 0;
+            Arrays.fill(groupHeights, 0D);
+            for (int index = 0; index < size; index++) {
+                NoiseBounds bounds = gridSampleBounds(terrainEngine, frozenInterpolators[group], group,
+                        generators, xs[index], zs[index]);
+                lows[index] = bounds.min();
+                highs[index] = bounds.max();
+                if (!Double.isFinite(lows[index]) || !Double.isFinite(highs[index])) {
+                    averageGeneratorHeights(generators, lows[index], highs[index], xs[index], zs[index], seed);
+                }
+                if (lows[index] != highs[index]) {
+                    active[activeCount] = index;
+                    activeXs[activeCount] = xs[index];
+                    activeZs[activeCount++] = zs[index];
+                } else {
+                    for (int generator = 0; generator < generators.length; generator++) {
+                        groupHeights[index] += lows[index];
+                    }
+                }
+            }
+            for (IrisGenerator generator : generators) {
+                if (activeCount == 0) {
+                    break;
+                }
+                generator.getHeights(activeXs, activeZs, seed, noise, activeCount);
+                for (int sample = 0; sample < activeCount; sample++) {
+                    int index = active[sample];
+                    if (!Double.isFinite(noise[sample])) {
+                        throw new IllegalStateException("Terrain generator noise was not finite at " + xs[index] + "," + zs[index]
+                                + " (generator=" + generator.getLoadKey() + ", noise=" + noise[sample]
+                                + ", bounds=" + lows[index] + ".." + highs[index] + ").");
+                    }
+                    groupHeights[index] += M.lerp(lows[index], highs[index], noise[sample]);
+                }
+            }
+            for (int index = 0; index < size; index++) {
+                values[index] += groupHeights[index] / generators.length;
+            }
+        }
+        for (int index = 0; index < size; index++) {
+            double height = Math.max(Math.min(values[index] + fluidHeight + overlayStream.get(xs[index], zs[index]),
+                    terrainEngine.getHeight()), 0);
+            values[index] = imageMapRuntime.sampleTerrainHeight(xs[index], zs[index], height);
+        }
+    }
+
+    private void sampleUnblendedHeightBatch(long[] coordinates, int count, double[] target) {
+        if (terrain3D == null) {
+            sampleBaseHeightBatch(coordinates, count, target);
+            return;
+        }
+        ((CachedDoubleStream2D) unblendedNaturalHeightStream).getBatch(coordinates, count, target, (missing, size, values) -> {
+            long[] required = new long[size];
+            int requiredCount = 0;
+            for (int index = 0; index < size; index++) {
+                if (terrain3D.requiresBaseHeight(RiverFootprint.unpackX(missing[index]), RiverFootprint.unpackZ(missing[index]))) {
+                    required[requiredCount++] = missing[index];
+                }
+            }
+            if (requiredCount > 0) {
+                sampleBaseHeightBatch(required, requiredCount, new double[requiredCount]);
+            }
+            for (int index = 0; index < size; index++) {
+                values[index] = sampleTerrain3DHeight(RiverFootprint.unpackX(missing[index]), RiverFootprint.unpackZ(missing[index]));
+            }
+        });
+    }
+
+    private final class HydrologyHeightProvider implements IrisHydrologyNaturalHeightProvider {
+        private final boolean batch = supportsHeightBatch();
+
+        @Override
+        public double sample(int blockX, int blockZ) {
+            return naturalHeightStream.getDouble(blockX, blockZ);
+        }
+
+        @Override
+        public boolean supportsBatch() {
+            return batch;
+        }
+
+        @Override
+        public void sampleBatch(long[] coordinates, int count, double[] heights) {
+            if (!batch) {
+                IrisHydrologyNaturalHeightProvider.super.sampleBatch(coordinates, count, heights);
+            } else if (transitionDisplacement == null) {
+                sampleUnblendedHeightBatch(coordinates, count, heights);
+            } else {
+                ((CachedDoubleStream2D) naturalHeightStream).getBatch(coordinates, count, heights, (missing, size, values) -> {
+                    sampleUnblendedHeightBatch(missing, size, values);
+                    for (int index = 0; index < size; index++) {
+                        values[index] = transitionDisplacement.height(RiverFootprint.unpackX(missing[index]),
+                                RiverFootprint.unpackZ(missing[index]), values[index]);
+                    }
+                });
+            }
+        }
+    }
+
     private double sampleUnblendedNaturalTerrainHeight(double x, double z) {
         double proceduralHeight = proceduralTerrainHeight.sample(x, z);
         return imageMapRuntime.sampleTerrainHeight(x, z, proceduralHeight);

core/src/main/java/art/arcane/iris/generation/stream/CachedDoubleStream2D.java

@@ -50,6 +50,20 @@ public class CachedDoubleStream2D extends BasicStream<Double> implements Procedu
         }
     }
 
+    public void getBatch(long[] coordinates, int count, double[] target, WorldCache2DDouble.BatchResolver resolver) {
+        try {
+            cache.getBatch(coordinates, count, target, (missing, size, values) ->
+                    ProvisionalSampling.memoizable(() -> {
+                        resolver.resolve(missing, size, values);
+                        return values;
+                    }));
+        } catch (ProvisionalSampling.Unmemoizable provisional) {
+            for (int index = 0; index < count; index++) {
+                target[index] = getDouble((int) (coordinates[index] >> 32), (int) coordinates[index]);
+            }
+        }
+    }
+
     @Override
     public long getSize() {
         return cache.getSize();

core/src/main/java/art/arcane/iris/generation/stream/ProvisionalSampling.java

@@ -16,6 +16,10 @@ public final class ProvisionalSampling {
     private ProvisionalSampling() {
     }
 
+    public static long revision() {
+        return TRACKERS.get().revision;
+    }
+
     /** Records that the calling thread just answered from inputs that are not final. */
     public static void mark() {
         TRACKERS.get().revision++;

core/src/main/java/art/arcane/iris/generation/terrain/Terrain3DRuntime.java

@@ -63,6 +63,10 @@ public final class Terrain3DRuntime {
         return Math.max(ANCHOR_BLOCK_SIZE, (int) (maximumEntries / ANCHOR_BLOCK_SIZE) * ANCHOR_BLOCK_SIZE);
     }
 
+    public boolean requiresBaseHeight(int x, int z) {
+        return !active() || columns.get(x, z) == null;
+    }
+
     public double height(int x, int z) {
         if (!active()) {
             return baseHeight(x, z);

core/src/test/java/art/arcane/iris/generation/hydrology/HydrologyBasisCacheTest.java

@@ -1,37 +1,385 @@
 package art.arcane.iris.generation.hydrology;
 
+import art.arcane.iris.generation.stream.ProvisionalSampling;
 import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
 import org.junit.Test;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.concurrent.ForkJoinPool;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.LockSupport;
 
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public class HydrologyBasisCacheTest {
     @Test
-    public void batchLookupPreservesNullAndFirstPublishedSample() {
+    public void batchLookupPreservesNullDuplicatesAndEviction() {
+        CountingSampler sampler = new CountingSampler();
         HydrologyBasisCache cache = new HydrologyBasisCache(1);
-        HydrologyTerrainSample[] samples = new HydrologyTerrainSample[1];
-        long key = RiverFootprint.pack(-17, Integer.MAX_VALUE);
-        assertTrue(!cache.findWithoutSlope(key, samples, 0));
-        assertNull(cache.rememberWithoutSlope(key, null));
-        assertTrue(cache.findWithoutSlope(key, samples, 0));
-        assertNull(samples[0]);
-        HydrologyTerrainSample later = HydrologyTerrainSample.openLand(73, 0D, "land");
-        assertNull(cache.rememberWithoutSlope(key, later));
-        cache.rememberWithoutSlope(key + 1, later);
-        assertTrue(!cache.findWithoutSlope(key, samples, 0));
-        assertEquals(later, cache.rememberWithoutSlope(key + 1, null));
+        long key = RiverFootprint.pack(Integer.MIN_VALUE, Integer.MAX_VALUE);
+        assertArrayEquals(new HydrologyTerrainSample[2],
+                cache.sampleWithoutSlopeBatch(new long[]{key, key}, 2, sampler));
+        assertNull(cache.sampleWithoutSlope(Integer.MIN_VALUE, Integer.MAX_VALUE, sampler));
+        assertEquals(1, sampler.slopeFreeCalls.get());
+        long later = RiverFootprint.pack(73, -17);
+        assertEquals(87, cache.sampleWithoutSlopeBatch(new long[]{later}, 1, sampler)[0].naturalHeight());
+        assertNull(cache.sampleWithoutSlopeBatch(new long[]{key}, 1, sampler)[0]);
+        assertEquals(3, sampler.slopeFreeCalls.get());
+    }
+
+    @Test
+    public void batchOwnershipKeepsProviderOrderAcrossStripes() {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                assertArrayEquals(new long[]{RiverFootprint.pack(7, 0), RiverFootprint.pack(-9, 0),
+                        RiverFootprint.pack(-17, 0)}, Arrays.copyOf(coordinates, count));
+                return super.sampleBasisWithoutSlopeBatch(coordinates, count);
+            }
+
+            @Override
+            public HydrologyTerrainSample sampleBasisWithoutSlope(int x, int z) {
+                return HydrologyTerrainSample.openLand(63 + x, 0D, "land");
+            }
+        };
+        HydrologyTerrainSample seeded = cache.sampleWithoutSlope(4, 0, sampler);
+        HydrologyTerrainSample[] samples = cache.sampleWithoutSlopeBatch(new long[]{
+                RiverFootprint.pack(7, 0), RiverFootprint.pack(-9, 0), RiverFootprint.pack(7, 0),
+                RiverFootprint.pack(4, 0), RiverFootprint.pack(-17, 0), RiverFootprint.pack(4, 0)}, 6, sampler);
+        assertEquals(70, samples[0].naturalHeight());
+        assertEquals(54, samples[1].naturalHeight());
+        assertSame(samples[0], samples[2]);
+        assertSame(seeded, samples[3]);
+        assertEquals(46, samples[4].naturalHeight());
+        assertSame(seeded, samples[5]);
+    }
+
+    @Test(timeout = 10_000)
+    public void overlappingBatchesDispatchOnlyTheirOwnedCoordinates() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountDownLatch firstStarted = new CountDownLatch(1);
+        CountDownLatch secondStarted = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        AtomicInteger batchCalls = new AtomicInteger();
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                if (batchCalls.getAndIncrement() == 0) {
+                    assertEquals(2, count);
+                    firstStarted.countDown();
+                } else {
+                    assertEquals(1, count);
+                    assertEquals(RiverFootprint.pack(3, 0), coordinates[0]);
+                    secondStarted.countDown();
+                }
+                await(release);
+                return super.sampleBasisWithoutSlopeBatch(coordinates, count);
+            }
+        };
+        ExecutorService workers = Executors.newFixedThreadPool(2);
+        try {
+            Future<HydrologyTerrainSample[]> first = workers.submit(() -> cache.sampleWithoutSlopeBatch(
+                    new long[]{RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)}, 2, sampler));
+            assertTrue(firstStarted.await(5, TimeUnit.SECONDS));
+            Future<HydrologyTerrainSample[]> second = workers.submit(() -> cache.sampleWithoutSlopeBatch(
+                    new long[]{RiverFootprint.pack(2, 0), RiverFootprint.pack(3, 0)}, 2, sampler));
+            assertTrue(secondStarted.await(5, TimeUnit.SECONDS));
+            release.countDown();
+            assertSame(first.get(5, TimeUnit.SECONDS)[1], second.get(5, TimeUnit.SECONDS)[0]);
+            assertEquals(3, sampler.slopeFreeCalls.get());
+            assertEquals(2, batchCalls.get());
+        } finally {
+            release.countDown();
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test(timeout = 10_000)
+    public void pointAndBatchSharePendingSamplesWithoutHoldingStripeLocks() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache(1);
+        CountDownLatch pointStarted = new CountDownLatch(1);
+        CountDownLatch batchStarted = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample sampleBasisWithoutSlope(int x, int z) {
+                if (x == 1) {
+                    pointStarted.countDown();
+                    await(release);
+                }
+                return super.sampleBasisWithoutSlope(x, z);
+            }
+
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                assertEquals(1, count);
+                assertEquals(RiverFootprint.pack(2, 0), coordinates[0]);
+                batchStarted.countDown();
+                return super.sampleBasisWithoutSlopeBatch(coordinates, count);
+            }
+        };
+        ExecutorService workers = Executors.newFixedThreadPool(2);
+        try {
+            Future<HydrologyTerrainSample> point = workers.submit(() -> cache.sampleWithoutSlope(1, 0, sampler));
+            assertTrue(pointStarted.await(5, TimeUnit.SECONDS));
+            Future<HydrologyTerrainSample[]> batch = workers.submit(() -> cache.sampleWithoutSlopeBatch(
+                    new long[]{RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)}, 2, sampler));
+            assertTrue(batchStarted.await(5, TimeUnit.SECONDS));
+            release.countDown();
+            assertSame(point.get(5, TimeUnit.SECONDS), batch.get(5, TimeUnit.SECONDS)[0]);
+            assertEquals(2, sampler.slopeFreeCalls.get());
+        } finally {
+            release.countDown();
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test(timeout = 10_000)
+    public void nestedBatchesFinishOnSingleWorkerPool() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        ForkJoinPool workers = new ForkJoinPool(1);
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                List<HydrologyTerrainSample> values = HydrologyForkJoin.invokeAll(List.of(
+                        () -> sampleBasisWithoutSlope(RiverFootprint.unpackX(coordinates[0]), 0),
+                        () -> sampleBasisWithoutSlope(RiverFootprint.unpackX(coordinates[1]), 0)), workers);
+                return values.toArray(HydrologyTerrainSample[]::new);
+            }
+        };
+        try {
+            workers.submit(() -> HydrologyForkJoin.invokeAll(List.of(
+                    () -> cache.sampleWithoutSlopeBatch(new long[]{RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)}, 2, sampler),
+                    () -> cache.sampleWithoutSlopeBatch(new long[]{RiverFootprint.pack(2, 0), RiverFootprint.pack(1, 0)}, 2, sampler)), workers))
+                    .get(5, TimeUnit.SECONDS);
+            assertEquals(2, sampler.slopeFreeCalls.get());
+        } finally {
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test
+    public void failedMalformedAndRecursiveBatchesReleaseEveryReservation() {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        long[] coordinates = {RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)};
+        CountingSampler failed = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] keys, int count) {
+                throw new IllegalArgumentException("failure");
+            }
+        };
+        assertThrows(IllegalArgumentException.class, () -> cache.sampleWithoutSlopeBatch(coordinates, 2, failed));
+        CountingSampler malformed = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] keys, int count) {
+                return new HydrologyTerrainSample[1];
+            }
+        };
+        assertThrows(IllegalStateException.class, () -> cache.sampleWithoutSlopeBatch(coordinates, 2, malformed));
+        CountingSampler absent = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] keys, int count) {
+                return null;
+            }
+        };
+        assertThrows(NullPointerException.class, () -> cache.sampleWithoutSlopeBatch(coordinates, 2, absent));
+        CountingSampler recursive = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] keys, int count) {
+                cache.sampleWithoutSlope(2, 0, this);
+                throw new AssertionError("Recursive sampling must not wait on itself");
+            }
+        };
+        assertThrows(IllegalStateException.class, () -> cache.sampleWithoutSlopeBatch(coordinates, 2, recursive));
+        CountingSampler successful = new CountingSampler();
+        assertEquals(2, cache.sampleWithoutSlopeBatch(coordinates, 2, successful).length);
+        assertEquals(2, successful.slopeFreeCalls.get());
+    }
+
+    @Test(timeout = 10_000)
+    public void interruptedPointWaiterReceivesBatchResultAndRestoresInterrupt() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountDownLatch started = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        AtomicReference<Thread> waiting = new AtomicReference<>();
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                started.countDown();
+                await(release);
+                return super.sampleBasisWithoutSlopeBatch(coordinates, count);
+            }
+        };
+        ExecutorService workers = Executors.newFixedThreadPool(2);
+        try {
+            Future<HydrologyTerrainSample[]> batch = workers.submit(() -> cache.sampleWithoutSlopeBatch(
+                    new long[]{RiverFootprint.pack(1, 0)}, 1, sampler));
+            assertTrue(started.await(5, TimeUnit.SECONDS));
+            Future<HydrologyTerrainSample> point = workers.submit(() -> {
+                waiting.set(Thread.currentThread());
+                HydrologyTerrainSample sample = cache.sampleWithoutSlope(1, 0, sampler);
+                assertTrue(Thread.interrupted());
+                return sample;
+            });
+            awaitWaiting(waiting);
+            waiting.get().interrupt();
+            release.countDown();
+            assertSame(batch.get(5, TimeUnit.SECONDS)[0], point.get(5, TimeUnit.SECONDS));
+            assertEquals(1, sampler.slopeFreeCalls.get());
+        } finally {
+            release.countDown();
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test(timeout = 10_000)
+    public void batchFailureReachesPointWaiterAndAllowsAllCoordinatesToRetry() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountDownLatch started = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        AtomicReference<Thread> waiting = new AtomicReference<>();
+        IllegalArgumentException failure = new IllegalArgumentException("retry");
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                started.countDown();
+                await(release);
+                throw failure;
+            }
+        };
+        long[] coordinates = {RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)};
+        ExecutorService workers = Executors.newFixedThreadPool(2);
+        try {
+            Future<IllegalArgumentException> batch = workers.submit(() -> assertThrows(IllegalArgumentException.class,
+                    () -> cache.sampleWithoutSlopeBatch(coordinates, 2, sampler)));
+            assertTrue(started.await(5, TimeUnit.SECONDS));
+            Future<IllegalArgumentException> point = workers.submit(() -> {
+                waiting.set(Thread.currentThread());
+                return assertThrows(IllegalArgumentException.class, () -> cache.sampleWithoutSlope(2, 0, sampler));
+            });
+            awaitWaiting(waiting);
+            release.countDown();
+            assertSame(failure, batch.get(5, TimeUnit.SECONDS));
+            assertSame(failure, point.get(5, TimeUnit.SECONDS));
+            CountingSampler successful = new CountingSampler();
+            assertEquals(2, cache.sampleWithoutSlopeBatch(coordinates, 2, successful).length);
+            assertEquals(2, successful.slopeFreeCalls.get());
+        } finally {
+            release.countDown();
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test
+    public void provisionalResultsAreNotRetained() {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample sampleBasisWithoutSlope(int x, int z) {
+                ProvisionalSampling.mark();
+                return super.sampleBasisWithoutSlope(x, z);
+            }
+        };
+        long[] coordinates = {RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)};
+        cache.sampleWithoutSlopeBatch(coordinates, 2, sampler);
+        cache.sampleWithoutSlopeBatch(coordinates, 2, sampler);
+        cache.sampleWithoutSlope(1, 0, sampler);
+        cache.sampleWithoutSlope(1, 0, sampler);
+        assertEquals(6, sampler.slopeFreeCalls.get());
+    }
+
+    @Test(timeout = 10_000)
+    public void provisionalWorkerResultMarksSharedCacheWaitersAndIsNotRetained() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountDownLatch started = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        AtomicReference<Thread> waiting = new AtomicReference<>();
+        ExecutorService providerWorkers = Executors.newFixedThreadPool(2);
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample[] sampleBasisWithoutSlopeBatch(long[] coordinates, int count) {
+                List<HydrologyTerrainSample> values = HydrologyForkJoin.invokeAll(List.of(() -> {
+                    started.countDown();
+                    await(release);
+                    ProvisionalSampling.mark();
+                    return sampleBasisWithoutSlope(RiverFootprint.unpackX(coordinates[0]), 0);
+                }, () -> sampleBasisWithoutSlope(RiverFootprint.unpackX(coordinates[1]), 0)), providerWorkers);
+                return values.toArray(HydrologyTerrainSample[]::new);
+            }
+        };
+        ExecutorService callers = Executors.newFixedThreadPool(2);
+        long[] coordinates = {RiverFootprint.pack(1, 0), RiverFootprint.pack(2, 0)};
+        try {
+            Future<HydrologyTerrainSample[]> batch = callers.submit(() -> cache.sampleWithoutSlopeBatch(coordinates, 2, sampler));
+            assertTrue(started.await(5, TimeUnit.SECONDS));
+            Future<ProvisionalSampling.Unmemoizable> point = callers.submit(() -> {
+                waiting.set(Thread.currentThread());
+                return assertThrows(ProvisionalSampling.Unmemoizable.class,
+                        () -> ProvisionalSampling.memoizable(() -> cache.sampleWithoutSlope(1, 0, sampler)));
+            });
+            awaitWaiting(waiting);
+            release.countDown();
+            assertSame(batch.get(5, TimeUnit.SECONDS)[0], point.get(5, TimeUnit.SECONDS).value());
+            cache.sampleWithoutSlopeBatch(coordinates, 2, sampler);
+            assertEquals(4, sampler.slopeFreeCalls.get());
+        } finally {
+            release.countDown();
+            callers.shutdownNow();
+            providerWorkers.shutdownNow();
+            assertTrue(callers.awaitTermination(5, TimeUnit.SECONDS));
+            assertTrue(providerWorkers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test(timeout = 10_000)
+    public void seedWinsPendingSample() throws Exception {
+        HydrologyBasisCache cache = new HydrologyBasisCache();
+        CountDownLatch started = new CountDownLatch(1);
+        CountDownLatch release = new CountDownLatch(1);
+        CountingSampler sampler = new CountingSampler() {
+            @Override
+            public HydrologyTerrainSample sampleBasisWithoutSlope(int x, int z) {
+                started.countDown();
+                await(release);
+                return super.sampleBasisWithoutSlope(x, z);
+            }
+        };
+        ExecutorService workers = Executors.newSingleThreadExecutor();
+        try {
+            Future<HydrologyTerrainSample[]> result = workers.submit(() -> cache.sampleWithoutSlopeBatch(
+                    new long[]{RiverFootprint.pack(1, 0)}, 1, sampler));
+            assertTrue(started.await(5, TimeUnit.SECONDS));
+            HydrologyTerrainSample seeded = HydrologyTerrainSample.openLand(73, 0D, "seed");
+            Long2ObjectOpenHashMap<HydrologyTerrainSample> seeds = new Long2ObjectOpenHashMap<>();
+            seeds.put(RiverFootprint.pack(1, 0), seeded);
+            cache.seedWithoutSlope(seeds);
+            release.countDown();
+            assertSame(seeded, result.get(5, TimeUnit.SECONDS)[0]);
+            assertSame(seeded, cache.sampleWithoutSlope(1, 0, sampler));
+        } finally {
+            release.countDown();
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
     }
 
     @Test
@@ -122,7 +470,28 @@ public class HydrologyBasisCacheTest {
         }
     }
 
-    private static final class CountingSampler implements HydrologyNaturalTerrainSampler {
+    private static void awaitWaiting(AtomicReference<Thread> thread) {
+        long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(5);
+        while (System.nanoTime() < deadline) {
+            Thread current = thread.get();
+            if (current != null && current.getState() == Thread.State.WAITING) {
+                return;
+            }
+            LockSupport.parkNanos(TimeUnit.MILLISECONDS.toNanos(1));
+        }
+        throw new AssertionError("Cache waiter did not wait for its owner");
+    }
+
+    private static void await(CountDownLatch latch) {
+        try {
+            assertTrue(latch.await(5, TimeUnit.SECONDS));
+        } catch (InterruptedException interruption) {
+            Thread.currentThread().interrupt();
+            throw new AssertionError(interruption);
+        }
+    }
+
+    private static class CountingSampler implements HydrologyNaturalTerrainSampler {
         private final AtomicInteger fullCalls = new AtomicInteger();
         private final AtomicInteger slopeFreeCalls = new AtomicInteger();
         private final AtomicInteger failures = new AtomicInteger();

core/src/test/java/art/arcane/iris/generation/hydrology/HydrologyForkJoinTest.java

@@ -1,5 +1,6 @@
 package art.arcane.iris.generation.hydrology;
 
+import art.arcane.iris.generation.stream.ProvisionalSampling;
 import org.junit.Test;
 
 import java.util.ArrayList;
@@ -23,6 +24,44 @@ import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 
 public class HydrologyForkJoinTest {
+    @Test(timeout = 10_000)
+    public void workerProvisionalAnswersReachEveryAwaitingCaller() throws Exception {
+        HydrologyForkJoin.Task<Integer> task = new HydrologyForkJoin.Task<>(() -> {
+            ProvisionalSampling.mark();
+            return 73;
+        });
+        ExecutorService workers = Executors.newFixedThreadPool(2);
+        try {
+            workers.submit(task).get(5, TimeUnit.SECONDS);
+            for (int attempt = 0; attempt < 2; attempt++) {
+                ProvisionalSampling.Unmemoizable result = workers.submit(() -> assertThrows(
+                        ProvisionalSampling.Unmemoizable.class,
+                        () -> ProvisionalSampling.memoizable(task::await))).get(5, TimeUnit.SECONDS);
+                assertEquals(Integer.valueOf(73), result.value());
+            }
+        } finally {
+            workers.shutdownNow();
+            assertTrue(workers.awaitTermination(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test(timeout = 10_000)
+    public void provisionalWorkerMarksTheBatchCaller() {
+        ExecutorService workers = Executors.newFixedThreadPool(2);
+        try {
+            ProvisionalSampling.Unmemoizable result = assertThrows(ProvisionalSampling.Unmemoizable.class,
+                    () -> ProvisionalSampling.memoizable(() -> HydrologyForkJoin.invokeAll(List.of(
+                            () -> 1,
+                            () -> {
+                                ProvisionalSampling.mark();
+                                return 2;
+                            }), workers)));
+            assertEquals(List.of(1, 2), result.value());
+        } finally {
+            workers.shutdownNow();
+        }
+    }
+
     @Test
     public void blockedGridBatchNeverHelpsUnrelatedOwnerWork() throws Exception {
         ForkJoinPool pool = new ForkJoinPool(2, ForkJoinPool.defaultForkJoinWorkerThreadFactory,

core/src/test/java/art/arcane/iris/generation/hydrology/PreparedHydrologyTileStoreTest.java

@@ -279,11 +279,22 @@ public class PreparedHydrologyTileStoreTest {
         HydrologyTile original = tile();
         PreparedHydrologyTileStore store = store();
         store.save(original);
-        HydrologyTile oversized = new HydrologyTile(original.key(), original.worldSeed(),
-                original.settingsFingerprint(), original.tileSize(), original.nodes(), original.edges(),
-                original.outlets(), original.courses(), original.regionalCourseIds(), original.cavePlans(),
-                Collections.nCopies(600_000, original.localDiagnosticCandidates().getFirst()), original.footprint());
-        assertThrows(IOException.class, () -> store.save(oversized));
+        long allocationLimit = Math.max(16L * 1024L * 1024L,
+                Math.min(512L * 1024L * 1024L, Runtime.getRuntime().maxMemory() / 8L));
+        int pointCount = 4096;
+        int courseCount = Math.toIntExact(allocationLimit / (256L * pointCount) + 1L);
+        HydraulicSegment segment = new HydraulicSegment(45L, 44L, HydrologyFeatureType.SURFACE_POOL,
+                72, 72, 4, 2, false, false, Collections.nCopies(pointCount, new HydrologyPoint(0, 72, 0)),
+                HydraulicChannelProfile.uniform(4D, 2D));
+        RiverCourse course = new RiverCourse(44L, RiverCourseType.SURFACE, OptionalLong.of(1L),
+                OptionalLong.of(2L), "default", 1, List.of(), List.of(segment));
+        HydrologyOwnerDraft draft = new HydrologyOwnerDraft(original.key(),
+                new HydrologyCaveCourseFilter.Result(original.nodes(), original.edges(), original.outlets(),
+                        original.courses(), original.cavePlans()), original.localDiagnosticCandidates(), null);
+        HydrologyTile oversized = original.withResolvedOwner(new CrossTileResolvedOwner(draft,
+                Collections.nCopies(courseCount, new CrossTileRejectedCourse(course, 4L))));
+        IOException failure = assertThrows(IOException.class, () -> store.save(oversized));
+        assertEquals("Prepared hydrology tile exceeds its allocation budget.", failure.getMessage());
         assertEquals(original, store.load(original.key()).orElseThrow());
         try (Stream<Path> files = Files.list(store.file(original.key()).getParent())) {
             assertEquals(List.of(store.file(original.key())), files.toList());

core/src/test/java/art/arcane/iris/generation/hydrology/runtime/IrisHydrologyRoutingTerrainSamplerTest.java

@@ -1,6 +1,7 @@
 package art.arcane.iris.generation.hydrology.runtime;
 
 import art.arcane.iris.generation.hydrology.HydrologyRoutingTerrainSampler;
+import art.arcane.iris.generation.stream.ProvisionalSampling;
 import art.arcane.iris.generation.hydrology.HydrologyTerrainSample;
 import art.arcane.iris.generation.hydrology.RiverFootprint;
 import art.arcane.iris.generation.concurrent.MultiBurst;
@@ -40,6 +41,132 @@ import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
 
 public class IrisHydrologyRoutingTerrainSamplerTest {
+    @Test
+    public void provisionalOceanClassificationIsReevaluated() {
+        AtomicInteger calls = new AtomicInteger();
+        IrisHydrologyRoutingTerrainSampler sampler = new IrisHydrologyRoutingTerrainSampler(
+                new IrisHydrologyRoutingTerrainSampler.Sources((x, z, height) -> {
+                    throw new AssertionError("Classification must not load a basis");
+                }, (x, z) -> {
+                    if (calls.incrementAndGet() == 1) {
+                        ProvisionalSampling.mark();
+                        return 100D;
+                    }
+                    return 40D;
+                }, (x, z) -> true, 60), IrisHydrologyRoutingTerrainSampler.SamplingOptions.serial(16));
+        assertEquals(IrisHydrologyRoutingTerrainSampler.NaturalClassification.LAND, sampler.classifyNatural(2, 3));
+        assertEquals(0, sampler.oceanClassificationCacheSize());
+        assertEquals(IrisHydrologyRoutingTerrainSampler.NaturalClassification.OCEAN, sampler.classifyNatural(2, 3));
+        assertEquals(1, sampler.oceanClassificationCacheSize());
+    }
+
+    @Test
+    public void bulkHeightProviderReceivesOnlyUniqueUncachedCoordinates() {
+        ArrayList<Long> requested = new ArrayList<>();
+        IrisHydrologyNaturalHeightProvider heights = new IrisHydrologyNaturalHeightProvider() {
+            @Override
+            public double sample(int x, int z) {
+                return 100D + Math.floorMod(x + z, 17);
+            }
+
+            @Override
+            public boolean supportsBatch() {
+                return true;
+            }
+
+            @Override
+            public void sampleBatch(long[] coordinates, int count, double[] target) {
+                for (int index = 0; index < count; index++) {
+                    requested.add(coordinates[index]);
+                    target[index] = sample(RiverFootprint.unpackX(coordinates[index]), RiverFootprint.unpackZ(coordinates[index]));
+                }
+            }
+        };
+        IrisHydrologyRoutingTerrainSampler sampler = new IrisHydrologyRoutingTerrainSampler(
+                new IrisHydrologyRoutingTerrainSampler.Sources((x, z, height) ->
+                        new IrisHydrologyRoutingTerrainSampler.TerrainBasis(height,
+                                HydrologyTerrainSample.openLand((int) height, 0D, "land")), heights, (x, z) -> false, 60),
+                IrisHydrologyRoutingTerrainSampler.SamplingOptions.serial(8192));
+        sampler.sampleBasisWithoutSlope(-1, 5);
+        sampler.sampleLandHeight(6, -7);
+        long[] coordinates = {RiverFootprint.pack(-1, 5), RiverFootprint.pack(6, -7),
+                RiverFootprint.pack(-9, 19), RiverFootprint.pack(-9, 19),
+                RiverFootprint.pack(Integer.MAX_VALUE, Integer.MIN_VALUE)};
+        for (int repeat = 0; repeat < 2; repeat++) {
+            HydrologyTerrainSample[] samples = sampler.sampleBasisWithoutSlopeBatch(coordinates, coordinates.length);
+            for (int index = 0; index < coordinates.length; index++) {
+                assertEquals((int) heights.sample(RiverFootprint.unpackX(coordinates[index]),
+                        RiverFootprint.unpackZ(coordinates[index])), samples[index].naturalHeight());
+            }
+        }
+        assertEquals(List.of(coordinates[2], coordinates[4]), requested);
+    }
+
+    @Test
+    public void gridUsesBoundedHeightSlices() {
+        ArrayList<Integer> sizes = new ArrayList<>();
+        IrisHydrologyNaturalHeightProvider heights = new IrisHydrologyNaturalHeightProvider() {
+            @Override
+            public double sample(int x, int z) {
+                throw new AssertionError("Expected bulk height sampling");
+            }
+
+            @Override
+            public boolean supportsBatch() {
+                return true;
+            }
+
+            @Override
+            public void sampleBatch(long[] coordinates, int count, double[] target) {
+                sizes.add(count);
+                for (int index = 0; index < count; index++) {
+                    target[index] = 100D;
+                }
+            }
+        };
+        IrisHydrologyRoutingTerrainSampler sampler = new IrisHydrologyRoutingTerrainSampler(
+                new IrisHydrologyRoutingTerrainSampler.Sources((x, z, height) ->
+                        new IrisHydrologyRoutingTerrainSampler.TerrainBasis(height,
+                                HydrologyTerrainSample.openLand((int) height, 0D, "land")), heights, (x, z) -> false, 60),
+                IrisHydrologyRoutingTerrainSampler.SamplingOptions.serial(8192));
+        HydrologyTerrainSample[] samples = sampler.sampleGrid(new HydrologyRoutingTerrainSampler.GridRequest(-1024, -4096, 65, 8));
+        assertEquals(65 * 65, samples.length);
+        assertEquals(List.of(4096, 260), sizes);
+        for (HydrologyTerrainSample sample : samples) {
+            assertEquals(100, sample.naturalHeight());
+            assertEquals(0D, sample.slope(), 0D);
+        }
+    }
+
+    @Test
+    public void provisionalBulkAndScalarHeightsNeverBecomeRoutingCacheEntries() {
+        AtomicInteger calls = new AtomicInteger();
+        IrisHydrologyNaturalHeightProvider heights = new IrisHydrologyNaturalHeightProvider() {
+            @Override
+            public double sample(int x, int z) {
+                ProvisionalSampling.mark();
+                return 100D + calls.incrementAndGet();
+            }
+
+            @Override
+            public boolean supportsBatch() {
+                return true;
+            }
+        };
+        IrisHydrologyRoutingTerrainSampler sampler = new IrisHydrologyRoutingTerrainSampler(
+                new IrisHydrologyRoutingTerrainSampler.Sources((x, z, height) ->
+                        new IrisHydrologyRoutingTerrainSampler.TerrainBasis(height,
+                                HydrologyTerrainSample.openLand((int) height, 0D, "land")), heights, (x, z) -> false, 60),
+                IrisHydrologyRoutingTerrainSampler.SamplingOptions.serial(16));
+        long[] coordinates = {RiverFootprint.pack(4, -3)};
+        assertEquals(101, sampler.sampleBasisWithoutSlopeBatch(coordinates, 1)[0].naturalHeight());
+        assertEquals(102, sampler.sampleBasisWithoutSlopeBatch(coordinates, 1)[0].naturalHeight());
+        assertEquals(103, sampler.sampleBasisWithoutSlope(4, -3).naturalHeight());
+        assertEquals(104, sampler.sampleBasisWithoutSlope(4, -3).naturalHeight());
+        assertEquals(0, sampler.basisCacheSize());
+        assertEquals(0, sampler.naturalHeightCacheSize());
+    }
+
     @Test
     public void boundedBasisBatchUsesScopedWorkersAndDrainsNestedPool() throws Exception {
         ThreadLocal<Integer> scope = new ThreadLocal<>();

core/src/test/java/art/arcane/iris/generation/noise/IrisGeneratorBatchTest.java

@@ -0,0 +1,129 @@
+package art.arcane.iris.generation.noise;
+
+import art.arcane.volmlib.util.collection.KList;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertThrows;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.anyLong;
+import static org.mockito.ArgumentMatchers.isNull;
+import static org.mockito.Mockito.clearInvocations;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+public class IrisGeneratorBatchTest {
+    private static final double[] XS = {-0D, 0D, -12D, -5.75D, 18D, 18D, 8191.25D, -29999999.5D, 2147483647D};
+    private static final double[] ZS = {0D, -0D, 6D, 2.5D, -6D, -6D, -4096.75D, 29999998D, -2147483648D};
+
+    @Test
+    public void batchPreservesRawBitsAcrossStylesSeedsAndSurfaceDetails() {
+        NoiseStyle[] styles = {NoiseStyle.SIMPLEX, NoiseStyle.IRIS, NoiseStyle.FRACTAL_SMOKE,
+                NoiseStyle.CLOVER, NoiseStyle.CELLULAR, NoiseStyle.FLAT};
+        long[] seeds = {0L, -1337L, Long.MAX_VALUE - 37L, Long.MIN_VALUE + 23L};
+        for (NoiseStyle style : styles) {
+            for (double detail : new double[]{0D, 0.5D, 1D}) {
+                for (boolean multiply : new boolean[]{false, true}) {
+                    IrisGenerator scalar = generator(style, detail, multiply);
+                    IrisGenerator batch = generator(style, detail, multiply);
+                    assertTrue(batch.supportsBatch());
+                    double[] sampled = new double[XS.length];
+                    for (long seed : seeds) {
+                        batch.getHeights(XS, ZS, seed, sampled, sampled.length);
+                        for (int index = 0; index < sampled.length; index++) {
+                            assertEquals(style + " detail=" + detail + " seed=" + seed + " index=" + index,
+                                    Double.doubleToRawLongBits(scalar.getHeight(XS[index], ZS[index], seed)),
+                                    Double.doubleToRawLongBits(sampled[index]));
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    @Test
+    public void unroundedCompositeBatchRetainsEveryNoiseBit() {
+        for (NoiseStyle style : new NoiseStyle[]{NoiseStyle.SIMPLEX, NoiseStyle.IRIS, NoiseStyle.CLOVER}) {
+            for (double detail : new double[]{0D, 0.5D, 1D}) {
+                IrisGenerator scalar = generator(style, detail, false).setCliffHeightMax(0D).setCellFractureHeight(0D);
+                IrisGenerator batch = generator(style, detail, false).setCliffHeightMax(0D).setCellFractureHeight(0D);
+                double[] values = new double[XS.length];
+                for (long seed : new long[]{-1337L, Long.MAX_VALUE - 37L}) {
+                    batch.getHeights(XS, ZS, seed, values, XS.length);
+                    for (int index = 0; index < XS.length; index++) {
+                        assertEquals(Double.doubleToRawLongBits(scalar.getHeight(XS[index], ZS[index], seed)),
+                                Double.doubleToRawLongBits(values[index]));
+                    }
+                }
+            }
+        }
+    }
+
+    @Test
+    public void resolvesLayerContextOncePerBatch() {
+        IrisNoiseGenerator layer = spy(new IrisNoiseGenerator().setStyle(NoiseStyle.SIMPLEX.style()));
+        IrisGenerator generator = new IrisGenerator().setComposite(new KList<>(layer));
+        double[] sampled = new double[XS.length];
+        generator.getHeights(XS, ZS, 99L, sampled, XS.length);
+        verify(layer, times(1)).getGenerator(anyLong(), isNull(), isNull());
+        clearInvocations(layer);
+        for (int index = 0; index < XS.length; index++) {
+            generator.getHeight(XS[index], ZS[index], 99L);
+        }
+        verify(layer, times(XS.length)).getGenerator(anyLong(), isNull(), isNull());
+    }
+
+    @Test
+    public void customGeneratorFallbackKeepsCoordinateOrder() {
+        List<Double> sampled = new ArrayList<>();
+        IrisGenerator generator = new IrisGenerator() {
+            @Override
+            public double getHeight(double x, double z, long seed) {
+                sampled.add(x);
+                return sampled.size();
+            }
+        };
+        assertFalse(generator.supportsBatch());
+        double[] values = new double[XS.length];
+        generator.getHeights(XS, ZS, 0L, values, values.length);
+        for (int index = 0; index < values.length; index++) {
+            assertEquals(Double.valueOf(XS[index]), sampled.get(index));
+            assertEquals(index + 1D, values[index], 0D);
+        }
+        assertThrows(IllegalArgumentException.class,
+                () -> generator.getHeights(new double[4097], new double[4097], 0L, new double[4097], 4097));
+    }
+
+    @Test
+    public void expressionsAndCustomStylesKeepScalarSampling() {
+        assertFalse(new IrisGenerator().setComposite(new KList<>(new IrisNoiseGenerator()
+                .setStyle(new IrisGeneratorStyle().setExpression("height")))).supportsBatch());
+        assertFalse(new IrisGenerator().setComposite(new KList<>(new IrisNoiseGenerator()
+                .setStyle(new IrisGeneratorStyle() {}))).supportsBatch());
+    }
+
+    private static IrisGenerator generator(NoiseStyle style, double detail, boolean multiply) {
+        IrisNoiseGenerator layer = new IrisNoiseGenerator().setStyle(style.style()).setSeed(-831L)
+                .setZoom(0.73D).setOffsetX(3.25D).setOffsetZ(-1.75D).setOpacity(0.7D)
+                .setNegative(true).setExponent(1.37D).setOffsetY(0.03D).setParametric(true);
+        IrisNoiseGenerator node = layer;
+        for (int depth = 0; depth < 5; depth++) {
+            IrisNoiseGenerator child = new IrisNoiseGenerator().setStyle(NoiseStyle.SIMPLEX.style())
+                    .setSeed(depth * 7L).setOpacity(3.1D).setZoom(1.7D);
+            node.setFracture(new KList<>(child));
+            node = child;
+        }
+        return new IrisGenerator().setComposite(new KList<>(layer,
+                        new IrisNoiseGenerator().setStyle(NoiseStyle.SIMPLEX.style()).setOpacity(0.2D)))
+                .setSurfaceDetail(detail).setMultiplicitive(multiply).setSeed(-93L).setZoom(1.3D)
+                .setOffsetX(7.25D).setOffsetZ(-9.125D).setOpacity(0.93D)
+                .setCliffHeightMin(3.5D).setCliffHeightMax(12.25D)
+                .setCliffHeightGenerator(new IrisNoiseGenerator().setStyle(NoiseStyle.SIMPLEX.style()))
+                .setCellFractureHeight(0.25D);
+    }
+}

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

@@ -0,0 +1,78 @@
+package art.arcane.iris.generation.runtime;
+
+import art.arcane.iris.generation.noise.IrisGenerator;
+import art.arcane.iris.generation.noise.IrisGeneratorStyle;
+import art.arcane.iris.generation.noise.IrisNoiseGenerator;
+import art.arcane.iris.generation.noise.IrisShapedGeneratorStyle;
+import art.arcane.iris.generation.noise.NoiseStyle;
+import art.arcane.iris.generation.terrain.IrisDimension;
+import art.arcane.volmlib.util.collection.KList;
+import org.junit.Test;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.util.Map;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.CALLS_REAL_METHODS;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class IrisComplexHeightBatchTest {
+    @Test
+    public void standardSurfaceGraphsCanBatchAndCoarseSamplingKeepsScalarPath() throws Exception {
+        IrisDimension dimension = new IrisDimension();
+        IrisGenerator generator = new IrisGenerator().setSurfaceDetail(0.5D)
+                .setComposite(new KList<>(new IrisNoiseGenerator().setStyle(NoiseStyle.FRACTAL_SMOKE.style())
+                        .setFracture(new KList<>(new IrisNoiseGenerator().setStyle(NoiseStyle.IRIS.style())))));
+        IrisComplex complex = complex(dimension, generator);
+        assertTrue(eligible(complex));
+        for (int step : new int[]{2, 4, 8}) {
+            dimension.setTerrainSamplingStep(step);
+            assertFalse(eligible(complex));
+        }
+        dimension.setTerrainSamplingStep(1);
+        assertTrue(eligible(complex));
+        generator.getComposite().getFirst().setStyle(new IrisGeneratorStyle().setExpression("height"));
+        assertFalse(eligible(complex));
+    }
+
+    @Test
+    public void statefulBiomeAndOverlaySourcesKeepScalarPath() throws Exception {
+        IrisDimension dimension = new IrisDimension();
+        IrisComplex complex = complex(dimension, new IrisGenerator()
+                .setComposite(new KList<>(new IrisNoiseGenerator().setStyle(NoiseStyle.SIMPLEX.style()))));
+        set(complex, "reuseNaturalBaseBiome", false);
+        assertFalse(eligible(complex));
+        set(complex, "reuseNaturalBaseBiome", true);
+        dimension.setOverlayNoise(new KList<>(new IrisShapedGeneratorStyle()
+                .setGenerator(new IrisGeneratorStyle() {})));
+        assertFalse(eligible(complex));
+        dimension.getOverlayNoise().getFirst().setGenerator(NoiseStyle.SIMPLEX.style());
+        assertTrue(eligible(complex));
+    }
+
+    private static IrisComplex complex(IrisDimension dimension, IrisGenerator generator) throws Exception {
+        Engine engine = mock(Engine.class);
+        when(engine.getDimension()).thenReturn(dimension);
+        IrisComplex complex = mock(IrisComplex.class, CALLS_REAL_METHODS);
+        set(complex, "terrainEngine", engine);
+        set(complex, "biomeBuffetGenerators", Map.of());
+        set(complex, "reuseNaturalBaseBiome", true);
+        set(complex, "frozenGenerators", new IrisGenerator[][]{{generator}});
+        return complex;
+    }
+
+    private static boolean eligible(IrisComplex complex) throws Exception {
+        Method method = IrisComplex.class.getDeclaredMethod("supportsHeightBatch");
+        method.setAccessible(true);
+        return (boolean) method.invoke(complex);
+    }
+
+    private static void set(IrisComplex complex, String name, Object value) throws Exception {
+        Field field = IrisComplex.class.getDeclaredField(name);
+        field.setAccessible(true);
+        field.set(complex, value);
+    }
+}