Lock-free volume reads

- Structure volume caches read through concurrent maps and publish only current builds
- Natural terrain receipts reuse a per-thread deflater with the platform gzip framing
- Tests pin receipt and saved biome bytes across reused compressors

core/src/main/java/art/arcane/iris/structure/nativegen/NativeStructureVolumeIndex.java

@@ -12,15 +12,14 @@ import art.arcane.volmlib.util.cache.CacheKey;
 import art.arcane.volmlib.util.collection.KList;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Collections;
-import java.util.LinkedHashMap;
-import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.WeakHashMap;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.function.BooleanSupplier;
 import java.util.function.IntConsumer;
 import java.util.function.Supplier;
 
@@ -36,7 +35,6 @@ public final class NativeStructureVolumeIndex {
     private static final int ORIGIN_REACH_CHUNKS = StructureOwnershipRecordView.MAX_REFERENCE_DISTANCE_CHUNKS;
     private static final int MAX_CACHED_ORIGIN_CHUNKS = 16_384;
     private static final int MAX_CACHED_QUERY_CHUNKS = 4_096;
-    private static final int CACHE_STRIPES = 32;
     private static final Map<Engine, NativeStructureVolumeIndex> INDEXES =
             Collections.synchronizedMap(new WeakHashMap<>());
 
@@ -223,12 +221,9 @@ public final class NativeStructureVolumeIndex {
             RuntimeChunkKey key,
             Supplier<KList<NativeStructureVolume>> loader
     ) {
-        Map<RuntimeChunkKey, KList<NativeStructureVolume>> cache = volumes.stripe(key);
-        synchronized (cache) {
-            KList<NativeStructureVolume> hit = cache.get(key);
-            if (hit != null) {
-                return hit;
-            }
+        KList<NativeStructureVolume> hit = volumes.get(key);
+        if (hit != null) {
+            return hit;
         }
 
         CompletableFuture<KList<NativeStructureVolume>> future = new CompletableFuture<>();
@@ -239,22 +234,16 @@ public final class NativeStructureVolumeIndex {
 
         // Close the check-then-claim window: a racer whose cache check missed before the
         // previous builder cached could claim the build slot after it retired and rebuild.
-        synchronized (cache) {
-            KList<NativeStructureVolume> published = cache.get(key);
-            if (published != null) {
-                future.complete(published);
-                builds.remove(key, future);
-                return published;
-            }
+        KList<NativeStructureVolume> published = volumes.get(key);
+        if (published != null) {
+            future.complete(published);
+            builds.remove(key, future);
+            return published;
         }
 
         try {
             KList<NativeStructureVolume> built = loader.get();
-            synchronized (cache) {
-                if (builds.get(key) == future) {
-                    cache.put(key, built);
-                }
-            }
+            volumes.publish(key, built, () -> builds.get(key) == future);
             future.complete(built);
             return built;
         } catch (RuntimeException | Error error) {
@@ -301,47 +290,44 @@ public final class NativeStructureVolumeIndex {
         }
     }
 
-    private static Map<RuntimeChunkKey, KList<NativeStructureVolume>> lru(int capacity) {
-        return new LinkedHashMap<>(16, 0.75F, true) {
-            @Override
-            protected boolean removeEldestEntry(
-                    Map.Entry<RuntimeChunkKey, KList<NativeStructureVolume>> eldest
-            ) {
-                return size() > capacity;
-            }
-        };
-    }
-
     private static final class VolumeCache {
-        private final List<Map<RuntimeChunkKey, KList<NativeStructureVolume>>> stripes;
+        private final int capacity;
+        private final ConcurrentHashMap<RuntimeChunkKey, KList<NativeStructureVolume>> entries = new ConcurrentHashMap<>();
+        private final ConcurrentLinkedQueue<RuntimeChunkKey> insertionOrder = new ConcurrentLinkedQueue<>();
 
         private VolumeCache(int capacity) {
-            int stripeCapacity = Math.max(1, capacity / CACHE_STRIPES);
-            List<Map<RuntimeChunkKey, KList<NativeStructureVolume>>> created = new ArrayList<>(CACHE_STRIPES);
-            for (int stripe = 0; stripe < CACHE_STRIPES; stripe++) {
-                created.add(lru(stripeCapacity));
-            }
-            stripes = List.copyOf(created);
-        }
-
-        private Map<RuntimeChunkKey, KList<NativeStructureVolume>> stripe(RuntimeChunkKey key) {
-            int hash = key.hashCode();
-            return stripes.get((hash ^ (hash >>> 16)) & (CACHE_STRIPES - 1));
+            this.capacity = capacity;
         }
 
         private KList<NativeStructureVolume> get(RuntimeChunkKey key) {
-            Map<RuntimeChunkKey, KList<NativeStructureVolume>> cache = stripe(key);
-            synchronized (cache) {
-                return cache.get(key);
+            return entries.get(key);
+        }
+
+        private void publish(RuntimeChunkKey key, KList<NativeStructureVolume> volumes, BooleanSupplier current) {
+            boolean[] inserted = new boolean[1];
+            entries.compute(key, (ignored, previous) -> {
+                if (!current.getAsBoolean()) {
+                    return previous;
+                }
+                inserted[0] = previous == null;
+                return volumes;
+            });
+            if (!inserted[0]) {
+                return;
+            }
+            insertionOrder.add(key);
+            while (entries.size() > capacity) {
+                RuntimeChunkKey eldest = insertionOrder.poll();
+                if (eldest == null) {
+                    return;
+                }
+                entries.remove(eldest);
             }
         }
 
         private void evictRuntime(int runtimeId) {
-            for (Map<RuntimeChunkKey, KList<NativeStructureVolume>> cache : stripes) {
-                synchronized (cache) {
-                    cache.keySet().removeIf(key -> key.runtimeId() == runtimeId);
-                }
-            }
+            entries.keySet().removeIf(key -> key.runtimeId() == runtimeId);
+            insertionOrder.removeIf(key -> key.runtimeId() == runtimeId);
         }
     }
 

core/src/main/java/art/arcane/iris/world/history/NativeTerrainReceipt.java

@@ -6,11 +6,16 @@ import java.io.ByteArrayOutputStream;
 import java.io.DataInputStream;
 import java.io.DataOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.OptionalInt;
+import java.util.zip.CRC32;
+import java.util.zip.Deflater;
+import java.util.zip.DeflaterOutputStream;
 import java.util.zip.GZIPInputStream;
 import java.util.zip.GZIPOutputStream;
 
@@ -18,6 +23,8 @@ public final class NativeTerrainReceipt {
     private static final int MAGIC = 0x4952544E;
     private static final int VERSION = 1;
     private static final int MAXIMUM_BYTES = 64 * 1024 * 1024;
+    private static final ThreadLocal<Deflater> DEFLATERS =
+            ThreadLocal.withInitial(() -> new Deflater(Deflater.DEFAULT_COMPRESSION, true));
 
     private NativeTerrainReceipt() {
     }
@@ -25,7 +32,9 @@ public final class NativeTerrainReceipt {
     public static byte[] encode(SavedTerrainChunk chunk, long activationId, String epochId) throws IOException {
         ByteArrayOutputStream bytes = new ByteArrayOutputStream();
         UtfCache strings = new UtfCache();
-        try (DataOutputStream output = new DataOutputStream(new BufferedOutputStream(new GZIPOutputStream(bytes)))) {
+        Deflater deflater = DEFLATERS.get();
+        deflater.reset();
+        try (DataOutputStream output = new DataOutputStream(new BufferedOutputStream(new GzipStream(bytes, deflater)))) {
             output.writeInt(MAGIC);
             output.writeInt(VERSION);
             output.writeInt(chunk.chunkX());
@@ -196,6 +205,60 @@ public final class NativeTerrainReceipt {
     public record Decoded(SavedTerrainChunk terrain, long activationId, String epochId) {
     }
 
+    private static final class GzipStream extends DeflaterOutputStream {
+        private static final int BUFFER_BYTES = 512;
+        private static final int TRAILER_BYTES = 8;
+        private static final byte[] HEADER = gzipHeader();
+
+        private final CRC32 checksum = new CRC32();
+
+        private GzipStream(OutputStream out, Deflater deflater) throws IOException {
+            super(out, deflater, BUFFER_BYTES);
+            out.write(HEADER);
+        }
+
+        @Override
+        public void write(byte[] buffer, int offset, int length) throws IOException {
+            super.write(buffer, offset, length);
+            checksum.update(buffer, offset, length);
+        }
+
+        @Override
+        public void finish() throws IOException {
+            if (def.finished()) {
+                return;
+            }
+            def.finish();
+            while (!def.finished()) {
+                int length = def.deflate(buf, 0, buf.length);
+                if (length > 0) {
+                    out.write(buf, 0, length);
+                }
+            }
+            byte[] trailer = new byte[TRAILER_BYTES];
+            writeLittleEndian(trailer, 0, (int) checksum.getValue());
+            writeLittleEndian(trailer, 4, (int) def.getBytesRead());
+            out.write(trailer);
+        }
+
+        private static void writeLittleEndian(byte[] target, int offset, int value) {
+            target[offset] = (byte) value;
+            target[offset + 1] = (byte) (value >>> 8);
+            target[offset + 2] = (byte) (value >>> 16);
+            target[offset + 3] = (byte) (value >>> 24);
+        }
+
+        private static byte[] gzipHeader() {
+            ByteArrayOutputStream empty = new ByteArrayOutputStream();
+            try (GZIPOutputStream gzip = new GZIPOutputStream(empty)) {
+                gzip.finish();
+            } catch (IOException failure) {
+                throw new IllegalStateException("Unable to resolve the platform gzip header", failure);
+            }
+            return Arrays.copyOf(empty.toByteArray(), 10);
+        }
+    }
+
     private static final class UtfCache {
         private static final int MAXIMUM_ENTRIES = 256;
         private static final int MAXIMUM_ENCODED_BYTES = 64 * 1024;

core/src/test/java/art/arcane/iris/world/history/NativeTerrainReceiptTest.java

@@ -60,6 +60,15 @@ public class NativeTerrainReceiptTest {
         }
     }
 
+    @Test
+    public void repeatedEncodingOnOneThreadKeepsLegacyBytes() throws Exception {
+        for (int round = 0; round < 6; round++) {
+            SavedTerrainChunk chunk = chunk(round % 2 == 0);
+            String epoch = "epoch-" + round;
+            assertArrayEquals(legacyEncode(chunk, round, epoch), NativeTerrainReceipt.encode(chunk, round, epoch));
+        }
+    }
+
     @Test
     public void saturatedStringCachesPreserveModifiedUtfBytes() throws Exception {
         for (int padding : new int[]{0, 300}) {

core/src/test/java/art/arcane/iris/world/history/SavedBiomeStoreWriteTest.java

@@ -60,6 +60,16 @@ public class SavedBiomeStoreWriteTest {
         assertArrayEquals(expectedRegion(), Files.readAllBytes(regionPath(root)));
     }
 
+    @Test
+    public void consecutiveRecordsKeepIndependentlyCompressedBytes() throws Exception {
+        Path root = temporaryFolder.newFolder().toPath();
+        SavedBiomeStore store = SavedBiomeStore.open(root);
+        for (int x = 0; x < 4; x++) {
+            store.claimAndPersist(chunk(x, 3L));
+        }
+        assertArrayEquals(expectedRegion(4), Files.readAllBytes(regionPath(root)));
+    }
+
     @Test
     public void relaxedDurabilityPreservesRecordsWithoutForcingEachAppend() throws Exception {
         String previousMode = System.getProperty(Durability.MODE_PROPERTY);
@@ -379,6 +389,10 @@ public class SavedBiomeStoreWriteTest {
     }
 
     private static byte[] expectedRegion() throws IOException {
+        return expectedRegion(1);
+    }
+
+    private static byte[] expectedRegion(int records) throws IOException {
         ByteArrayOutputStream raw = new ByteArrayOutputStream();
         DataOutputStream data = new DataOutputStream(raw);
         data.writeLong(3L);
@@ -392,17 +406,6 @@ public class SavedBiomeStoreWriteTest {
         data.writeInt(1);
         data.write(new byte[]{0, 0, 1, (byte) 0x80, 3, 0});
         data.write(new byte[256]);
-        ByteArrayOutputStream body = new ByteArrayOutputStream();
-        DataOutputStream coordinates = new DataOutputStream(body);
-        coordinates.writeInt(0);
-        coordinates.writeInt(0);
-        coordinates.writeInt(raw.size());
-        Deflater deflater = new Deflater(Deflater.BEST_SPEED);
-        try (DeflaterOutputStream compressed = new DeflaterOutputStream(coordinates, deflater)) {
-            raw.writeTo(compressed);
-        } finally {
-            deflater.end();
-        }
         ByteArrayOutputStream region = new ByteArrayOutputStream();
         DataOutputStream output = new DataOutputStream(region);
         output.writeInt(0x4942494F);
@@ -410,9 +413,22 @@ public class SavedBiomeStoreWriteTest {
         output.writeInt(0);
         output.writeInt(0);
         output.writeInt(checksum(region.toByteArray()));
-        output.writeInt(body.size());
-        output.write(body.toByteArray());
-        output.writeInt(checksum(body.toByteArray()));
+        for (int x = 0; x < records; x++) {
+            ByteArrayOutputStream body = new ByteArrayOutputStream();
+            DataOutputStream coordinates = new DataOutputStream(body);
+            coordinates.writeInt(x);
+            coordinates.writeInt(0);
+            coordinates.writeInt(raw.size());
+            Deflater deflater = new Deflater(Deflater.BEST_SPEED);
+            try (DeflaterOutputStream compressed = new DeflaterOutputStream(coordinates, deflater)) {
+                raw.writeTo(compressed);
+            } finally {
+                deflater.end();
+            }
+            output.writeInt(body.size());
+            output.write(body.toByteArray());
+            output.writeInt(checksum(body.toByteArray()));
+        }
         return region.toByteArray();
     }