Optimize DFU / tree implementations

dfu/src/main/java/org/enginehub/linbus/dfu/LinOps.java

@@ -44,7 +44,7 @@
 import java.nio.IntBuffer;
 import java.nio.LongBuffer;
 import java.util.ArrayList;
-import java.util.Arrays;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map.Entry;
 import java.util.function.BiConsumer;
@@ -86,7 +86,7 @@ public LinTag<?> emptyList() {
 
     @Override
     public LinTag<?> emptyMap() {
-        return LinCompoundTag.builder().build();
+        return LinCompoundTag.empty();
     }
 
     @Override
@@ -99,12 +99,18 @@ public <U> U convertTo(DynamicOps<U> outOps, LinTag<?> input) {
             case LinLongTag tag -> outOps.createLong(tag.valueAsLong());
             case LinFloatTag tag -> outOps.createFloat(tag.valueAsFloat());
             case LinDoubleTag tag -> outOps.createDouble(tag.valueAsDouble());
-            case LinByteArrayTag tag -> outOps.createByteList(tag.view());
             case LinStringTag tag -> outOps.createString(tag.value());
             case LinListTag<?> tag -> convertList(outOps, tag);
             case LinCompoundTag tag -> convertMap(outOps, tag);
-            case LinIntArrayTag tag -> outOps.createIntList(Arrays.stream(tag.value()));
-            case LinLongArrayTag tag -> outOps.createLongList(Arrays.stream(tag.value()));
+            case LinByteArrayTag tag -> outOps.createByteList(tag.view());
+            case LinIntArrayTag tag -> {
+                IntBuffer view = tag.view();
+                yield outOps.createIntList(IntStream.range(0, view.limit()).map(view::get));
+            }
+            case LinLongArrayTag tag -> {
+                LongBuffer view = tag.view();
+                yield outOps.createLongList(IntStream.range(0, view.limit()).mapToLong(view::get));
+            }
         };
     }
 
@@ -293,21 +299,27 @@ public DataResult<LinTag<?>> mergeToMap(LinTag<?> map, MapLike<LinTag<?>> values
             return DataResult.error(() -> "mergeToMap called with non-map: " + map, map);
         }
         LinCompoundTag.Builder output = builderFrom(map);
-        List<LinTag<?>> missed = new ArrayList<>();
+        List<LinTag<?>> missed = null;
+        Iterator<Pair<LinTag<?>, LinTag<?>>> entries = values.entries().iterator();
         try {
-            values.entries().forEach(entry -> {
+            while (entries.hasNext()) {
+                Pair<LinTag<?>, LinTag<?>> entry = entries.next();
                 LinTag<?> key = entry.getFirst();
                 if (key instanceof LinStringTag stringKey) {
                     output.put(stringKey.value(), entry.getSecond());
                 } else {
+                    if (missed == null) {
+                        missed = new ArrayList<>();
+                    }
                     missed.add(key);
                 }
-            });
+            }
         } catch (IllegalArgumentException e) {
             return DataResult.error(e::getMessage);
         }
-        if (!missed.isEmpty()) {
-            return DataResult.error(() -> "some keys are not strings: " + missed, output.build());
+        if (missed != null) {
+            List<LinTag<?>> missedKeys = missed;
+            return DataResult.error(() -> "some keys are not strings: " + missedKeys, output.build());
         }
         return DataResult.success(output.build());
     }
@@ -368,10 +380,18 @@ public DataResult<Stream<LinTag<?>>> getStream(LinTag<?> input) {
                     IntStream.range(0, values.limit()).mapToObj(i -> LinByteTag.of(values.get(i)))
                 );
             }
-            case LinIntArrayTag tag ->
-                DataResult.success(Arrays.stream(tag.value()).mapToObj(value -> (LinTag<?>) LinIntTag.of(value)));
-            case LinLongArrayTag tag ->
-                DataResult.success(Arrays.stream(tag.value()).mapToObj(value -> (LinTag<?>) LinLongTag.of(value)));
+            case LinIntArrayTag tag -> {
+                IntBuffer values = tag.view();
+                yield DataResult.success(
+                    IntStream.range(0, values.limit()).mapToObj(i -> (LinTag<?>) LinIntTag.of(values.get(i)))
+                );
+            }
+            case LinLongArrayTag tag -> {
+                LongBuffer values = tag.view();
+                yield DataResult.success(
+                    IntStream.range(0, values.limit()).mapToObj(i -> (LinTag<?>) LinLongTag.of(values.get(i)))
+                );
+            }
             default -> DataResult.error(() -> "Not a list");
         };
     }
@@ -395,7 +415,8 @@ public LinTag<?> createByteList(ByteBuffer input) {
     @Override
     public DataResult<IntStream> getIntStream(LinTag<?> input) {
         if (input instanceof LinIntArrayTag tag) {
-            return DataResult.success(Arrays.stream(tag.value()));
+            IntBuffer view = tag.view();
+            return DataResult.success(IntStream.range(0, view.limit()).map(view::get));
         }
         return DynamicOps.super.getIntStream(input);
     }
@@ -408,7 +429,8 @@ public LinTag<?> createIntList(IntStream input) {
     @Override
     public DataResult<LongStream> getLongStream(LinTag<?> input) {
         if (input instanceof LinLongArrayTag tag) {
-            return DataResult.success(Arrays.stream(tag.value()));
+            LongBuffer view = tag.view();
+            return DataResult.success(IntStream.range(0, view.limit()).mapToLong(view::get));
         }
         return DynamicOps.super.getLongStream(input);
     }

gradle/libs.versions.toml

@@ -2,6 +2,7 @@
 javafx = "22.0.2"
 tinylog = "2.7.0"
 crankcase = "0.1.1"
+jmh = "1.37"
 
 [plugins]
 crankcase-java = { id = "org.enginehub.crankcase.java", version.ref = "crankcase" }
@@ -10,6 +11,7 @@ crankcase-licensing = { id = "org.enginehub.crankcase.licensing", version.ref =
 crankcase-publishing = { id = "org.enginehub.crankcase.publishing", version.ref = "crankcase" }
 crankcase-release = { id = "org.enginehub.crankcase.release", version.ref = "crankcase" }
 osdetector = { id = "com.google.osdetector", version = "1.7.3" }
+jmh = { id = "me.champeau.jmh", version = "0.7.3" }
 
 [libraries]
 crankcase-checkstyle = { module = "org.enginehub.crankcase:checkstyle", version.ref = "crankcase" }

tree/build.gradle.kts

@@ -2,6 +2,7 @@ plugins {
     id("org.enginehub.lin-bus.java-library-conventions")
     alias(libs.plugins.crankcase.licensing)
     alias(libs.plugins.crankcase.publishing)
+    alias(libs.plugins.jmh)
 }
 
 dependencies {
@@ -15,6 +16,15 @@ dependencies {
     }
 }
 
+jmh {
+    jmhVersion = libs.versions.jmh
+    fork = 2
+    warmupIterations = 3
+    warmup = "1s"
+    iterations = 5
+    timeOnIteration = "1s"
+}
+
 publishing {
     publications {
         create<MavenPublication>("maven") {

tree/src/jmh/README.md

@@ -0,0 +1,27 @@
+# CompoundValueMap benchmarks
+
+JMH benchmarks for the production `CompoundValueMap`, the open-addressed map backing
+`LinCompoundTag`. The benchmarks live in the `org.enginehub.linbus.tree` package
+so they can construct the package-private map directly.
+
+`CompoundValueMapBenchmark` covers the map's hot paths across several sizes:
+
+- `getHit` tests a successful get with a reused key (its `String.hashCode` is cached after the first lookup)
+- `getMiss` tests an unsuccessful get with a reused key
+- `getHitFreshKey` / `getMissFreshKey` build a new `String` per lookup so the hash is uncached, forcing the map to
+  rehash the key every time
+- `construct` tests the time to build the copy of another map (the source's keys have cached hashes)
+- `constructFreshKey` builds from a source whose keys have uncached hashes, so both maps hash every key during the
+  copy rather than the `LinkedHashMap` path reusing cached hashes
+- `iterate` tests the time to iterate over the map's entries, which is a common operation when serializing
+
+## Running
+
+```sh
+# CPU: all JMH benchmarks (fork/warmup/iteration counts come from the jmh { } block in build.gradle.kts)
+./gradlew :tree:jmh
+
+# CPU + allocation: add `profilers.add("gc")` to the jmh { } block so the benchmarks report
+# `gc.alloc.rate.norm` (bytes allocated per op), or run the jar directly:
+#   ./gradlew :tree:jmhJar && java -jar tree/build/libs/tree-*-jmh.jar -prof gc
+```