HashTableInterner fixes

build.gradle.kts

@@ -3,6 +3,7 @@ import org.gradle.internal.jvm.Jvm
 
 plugins {
 	kotlin("jvm") version "1.9.10"
+	id("me.champeau.jmh") version "0.7.1"
 	java
 	application
 }
@@ -87,6 +88,16 @@ dependencies {
 	implementation("com.github.ben-manes.caffeine:caffeine:3.1.5")
 }
 
+jmh {
+	iterations.set(5)
+	timeOnIteration.set("1s")
+	warmup.set("1s")
+	fork.set(1)
+	includes.add("ht")
+	synchronizeIterations.set(false)
+	threads.set(4)
+}
+
 tasks.getByName<Test>("test") {
 	useJUnitPlatform()
 }

src/jmh/java/ru/dbotthepony/kstarbound/jmh/Interning.java

@@ -0,0 +1,118 @@
+package ru.dbotthepony.kstarbound.jmh;
+
+import com.github.benmanes.caffeine.cache.Interner;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Param;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.infra.Blackhole;
+import ru.dbotthepony.kstarbound.util.HashTableInterner;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+@State(Scope.Benchmark)
+public class Interning {
+	@Param({"1", "100", "10000", "1000000"})
+	private int size;
+
+	private StringInterner str;
+	private CHMInterner chm;
+	private HMInterner hm;
+	private HTInterner ht;
+	private CaffeineInterner ct;
+
+	@Setup
+	public void setup() {
+		str = new StringInterner();
+		chm = new CHMInterner();
+		hm = new HMInterner();
+		ht = new HTInterner();
+		ct = new CaffeineInterner();
+	}
+
+	public static class StringInterner {
+		public String intern(String s) {
+			return s.intern();
+		}
+	}
+
+	public static class HTInterner {
+		private final HashTableInterner<String> interner = new HashTableInterner<>(5);
+
+		public String intern(String s) {
+			return interner.intern(s);
+		}
+	}
+
+	public static class CaffeineInterner {
+		private final Interner<String> interner = Interner.newWeakInterner();
+
+		public String intern(String s) {
+			return interner.intern(s);
+		}
+	}
+
+	@Benchmark
+	public void intern(Blackhole bh) {
+		for (int c = 0; c < size; c++) {
+			bh.consume(str.intern("String" + c));
+		}
+	}
+
+	public static class CHMInterner {
+		private final Map<String, String> map;
+
+		public CHMInterner() {
+			map = new ConcurrentHashMap<>();
+		}
+
+		public String intern(String s) {
+			String exist = map.putIfAbsent(s, s);
+			return (exist == null) ? s : exist;
+		}
+	}
+
+	@Benchmark
+	public void chm(Blackhole bh) {
+		for (int c = 0; c < size; c++) {
+			bh.consume(chm.intern("String" + c));
+		}
+	}
+
+	public static class HMInterner {
+		private final Map<String, String> map;
+
+		public HMInterner() {
+			map = new HashMap<>();
+		}
+
+		public String intern(String s) {
+			String exist = map.putIfAbsent(s, s);
+			return (exist == null) ? s : exist;
+		}
+	}
+
+	@Benchmark
+	public void hm(Blackhole bh) {
+		for (int c = 0; c < size; c++) {
+			bh.consume(hm.intern("String" + c));
+		}
+	}
+
+	@Benchmark
+	public void ht(Blackhole bh) {
+		for (int c = 0; c < size; c++) {
+			bh.consume(ht.intern("String" + c));
+		}
+	}
+
+	@Benchmark
+	public void ct(Blackhole bh) {
+		for (int c = 0; c < size; c++) {
+			bh.consume(ct.intern("String" + c));
+		}
+	}
+}

src/main/kotlin/ru/dbotthepony/kstarbound/Starbound.kt

@@ -85,8 +85,6 @@ import ru.dbotthepony.kstarbound.util.set
 import ru.dbotthepony.kstarbound.util.traverseJsonPath
 import java.io.*
 import java.text.DateFormat
-import java.time.Duration
-import java.time.temporal.ChronoUnit
 import java.util.function.BiConsumer
 import java.util.function.BinaryOperator
 import java.util.function.Function

src/main/kotlin/ru/dbotthepony/kstarbound/util/HashTableInterner.kt

@@ -7,8 +7,10 @@ import ru.dbotthepony.kstarbound.stream
 import java.lang.ref.ReferenceQueue
 import java.lang.ref.WeakReference
 import java.util.concurrent.locks.LockSupport
-import java.util.stream.StreamSupport
 
+// hand-rolled interner, which has similar performance to ConcurrentHashMap
+// (given there is no strong congestion, in which case it performs somewhere above Caffeine interner),
+// while yielding significantly better memory utilization than both
 class HashTableInterner<T : Any>(private val segmentBits: Int) : Interner<T> {
 	companion object {
 		private val interners = ArrayList<WeakReference<HashTableInterner<*>>>()
@@ -31,9 +33,7 @@ class HashTableInterner<T : Any>(private val segmentBits: Int) : Interner<T> {
 							i.remove()
 						} else {
 							for (segment in get.segments) {
-								synchronized(segment) {
-									any += segment.cleanup()
-								}
+								any += segment.cleanup()
 							}
 						}
 					}
@@ -124,7 +124,8 @@ class HashTableInterner<T : Any>(private val segmentBits: Int) : Interner<T> {
 		actualSegmentBits = result
 	}
 
-	private val segments: Array<Segment> = Array(1.shl(segmentBits)) { Segment() }
+	private val locks: Array<Any> = Array(1.shl(segmentBits)) { Any() }
+	private val segments: Array<Segment> = Array(1.shl(segmentBits)) { Segment(32, locks[it]) }
 
 	init {
 		synchronized(interners) {
@@ -136,54 +137,17 @@ class HashTableInterner<T : Any>(private val segmentBits: Int) : Interner<T> {
 	// while this increase memory usage (linked list), this greatly
 	// simplify logic, and make scanning a bit faster because we don't jump to neighbour nodes
 	// (assuming past our neighbour there is no such key)
-	private inner class Segment : Interner<T> {
-		private var mask = 31
-		private var mem = arrayOfNulls<Ref<T>>(32)
-		private var stored = 0
+	private inner class Segment(val size: Int, private val lock: Any) {
 		private val queue = ReferenceQueue<T>()
 
-		fun cleanup(): Int {
-			var any = 0
-
-			while (true) {
-				val p = queue.poll() as Ref<T>? ?: return any
-				remove(p)
-				any++
-			}
-		}
+		val mask = size - 1
+		val mem = arrayOfNulls<Ref<T>>(size)
+		var stored = 0
 
 		private fun hash(e: Any): Int {
 			return HashCommon.mix(e.hashCode().rotateRight(segmentBits)) and mask
 		}
 
-		private fun grow() {
-			mask = (mask shl 1) or 1
-
-			val old = mem.stream()
-				.filter { it != null }
-				.flatMap { ObjectArrayList(it!!.iterator()).stream() }
-				.filter { !it.refersTo(null) }
-				.collect(ObjectArrayList.toList())
-
-			for (elem in old) {
-				elem.nextEntry = null
-			}
-
-			mem = arrayOfNulls(mem.size shl 1)
-			val mem = mem
-
-			for (elem in old) {
-				val ehash = hash(elem)
-				val existing = mem[ehash]
-
-				if (existing == null) {
-					mem[ehash] = elem
-				} else {
-					existing.insert(elem)
-				}
-			}
-		}
-
 		fun remove(ref: Ref<T>): Boolean {
 			val hash = hash(ref)
 			val mem = mem
@@ -202,8 +166,49 @@ class HashTableInterner<T : Any>(private val segmentBits: Int) : Interner<T> {
 			}
 		}
 
-		override fun intern(sample: T): T {
-			if (stored >= mem.size * 0.75f) grow()
+		fun insert(sample: T) {
+			stored++
+			val ref = Ref(sample, queue)
+			val mem = this.mem
+			val hash = hash(ref)
+			val existing = mem[hash]
+
+			if (existing == null)
+				mem[hash] = ref
+			else
+				existing.insert(ref)
+		}
+
+		fun cleanup(): Int {
+			var p: Ref<T>? = queue.poll() as Ref<T>? ?: return 0
+			var any = 0
+
+			synchronized(lock) {
+				while (p != null) {
+					check(remove(p!!)) { "Unable to remove null entry $p at hash ${hash(p!!)}" }
+					p = queue.poll() as Ref<T>?
+					any++
+				}
+			}
+
+			return any
+		}
+
+		fun grow(): Segment {
+			val old = mem.stream()
+				.filter { it != null }
+				.flatMap { ObjectArrayList(it!!.iterator()).stream() }
+				//.filter { !it.refersTo(null) }
+				.map { val v = it.get(); it.clear(); v }
+				.filter { it != null }
+				.collect(ObjectArrayList.toList())
+
+			val new = Segment(size * 2, lock)
+			for (elem in old) new.insert(elem as T)
+			return new
+		}
+
+		fun search(sample: T): T? {
 			val mem = mem
 			val hash = hash(sample)
 			var search = mem[hash]
@@ -213,33 +218,35 @@ class HashTableInterner<T : Any>(private val segmentBits: Int) : Interner<T> {
 
 				if (get == sample)
 					return get
-				else if (get == null) {
-					check(remove(search)) { "Unable to remove null entry $search at hash $hash" }
+				else
 					search = search.nextEntry
-				} else {
-					search = search.nextEntry
-				}
 			}
 
-			val ref = Ref(sample, queue)
-			val existing = mem[hash]
-
-			if (existing == null)
-				mem[hash] = ref
-			else
-				existing.insert(ref)
-
-			stored++
-			return sample
+			return null
 		}
 	}
 
 	override fun intern(sample: T): T {
 		val hash = HashCommon.mix(sample.hashCode())
-		val segment = segments[hash and actualSegmentBits]
+		val segmentIndex = hash and actualSegmentBits
+		var segment = segments[segmentIndex]
 
-		synchronized(segment) {
-			return segment.intern(sample)
+		val find = segment.search(sample)
+		if (find != null) return find
+
+		synchronized(locks[segmentIndex]) {
+			segment = segments[segmentIndex]
+
+			val find = segment.search(sample)
+			if (find != null) return find
+
+			if (segment.stored >= segment.mem.size * 0.75f) {
+				segment = segment.grow()
+				segments[segmentIndex] = segment
+			}
+
+			segment.insert(sample)
+			return sample
 		}
 	}
 }

src/test/kotlin/ru/dbotthepony/kstarbound/test/InternerTest.kt

@@ -0,0 +1,40 @@
+package ru.dbotthepony.kstarbound.test
+
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import ru.dbotthepony.kstarbound.util.HashTableInterner
+import java.util.concurrent.atomic.AtomicInteger
+import java.util.random.RandomGenerator
+
+object InternerTest {
+	@Test
+	@DisplayName("Interner stress test in high concurrency")
+	fun test() {
+		val interner = HashTableInterner<String>(5)
+		val threads = ArrayList<Thread>()
+		val misses = AtomicInteger()
+
+		for (i in 0 until 8) {
+			threads.add(Thread {
+				val rand = RandomGenerator.of("Xoroshiro128PlusPlus")
+
+				for (i2 in 0 until 100_000) {
+					val v = rand.nextInt()
+					val s1 = "String$v"
+					val s2 = "String$v"
+
+					if (interner.intern(s1) !== interner.intern(s2)) {
+						misses.incrementAndGet()
+					}
+				}
+			})
+		}
+
+		threads.forEach { it.start() }
+		threads.forEach { it.join() }
+
+		if (misses.get() != 0) {
+			throw IllegalStateException("Interner stress test failed ($misses misses)")
+		}
+	}
+}