Benchmark for groupBy

Author: retronym

test/benchmarks/src/main/scala/scala/collection/GroupByBenchmark.scala

@@ -0,0 +1,73 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc.
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.collection
+
+
+import java.util.concurrent.TimeUnit
+import org.openjdk.jmh.annotations.{Benchmark, BenchmarkMode, Fork, Level, Measurement, Mode, OutputTimeUnit, Param, Scope, Setup, State, Threads, Warmup}
+import org.openjdk.jmh.infra.Blackhole
+import scala.collection.mutable.ArrayBuffer
+
+
+@BenchmarkMode(Array(Mode.AverageTime))
+@Fork(2)
+@Threads(1)
+@Warmup(iterations = 10)
+@Measurement(iterations = 10)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+class GroupByBenchmark {
+  @Param(Array("128", "512", "2048", "8192"))
+  var size        : Int = _
+
+  @Param(Array("0", "32"))
+  var hashCodeCost: Int = _
+
+  @Param(Array("8", "2147483647"))
+  var maxNumGroups: Int = _
+
+  private case class Key(a: Int) {
+    override def hashCode(): Int = {
+      Blackhole.consumeCPU(hashCodeCost)
+      Integer.hashCode(a)
+    }
+  }
+
+  private case class Groupable(a: Int) {
+    val key = new Key(a % maxNumGroups)
+  }
+
+  private var groupables: ArrayBuffer[Groupable] = _
+
+  private class GroupByWrapper[A](as: collection.Iterable[A]) extends collection.Iterable[A] {
+    override def iterator: Iterator[A] = as.iterator
+    override protected def newBuilder = new mutable.Builder[A, Iterable[A]] {
+      override def clear(): Unit = ()
+      override def result(): Iterable[A] = Nil
+      override def +=(elem: A): this.type = this
+    }
+  }
+
+  @Setup(Level.Trial) def setup(): Unit = {
+    groupables = ArrayBuffer.tabulate(size)(Groupable(_))
+  }
+
+  @Benchmark def buildArrayBuffer(): AnyRef = {
+    groupBy(groupables)
+  }
+  @Benchmark def buildNil(): AnyRef = {
+    groupBy(new GroupByWrapper[Groupable](groupables))
+  }
+
+  private def groupBy[B](as: collection.Iterable[Groupable]) = as.groupBy(_.key)
+}