1 files changed, 29 insertions, 0 deletions
diff --git a/test/benchmarks/src/main/scala/scala/collection/immutable/MapBenchmark.scala b/test/benchmarks/src/main/scala/scala/collection/immutable/MapBenchmark.scala
new file mode 100644
index 0000000000..a0358d6a1a
--- /dev/null
+++ b/test/benchmarks/src/main/scala/scala/collection/immutable/MapBenchmark.scala
@@ -0,0 +1,29 @@
+package scala.collection.immutable
+
+import java.util.concurrent.TimeUnit
+
+import org.openjdk.jmh.annotations._
+import org.openjdk.jmh.infra._
+
+@BenchmarkMode(Array(Mode.AverageTime))
+@Fork(2)
+@Threads(1)
+@Warmup(iterations = 10)
+@Measurement(iterations = 10)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+class MapBenchmark {
+
+  var base: Map[String,String] = _
+
+
+  @Setup(Level.Trial) def initKeys(): Unit = {
+    base = Map("a" -> "a", "b" -> "b", "c" -> "c", "d" -> "d")
+  }
+
+  // immutable map is implemented as EmptyMap -> Map1 -> Map2 -> Map3 -> Map4 -> Hashmap
+  // add an extra entry to Map4 causes a lot of work, benchmark the transition
+  @Benchmark def map4AddElement(bh: Blackhole): Unit = {
+    bh.consume(base.updated("e", "e"))
+  }
+}