1 files changed, 76 insertions, 0 deletions
diff --git a/test/benchmarks/src/main/scala/scala/collection/mutable/OpenHashMapBenchmark.scala b/test/benchmarks/src/main/scala/scala/collection/mutable/OpenHashMapBenchmark.scala
new file mode 100644
index 0000000000..eeea8f6508
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+++ b/test/benchmarks/src/main/scala/scala/collection/mutable/OpenHashMapBenchmark.scala
@@ -0,0 +1,76 @@
+package scala.collection.mutable;
+
+import java.util.concurrent.TimeUnit
+import org.openjdk.jmh.annotations._
+
+private object OpenHashMapBenchmark {
+  /** State container for the `put()` bulk calling tests.
+    * 
+    * Provides a thread-scoped map, so that allocation for the hash table will be done
+    * in the first warm-up iteration, not during measurement.
+    * 
+    * Performs a GC after every invocation, so that only the GCs caused by the invocation
+    * contribute to the measurement.
+    */
+  @State(Scope.Thread)
+  class BulkPutState {
+    val map = new OpenHashMap[Int,Int].empty
+  
+    @TearDown(Level.Invocation)
+    def teardown { map.clear(); System.gc() }
+  }
+}
+
+/** Benchmark for the library's [[OpenHashMap]].
+  * 
+  * The `put()` calls are tested by looping to the size desired for the map;
+  * instead of using the JMH harness, which iterates for a fixed length of time.
+  */
+@BenchmarkMode(Array(Mode.AverageTime))
+@Threads(1)
+@Fork(1)
+@Warmup(iterations = 20)
+@Measurement(iterations = 20)
+@OutputTimeUnit(TimeUnit.MICROSECONDS)
+@State(Scope.Benchmark)
+class OpenHashMapBenchmark {
+  import OpenHashMapBenchmark._
+
+  @Param(Array("100", "250", "1000", "2500", "10000", "25000", "100000", "250000", "1000000", "2500000",
+               "5000000", "7500000", "10000000", "25000000"))
+  var size: Int = _
+
+  /** Put elements into the given map. */
+  private[this] def put_Int(map: OpenHashMap[Int,Int], from: Int, to: Int) {
+    var i = from
+    while (i <= to) {  // using a `for` expression instead adds significant overhead
+      map.put(i, i)
+      i += 1
+    }
+  }
+
+  /** Test putting elements to a map of `Int` to `Int`. */
+  @Benchmark
+  def put_Int(state: BulkPutState) { put_Int(state.map, 1, size) }
+
+  /** Test putting and removing elements to a growing map of `Int` to `Int`. */
+  @Benchmark
+  def put_remove_Int(state: BulkPutState) {
+    val blocks = 50  // should be a factor of `size`
+    val totalPuts = 2 * size  // add twice as many, because we remove half of them
+    val blockSize: Int = totalPuts / blocks
+    var base = 0
+    while (base < totalPuts) {
+      put_Int(state.map, base + 1, base + blockSize)
+
+      // remove every other entry
+      var i = base + 1
+      while (i <= base + blockSize) {
+        state.map.remove(i)
+        i += 2
+      }
+
+      base += blockSize
+    }
+  }
+}