OPENNLP-421

- adds StringDeduplicationBenchmark (jmh), adapted from A. Shipilëv for benchmarking on different operating systems / Java environments
- fixes inconsistent path in build-helper-maven-plugin config for jmh test addition

opennlp-tools/pom.xml

@@ -187,7 +187,7 @@
                 </goals>
                 <configuration>
                   <sources>
-                    <source>src/jmh/</source>
+                    <source>src/jmh/java</source>
                   </sources>
                 </configuration>
               </execution>

opennlp-tools/src/jmh/java/opennlp/tools/StringDeduplicationBenchmark.java

@@ -0,0 +1,111 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package opennlp.tools;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+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;
+
+/**
+ * A benchmark class / setup by Aleksey Shipilëv.
+ * Resides here to investigate performance of String deduplication approaches
+ * on different environments.
+ * <p>
+ * Origin:
+ * <a href="https://shipilev.net/jvm/anatomy-quarks/10-string-intern/">
+ *   https://shipilev.net/jvm/anatomy-quarks/10-string-intern/</a>
+ * <p>
+ * His conclusion:<br>
+ * "Do not use String.intern() without thinking very hard about it, okay?"
+ */
+@State(Scope.Benchmark)
+public class StringDeduplicationBenchmark {
+
+  @Param({"1", "100", "10000", "1000000"})
+  private int size;
+
+  private StringInterner str;
+  private CHMInterner chm;
+  private HMInterner hm;
+
+  @Setup
+  public void setup() {
+    str = new StringInterner();
+    chm = new CHMInterner();
+    hm = new HMInterner();
+  }
+
+  public static class StringInterner {
+    public String intern(String s) {
+      return s.intern();
+    }
+  }
+
+  @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));
+    }
+  }
+}