[benchmark] Add JMH Benchmark for Java String Join operations

Author: adamretter

exist-core-jmh/pom.xml

@@ -78,6 +78,7 @@
                             <header>${project.parent.relativePath}/LGPL-21-license.template.txt</header>
                             <excludes>
                                 <exclude>src/main/java/org/exist/storage/lock/LockTableBenchmark.java</exclude>
+                                <exclude>src/main/java/org/exist/xquery/utils/StringJoinBenchmark.java</exclude>
                                 <exclude>src/main/java/org/exist/xquery/utils/URIUtilsBenchmark.java</exclude>
                             </excludes>
                         </licenseSet>
@@ -89,6 +90,7 @@
                             <header>${project.parent.relativePath}/FDB-backport-LGPL-21-ONLY-license.template.txt</header>
                             <includes>
                                 <include>src/main/java/org/exist/storage/lock/LockTableBenchmark.java</include>
+                                <include>src/main/java/org/exist/xquery/utils/StringJoinBenchmark.java</include>
                                 <include>src/main/java/org/exist/xquery/utils/URIUtilsBenchmark.java</include>
                             </includes>
 

exist-core-jmh/src/main/java/org/exist/xquery/utils/StringJoinBenchmark.java

@@ -0,0 +1,121 @@
+/*
+ * Copyright (C) 2014, Evolved Binary Ltd
+ *
+ * This file was originally ported from FusionDB to eXist-db by
+ * Evolved Binary, for the benefit of the eXist-db Open Source community.
+ * Only the ported code as it appears in this file, at the time that
+ * it was contributed to eXist-db, was re-licensed under The GNU
+ * Lesser General Public License v2.1 only for use in eXist-db.
+ *
+ * This license grant applies only to a snapshot of the code as it
+ * appeared when ported, it does not offer or infer any rights to either
+ * updates of this source code or access to the original source code.
+ *
+ * The GNU Lesser General Public License v2.1 only license follows.
+ *
+ * ---------------------------------------------------------------------
+ *
+ * Copyright (C) 2014, Evolved Binary Ltd
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; version 2.1.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+package org.exist.xquery.utils;
+
+import org.openjdk.jmh.annotations.*;
+
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * Benchmarks on variations of Java String Join operations.
+ *
+ * @author <a href="mailto:[email protected]">Adam Retter</a>
+ */
+@State(Scope.Benchmark)
+public class StringJoinBenchmark {
+
+    private final int maxStringLength = 20;
+
+    @Param({ "1", "2", "5", "10", "100", "1000", "10000" })
+    private int numOfStrings;
+
+    private final List<String> strings = new ArrayList();
+
+//    @State(Scope.Thread)
+//    public static class BuilderState {
+//        StringBuilder builder;
+//
+//        @Setup(Level.Invocation)  //TODO(AR) check that Level.Invocation is correct
+//        public void setUp() {
+//            builder = new StringBuilder();
+//        }
+//    }
+
+    @Setup(Level.Trial)
+    public void setUp() {
+        final byte[] strData = new byte[maxStringLength];
+        final Random random = new Random();
+        for (int i = 0; i < numOfStrings; i++) {
+            final int strLen = random.nextInt(maxStringLength) + 1;
+            random.nextBytes(strData);
+            strings.add(new String(strData, 0, strLen, StandardCharsets.UTF_8));
+        }
+    }
+
+    @Benchmark
+    public StringBuilder forApproach(/*final BuilderState builderState*/) {
+//        final StringBuilder builder = builderState.builder;
+        final StringBuilder builder = new StringBuilder();
+
+        for (int i = 0; i < strings.size(); i++) {
+            if (i > 0) {
+                builder.append(", ");
+            }
+            builder.append(strings.get(i));
+        }
+        return builder;
+    }
+
+    @Benchmark
+    public StringBuilder forEachApproach(/*final BuilderState builderState*/) {
+//        final StringBuilder builder = builderState.builder;
+        final StringBuilder builder = new StringBuilder();
+
+        boolean firstArgument = true;
+        for (final String str : strings) {
+            builder.append(str);
+            if (firstArgument) {
+                firstArgument = false;
+            } else {
+                builder.append(", ");
+            }
+        }
+        return builder;
+    }
+
+    @Benchmark
+    public String jdkApproach() {
+        return String.join(", ", strings);
+    }
+
+    public static void main(final String args[]) {
+        // NOTE: just for running with the java debugger
+        final StringJoinBenchmark stringJoinBenchmark = new StringJoinBenchmark();
+        // stringJoinBenchmark.forApproach();
+        // stringJoinBenchmark.forEachApproach();
+        stringJoinBenchmark.jdkApproach();
+    }
+}