ICU-23061: LowercaseTransliterator has poor scalability due to synchronized state

icu4j/main/translit/src/main/java/com/ibm/icu/text/LowercaseTransliterator.java

@@ -42,8 +42,6 @@ public Transliterator getInstance(String ID) {
     private final ULocale locale;
 
     private final UCaseProps csp;
-    private ReplaceableContextIterator iter;
-    private StringBuilder result;
     private int caseLocale;
 
     /**
@@ -54,16 +52,14 @@ public LowercaseTransliterator(ULocale loc) {
         super(_ID, null);
         locale = loc;
         csp=UCaseProps.INSTANCE;
-        iter=new ReplaceableContextIterator();
-        result = new StringBuilder();
         caseLocale = UCaseProps.getCaseLocale(locale);
     }
 
     /**
      * Implements {@link Transliterator#handleTransliterate}.
      */
     @Override
-    protected synchronized void handleTransliterate(Replaceable text,
+    protected void handleTransliterate(Replaceable text,
                                        Position offsets, boolean isIncremental) {
         if(csp==null) {
             return;
@@ -73,8 +69,10 @@ protected synchronized void handleTransliterate(Replaceable text,
             return;
         }
 
+        ReplaceableContextIterator iter = new ReplaceableContextIterator();
+        StringBuilder result = new StringBuilder();
+
         iter.setText(text);
-        result.setLength(0);
         int c, delta;
 
         // Walk through original string

icu4j/perf-tests/README.txt

@@ -43,6 +43,9 @@ COLLATION TESTS
     The collation tests run only on the command line with tabular output:
     perl collationperf.pl |& tee collation_output.txt
 
+JMH
+Some performance tests run using OpenJDK JMH. These may be launched with:
+    java -jar perf-tests/target/jmh-benchmarks.jar
 
 OTHER COMMAND LINE TESTS
 Additional tests are run from the command line, each producing an HTML

icu4j/perf-tests/pom.xml

@@ -15,6 +15,7 @@
 
   <properties>
     <module-name>perf_tests</module-name>
+    <jmh.version>1.37</jmh.version>
   </properties>
 
   <dependencies>
@@ -43,12 +44,23 @@
       <artifactId>commons-cli</artifactId>
       <version>${commons-cli.version}</version>
     </dependency>
+    <dependency>
+      <groupId>org.openjdk.jmh</groupId>
+      <artifactId>jmh-core</artifactId>
+      <version>${jmh.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>org.openjdk.jmh</groupId>
+      <artifactId>jmh-generator-annprocess</artifactId>
+      <version>${jmh.version}</version>
+      <scope>provided</scope>
+    </dependency>
   </dependencies>
 
   <build>
     <plugins>
       <plugin>
-        <!-- Copy dependencies by default, so that everythign is easier to run
+        <!-- Copy dependencies by default, so that everything is easier to run
           without having to explicitly list all kind of folders in classpath.
           Just use `./target/*` and `./target/dependency/*`
         -->
@@ -63,6 +75,49 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <configuration>
+          <annotationProcessors>
+            <annotationProcessor>org.openjdk.jmh.generators.BenchmarkProcessor</annotationProcessor>
+          </annotationProcessors>
+        </configuration>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-shade-plugin</artifactId>
+        <executions>
+          <execution>
+            <phase>package</phase>
+            <goals>
+              <goal>shade</goal>
+            </goals>
+            <configuration>
+              <finalName>jmh-benchmarks</finalName>
+              <transformers>
+                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+                  <mainClass>org.openjdk.jmh.Main</mainClass>
+                </transformer>
+                <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer" />
+              </transformers>
+              <filters>
+                <filter>
+                  <!-- Shading signed JARs will fail without this.
+                       http://stackoverflow.com/questions/999489/invalid-signature-file-when-attempting-to-run-a-jar
+                       -->
+                  <artifact>*:*</artifact>
+                  <excludes>
+                    <exclude>META-INF/*.SF</exclude>
+                    <exclude>META-INF/*.DSA</exclude>
+                    <exclude>META-INF/*.RSA</exclude>
+                  </excludes>
+                </filter>
+              </filters>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 

icu4j/perf-tests/src/main/java/com/ibm/icu/dev/test/perf/LowercaseTransliteratorPerf.java

@@ -0,0 +1,27 @@
+package com.ibm.icu.dev.test.perf;
+
+import java.util.concurrent.TimeUnit;
+
+import com.ibm.icu.text.Transliterator;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+
+@BenchmarkMode(Mode.Throughput)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+public class LowercaseTransliteratorPerf {
+
+    static final Transliterator LOWER = Transliterator.getInstance("Lower");
+
+    @Benchmark
+    public String testShort() {
+        return LOWER.transliterate("Cat");
+    }
+
+    @Benchmark
+    public String testSentence() {
+        return LOWER.transliterate("The Quick Brown Fox Jumped Over The Lazy Dog");
+    }
+
+}