SapMachine 21 #2379: Add StringDeduplication JFR Event

src/hotspot/share/gc/shared/stringdedup/stringDedupProcessor.cpp

@@ -193,10 +193,8 @@ void StringDedup::Processor::run(JavaThread* thread) {
 void StringDedup::Processor::log_statistics() {
   _total_stat.add(&_cur_stat);
   Stat::log_summary(&_cur_stat, &_total_stat);
-  if (log_is_enabled(Debug, stringdedup)) {
-    _cur_stat.log_statistics(false);
-    _total_stat.log_statistics(true);
-    Table::log_statistics();
-  }
+  _cur_stat.emit_statistics(false /* total */);
+  _total_stat.emit_statistics(true /* total */);
+  Table::log_statistics();
   _cur_stat = Stat{};
 }

src/hotspot/share/gc/shared/stringdedup/stringDedupStat.cpp

@@ -24,6 +24,7 @@
 
 #include "precompiled.hpp"
 #include "gc/shared/stringdedup/stringDedupStat.hpp"
+#include "jfr/jfrEvents.hpp"
 #include "logging/log.hpp"
 #include "utilities/globalDefinitions.hpp"
 
@@ -92,13 +93,6 @@ static double strdedup_elapsed_param_ms(Tickspan t) {
 }
 
 void StringDedup::Stat::log_summary(const Stat* last_stat, const Stat* total_stat) {
-  double total_deduped_bytes_percent = 0.0;
-
-  if (total_stat->_new_bytes > 0) {
-    // Avoid division by zero
-    total_deduped_bytes_percent = percent_of(total_stat->_deduped_bytes, total_stat->_new_bytes);
-  }
-
   log_info(stringdedup)(
     "Concurrent String Deduplication "
     "%zu (inspected), "
@@ -110,7 +104,7 @@ void StringDedup::Stat::log_summary(const Stat* last_stat, const Stat* total_sta
     last_stat->_inspected,
     last_stat->_new, STRDEDUP_BYTES_PARAM(last_stat->_new_bytes),
     last_stat->_deduped, STRDEDUP_BYTES_PARAM(last_stat->_deduped_bytes),
-    total_deduped_bytes_percent,
+    percent_of(total_stat->_deduped_bytes, total_stat->_new_bytes),
     STRDEDUP_BYTES_PARAM(total_stat->_deduped_bytes), STRDEDUP_BYTES_PARAM(total_stat->_new_bytes),
     strdedup_elapsed_param_ms(last_stat->_process_elapsed),
     strdedup_elapsed_param_ms(last_stat->_active_elapsed));
@@ -213,15 +207,14 @@ void StringDedup::Stat::log_times(const char* prefix) const {
   }
 }
 
-void StringDedup::Stat::log_statistics(bool total) const {
+void StringDedup::Stat::log_statistics() const {
   double known_percent               = percent_of(_known, _inspected);
   double known_shared_percent        = percent_of(_known_shared, _inspected);
   double new_percent                 = percent_of(_new, _inspected);
   double deduped_percent             = percent_of(_deduped, _inspected);
   double deduped_bytes_percent       = percent_of(_deduped_bytes, _new_bytes);
   double replaced_percent            = percent_of(_replaced, _new);
   double deleted_percent             = percent_of(_deleted, _new);
-  log_times(total ? "Total" : "Last");
   log_debug(stringdedup)("    Inspected:     %12zu", _inspected);
   log_debug(stringdedup)("      Known:       %12zu(%5.1f%%)", _known, known_percent);
   log_debug(stringdedup)("      Shared:      %12zu(%5.1f%%)", _known_shared, known_shared_percent);
@@ -234,3 +227,40 @@ void StringDedup::Stat::log_statistics(bool total) const {
   log_debug(stringdedup)("    Skipped: %zu (dead), %zu (incomplete), %zu (shared)",
                          _skipped_dead, _skipped_incomplete, _skipped_shared);
 }
+
+void StringDedup::Stat::emit_statistics(bool total) const {
+  if (log_is_enabled(Debug, stringdedup)) {
+    log_times(total ? "Total" : "Last");
+    log_statistics();
+  }
+
+  if (total) {
+    // Send only JFR events about the last stats
+    return;
+  }
+
+  EventStringDeduplication e;
+  if (e.should_commit()) {
+    e.set_starttime(_active_start);
+    Ticks active_end = _active_start;
+    active_end += _active_elapsed;
+    e.set_endtime(active_end);
+
+    e.set_inspected(_inspected);
+    e.set_known(_known);
+    e.set_shared(_known_shared);
+    e.set_newStrings(_new);
+    e.set_newSize(_new_bytes);
+    e.set_replaced(_replaced);
+    e.set_deleted(_deleted);
+    e.set_deduplicated(_deduped);
+    e.set_deduplicatedSize(_deduped_bytes);
+    e.set_skippedDead(_skipped_dead);
+    e.set_skippedIncomplete(_skipped_incomplete);
+    e.set_skippedShared(_skipped_shared);
+    e.set_processing(_process_elapsed);
+    e.set_tableResize(_resize_table_elapsed);
+    e.set_tableCleanup(_cleanup_table_elapsed);
+    e.commit();
+  }
+}

src/hotspot/share/gc/shared/stringdedup/stringDedupStat.hpp

@@ -71,6 +71,7 @@ class StringDedup::Stat {
   void report_phase_end(const char* phase, Tickspan* elapsed);
 
   void log_times(const char* prefix) const;
+  void log_statistics() const;
 
 public:
   Stat();
@@ -148,7 +149,7 @@ class StringDedup::Stat {
   void report_active_end();
 
   void add(const Stat* const stat);
-  void log_statistics(bool total) const;
+  void emit_statistics(bool total) const;
 
   static void log_summary(const Stat* last_stat, const Stat* total_stat);
 };

src/hotspot/share/gc/shared/stringdedup/stringDedupTable.cpp

@@ -724,6 +724,10 @@ void StringDedup::Table::verify() {
 }
 
 void StringDedup::Table::log_statistics() {
+  if (!log_is_enabled(Debug, stringdedup)) {
+    return;
+  }
+
   size_t dead_count;
   int dead_state;
   {

src/hotspot/share/jfr/metadata/metadata.xml

@@ -1178,6 +1178,24 @@
     <Field type="string" name="state" label="State" />
   </Type>
 
+  <Event name="StringDeduplication" category="Java Virtual Machine, GC, Detailed" label="String Deduplication Statistics" stackTrace="false">
+    <Field type="ulong" name="inspected" label="Inspected" />
+    <Field type="ulong" name="known" label="Known" />
+    <Field type="ulong" name="shared" label="Shared" />
+    <Field type="ulong" name="newStrings" label="New Strings" description="New unknown strings" />
+    <Field type="ulong" name="newSize" contentType="bytes" label="New Size" description="Size of new unknown strings" />
+    <Field type="ulong" name="replaced" label="Replaced" />
+    <Field type="ulong" name="deleted" label="Deleted" />
+    <Field type="ulong" name="deduplicated" label="Deduplicated" />
+    <Field type="ulong" name="deduplicatedSize" contentType="bytes" label="Deduplicated Size" />
+    <Field type="ulong" name="skippedDead" label="Skipped Dead" />
+    <Field type="ulong" name="skippedIncomplete" label="Skipped Incomplete" />
+    <Field type="ulong" name="skippedShared" label="Skipped Shared" />
+    <Field type="Tickspan" name="processing" label="Processing" />
+    <Field type="Tickspan" name="tableResize" label="Table Resize" />
+    <Field type="Tickspan" name="tableCleanup" label="Table Cleanup" />
+  </Event>
+
   <Event name="Flush" category="Flight Recorder" label="Flush" thread="false" experimental="true">
     <Field type="ulong" name="flushId" label="Flush Identifier" relation="FlushId" />
     <Field type="ulong" name="elements" label="Elements Written" />

src/jdk.jfr/share/conf/jfr/default.jfc

@@ -450,6 +450,11 @@
       <setting name="enabled" control="gc-enabled-normal">true</setting>
     </event>
 
+    <event name="jdk.StringDeduplication">
+      <setting name="enabled" control="gc-enabled-normal">true</setting>
+      <setting name="threshold">0 ms</setting>
+    </event>
+
     <event name="jdk.PromotionFailed">
       <setting name="enabled" control="gc-enabled-normal">true</setting>
     </event>

src/jdk.jfr/share/conf/jfr/profile.jfc

@@ -450,6 +450,11 @@
       <setting name="enabled" control="gc-enabled-normal">true</setting>
     </event>
 
+    <event name="jdk.StringDeduplication">
+      <setting name="enabled" control="gc-enabled-normal">true</setting>
+      <setting name="threshold">0 ms</setting>
+    </event>
+
     <event name="jdk.PromotionFailed">
       <setting name="enabled" control="gc-enabled-normal">true</setting>
     </event>

test/jdk/jdk/jfr/event/gc/detailed/TestStringDeduplicationEvent.java

@@ -0,0 +1,172 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code 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 General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package jdk.jfr.event.gc.detailed;
+
+import java.lang.reflect.Field;
+import java.lang.management.ManagementFactory;
+import java.lang.management.GarbageCollectorMXBean;
+import java.util.List;
+import java.util.ArrayList;
+
+import jdk.jfr.consumer.RecordingStream;
+import jdk.test.lib.jfr.EventNames;
+import jdk.test.whitebox.WhiteBox;
+
+/**
+ * @test id=Serial
+ * @requires vm.flagless
+ * @requires vm.hasJFR
+ * @requires vm.gc.Serial
+ * @library /test/lib /test/jdk
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. --add-opens=java.base/java.lang=ALL-UNNAMED
+ *                                       -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *                                       -ea
+ *                                       -XX:+UseSerialGC
+ *                                       -XX:+UseStringDeduplication
+ *                                       -XX:StringDeduplicationAgeThreshold=1
+ *                                       -Xlog:stringdedup*=debug
+ *                                       jdk.jfr.event.gc.detailed.TestStringDeduplicationEvent
+ */
+
+/**
+ * @test id=Parallel
+ * @requires vm.flagless
+ * @requires vm.hasJFR
+ * @requires vm.gc.Parallel
+ * @library /test/lib /test/jdk
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. --add-opens=java.base/java.lang=ALL-UNNAMED
+ *                                       -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *                                       -ea
+ *                                       -XX:+UseParallelGC
+ *                                       -XX:+UseStringDeduplication
+ *                                       -XX:StringDeduplicationAgeThreshold=1
+ *                                       -Xlog:stringdedup*=debug
+ *                                       jdk.jfr.event.gc.detailed.TestStringDeduplicationEvent
+ */
+
+/**
+ * @test id=G1
+ * @requires vm.flagless
+ * @requires vm.hasJFR
+ * @requires vm.gc.G1
+ * @library /test/lib /test/jdk
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. --add-opens=java.base/java.lang=ALL-UNNAMED
+ *                                       -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *                                       -ea
+ *                                       -XX:+UseG1GC
+ *                                       -XX:+UseStringDeduplication
+ *                                       -XX:StringDeduplicationAgeThreshold=1
+ *                                       -Xlog:stringdedup*=debug
+ *                                       jdk.jfr.event.gc.detailed.TestStringDeduplicationEvent
+ */
+
+/**
+ * @test id=Z
+ * @requires vm.flagless
+ * @requires vm.hasJFR
+ * @requires vm.gc.Z
+ * @library /test/lib /test/jdk
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. --add-opens=java.base/java.lang=ALL-UNNAMED
+ *                                       -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *                                       -ea
+ *                                       -XX:+UseZGC
+ *                                       -XX:+UseStringDeduplication
+ *                                       -XX:StringDeduplicationAgeThreshold=1
+ *                                       -Xlog:stringdedup*=debug
+ *                                       jdk.jfr.event.gc.detailed.TestStringDeduplicationEvent
+ */
+
+/**
+ * @test id=Shenandoah
+ * @requires vm.flagless
+ * @requires vm.hasJFR
+ * @requires vm.gc.Shenandoah
+ * @library /test/lib /test/jdk
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -Xbootclasspath/a:. --add-opens=java.base/java.lang=ALL-UNNAMED
+ *                                       -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI
+ *                                       -ea
+ *                                       -XX:+UseShenandoahGC
+ *                                       -XX:+UseStringDeduplication
+ *                                       -XX:StringDeduplicationAgeThreshold=1
+ *                                       -Xlog:stringdedup*=debug
+ *                                       jdk.jfr.event.gc.detailed.TestStringDeduplicationEvent
+ */
+
+public class TestStringDeduplicationEvent {
+    private static Field valueField;
+
+    static {
+        try {
+            valueField = String.class.getDeclaredField("value");
+            valueField.setAccessible(true);
+        } catch (Exception exception) {
+            throw new RuntimeException(exception);
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        boolean zgc = isZgc();
+
+        try (RecordingStream recording = new RecordingStream()) {
+            recording.enable(EventNames.StringDeduplication);
+            recording.onEvent(EventNames.StringDeduplication, e -> recording.close());
+            recording.startAsync();
+
+            String base = TestStringDeduplicationEvent.class.getSimpleName();
+            String duplicate = new StringBuilder(base).toString();
+            assert(getValue(base) != getValue(duplicate));
+
+            if (zgc) {
+                // ZGC only triggers string deduplications from major collections
+                WhiteBox.getWhiteBox().fullGC();
+            } else {
+                WhiteBox.getWhiteBox().youngGC();
+            }
+
+            recording.awaitTermination();
+        }
+    }
+
+    private static Object getValue(String string) {
+        try {
+            return valueField.get(string);
+        } catch (Exception e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private static boolean isZgc() {
+        List<GarbageCollectorMXBean> gcs = ManagementFactory.getGarbageCollectorMXBeans();
+        return gcs.getFirst().getName().contains("ZGC");
+    }
+}

test/lib/jdk/test/lib/jfr/EventNames.java

@@ -154,6 +154,7 @@ public class EventNames {
     public static final String GCLocker = PREFIX + "GCLocker";
     public static final String SystemGC = PREFIX + "SystemGC";
     public static final String GCCPUTime = PREFIX + "GCCPUTime";
+    public static final String StringDeduplication = PREFIX + "StringDeduplication";
 
     // Compiler
     public static final String Compilation = PREFIX + "Compilation";