8368527: JMX: Add an MXBeans method to query GC CPU time

Reviewed-by: phh, kevinw

Author: JonasNorlinder

src/hotspot/share/include/jmm.h

@@ -53,7 +53,8 @@ enum {
   JMM_VERSION_2   = 0x20020000, // JDK 10
   JMM_VERSION_3   = 0x20030000, // JDK 14
   JMM_VERSION_4   = 0x20040000, // JDK 21
-  JMM_VERSION     = JMM_VERSION_4
+  JMM_VERSION_5   = 0x20050000, // JDK 26
+  JMM_VERSION     = JMM_VERSION_5
 };
 
 typedef struct {
@@ -81,6 +82,7 @@ typedef enum {
   JMM_GC_TIME_MS                     = 9,    /* Total accumulated time spent in collection */
   JMM_GC_COUNT                       = 10,   /* Total number of collections */
   JMM_JVM_UPTIME_MS                  = 11,   /* The JVM uptime in milliseconds */
+  JMM_TOTAL_GC_CPU_TIME              = 12,   /* Total accumulated GC CPU time */
 
   JMM_INTERNAL_ATTRIBUTE_INDEX       = 100,
   JMM_CLASS_LOADED_BYTES             = 101,  /* Number of bytes loaded instance classes */

src/hotspot/share/services/cpuTimeUsage.cpp

@@ -36,6 +36,7 @@
 volatile bool CPUTimeUsage::Error::_has_error = false;
 
 static inline jlong thread_cpu_time_or_zero(Thread* thread) {
+  assert(!Universe::is_shutting_down(), "Should not query during shutdown");
   jlong cpu_time = os::thread_cpu_time(thread);
   if (cpu_time == -1) {
     CPUTimeUsage::Error::mark_error();

src/hotspot/share/services/management.cpp

@@ -54,6 +54,7 @@
 #include "runtime/threadSMR.hpp"
 #include "runtime/vmOperations.hpp"
 #include "services/classLoadingService.hpp"
+#include "services/cpuTimeUsage.hpp"
 #include "services/diagnosticCommand.hpp"
 #include "services/diagnosticFramework.hpp"
 #include "services/finalizerService.hpp"
@@ -889,6 +890,21 @@ static jint get_num_flags() {
   return count;
 }
 
+static jlong get_gc_cpu_time() {
+  if (!os::is_thread_cpu_time_supported()) {
+    return -1;
+  }
+
+  {
+    MutexLocker hl(Heap_lock);
+    if (Universe::heap()->is_shutting_down()) {
+      return -1;
+    }
+
+    return CPUTimeUsage::GC::total();
+  }
+}
+
 static jlong get_long_attribute(jmmLongAttribute att) {
   switch (att) {
   case JMM_CLASS_LOADED_COUNT:
@@ -915,6 +931,9 @@ static jlong get_long_attribute(jmmLongAttribute att) {
   case JMM_JVM_UPTIME_MS:
     return Management::ticks_to_ms(os::elapsed_counter());
 
+  case JMM_TOTAL_GC_CPU_TIME:
+    return get_gc_cpu_time();
+
   case JMM_COMPILE_TOTAL_TIME_MS:
     return Management::ticks_to_ms(CompileBroker::total_compilation_ticks());
 

src/java.management/share/classes/java/lang/management/MemoryMXBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 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
@@ -267,6 +267,43 @@ public interface MemoryMXBean extends PlatformManagedObject {
      */
     public MemoryUsage getNonHeapMemoryUsage();
 
+    /**
+     * Returns the approximate accumulated time, in nanoseconds,
+     * spent in garbage collection (GC).
+     *
+     * <p> The time spent in spent in GC is the CPU time used by
+     * all GC activity, including any overhead, which means the
+     * result may be non-zero even if no GC has occurred.
+     *
+     * This method returns {@code -1} if the platform does
+     * not support this operation or the information is not
+     * available.
+     *
+     * @apiNote
+     * May be used in conjunction with {@link jdk.management/com.sun.management.OperatingSystemMXBean#getProcessCpuTime()}
+     * for calculating the GC's usage of CPU time as a whole.
+     *
+     * @implNote The specifics on what constitutes the time spent
+     * in GC are highly implementation dependent. In the HotSpot
+     * Virtual Machine, this time includes relevant
+     * implementation-specific details such as driver threads,
+     * workers, VM Operations and string deduplication (if
+     * enabled). Driver threads may be created by a GC to
+     * orchestrate its work. The return value can be -1 if called
+     * when measurement is not possible, such as during shutdown.
+     *
+     * @implSpec The default implementation returns {@code -1}.
+     *
+     * @return the total accumulated CPU time for GC in
+     * nanoseconds, or {@code -1}.
+     *
+     * @since 26
+     */
+    @SuppressWarnings("doclint:reference")
+    default public long getTotalGcCpuTime() {
+        return -1;
+    }
+
     /**
      * Tests if verbose output for the memory system is enabled.
      *
@@ -302,5 +339,4 @@ public interface MemoryMXBean extends PlatformManagedObject {
      * @see     java.lang.System#gc()
      */
     public void gc();
-
 }

src/java.management/share/classes/sun/management/MemoryImpl.java

@@ -67,6 +67,10 @@ public void gc() {
         Runtime.getRuntime().gc();
     }
 
+    public long getTotalGcCpuTime() {
+        return jvm.getTotalGcCpuTime();
+    }
+
     // Need to make a VM call to get coherent value
     public MemoryUsage getHeapMemoryUsage() {
         return getMemoryUsage0(true);

src/java.management/share/classes/sun/management/VMManagement.java

@@ -55,6 +55,7 @@ public interface VMManagement {
     public boolean getVerboseClass();
 
     // Memory Subsystem
+    public long    getTotalGcCpuTime();
     public boolean getVerboseGC();
 
     // Runtime Subsystem

src/java.management/share/classes/sun/management/VMManagementImpl.java

@@ -128,6 +128,7 @@ public int    getLoadedClassCount() {
     public native boolean getVerboseClass();
 
     // Memory Subsystem
+    public native long getTotalGcCpuTime();
     public native boolean getVerboseGC();
 
     // Runtime Subsystem

src/java.management/share/native/libmanagement/VMManagementImpl.c

@@ -121,6 +121,13 @@ Java_sun_management_VMManagementImpl_getUnloadedClassCount
     return count;
 }
 
+JNIEXPORT jlong JNICALL
+Java_sun_management_VMManagementImpl_getTotalGcCpuTime
+  (JNIEnv *env, jobject dummy)
+{
+    return jmm_interface->GetLongAttribute(env, NULL, JMM_TOTAL_GC_CPU_TIME);
+}
+
 JNIEXPORT jboolean JNICALL
 Java_sun_management_VMManagementImpl_getVerboseGC
   (JNIEnv *env, jobject dummy)

test/hotspot/jtreg/vmTestbase/nsk/monitoring/share/server/ServerMemoryMXBean.java

@@ -58,6 +58,10 @@ public int getObjectPendingFinalizationCount() {
                 return getIntAttribute(OBJECT_PENDING_FINALIZATION_COUNT);
         }
 
+        public long getTotalGcCpuTime() {
+                throw new UnsupportedOperationException("This method is not supported");
+        }
+
         public boolean isVerbose() {
                 return getBooleanAttribute(VERBOSE);
         }

test/jdk/java/lang/management/MemoryMXBean/StressGetTotalGcCpuTimeDuringShutdown.java

@@ -0,0 +1,112 @@
+/*
+ * 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.
+ */
+
+/*
+ * @test id=Epsilon
+ * @requires vm.gc.Epsilon
+ * @bug     8368527
+ * @summary Stress MemoryMXBean.getTotalGcCpuTime during shutdown
+ * @library /test/lib
+ * @run main/othervm -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC StressGetTotalGcCpuTimeDuringShutdown
+ */
+
+/*
+ * @test id=Serial
+ * @requires vm.gc.Serial
+ * @bug     8368527
+ * @summary Stress MemoryMXBean.getTotalGcCpuTime during shutdown
+ * @library /test/lib
+ * @run main/othervm -XX:+UseSerialGC StressGetTotalGcCpuTimeDuringShutdown
+ */
+
+/*
+ * @test id=Parallel
+ * @requires vm.gc.Parallel
+ * @bug     8368527
+ * @summary Stress MemoryMXBean.getTotalGcCpuTime during shutdown
+ * @library /test/lib
+ * @run main/othervm -XX:+UseParallelGC StressGetTotalGcCpuTimeDuringShutdown
+ */
+
+/*
+ * @test id=G1
+ * @requires vm.gc.G1
+ * @bug     8368527
+ * @summary Stress MemoryMXBean.getTotalGcCpuTime during shutdown
+ * @library /test/lib
+ * @run main/othervm -XX:+UseG1GC StressGetTotalGcCpuTimeDuringShutdown
+ */
+
+/*
+ * @test id=ZGC
+ * @requires vm.gc.Z
+ * @bug     8368527
+ * @summary Stress MemoryMXBean.getTotalGcCpuTime during shutdown
+ * @library /test/lib
+ * @run main/othervm -XX:+UseZGC StressGetTotalGcCpuTimeDuringShutdown
+ */
+
+/*
+ * @test id=Shenandoah
+ * @requires vm.gc.Shenandoah
+ * @bug     8368527
+ * @summary Stress MemoryMXBean.getTotalGcCpuTime during shutdown
+ * @library /test/lib
+ * @run main/othervm -XX:+UseShenandoahGC StressGetTotalGcCpuTimeDuringShutdown
+ */
+
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryMXBean;
+import java.lang.management.ThreadMXBean;
+
+public class StressGetTotalGcCpuTimeDuringShutdown {
+    static final ThreadMXBean mxThreadBean = ManagementFactory.getThreadMXBean();
+    static final MemoryMXBean mxMemoryBean = ManagementFactory.getMemoryMXBean();
+
+    public static void main(String[] args) throws Exception {
+        try {
+            if (!mxThreadBean.isThreadCpuTimeEnabled()) {
+                return;
+            }
+        } catch (UnsupportedOperationException e) {
+            if (mxMemoryBean.getTotalGcCpuTime() != -1) {
+                throw new RuntimeException("GC CPU time should be -1");
+            }
+            return;
+        }
+
+        final int numberOfThreads = Runtime.getRuntime().availableProcessors() * 8;
+        for (int i = 0; i < numberOfThreads; i++) {
+            Thread t = new Thread(() -> {
+                while (true) {
+                    long gcCpuTimeFromThread = mxMemoryBean.getTotalGcCpuTime();
+                    if (gcCpuTimeFromThread < -1) {
+                        throw new RuntimeException("GC CPU time should never be less than -1 but was " + gcCpuTimeFromThread);
+                    }
+                }
+            });
+            t.setDaemon(true);
+            t.start();
+        }
+    }
+}