[GR-57064] Skip unnecessary JFR registrations for virtual threads.

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/JfrNativeEventWriter.java

@@ -24,7 +24,6 @@
  */
 package com.oracle.svm.core.jfr;
 
-import jdk.graal.compiler.word.Word;
 import org.graalvm.word.Pointer;
 import org.graalvm.word.UnsignedWord;
 
@@ -35,6 +34,8 @@
 import com.oracle.svm.core.util.DuplicatedInNativeCode;
 import com.oracle.svm.core.util.VMError;
 
+import jdk.graal.compiler.word.Word;
+
 /**
  * A JFR event writer that does not allocate any objects in the Java heap. Can only be used from
  * {@link Uninterruptible} code to prevent races between threads that try to write a native JFR

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/JfrThreadRepository.java

@@ -24,7 +24,6 @@
  */
 package com.oracle.svm.core.jfr;
 
-import jdk.graal.compiler.word.Word;
 import org.graalvm.nativeimage.IsolateThread;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
@@ -40,9 +39,12 @@
 import com.oracle.svm.core.thread.JavaThreads;
 import com.oracle.svm.core.thread.PlatformThreads;
 import com.oracle.svm.core.thread.Target_java_lang_Thread;
+import com.oracle.svm.core.thread.Target_java_lang_VirtualThread;
 import com.oracle.svm.core.thread.VMOperation;
 import com.oracle.svm.core.thread.VMThreads;
 
+import jdk.graal.compiler.word.Word;
+
 /**
  * Repository that collects all metadata about threads and thread groups.
  *
@@ -101,14 +103,23 @@ public void registerRunningThreads() {
         }
     }
 
-    @Uninterruptible(reason = "Locking without transition requires that the whole critical section is uninterruptible.")
+    @Uninterruptible(reason = "Prevent epoch changes. Prevent races with VM operations that start/stop recording.")
     public void registerThread(Thread thread) {
         if (!SubstrateJVM.get().isRecording()) {
             return;
         }
 
-        long threadId = JavaThreads.getThreadId(thread);
+        boolean isVirtual = JavaThreads.isVirtual(thread);
+        if (isVirtual && isVirtualThreadAlreadyRegistered(thread)) {
+            return;
+        }
+
+        registerThread0(thread, isVirtual);
+    }
 
+    @Uninterruptible(reason = "Locking without transition requires that the whole critical section is uninterruptible.")
+    private void registerThread0(Thread thread, boolean isVirtual) {
+        long threadId = JavaThreads.getThreadId(thread);
         JfrVisited visitedThread = StackValue.get(JfrVisited.class);
         visitedThread.setId(threadId);
         visitedThread.setHash(UninterruptibleUtils.Long.hashCode(threadId));
@@ -129,21 +140,26 @@ public void registerThread(Thread thread) {
             JfrNativeEventWriterDataAccess.initialize(data, epochData.threadBuffer);
 
             /* Similar to JfrThreadConstant::serialize in HotSpot. */
-            boolean isVirtual = JavaThreads.isVirtual(thread);
             long osThreadId = isVirtual ? 0 : threadId;
             long threadGroupId = registerThreadGroup(thread, isVirtual);
+            String name = thread.getName();
 
             JfrNativeEventWriter.putLong(data, threadId);
-            JfrNativeEventWriter.putString(data, thread.getName()); // OS thread name
+            JfrNativeEventWriter.putString(data, name); // OS thread name
             JfrNativeEventWriter.putLong(data, osThreadId); // OS thread id
-            JfrNativeEventWriter.putString(data, thread.getName()); // Java thread name
+            JfrNativeEventWriter.putString(data, name); // Java thread name
             JfrNativeEventWriter.putLong(data, threadId); // Java thread id
             JfrNativeEventWriter.putLong(data, threadGroupId); // Java thread group
             JfrNativeEventWriter.putBoolean(data, isVirtual);
             if (!JfrNativeEventWriter.commit(data)) {
                 return;
             }
 
+            if (isVirtual) {
+                Target_java_lang_VirtualThread vthread = JavaThreads.toVirtualTarget(thread);
+                vthread.jfrEpochId = JfrTraceIdEpoch.getInstance().currentEpochId();
+            }
+
             epochData.unflushedThreadCount++;
             /* The buffer may have been replaced with a new one. */
             epochData.threadBuffer = data.getJfrBuffer();
@@ -152,6 +168,16 @@ public void registerThread(Thread thread) {
         }
     }
 
+    @Uninterruptible(reason = "Epoch must not change while in this method.", callerMustBe = true)
+    private static boolean isVirtualThreadAlreadyRegistered(Thread thread) {
+        assert JavaThreads.isVirtual(thread);
+
+        /* Threads only need to be registered once per epoch. */
+        Target_java_lang_VirtualThread vthread = JavaThreads.toVirtualTarget(thread);
+        long epochId = JfrTraceIdEpoch.getInstance().currentEpochId();
+        return vthread.jfrEpochId == epochId;
+    }
+
     @Uninterruptible(reason = "Epoch must not change while in this method.")
     private long registerThreadGroup(Thread thread, boolean isVirtual) {
         if (isVirtual) {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/events/ExecutionSampleEvent.java

@@ -41,7 +41,7 @@ public static void writeExecutionSample(long elapsedTicks, long threadId, long s
 
             JfrNativeEventWriter.beginSmallEvent(data, JfrEvent.ExecutionSample);
             JfrNativeEventWriter.putLong(data, elapsedTicks);
-            JfrNativeEventWriter.putLong(data, threadId);
+            JfrNativeEventWriter.putThread(data, threadId);
             JfrNativeEventWriter.putLong(data, stackTraceId);
             JfrNativeEventWriter.putLong(data, threadState);
             JfrNativeEventWriter.endSmallEvent(data);

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/events/JavaMonitorEnterEvent.java

@@ -26,7 +26,6 @@
 
 package com.oracle.svm.core.jfr.events;
 
-import jdk.graal.compiler.word.Word;
 import org.graalvm.nativeimage.StackValue;
 
 import com.oracle.svm.core.Uninterruptible;
@@ -38,6 +37,8 @@
 import com.oracle.svm.core.jfr.JfrTicks;
 import com.oracle.svm.core.jfr.SubstrateJVM;
 
+import jdk.graal.compiler.word.Word;
+
 public class JavaMonitorEnterEvent {
     public static void emit(Object obj, long previousOwnerTid, long startTicks) {
         if (HasJfrSupport.get()) {
@@ -58,7 +59,7 @@ public static void emit0(Object obj, long previousOwnerTid, long startTicks) {
             JfrNativeEventWriter.putEventThread(data);
             JfrNativeEventWriter.putLong(data, SubstrateJVM.get().getStackTraceId(JfrEvent.JavaMonitorEnter, 0));
             JfrNativeEventWriter.putClass(data, obj.getClass());
-            JfrNativeEventWriter.putLong(data, previousOwnerTid);
+            JfrNativeEventWriter.putThread(data, previousOwnerTid);
             JfrNativeEventWriter.putLong(data, Word.objectToUntrackedPointer(obj).rawValue());
             JfrNativeEventWriter.endSmallEvent(data);
         }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/events/JavaMonitorWaitEvent.java

@@ -40,15 +40,15 @@
 import jdk.graal.compiler.word.Word;
 
 public class JavaMonitorWaitEvent {
-    public static void emit(long startTicks, Object obj, long notifier, long timeout, boolean timedOut) {
+    public static void emit(long startTicks, Object obj, long notifierTid, long timeout, boolean timedOut) {
         if (HasJfrSupport.get() && obj != null && !Target_jdk_jfr_internal_JVM_ChunkRotationMonitor.class.equals(obj.getClass()) &&
                         !Target_jdk_jfr_internal_management_HiddenWait.class.equals(obj.getClass())) {
-            emit0(startTicks, obj, notifier, timeout, timedOut);
+            emit0(startTicks, obj, notifierTid, timeout, timedOut);
         }
     }
 
     @Uninterruptible(reason = "Accesses a JFR buffer.")
-    private static void emit0(long startTicks, Object obj, long notifier, long timeout, boolean timedOut) {
+    private static void emit0(long startTicks, Object obj, long notifierTid, long timeout, boolean timedOut) {
         long duration = JfrTicks.duration(startTicks);
         if (JfrEvent.JavaMonitorWait.shouldEmit(duration)) {
             JfrNativeEventWriterData data = org.graalvm.nativeimage.StackValue.get(JfrNativeEventWriterData.class);
@@ -60,7 +60,7 @@ private static void emit0(long startTicks, Object obj, long notifier, long timeo
             JfrNativeEventWriter.putEventThread(data);
             JfrNativeEventWriter.putLong(data, SubstrateJVM.get().getStackTraceId(JfrEvent.JavaMonitorWait, 0));
             JfrNativeEventWriter.putClass(data, obj.getClass());
-            JfrNativeEventWriter.putLong(data, notifier);
+            JfrNativeEventWriter.putThread(data, notifierTid);
             JfrNativeEventWriter.putLong(data, timeout);
             JfrNativeEventWriter.putBoolean(data, timedOut);
             JfrNativeEventWriter.putLong(data, Word.objectToUntrackedPointer(obj).rawValue());

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/events/ThreadStartEvent.java

@@ -47,7 +47,7 @@ public static void emit(Thread thread) {
             JfrNativeEventWriter.putEventThread(data);
             JfrNativeEventWriter.putLong(data, SubstrateJVM.get().getStackTraceId(JfrEvent.ThreadStart, 0));
             JfrNativeEventWriter.putThread(data, thread);
-            JfrNativeEventWriter.putLong(data, JavaThreads.getParentThreadId(thread));
+            JfrNativeEventWriter.putThread(data, JavaThreads.getParentThreadId(thread));
             JfrNativeEventWriter.endSmallEvent(data);
         }
     }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/traceid/JfrTraceIdEpoch.java

@@ -25,14 +25,15 @@
 
 package com.oracle.svm.core.jfr.traceid;
 
-import jdk.graal.compiler.api.replacements.Fold;
 import org.graalvm.nativeimage.ImageSingletons;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
 
 import com.oracle.svm.core.Uninterruptible;
 import com.oracle.svm.core.thread.VMOperation;
 
+import jdk.graal.compiler.api.replacements.Fold;
+
 /**
  * Class holding the current JFR epoch. JFR uses an epoch system to safely separate constant pool
  * entries between adjacent chunks. Used to get the current or previous epoch and switch from one
@@ -42,7 +43,7 @@ public class JfrTraceIdEpoch {
     private static final long EPOCH_0_BIT = 0b01;
     private static final long EPOCH_1_BIT = 0b10;
 
-    private boolean epoch;
+    private long epochId;
 
     @Fold
     public static JfrTraceIdEpoch getInstance() {
@@ -56,26 +57,36 @@ public JfrTraceIdEpoch() {
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public void changeEpoch() {
         assert VMOperation.isInProgressAtSafepoint();
-        epoch = !epoch;
+        epochId++;
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     long thisEpochBit() {
-        return epoch ? EPOCH_1_BIT : EPOCH_0_BIT;
+        return getEpoch() ? EPOCH_1_BIT : EPOCH_0_BIT;
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     long previousEpochBit() {
-        return epoch ? EPOCH_0_BIT : EPOCH_1_BIT;
+        return getEpoch() ? EPOCH_0_BIT : EPOCH_1_BIT;
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public boolean currentEpoch() {
-        return epoch;
+        return getEpoch();
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public boolean previousEpoch() {
-        return !epoch;
+        return !getEpoch();
+    }
+
+    @Uninterruptible(reason = "Prevent epoch from changing.", callerMustBe = true)
+    public long currentEpochId() {
+        return epochId;
+    }
+
+    @Uninterruptible(reason = "Prevent epoch from changing.", callerMustBe = true)
+    private boolean getEpoch() {
+        return (epochId & 1) == 0;
     }
 }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaThreads.java

@@ -24,6 +24,8 @@
  */
 package com.oracle.svm.core.thread;
 
+import static com.oracle.svm.core.Uninterruptible.CALLED_FROM_UNINTERRUPTIBLE_CODE;
+
 import java.lang.Thread.UncaughtExceptionHandler;
 import java.security.AccessControlContext;
 import java.security.AccessController;
@@ -220,8 +222,9 @@ static Target_java_lang_ThreadGroup toTarget(ThreadGroup threadGroup) {
         return Target_java_lang_ThreadGroup.class.cast(threadGroup);
     }
 
+    @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
     @SuppressFBWarnings(value = "BC", justification = "Cast for @TargetClass")
-    private static Target_java_lang_VirtualThread toVirtualTarget(Thread thread) {
+    public static Target_java_lang_VirtualThread toVirtualTarget(Thread thread) {
         return Target_java_lang_VirtualThread.class.cast(thread);
     }
 

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_VirtualThread.java

@@ -122,6 +122,10 @@ public final class Target_java_lang_VirtualThread {
     @TargetElement(onlyWith = JDKLatest.class) @Alias @InjectAccessors(AlwaysFalseAccessor.class) boolean notified;
     // Checkstyle: resume
 
+    @Inject //
+    @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.Custom, declClass = ResetToMinusOneTransformer.class) //
+    public long jfrEpochId = -1;
+
     @Alias
     private static native ForkJoinPool createDefaultScheduler();
 
@@ -598,3 +602,10 @@ static Thread asThread(Object obj) {
     private VirtualThreadHelper() {
     }
 }
+
+final class ResetToMinusOneTransformer implements FieldValueTransformer {
+    @Override
+    public Object transform(Object receiver, Object originalValue) {
+        return -1L;
+    }
+}