8348907: Stress times out when is executed with ZGC

Reviewed-by: egahlin, aboldtch, eosterlund

Author: Markus Grönlund

make/src/classes/build/tools/jfr/GenerateJfrFiles.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 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
@@ -768,9 +768,10 @@ private static void printJfrEventClassesHpp(Metadata metadata, File outputFile)
             out.write("#ifndef JFRFILES_JFREVENTCLASSES_HPP");
             out.write("#define JFRFILES_JFREVENTCLASSES_HPP");
             out.write("");
-            out.write("#include \"oops/klass.hpp\"");
             out.write("#include \"jfrfiles/jfrTypes.hpp\"");
             out.write("#include \"jfr/utilities/jfrTypes.hpp\"");
+            out.write("#include \"oops/klass.hpp\"");
+            out.write("#include \"runtime/thread.hpp\"");
             out.write("#include \"utilities/macros.hpp\"");
             out.write("#include \"utilities/ticks.hpp\"");
             out.write("#if INCLUDE_JFR");
@@ -789,6 +790,7 @@ private static void printJfrEventClassesHpp(Metadata metadata, File outputFile)
             out.write(" */");
             out.write("");
             printTypes(out, metadata, false);
+            printHelpers(out, false);
             out.write("");
             out.write("");
             out.write("#else // !INCLUDE_JFR");
@@ -806,13 +808,43 @@ private static void printJfrEventClassesHpp(Metadata metadata, File outputFile)
             out.write("};");
             out.write("");
             printTypes(out, metadata, true);
+            printHelpers(out, true);
             out.write("");
             out.write("");
             out.write("#endif // INCLUDE_JFR");
             out.write("#endif // JFRFILES_JFREVENTCLASSES_HPP");
         }
     }
 
+    private static void printHelpers(Printer out, boolean empty) {
+        out.write("template <typename EventType>");
+        out.write("class JfrNonReentrant : public EventType {");
+        if (!empty) {
+            out.write(" private:");
+            out.write("  Thread* const _thread;");
+            out.write("  int32_t _previous_nesting;");
+        }
+        out.write(" public:");
+        out.write("  JfrNonReentrant(EventStartTime timing = TIMED)");
+        if (empty) {
+            out.write("  {}");
+        } else {
+            out.write("    : EventType(timing), _thread(Thread::current()), _previous_nesting(JfrThreadLocal::make_non_reentrant(_thread)) {}");
+            out.write("");
+            out.write("  JfrNonReentrant(Thread* thread, EventStartTime timing = TIMED)");
+            out.write("    : EventType(timing), _thread(thread), _previous_nesting(JfrThreadLocal::make_non_reentrant(_thread)) {}");
+        }
+        if (!empty) {
+          out.write("");
+          out.write("  ~JfrNonReentrant() {");
+          out.write("    if (_previous_nesting != -1) {");
+          out.write("      JfrThreadLocal::make_reentrant(_thread, _previous_nesting);");
+          out.write("    }");
+          out.write("  }");
+        }
+        out.write("}; ");
+    }
+
     private static void printTypes(Printer out, Metadata metadata, boolean empty) {
         for (TypeElement t : metadata.getStructs()) {
             printType(out, t, empty);

src/hotspot/share/gc/z/zTracer.cpp

@@ -124,7 +124,7 @@ void ZTracer::initialize() {
 void ZTracer::send_stat_counter(const ZStatCounter& counter, uint64_t increment, uint64_t value) {
   NoSafepointVerifier nsv;
 
-  EventZStatisticsCounter e;
+  JfrNonReentrant<EventZStatisticsCounter> e;
   if (e.should_commit()) {
     e.set_id(counter.id());
     e.set_increment(increment);
@@ -136,7 +136,7 @@ void ZTracer::send_stat_counter(const ZStatCounter& counter, uint64_t increment,
 void ZTracer::send_stat_sampler(const ZStatSampler& sampler, uint64_t value) {
   NoSafepointVerifier nsv;
 
-  EventZStatisticsSampler e;
+  JfrNonReentrant<EventZStatisticsSampler> e;
   if (e.should_commit()) {
     e.set_id(sampler.id());
     e.set_value(value);

src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.cpp

@@ -677,6 +677,10 @@ void JfrCheckpointManager::write_checkpoint(Thread* thread, traceid tid /* 0 */,
   JfrTypeManager::write_checkpoint(thread, tid, vthread);
 }
 
+void JfrCheckpointManager::write_simplified_vthread_checkpoint(traceid vtid) {
+  JfrTypeManager::write_simplified_vthread_checkpoint(vtid);
+}
+
 class JfrNotifyClosure : public ThreadClosure {
  public:
   void do_thread(Thread* thread) {

src/hotspot/share/jfr/recorder/checkpoint/jfrCheckpointManager.hpp

@@ -108,6 +108,7 @@ class JfrCheckpointManager : public JfrCHeapObj {
  public:
   static JfrBlobHandle create_thread_blob(JavaThread* jt, traceid tid = 0, oop vthread = nullptr);
   static void write_checkpoint(Thread* t, traceid tid = 0, oop vthread = nullptr);
+  static void write_simplified_vthread_checkpoint(traceid vtid);
   size_t flush_type_set();
 
   friend class Jfr;

src/hotspot/share/jfr/recorder/checkpoint/types/jfrType.cpp

@@ -312,6 +312,23 @@ void JfrThreadConstant::serialize(JfrCheckpointWriter& writer) {
   // VirtualThread threadgroup already serialized invariant.
 }
 
+// This serializer is used when the vthread name cannot
+// be determined because we cannot access any oops.
+void JfrSimplifiedVirtualThreadConstant::serialize(JfrCheckpointWriter & writer) {
+  writer.write_key(_vtid);
+  // Write the null string categorically as the os name for virtual threads.
+  writer.write((const char*)nullptr); // os name
+  writer.write(0); // os id
+  // vthread name cannot be determined for this simplified version.
+  // This is because we cannot access any oops.
+  writer.write_empty_string();
+  writer.write(_vtid); // java tid
+  // java thread group - VirtualThread threadgroup reserved id 1
+  writer.write(1);
+  writer.write<bool>(true); // isVirtual
+  // VirtualThread threadgroup already serialized invariant.
+}
+
 void BytecodeConstant::serialize(JfrCheckpointWriter& writer) {
   static const u4 nof_entries = Bytecodes::number_of_codes;
   writer.write_count(nof_entries);

src/hotspot/share/jfr/recorder/checkpoint/types/jfrType.hpp

@@ -117,6 +117,14 @@ class JfrThreadConstant : public JfrSerializer {
   void serialize(JfrCheckpointWriter& writer);
 };
 
+class JfrSimplifiedVirtualThreadConstant : public JfrSerializer {
+ private:
+  traceid _vtid;
+ public:
+  JfrSimplifiedVirtualThreadConstant(traceid vtid) : _vtid(vtid) {}
+  void serialize(JfrCheckpointWriter & writer);
+};
+
 class BytecodeConstant : public JfrSerializer {
  public:
   void serialize(JfrCheckpointWriter& writer);

src/hotspot/share/jfr/recorder/checkpoint/types/jfrTypeManager.cpp

@@ -132,6 +132,17 @@ void JfrTypeManager::write_checkpoint(Thread* t, traceid tid /* 0 */, oop vthrea
   type_thread.serialize(writer);
 }
 
+void JfrTypeManager::write_simplified_vthread_checkpoint(traceid vtid) {
+  Thread* const current = Thread::current();
+  assert(current != nullptr, "invariant");
+  ResourceMark rm(current);
+  JfrCheckpointWriter writer(current, true, THREADS, JFR_VIRTUAL_THREADLOCAL);
+  // TYPE_THREAD and count is written later as part of vthread bulk serialization.
+  writer.set_count(1); // Only a logical marker for the checkpoint header.
+  JfrSimplifiedVirtualThreadConstant type_simple_vthread(vtid);
+  type_simple_vthread.serialize(writer);
+}
+
 class SerializerRegistrationGuard : public StackObj {
  private:
   static Semaphore _mutex_semaphore;

src/hotspot/share/jfr/recorder/checkpoint/types/jfrTypeManager.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016, 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
@@ -41,6 +41,7 @@ class JfrTypeManager : public AllStatic {
   static void write_threads(JfrCheckpointWriter& writer);
   static JfrBlobHandle create_thread_blob(JavaThread* jt, traceid tid = 0, oop vthread = nullptr);
   static void write_checkpoint(Thread* t, traceid tid = 0, oop vthread = nullptr);
+  static void write_simplified_vthread_checkpoint(traceid vtid);
   static void write_static_types(JfrCheckpointWriter& writer);
 };
 

src/hotspot/share/jfr/support/jfrThreadLocal.cpp

@@ -70,6 +70,7 @@ JfrThreadLocal::JfrThreadLocal() :
   _wallclock_time(os::javaTimeNanos()),
   _stackdepth(0),
   _entering_suspend_flag(0),
+  _non_reentrant_nesting(0),
   _vthread_epoch(0),
   _vthread_excluded(false),
   _jvm_thread_excluded(false),
@@ -365,28 +366,32 @@ typedef JfrOopTraceId<ThreadIdAccess> AccessThreadTraceId;
 void JfrThreadLocal::set_vthread_epoch(const JavaThread* jt, traceid tid, u2 epoch) {
   assert(jt != nullptr, "invariant");
   assert(is_vthread(jt), "invariant");
-  // To support event recursion, we update the native side first,
-  // this provides the terminating case.
+  assert(!is_non_reentrant(), "invariant");
+
   Atomic::store(&jt->jfr_thread_local()->_vthread_epoch, epoch);
-  /*
-  * The java side, i.e. the vthread object, can now be updated.
-  * Accessing the vthread object itself is a recursive case,
-  * because it can trigger additional events, e.g.
-  * loading the oop through load barriers.
-  * Note there is a potential problem with this solution:
-  * The recursive write hitting the terminating case will
-  * use the thread id _before_ the checkpoint is committed.
-  * Hence, the periodic thread can possibly flush that event
-  * to a segment that does not include an associated checkpoint.
-  * Considered rare and quite benign for now. The worst case is
-  * that thread information for that event is not resolvable, i.e. null.
-  */
+
   oop vthread = jt->vthread();
   assert(vthread != nullptr, "invariant");
+
   AccessThreadTraceId::set_epoch(vthread, epoch);
   JfrCheckpointManager::write_checkpoint(const_cast<JavaThread*>(jt), tid, vthread);
 }
 
+void JfrThreadLocal::set_vthread_epoch_checked(const JavaThread* jt, traceid tid, u2 epoch) {
+  assert(jt != nullptr, "invariant");
+  assert(is_vthread(jt), "invariant");
+
+  // If the event is marked as non reentrant, write only a simplified version of the vthread info.
+  // Essentially all the same info except the vthread name, because we cannot touch the oop.
+  // Since we cannot touch the oop, we also cannot update its vthread epoch.
+  if (is_non_reentrant()) {
+    JfrCheckpointManager::write_simplified_vthread_checkpoint(tid);
+    return;
+  }
+
+  set_vthread_epoch(jt, tid, epoch);
+}
+
 traceid JfrThreadLocal::vthread_id(const Thread* t) {
   assert(t != nullptr, "invariant");
   return Atomic::load(&t->jfr_thread_local()->_vthread_id);
@@ -416,7 +421,7 @@ traceid JfrThreadLocal::thread_id(const Thread* t) {
   if (!tl->is_vthread_excluded()) {
     const u2 current_epoch = AccessThreadTraceId::current_epoch();
     if (vthread_epoch(jt) != current_epoch) {
-      set_vthread_epoch(jt, tid, current_epoch);
+      set_vthread_epoch_checked(jt, tid, current_epoch);
     }
   }
   return tid;
@@ -480,6 +485,26 @@ bool JfrThreadLocal::is_vthread(const JavaThread* jt) {
   return Atomic::load_acquire(&jt->jfr_thread_local()->_vthread) && jt->last_continuation() != nullptr;
 }
 
+int32_t JfrThreadLocal::make_non_reentrant(Thread* t) {
+  assert(t != nullptr, "invariant");
+  if (!t->is_Java_thread() || !is_vthread(JavaThread::cast(t))) {
+    return -1;
+  }
+  return t->jfr_thread_local()->_non_reentrant_nesting++;
+}
+
+void JfrThreadLocal::make_reentrant(Thread* t, int32_t previous_nesting) {
+  assert(t->is_Java_thread() && is_vthread(JavaThread::cast(t)), "invariant");
+  assert(previous_nesting >= 0, "invariant");
+  t->jfr_thread_local()->_non_reentrant_nesting = previous_nesting;
+}
+
+bool JfrThreadLocal::is_non_reentrant() {
+  Thread* const current_thread = Thread::current();
+  assert(current_thread != nullptr, "invariant");
+  return current_thread->jfr_thread_local()->_non_reentrant_nesting > 0;
+}
+
 inline bool is_virtual(const JavaThread* jt, oop thread) {
   assert(jt != nullptr, "invariant");
   return thread != jt->threadObj();
@@ -493,6 +518,7 @@ void JfrThreadLocal::on_set_current_thread(JavaThread* jt, oop thread) {
     Atomic::release_store(&tl->_vthread, false);
     return;
   }
+  assert(tl->_non_reentrant_nesting == 0, "invariant");
   Atomic::store(&tl->_vthread_id, AccessThreadTraceId::id(thread));
   const u2 epoch_raw = AccessThreadTraceId::epoch(thread);
   const bool excluded = epoch_raw & excluded_bit;

src/hotspot/share/jfr/support/jfrThreadLocal.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 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
@@ -64,6 +64,7 @@ class JfrThreadLocal {
   jlong _wallclock_time;
   mutable u4 _stackdepth;
   volatile jint _entering_suspend_flag;
+  int32_t _non_reentrant_nesting;
   u2 _vthread_epoch;
   bool _vthread_excluded;
   bool _jvm_thread_excluded;
@@ -81,14 +82,16 @@ class JfrThreadLocal {
   static void set(bool* excluded_field, bool state);
   static traceid assign_thread_id(const Thread* t, JfrThreadLocal* tl);
   static traceid vthread_id(const Thread* t);
-  static void set_vthread_epoch(const JavaThread* jt, traceid id, u2 epoch);
+  static void set_vthread_epoch(const JavaThread* jt, traceid tid, u2 epoch);
+  static void set_vthread_epoch_checked(const JavaThread* jt, traceid tid, u2 epoch);
   static traceid jvm_thread_id(const JfrThreadLocal* tl);
   bool is_vthread_excluded() const;
   static void exclude_vthread(const JavaThread* jt);
   static void include_vthread(const JavaThread* jt);
   static bool is_jvm_thread_excluded(const Thread* t);
   static void exclude_jvm_thread(const Thread* t);
   static void include_jvm_thread(const Thread* t);
+  static bool is_non_reentrant();
 
  public:
   JfrThreadLocal();
@@ -266,6 +269,9 @@ class JfrThreadLocal {
     return _dead;
   }
 
+  static int32_t make_non_reentrant(Thread* thread);
+  static void make_reentrant(Thread* thread, int32_t previous_nesting);
+
   bool is_excluded() const;
   bool is_included() const;
   static bool is_excluded(const Thread* thread);