8361912: ThreadsListHandle::cv_internal_thread_to_JavaThread does not deal with a virtual thread's carrier thread

Reviewed-by: pchilanomate, dcubed, amenkov, sspitsyn

Author: David Holmes

src/hotspot/share/prims/jvmtiExport.cpp

@@ -865,47 +865,6 @@ JvmtiExport::cv_external_thread_to_JavaThread(ThreadsList * t_list,
   return JVMTI_ERROR_NONE;
 }
 
-// Convert an oop to a JavaThread found on the specified ThreadsList.
-// The ThreadsListHandle in the caller "protects" the returned
-// JavaThread *.
-//
-// On success, *jt_pp is set to the converted JavaThread * and
-// JVMTI_ERROR_NONE is returned. On error, returns various
-// JVMTI_ERROR_* values.
-//
-jvmtiError
-JvmtiExport::cv_oop_to_JavaThread(ThreadsList * t_list, oop thread_oop,
-                                  JavaThread ** jt_pp) {
-  assert(t_list != nullptr, "must have a ThreadsList");
-  assert(thread_oop != nullptr, "must have an oop");
-  assert(jt_pp != nullptr, "must have a return JavaThread pointer");
-
-  if (!thread_oop->is_a(vmClasses::Thread_klass())) {
-    // The oop is not a java.lang.Thread.
-    return JVMTI_ERROR_INVALID_THREAD;
-  }
-  // Looks like a java.lang.Thread oop at this point.
-
-  JavaThread * java_thread = java_lang_Thread::thread(thread_oop);
-  if (java_thread == nullptr) {
-    // The java.lang.Thread does not contain a JavaThread * so it has
-    // not yet run or it has died.
-    return JVMTI_ERROR_THREAD_NOT_ALIVE;
-  }
-  // Looks like a live JavaThread at this point.
-
-  if (!t_list->includes(java_thread)) {
-    // Not on the JavaThreads list so it is not alive.
-    return JVMTI_ERROR_THREAD_NOT_ALIVE;
-  }
-
-  // Return a live JavaThread that is "protected" by the
-  // ThreadsListHandle in the caller.
-  *jt_pp = java_thread;
-
-  return JVMTI_ERROR_NONE;
-}
-
 class JvmtiClassFileLoadHookPoster : public StackObj {
  private:
   Symbol*            _h_name;

src/hotspot/share/prims/jvmtiExport.hpp

@@ -454,8 +454,6 @@ class JvmtiExport : public AllStatic {
                                                      jthread thread,
                                                      JavaThread ** jt_pp,
                                                      oop * thread_oop_p);
-  static jvmtiError cv_oop_to_JavaThread(ThreadsList * t_list, oop thread_oop,
-                                         JavaThread ** jt_pp);
 };
 
 // Support class used by JvmtiDynamicCodeEventCollector and others. It

src/hotspot/share/runtime/threadSMR.cpp

@@ -791,10 +791,16 @@ ThreadsListHandle::~ThreadsListHandle() {
 // associated ThreadsList. This ThreadsListHandle "protects" the
 // returned JavaThread *.
 //
+// If the jthread resolves to a virtual thread then the JavaThread *
+// for its current carrier thread (if any) is returned via *jt_pp.
+// It is up to the caller to prevent the virtual thread from changing
+// its mounted status, or else account for it when acting on the carrier
+// JavaThread.
+//
 // If thread_oop_p is not null, then the caller wants to use the oop
-// after this call so the oop is returned. On success, *jt_pp is set
+// after this call so the oop is always returned. On success, *jt_pp is set
 // to the converted JavaThread * and true is returned. On error,
-// returns false.
+// returns false, and *jt_pp is unchanged.
 //
 bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
                                                          JavaThread ** jt_pp,
@@ -818,10 +824,22 @@ bool ThreadsListHandle::cv_internal_thread_to_JavaThread(jobject jthread,
 
   JavaThread *java_thread = java_lang_Thread::thread_acquire(thread_oop);
   if (java_thread == nullptr) {
-    // The java.lang.Thread does not contain a JavaThread* so it has not
-    // run enough to be put on a ThreadsList or it has exited enough to
-    // make it past ensure_join() where the JavaThread* is cleared.
-    return false;
+    if (!java_lang_VirtualThread::is_instance(thread_oop)) {
+      // The java.lang.Thread does not contain a JavaThread* so it has not
+      // run enough to be put on a ThreadsList or it has exited enough to
+      // make it past ensure_join() where the JavaThread* is cleared.
+      return false;
+    } else {
+      // For virtual threads we need to extract the carrier's JavaThread - if any.
+       oop carrier_thread = java_lang_VirtualThread::carrier_thread(thread_oop);
+       if (carrier_thread != nullptr) {
+         java_thread = java_lang_Thread::thread(carrier_thread);
+       }
+       if (java_thread == nullptr) {
+         // Virtual thread was unmounted, or else carrier has now terminated.
+         return false;
+       }
+    }
   }
   // Looks like a live JavaThread at this point.
 

src/hotspot/share/runtime/threadSMR.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 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
@@ -45,8 +45,8 @@ class ThreadsList;
 // operation. It is no longer necessary to hold the Threads_lock to safely
 // perform an operation on a target thread.
 //
-// There are several different ways to refer to java.lang.Thread objects
-// so we have a few ways to get a protected JavaThread *:
+// There are two ways to refer to java.lang.Thread objects so we have two ways
+// to get a protected JavaThread*:
 //
 // JNI jobject example:
 //   jobject jthread = ...;
@@ -69,21 +69,10 @@ class ThreadsList;
 //   }
 //   :  // do stuff with 'jt'...
 //
-// JVM/TI oop example (this one should be very rare):
-//   oop thread_obj = ...;
-//   :
-//   JavaThread *jt = nullptr;
-//   ThreadsListHandle tlh;
-//   jvmtiError err = JvmtiExport::cv_oop_to_JavaThread(tlh.list(), thread_obj, &jt);
-//   if (err != JVMTI_ERROR_NONE) {
-//     return err;
-//   }
-//   :  // do stuff with 'jt'...
-//
 // A JavaThread * that is included in the ThreadsList that is held by
 // a ThreadsListHandle is protected as long as the ThreadsListHandle
-// remains in scope. The target JavaThread * may have logically exited,
-// but that target JavaThread * will not be deleted until it is no
+// remains in scope. The target JavaThread* may have logically exited,
+// but that target JavaThread* will not be deleted until it is no
 // longer protected by a ThreadsListHandle.
 //
 // SMR Support for the Threads class.
@@ -318,7 +307,7 @@ class ThreadsListHandle : public StackObj {
   inline Iterator begin();
   inline Iterator end();
 
-  bool cv_internal_thread_to_JavaThread(jobject jthread, JavaThread ** jt_pp, oop * thread_oop_p);
+  bool cv_internal_thread_to_JavaThread(jobject jthread, JavaThread** jt_pp, oop* thread_oop_p);
 
   bool includes(JavaThread* p) {
     return list()->includes(p);