From b957ee40f302d54edf704b36120ef21fe977453a Mon Sep 17 00:00:00 2001
From: Peter Hofer <peter.hofer@oracle.com>
Date: Thu, 5 Oct 2023 14:09:26 +0200
Subject: [PATCH] Remove virtual thread and continuation abstractions and code
 paths that have become unnecessary.

---
 .../genscavenge/ThreadLocalAllocation.java    |   4 +-
 .../graal/GenScavengeAllocationSnippets.java  |   5 +-
 .../graal/GenScavengeAllocationSupport.java   |  13 +-
 .../ClassInitializationInfo.java              |  11 +-
 .../snippets/SubstrateAllocationSnippets.java |   5 +-
 .../core/graal/stackvalue/StackValueNode.java |   3 +-
 .../core/heap/StoredContinuationAccess.java   |  10 +-
 .../svm/core/hub/InteriorObjRefWalker.java    |   4 +-
 .../image/DisallowedImageHeapObjects.java     |  28 +--
 .../core/jdk/ContinuationsNotSupported.java   |  36 ---
 .../svm/core/jdk/ContinuationsSupported.java  |  36 ---
 .../src/com/oracle/svm/core/jdk/LoomJDK.java  |  36 ---
 .../com/oracle/svm/core/jdk/NotLoomJDK.java   |  36 ---
 .../oracle/svm/core/jdk/StackTraceUtils.java  |  10 +-
 .../jdk/Target_java_lang_StackWalker.java     |  15 +-
 .../svm/core/jni/functions/JNIFunctions.java  |  13 +-
 .../monitor/MultiThreadedMonitorSupport.java  |   5 +-
 .../oracle/svm/core/thread/Continuation.java  |  15 +-
 .../svm/core/thread/ContinuationSupport.java  |  25 +-
 .../svm/core/thread/ContinuationsFeature.java |  64 ++---
 .../oracle/svm/core/thread/JavaThreads.java   | 155 +++++++-----
 .../oracle/svm/core/thread/LoomSupport.java   |  52 ----
 .../svm/core/thread/LoomVirtualThreads.java   | 230 ------------------
 .../svm/core/thread/PlatformThreads.java      |  75 +++---
 .../com/oracle/svm/core/thread/Safepoint.java |   2 +-
 .../core/thread/Target_java_lang_Thread.java  | 101 ++------
 .../Target_java_lang_VirtualThread.java       |   9 +-
 ..._jdk_internal_misc_Unsafe_JavaThreads.java |   5 +-
 .../Target_jdk_internal_vm_Continuation.java  |  37 +--
 ..._jdk_internal_vm_ContinuationSupport.java} |  25 +-
 .../svm/core/thread/VirtualThreads.java       |  76 ------
 .../src/com/oracle/svm/hosted/SVMHost.java    |   4 +-
 .../thread/HostedContinuationsFeature.java    |   3 +-
 .../jfr/TestJavaLevelVirtualThreadEvents.java |   4 +-
 34 files changed, 269 insertions(+), 883 deletions(-)
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsNotSupported.java
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsSupported.java
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/LoomJDK.java
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/NotLoomJDK.java
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomSupport.java
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomVirtualThreads.java
 rename substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/{Continuations.java => Target_jdk_internal_vm_ContinuationSupport.java} (57%)
 delete mode 100644 substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/VirtualThreads.java

diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/ThreadLocalAllocation.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/ThreadLocalAllocation.java
index 1c27f3931935..2c123a36acd3 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/ThreadLocalAllocation.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/ThreadLocalAllocation.java
@@ -67,7 +67,7 @@
 import com.oracle.svm.core.snippets.KnownIntrinsics;
 import com.oracle.svm.core.snippets.SubstrateForeignCallTarget;
 import com.oracle.svm.core.stack.StackOverflowCheck;
-import com.oracle.svm.core.thread.Continuation;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.thread.VMOperation;
 import com.oracle.svm.core.thread.VMThreads;
 import com.oracle.svm.core.threadlocal.FastThreadLocal;
@@ -375,7 +375,7 @@ private static Object allocateLargeArrayLikeObjectInNewTlab(DynamicHub hub, int
     @Uninterruptible(reason = "Holds uninitialized memory")
     private static Object formatArrayLikeObject(Pointer memory, DynamicHub hub, int length, boolean unaligned, FillContent fillContent, byte[] podReferenceMap) {
         Class<?> clazz = DynamicHub.toClass(hub);
-        if (Continuation.isSupported() && clazz == StoredContinuation.class) {
+        if (ContinuationSupport.isSupported() && clazz == StoredContinuation.class) {
             return FormatStoredContinuationNode.formatStoredContinuation(memory, clazz, length, false, unaligned, true);
         } else if (Pod.RuntimeSupport.isPresent() && podReferenceMap != null) {
             return FormatPodNode.formatPod(memory, clazz, length, podReferenceMap, false, unaligned, fillContent, true);
diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSnippets.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSnippets.java
index 247f6d6f6d3c..000c85080d58 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSnippets.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSnippets.java
@@ -58,7 +58,6 @@
 import com.oracle.svm.core.heap.Pod;
 import com.oracle.svm.core.hub.DynamicHub;
 import com.oracle.svm.core.hub.LayoutEncoding;
-import com.oracle.svm.core.thread.Continuation;
 import com.oracle.svm.core.thread.ContinuationSupport;
 
 import jdk.vm.ci.meta.JavaKind;
@@ -130,7 +129,7 @@ public Templates(OptionValues options, Providers providers, SubstrateAllocationS
             this.baseTemplates = baseTemplates;
             formatObject = snippet(providers, GenScavengeAllocationSnippets.class, "formatObjectSnippet");
             formatArray = snippet(providers, GenScavengeAllocationSnippets.class, "formatArraySnippet");
-            formatStoredContinuation = Continuation.isSupported() ? snippet(providers, GenScavengeAllocationSnippets.class, "formatStoredContinuation") : null;
+            formatStoredContinuation = ContinuationSupport.isSupported() ? snippet(providers, GenScavengeAllocationSnippets.class, "formatStoredContinuation") : null;
             formatPod = Pod.RuntimeSupport.isPresent() ? snippet(providers,
                             GenScavengeAllocationSnippets.class,
                             "formatPodSnippet",
@@ -141,7 +140,7 @@ public Templates(OptionValues options, Providers providers, SubstrateAllocationS
         public void registerLowering(Map<Class<? extends Node>, NodeLoweringProvider<?>> lowerings) {
             lowerings.put(FormatObjectNode.class, new FormatObjectLowering());
             lowerings.put(FormatArrayNode.class, new FormatArrayLowering());
-            if (Continuation.isSupported()) {
+            if (ContinuationSupport.isSupported()) {
                 lowerings.put(FormatStoredContinuationNode.class, new FormatStoredContinuationLowering());
             }
             if (Pod.RuntimeSupport.isPresent()) {
diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSupport.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSupport.java
index 5af97cbc22e5..f99a080c56a8 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSupport.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/GenScavengeAllocationSupport.java
@@ -24,18 +24,19 @@
  */
 package com.oracle.svm.core.genscavenge.graal;
 
-import com.oracle.svm.core.heap.Pod;
-import com.oracle.svm.core.snippets.SnippetRuntime.SubstrateForeignCallDescriptor;
-import com.oracle.svm.core.thread.Continuation;
-import jdk.compiler.graal.core.common.spi.ForeignCallDescriptor;
-import jdk.compiler.graal.word.Word;
 import org.graalvm.word.UnsignedWord;
 
 import com.oracle.svm.core.genscavenge.HeapParameters;
 import com.oracle.svm.core.genscavenge.ThreadLocalAllocation;
 import com.oracle.svm.core.graal.meta.SubstrateForeignCallsProvider;
 import com.oracle.svm.core.graal.snippets.GCAllocationSupport;
+import com.oracle.svm.core.heap.Pod;
 import com.oracle.svm.core.snippets.SnippetRuntime;
+import com.oracle.svm.core.snippets.SnippetRuntime.SubstrateForeignCallDescriptor;
+import com.oracle.svm.core.thread.ContinuationSupport;
+
+import jdk.compiler.graal.core.common.spi.ForeignCallDescriptor;
+import jdk.compiler.graal.word.Word;
 
 public class GenScavengeAllocationSupport implements GCAllocationSupport {
     private static final SubstrateForeignCallDescriptor SLOW_NEW_INSTANCE = SnippetRuntime.findForeignCall(ThreadLocalAllocation.class, "slowPathNewInstance", true);
@@ -46,7 +47,7 @@ public class GenScavengeAllocationSupport implements GCAllocationSupport {
 
     public static void registerForeignCalls(SubstrateForeignCallsProvider foreignCalls) {
         foreignCalls.register(UNCONDITIONAL_FOREIGN_CALLS);
-        if (Continuation.isSupported()) {
+        if (ContinuationSupport.isSupported()) {
             foreignCalls.register(SLOW_NEW_STORED_CONTINUATION);
         }
         if (Pod.RuntimeSupport.isPresent()) {
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/classinitialization/ClassInitializationInfo.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/classinitialization/ClassInitializationInfo.java
index c723a428a5cf..f13625d036df 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/classinitialization/ClassInitializationInfo.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/classinitialization/ClassInitializationInfo.java
@@ -29,7 +29,6 @@
 
 import org.graalvm.nativeimage.CurrentIsolate;
 import org.graalvm.nativeimage.IsolateThread;
-import com.oracle.svm.core.hub.PredefinedClassesSupport;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
 import org.graalvm.nativeimage.c.function.CFunctionPointer;
@@ -38,10 +37,12 @@
 import com.oracle.svm.core.FunctionPointerHolder;
 import com.oracle.svm.core.c.InvokeJavaFunctionPointer;
 import com.oracle.svm.core.hub.DynamicHub;
+import com.oracle.svm.core.hub.PredefinedClassesSupport;
 import com.oracle.svm.core.jdk.InternalVMMethod;
 import com.oracle.svm.core.snippets.SubstrateForeignCallTarget;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.thread.JavaThreads;
-import com.oracle.svm.core.thread.VirtualThreads;
+import com.oracle.svm.core.thread.Target_jdk_internal_vm_Continuation;
 import com.oracle.svm.core.util.VMError;
 
 import jdk.internal.misc.Unsafe;
@@ -263,16 +264,16 @@ private static void initialize(ClassInitializationInfo info, DynamicHub hub) {
         }
 
         boolean pinned = false;
-        if (VirtualThreads.isSupported() && JavaThreads.isCurrentThreadVirtual()) {
+        if (ContinuationSupport.isSupported() && JavaThreads.isCurrentThreadVirtual()) {
             // See comment on field `initThread`
-            VirtualThreads.singleton().pinCurrent();
+            Target_jdk_internal_vm_Continuation.pin();
             pinned = true;
         }
         try {
             doInitialize(info, hub);
         } finally {
             if (pinned) {
-                VirtualThreads.singleton().unpinCurrent();
+                Target_jdk_internal_vm_Continuation.unpin();
             }
         }
     }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/snippets/SubstrateAllocationSnippets.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/snippets/SubstrateAllocationSnippets.java
index f3fa72e27dc1..1755d04ffd69 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/snippets/SubstrateAllocationSnippets.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/snippets/SubstrateAllocationSnippets.java
@@ -102,7 +102,6 @@
 import com.oracle.svm.core.snippets.SnippetRuntime;
 import com.oracle.svm.core.snippets.SnippetRuntime.SubstrateForeignCallDescriptor;
 import com.oracle.svm.core.snippets.SubstrateForeignCallTarget;
-import com.oracle.svm.core.thread.Continuation;
 import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.util.VMError;
 
@@ -600,7 +599,7 @@ public Templates(OptionValues options, Providers providers, SubstrateAllocationS
                             ALLOCATION_LOCATIONS);
 
             SnippetInfo allocateStoredContinuationSnippet = null;
-            if (Continuation.isSupported()) {
+            if (ContinuationSupport.isSupported()) {
                 allocateStoredContinuationSnippet = snippet(providers,
                                 SubstrateAllocationSnippets.class,
                                 "allocateStoredContinuation",
@@ -634,7 +633,7 @@ public void registerLowering(Map<Class<? extends Node>, NodeLoweringProvider<?>>
             lowerings.put(NewMultiArrayNode.class, new NewMultiArrayLowering());
             lowerings.put(ValidateNewInstanceClassNode.class, new ValidateNewInstanceClassLowering());
 
-            if (Continuation.isSupported()) {
+            if (ContinuationSupport.isSupported()) {
                 lowerings.put(NewStoredContinuationNode.class, new NewStoredContinuationLowering());
             }
             if (Pod.RuntimeSupport.isPresent()) {
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/stackvalue/StackValueNode.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/stackvalue/StackValueNode.java
index f7d9c8454a4c..8c2785c164ed 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/stackvalue/StackValueNode.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/graal/stackvalue/StackValueNode.java
@@ -46,7 +46,6 @@
 import com.oracle.svm.core.FrameAccess;
 import com.oracle.svm.core.Uninterruptible;
 import com.oracle.svm.core.config.ConfigurationValues;
-import com.oracle.svm.core.thread.VirtualThreads;
 
 import jdk.vm.ci.meta.ResolvedJavaMethod;
 
@@ -153,7 +152,7 @@ public static StackValueNode create(int sizeInBytes, ResolvedJavaMethod method,
          * around in a caller, but these are difficult to ensure across multiple callers and
          * callees.
          */
-        boolean checkVirtualThread = disallowVirtualThread && VirtualThreads.isSupported() && !Uninterruptible.Utils.isUninterruptible(method);
+        boolean checkVirtualThread = disallowVirtualThread && !Uninterruptible.Utils.isUninterruptible(method);
         return create(sizeInBytes, slotIdentity, checkVirtualThread);
     }
 
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/StoredContinuationAccess.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/StoredContinuationAccess.java
index e8da66702ef1..ca165013e1f1 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/StoredContinuationAccess.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/StoredContinuationAccess.java
@@ -39,9 +39,9 @@
 import org.graalvm.word.UnsignedWord;
 import org.graalvm.word.WordFactory;
 
-import com.oracle.svm.core.UnmanagedMemoryUtil;
 import com.oracle.svm.core.AlwaysInline;
 import com.oracle.svm.core.Uninterruptible;
+import com.oracle.svm.core.UnmanagedMemoryUtil;
 import com.oracle.svm.core.c.NonmovableArray;
 import com.oracle.svm.core.code.CodeInfo;
 import com.oracle.svm.core.code.CodeInfoAccess;
@@ -126,7 +126,7 @@ private static int allocateFromStack(Continuation cont, Pointer baseSp, Pointer
         if (!yield) {
             PreemptVisitor visitor = new PreemptVisitor(baseSp);
             JavaStackWalker.walkThread(targetThread, visitor);
-            if (visitor.preemptStatus != Continuation.FREEZE_OK) {
+            if (visitor.preemptStatus != ContinuationSupport.FREEZE_OK) {
                 return visitor.preemptStatus;
             }
             startSp = visitor.leafSP;
@@ -139,7 +139,7 @@ private static int allocateFromStack(Continuation cont, Pointer baseSp, Pointer
         StoredContinuation instance = allocate(framesSize);
         fillUninterruptibly(instance, startIp, startSp, framesSize);
         cont.stored = instance;
-        return Continuation.FREEZE_OK;
+        return ContinuationSupport.FREEZE_OK;
     }
 
     @Uninterruptible(reason = "Prevent modifications to the stack while initializing instance and copying frames.")
@@ -300,7 +300,7 @@ private static final class PreemptVisitor extends StackFrameVisitor {
 
         Pointer leafSP;
         CodePointer leafIP;
-        int preemptStatus = Continuation.FREEZE_OK;
+        int preemptStatus = ContinuationSupport.FREEZE_OK;
 
         PreemptVisitor(Pointer endSP) {
             this.endSP = endSP;
@@ -315,7 +315,7 @@ protected boolean visitFrame(Pointer sp, CodePointer ip, CodeInfo codeInfo, Deop
             FrameInfoQueryResult frameInfo = CodeInfoTable.lookupCodeInfoQueryResult(codeInfo, ip).getFrameInfo();
             if (frameInfo.getSourceClass().equals(StoredContinuationAccess.class) && frameInfo.getSourceMethodName().equals("allocateToYield")) {
                 // Continuation is already in the process of yielding, cancel preemption.
-                preemptStatus = Continuation.YIELDING;
+                preemptStatus = ContinuationSupport.FREEZE_YIELDING;
                 return false;
             }
 
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/InteriorObjRefWalker.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/InteriorObjRefWalker.java
index cc7a03916128..25c128eaf93a 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/InteriorObjRefWalker.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/InteriorObjRefWalker.java
@@ -43,7 +43,7 @@
 import com.oracle.svm.core.heap.PodReferenceMapDecoder;
 import com.oracle.svm.core.heap.ReferenceAccess;
 import com.oracle.svm.core.heap.StoredContinuationAccess;
-import com.oracle.svm.core.thread.Continuation;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.util.VMError;
 
 /**
@@ -130,7 +130,7 @@ private static boolean walkPod(Object obj, ObjectReferenceVisitor visitor, Dynam
     @AlwaysInline("Performance critical version")
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     private static boolean walkStoredContinuation(Object obj, ObjectReferenceVisitor visitor) {
-        if (!Continuation.isSupported()) {
+        if (!ContinuationSupport.isSupported()) {
             throw VMError.shouldNotReachHere("Stored continuation objects cannot be in the heap if the continuation support is disabled.");
         }
         return StoredContinuationAccess.walkReferences(obj, visitor);
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/image/DisallowedImageHeapObjects.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/image/DisallowedImageHeapObjects.java
index 125efc0dba22..b6ccc67d8976 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/image/DisallowedImageHeapObjects.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/image/DisallowedImageHeapObjects.java
@@ -37,7 +37,6 @@
 import java.util.concurrent.ThreadLocalRandom;
 
 import com.oracle.svm.core.SubstrateUtil;
-import com.oracle.svm.core.thread.VirtualThreads;
 import com.oracle.svm.core.util.VMError;
 import com.oracle.svm.util.ReflectionUtil;
 
@@ -52,20 +51,12 @@ public interface DisallowedObjectReporter {
         RuntimeException raise(String msg, Object obj, String initializerAction);
     }
 
-    private static final Class<?> CANCELLABLE_CLASS;
-    private static final Class<?> JDK_VIRTUAL_THREAD_CLASS;
-    private static final Class<?> CONTINUATION_CLASS;
-    private static final Method CONTINUATION_IS_STARTED_METHOD;
-    private static final Class<?> CLEANER_CLEANABLE_CLASS;
-    private static final Class<?> LEGACY_CLEANER_CLASS;
-    static {
-        CANCELLABLE_CLASS = ReflectionUtil.lookupClass(false, "sun.nio.fs.Cancellable");
-        JDK_VIRTUAL_THREAD_CLASS = ReflectionUtil.lookupClass(true, "java.lang.VirtualThread");
-        CONTINUATION_CLASS = ReflectionUtil.lookupClass(true, "jdk.internal.vm.Continuation");
-        CONTINUATION_IS_STARTED_METHOD = (CONTINUATION_CLASS == null) ? null : ReflectionUtil.lookupMethod(CONTINUATION_CLASS, "isStarted");
-        CLEANER_CLEANABLE_CLASS = ReflectionUtil.lookupClass(false, "jdk.internal.ref.CleanerImpl$CleanerCleanable");
-        LEGACY_CLEANER_CLASS = ReflectionUtil.lookupClass(false, "jdk.internal.ref.Cleaner");
-    }
+    private static final Class<?> CANCELLABLE_CLASS = ReflectionUtil.lookupClass(false, "sun.nio.fs.Cancellable");
+    private static final Class<?> VIRTUAL_THREAD_CLASS = ReflectionUtil.lookupClass(false, "java.lang.VirtualThread");
+    private static final Class<?> CONTINUATION_CLASS = ReflectionUtil.lookupClass(false, "jdk.internal.vm.Continuation");
+    private static final Method CONTINUATION_IS_STARTED_METHOD = ReflectionUtil.lookupMethod(CONTINUATION_CLASS, "isStarted");
+    private static final Class<?> CLEANER_CLEANABLE_CLASS = ReflectionUtil.lookupClass(false, "jdk.internal.ref.CleanerImpl$CleanerCleanable");
+    private static final Class<?> LEGACY_CLEANER_CLASS = ReflectionUtil.lookupClass(false, "jdk.internal.ref.Cleaner");
 
     public static void check(Object obj, DisallowedObjectReporter reporter) {
         if (((obj instanceof Random) && !(obj instanceof ThreadLocalRandom)) || obj instanceof SplittableRandom) {
@@ -75,9 +66,8 @@ public static void check(Object obj, DisallowedObjectReporter reporter) {
         }
 
         /* Started platform threads */
-        if (obj instanceof Thread) {
-            final Thread asThread = (Thread) obj;
-            if (VirtualThreads.isSupported() && (VirtualThreads.singleton().isVirtual(asThread) || (JDK_VIRTUAL_THREAD_CLASS != null && JDK_VIRTUAL_THREAD_CLASS.isInstance(asThread)))) {
+        if (obj instanceof Thread asThread) {
+            if (VIRTUAL_THREAD_CLASS.isInstance(asThread)) {
                 // allowed unless the thread is mounted, in which case it references its carrier
                 // thread and fails
             } else if (asThread.getState() != Thread.State.NEW && asThread.getState() != Thread.State.TERMINATED) {
@@ -86,7 +76,7 @@ public static void check(Object obj, DisallowedObjectReporter reporter) {
                                 asThread, "Prevent threads from starting during image generation, or a started thread from being included in the image.");
             }
         }
-        if (SubstrateUtil.HOSTED && CONTINUATION_CLASS != null && CONTINUATION_CLASS.isInstance(obj)) {
+        if (SubstrateUtil.HOSTED && CONTINUATION_CLASS.isInstance(obj)) {
             boolean isStarted;
             try {
                 isStarted = (Boolean) CONTINUATION_IS_STARTED_METHOD.invoke(obj);
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsNotSupported.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsNotSupported.java
deleted file mode 100644
index 070f91430ff9..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsNotSupported.java
+++ /dev/null
@@ -1,36 +0,0 @@
-/*
- * Copyright (c) 2021, 2021, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.jdk;
-
-import java.util.function.BooleanSupplier;
-
-import com.oracle.svm.core.thread.Continuation;
-
-public class ContinuationsNotSupported implements BooleanSupplier {
-    @Override
-    public boolean getAsBoolean() {
-        return !Continuation.isSupported();
-    }
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsSupported.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsSupported.java
deleted file mode 100644
index 58e6fbf190ce..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/ContinuationsSupported.java
+++ /dev/null
@@ -1,36 +0,0 @@
-/*
- * Copyright (c) 2021, 2021, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.jdk;
-
-import java.util.function.BooleanSupplier;
-
-import com.oracle.svm.core.thread.Continuation;
-
-public class ContinuationsSupported implements BooleanSupplier {
-    @Override
-    public boolean getAsBoolean() {
-        return Continuation.isSupported();
-    }
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/LoomJDK.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/LoomJDK.java
deleted file mode 100644
index 308577de3d72..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/LoomJDK.java
+++ /dev/null
@@ -1,36 +0,0 @@
-/*
- * Copyright (c) 2020, 2020, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.jdk;
-
-import java.util.function.BooleanSupplier;
-
-import com.oracle.svm.core.thread.LoomSupport;
-
-public class LoomJDK implements BooleanSupplier {
-    @Override
-    public boolean getAsBoolean() {
-        return LoomSupport.isEnabled();
-    }
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/NotLoomJDK.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/NotLoomJDK.java
deleted file mode 100644
index 3107a626cad7..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/NotLoomJDK.java
+++ /dev/null
@@ -1,36 +0,0 @@
-/*
- * Copyright (c) 2020, 2020, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.jdk;
-
-import java.util.function.BooleanSupplier;
-
-import com.oracle.svm.core.thread.LoomSupport;
-
-public class NotLoomJDK implements BooleanSupplier {
-    @Override
-    public boolean getAsBoolean() {
-        return !LoomSupport.isEnabled();
-    }
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/StackTraceUtils.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/StackTraceUtils.java
index 308f01da0ec7..38cc6bf04a62 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/StackTraceUtils.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/StackTraceUtils.java
@@ -61,11 +61,8 @@
 import com.oracle.svm.core.stack.StackFrameVisitor;
 import com.oracle.svm.core.thread.JavaThreads;
 import com.oracle.svm.core.thread.JavaVMOperation;
-import com.oracle.svm.core.thread.LoomSupport;
-import com.oracle.svm.core.thread.PlatformThreads;
 import com.oracle.svm.core.thread.Target_jdk_internal_vm_Continuation;
 import com.oracle.svm.core.thread.VMOperation;
-import com.oracle.svm.core.thread.VirtualThreads;
 import com.oracle.svm.core.util.VMError;
 
 import jdk.vm.ci.meta.MetaAccessProvider;
@@ -104,10 +101,7 @@ public static void visitCurrentThreadStackFrames(Pointer startSP, Pointer endSP,
     @NeverInline("Potentially starting a stack walk in the caller frame")
     public static StackTraceElement[] getStackTraceAtSafepoint(Thread thread) {
         assert VMOperation.isInProgressAtSafepoint();
-        if (VirtualThreads.isSupported()) { // NOTE: also for platform threads!
-            return VirtualThreads.singleton().getVirtualOrPlatformThreadStackTraceAtSafepoint(thread, readCallerStackPointer());
-        }
-        return PlatformThreads.getStackTraceAtSafepoint(thread, readCallerStackPointer());
+        return JavaThreads.getStackTraceAtSafepoint(thread, readCallerStackPointer());
     }
 
     public static StackTraceElement[] getThreadStackTraceAtSafepoint(IsolateThread isolateThread, Pointer endSP) {
@@ -186,7 +180,7 @@ public static boolean shouldShowFrame(FrameInfoQueryResult frameInfo, boolean sh
             return false;
         }
 
-        if (LoomSupport.isEnabled() && clazz == Target_jdk_internal_vm_Continuation.class) {
+        if (clazz == Target_jdk_internal_vm_Continuation.class) {
             String name = frameInfo.getSourceMethodName();
             if (name.startsWith("enter") || name.startsWith("yield")) {
                 return false;
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_java_lang_StackWalker.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_java_lang_StackWalker.java
index e6aed227bf14..4ab3bd5db3cc 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_java_lang_StackWalker.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/Target_java_lang_StackWalker.java
@@ -48,7 +48,6 @@
 import com.oracle.svm.core.annotate.Delete;
 import com.oracle.svm.core.annotate.Substitute;
 import com.oracle.svm.core.annotate.TargetClass;
-import com.oracle.svm.core.annotate.TargetElement;
 import com.oracle.svm.core.code.CodeInfo;
 import com.oracle.svm.core.code.CodeInfoAccess;
 import com.oracle.svm.core.code.CodeInfoTable;
@@ -65,8 +64,8 @@
 import com.oracle.svm.core.stack.JavaStackWalk;
 import com.oracle.svm.core.stack.JavaStackWalker;
 import com.oracle.svm.core.thread.Continuation;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.thread.JavaThreads;
-import com.oracle.svm.core.thread.LoomSupport;
 import com.oracle.svm.core.thread.Target_java_lang_VirtualThread;
 import com.oracle.svm.core.thread.Target_jdk_internal_vm_Continuation;
 import com.oracle.svm.core.thread.Target_jdk_internal_vm_ContinuationScope;
@@ -79,13 +78,13 @@ final class Target_java_lang_StackWalker {
     /**
      * Current continuation that the stack walker is on.
      */
-    @Alias @TargetElement(onlyWith = LoomJDK.class)//
+    @Alias //
     Target_jdk_internal_vm_Continuation continuation;
 
     /**
      * Target continuation scope if we're iterating a {@link Target_jdk_internal_vm_Continuation}.
      */
-    @Alias @TargetElement(onlyWith = LoomJDK.class)//
+    @Alias //
     Target_jdk_internal_vm_ContinuationScope contScope;
 
     @Alias Set<Option> options;
@@ -141,17 +140,17 @@ private Class<?> getCallerClass() {
     private <T> T walk(Function<? super Stream<StackFrame>, ? extends T> function) {
         JavaStackWalk walk = UnsafeStackValue.get(JavaStackWalk.class);
         AbstractStackFrameSpliterator spliterator;
-        if (LoomSupport.isEnabled() && continuation != null) {
+        if (ContinuationSupport.isSupported() && continuation != null) {
             // walking a yielded continuation
             spliterator = new ContinuationSpliterator(walk, contScope, continuation);
         } else {
             // walking a platform thread or mounted continuation
             Pointer sp = KnownIntrinsics.readCallerStackPointer();
-            if (LoomSupport.isEnabled() && (contScope != null || JavaThreads.isCurrentThreadVirtual())) {
+            if (ContinuationSupport.isSupported() && (contScope != null || JavaThreads.isCurrentThreadVirtual())) {
                 var scope = (contScope != null) ? contScope : Target_java_lang_VirtualThread.continuationScope();
                 var top = Target_jdk_internal_vm_Continuation.getCurrentContinuation(scope);
                 if (top != null) { // has a delimitation scope
-                    JavaStackWalker.initWalk(walk, sp, LoomSupport.getInternalContinuation(top).getBaseSP());
+                    JavaStackWalker.initWalk(walk, sp, top.internal.getBaseSP());
                 } else { // scope is not present in current continuation chain or null
                     JavaStackWalker.initWalk(walk, sp);
                 }
@@ -269,7 +268,7 @@ final class ContinuationSpliterator extends AbstractStackFrameSpliterator {
         @Uninterruptible(reason = "Prevent GC while in this method.")
         private boolean initWalk() {
             assert stored == null;
-            Continuation internal = (continuation != null) ? LoomSupport.getInternalContinuation(continuation) : null;
+            Continuation internal = (continuation != null) ? continuation.internal : null;
             if (internal == null || internal.stored == null) {
                 walk.setPossiblyStaleIP(WordFactory.nullPointer());
                 return false;
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jni/functions/JNIFunctions.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jni/functions/JNIFunctions.java
index 1b50dd939285..dc3219f87873 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jni/functions/JNIFunctions.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jni/functions/JNIFunctions.java
@@ -112,10 +112,11 @@
 import com.oracle.svm.core.monitor.MonitorSupport;
 import com.oracle.svm.core.snippets.KnownIntrinsics;
 import com.oracle.svm.core.stack.StackOverflowCheck;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.thread.JavaThreads;
 import com.oracle.svm.core.thread.Target_java_lang_BaseVirtualThread;
+import com.oracle.svm.core.thread.Target_jdk_internal_vm_Continuation;
 import com.oracle.svm.core.thread.VMThreads.SafepointBehavior;
-import com.oracle.svm.core.thread.VirtualThreads;
 import com.oracle.svm.core.util.Utf8;
 import com.oracle.svm.core.util.VMError;
 
@@ -1028,11 +1029,11 @@ static int MonitorEnter(JNIEnvironment env, JNIObjectHandle handle) {
             throw new NullPointerException();
         }
         boolean pinned = false;
-        if (VirtualThreads.isSupported() && JavaThreads.isCurrentThreadVirtual()) {
+        if (ContinuationSupport.isSupported() && JavaThreads.isCurrentThreadVirtual()) {
             // Acquiring monitors via JNI associates them with the carrier thread via
             // JNIThreadOwnedMonitors, so we must pin the virtual thread
             try {
-                VirtualThreads.singleton().pinCurrent();
+                Target_jdk_internal_vm_Continuation.pin();
             } catch (IllegalStateException e) { // too many pins
                 throw new IllegalMonitorStateException();
             }
@@ -1053,7 +1054,7 @@ static int MonitorEnter(JNIEnvironment env, JNIObjectHandle handle) {
                     MonitorSupport.singleton().monitorExit(obj, MonitorInflationCause.VM_INTERNAL);
                 }
                 if (pinned) {
-                    VirtualThreads.singleton().unpinCurrent();
+                    Target_jdk_internal_vm_Continuation.unpin();
                 }
             } catch (Throwable u) {
                 throw VMError.shouldNotReachHere(u);
@@ -1077,9 +1078,9 @@ static int MonitorExit(JNIEnvironment env, JNIObjectHandle handle) {
         }
         MonitorSupport.singleton().monitorExit(obj, MonitorInflationCause.JNI_EXIT);
         JNIThreadOwnedMonitors.exited(obj);
-        if (VirtualThreads.isSupported() && JavaThreads.isCurrentThreadVirtual()) {
+        if (ContinuationSupport.isSupported() && JavaThreads.isCurrentThreadVirtual()) {
             try {
-                VirtualThreads.singleton().unpinCurrent();
+                Target_jdk_internal_vm_Continuation.unpin();
             } catch (IllegalStateException e) { // not pinned?
                 throw new IllegalMonitorStateException();
             }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/monitor/MultiThreadedMonitorSupport.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/monitor/MultiThreadedMonitorSupport.java
index 39ce7a19aa02..030b583a5e16 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/monitor/MultiThreadedMonitorSupport.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/monitor/MultiThreadedMonitorSupport.java
@@ -51,9 +51,9 @@
 import com.oracle.svm.core.monitor.JavaMonitorQueuedSynchronizer.JavaMonitorConditionObject;
 import com.oracle.svm.core.snippets.SubstrateForeignCallTarget;
 import com.oracle.svm.core.stack.StackOverflowCheck;
+import com.oracle.svm.core.thread.JavaThreads;
 import com.oracle.svm.core.thread.ThreadStatus;
 import com.oracle.svm.core.thread.VMOperationControl;
-import com.oracle.svm.core.thread.VirtualThreads;
 import com.oracle.svm.core.util.VMError;
 
 import jdk.internal.misc.Unsafe;
@@ -325,8 +325,7 @@ protected void doWait(Object obj, long timeoutMillis) throws InterruptedExceptio
          * clear the virtual thread interrupt.
          */
         long compensation = -1;
-        boolean pinned = VirtualThreads.isSupported() &&
-                        VirtualThreads.singleton().isVirtual(Thread.currentThread()) && VirtualThreads.singleton().isCurrentPinned();
+        boolean pinned = JavaThreads.isCurrentThreadVirtualAndPinned();
         if (pinned) {
             compensation = Target_jdk_internal_misc_Blocker.begin();
         }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuation.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuation.java
index e1abbde3e83e..09d5c7ea8838 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuation.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuation.java
@@ -24,7 +24,6 @@
  */
 package com.oracle.svm.core.thread;
 
-import jdk.compiler.graal.api.replacements.Fold;
 import org.graalvm.nativeimage.ImageSingletons;
 import org.graalvm.nativeimage.IsolateThread;
 import org.graalvm.nativeimage.c.function.CodePointer;
@@ -44,14 +43,6 @@
 /** Foundation for {@linkplain Target_jdk_internal_vm_Continuation Project Loom} support. */
 @InternalVMMethod
 public final class Continuation {
-    @Fold
-    public static boolean isSupported() {
-        return LoomSupport.isEnabled();
-    }
-
-    public static final int YIELDING = -2;
-    public static final int FREEZE_OK = LoomSupport.FREEZE_OK;
-
     private final Runnable target;
 
     public StoredContinuation stored;
@@ -185,7 +176,7 @@ Integer yield() {
 
     /**
      * @return {@link Integer} because we return here via {@link KnownIntrinsics#farReturn} and pass
-     *         boxed {@link #FREEZE_OK} as result code.
+     *         boxed {@link ContinuationSupport#FREEZE_OK} as result code.
      */
     @NeverInline("Accesses caller stack pointer and return address.")
     private Integer yield0() {
@@ -217,7 +208,7 @@ boolean isEmpty() {
     }
 
     private static final class TryPreemptOperation extends JavaVMOperation {
-        int preemptStatus = FREEZE_OK;
+        int preemptStatus = ContinuationSupport.FREEZE_OK;
 
         final Continuation cont;
         final Thread thread;
@@ -235,7 +226,7 @@ public void operate() {
             Pointer returnSP = cont.sp;
             CodePointer returnIP = cont.ip;
             preemptStatus = StoredContinuationAccess.allocateToPreempt(cont, baseSP, vmThread);
-            if (preemptStatus == FREEZE_OK) {
+            if (preemptStatus == ContinuationSupport.FREEZE_OK) {
                 cont.sp = WordFactory.nullPointer();
                 cont.baseSP = WordFactory.nullPointer();
                 cont.ip = WordFactory.nullPointer();
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationSupport.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationSupport.java
index 6eee1454bc19..2943946c0d60 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationSupport.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationSupport.java
@@ -24,7 +24,6 @@
  */
 package com.oracle.svm.core.thread;
 
-import jdk.compiler.graal.api.replacements.Fold;
 import org.graalvm.nativeimage.ImageSingletons;
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
@@ -39,9 +38,31 @@
 import com.oracle.svm.core.graal.nodes.WriteStackPointerNode;
 import com.oracle.svm.core.heap.StoredContinuation;
 import com.oracle.svm.core.heap.StoredContinuationAccess;
+import com.oracle.svm.core.option.HostedOptionKey;
 import com.oracle.svm.core.snippets.KnownIntrinsics;
 
+import jdk.compiler.graal.api.replacements.Fold;
+import jdk.compiler.graal.options.Option;
+import jdk.compiler.graal.options.OptionType;
+
 public class ContinuationSupport {
+    static final class Options {
+        @Option(type = OptionType.Expert, help = "Support for continuations which are used by virtual threads. " +
+                        "If disabled, virtual threads can be started but each of them is backed by a platform thread.") //
+        public static final HostedOptionKey<Boolean> VMContinuations = new HostedOptionKey<>(true);
+    }
+
+    @Fold
+    public static boolean isSupported() {
+        return ContinuationsFeature.isSupported();
+    }
+
+    /* See JDK native enum {@code freeze_result}. */
+    public static final int FREEZE_OK = 0;
+    public static final int FREEZE_PINNED_CS = 2; // critical section
+    public static final int FREEZE_PINNED_NATIVE = 3;
+    public static final int FREEZE_YIELDING = -2;
+
     private long ipOffset;
 
     @Platforms(Platform.HOSTED_ONLY.class)
@@ -93,7 +114,7 @@ private static void enter0(StoredContinuation storedCont, Pointer topSP, Object
         // copyFrames() may do something interruptible before uninterruptibly copying frames.
         // Code must not rely on remaining uninterruptible until after frames were copied.
         CodePointer enterIP = singleton().copyFrames(storedCont, topSP, preparedData);
-        KnownIntrinsics.farReturn(Continuation.FREEZE_OK, topSP, enterIP, false);
+        KnownIntrinsics.farReturn(FREEZE_OK, topSP, enterIP, false);
     }
 
     @Uninterruptible(reason = "Copies stack frames containing references.")
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationsFeature.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationsFeature.java
index f40e11e5d72a..b5aa468a7de4 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationsFeature.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/ContinuationsFeature.java
@@ -26,9 +26,7 @@
 
 import java.lang.reflect.Field;
 
-import jdk.compiler.graal.serviceprovider.JavaVersionUtil;
 import org.graalvm.nativeimage.ImageSingletons;
-import org.graalvm.nativeimage.hosted.RuntimeClassInitialization;
 
 import com.oracle.svm.core.SubstrateControlFlowIntegrity;
 import com.oracle.svm.core.SubstrateOptions;
@@ -37,57 +35,35 @@
 import com.oracle.svm.core.feature.InternalFeature;
 import com.oracle.svm.core.heap.StoredContinuation;
 import com.oracle.svm.core.heap.StoredContinuationAccess;
+import com.oracle.svm.core.util.UserError;
 import com.oracle.svm.core.util.VMError;
 import com.oracle.svm.util.ReflectionUtil;
 
 @AutomaticallyRegisteredFeature
 public class ContinuationsFeature implements InternalFeature {
-    private boolean finishedRegistration = false;
+    private Boolean supported;
+
+    public static boolean isSupported() {
+        return ImageSingletons.lookup(ContinuationsFeature.class).supported;
+    }
 
     @Override
     public void afterRegistration(AfterRegistrationAccess access) {
-        final int firstLoomPreviewVersion = 19;
-        final int lastLoomPreviewVersion = 20;
-
-        boolean supportLoom = false;
-        if (JavaVersionUtil.JAVA_SPEC >= firstLoomPreviewVersion) {
-            boolean haveLoom;
-            if (JavaVersionUtil.JAVA_SPEC > lastLoomPreviewVersion) {
-                haveLoom = true;
-            } else {
-                try {
-                    haveLoom = (Boolean) Class.forName("jdk.internal.misc.PreviewFeatures")
-                                    .getDeclaredMethod("isEnabled").invoke(null);
-                } catch (ReflectiveOperationException e) {
-                    throw VMError.shouldNotReachHere(e);
-                }
-                if (!haveLoom) {
-                    // Defer: can get initialized and fail the image build despite substitution
-                    RuntimeClassInitialization.initializeAtRunTime("jdk.internal.vm.Continuation");
-                }
-            }
-            supportLoom = haveLoom && !DeoptimizationSupport.enabled() && !SubstrateOptions.useLLVMBackend() && !SubstrateControlFlowIntegrity.enabled();
-        }
-
-        /*
-         * Note: missing support for Loom due to preview features being off, runtime compilation, or
-         * the LLVM backend is reported at runtime to allow probing without failing the image build.
-         */
-        if (supportLoom) {
-            LoomVirtualThreads vt = new LoomVirtualThreads();
-            ImageSingletons.add(VirtualThreads.class, vt);
-            ImageSingletons.add(LoomVirtualThreads.class, vt); // for simpler check in LoomSupport
+        /* If continuations are not supported, "virtual" threads are bound to platform threads. */
+        if (ContinuationSupport.Options.VMContinuations.getValue()) {
+            supported = !DeoptimizationSupport.enabled() && !SubstrateOptions.useLLVMBackend() && !SubstrateControlFlowIntegrity.enabled();
+            UserError.guarantee(supported || !ContinuationSupport.Options.VMContinuations.hasBeenSet(),
+                            "Continuation support has been explicitly enabled with option %s but is not available " +
+                                            "because of the runtime compilation, LLVM backend, or control flow integrity features.",
+                            ContinuationSupport.Options.VMContinuations.getName());
+        } else {
+            supported = false;
         }
-        finishedRegistration = true;
-    }
-
-    boolean hasFinishedRegistration() {
-        return finishedRegistration;
     }
 
     @Override
     public void beforeAnalysis(BeforeAnalysisAccess access) {
-        if (Continuation.isSupported()) {
+        if (isSupported()) {
             if (!ImageSingletons.contains(ContinuationSupport.class)) {
                 ImageSingletons.add(ContinuationSupport.class, new ContinuationSupport());
             }
@@ -98,20 +74,16 @@ public void beforeAnalysis(BeforeAnalysisAccess access) {
             access.registerReachabilityHandler(a -> access.registerAsInHeap(StoredContinuation.class),
                             ReflectionUtil.lookupMethod(StoredContinuationAccess.class, "allocate", int.class));
         } else {
-            access.registerReachabilityHandler(a -> abortIfUnsupported(), StoredContinuationAccess.class);
+            access.registerReachabilityHandler(a -> VMError.shouldNotReachHere("Virtual threads internals are reachable but support is not available or active."), StoredContinuationAccess.class);
         }
     }
 
     @Override
     public void beforeCompilation(BeforeCompilationAccess access) {
-        if (Continuation.isSupported()) {
+        if (isSupported()) {
             Field ipField = ReflectionUtil.lookupField(StoredContinuation.class, "ip");
             long offset = access.objectFieldOffset(ipField);
             ContinuationSupport.singleton().setIPOffset(offset);
         }
     }
-
-    static void abortIfUnsupported() {
-        VMError.guarantee(Continuation.isSupported(), "Virtual threads internals are reachable but support is not available or active.");
-    }
 }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaThreads.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaThreads.java
index bcb07cb67735..e82be1ee145a 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaThreads.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaThreads.java
@@ -30,24 +30,26 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 
-import jdk.compiler.graal.api.directives.GraalDirectives;
-import jdk.compiler.graal.api.replacements.Fold;
-import jdk.compiler.graal.core.common.SuppressFBWarnings;
-import jdk.compiler.graal.replacements.ReplacementsUtil;
 import org.graalvm.nativeimage.CurrentIsolate;
 import org.graalvm.nativeimage.IsolateThread;
 import org.graalvm.nativeimage.Platforms;
 import org.graalvm.nativeimage.impl.InternalPlatform;
 import org.graalvm.word.Pointer;
+import org.graalvm.word.WordFactory;
 
 import com.oracle.svm.core.AlwaysInline;
 import com.oracle.svm.core.NeverInline;
 import com.oracle.svm.core.SubstrateUtil;
 import com.oracle.svm.core.Uninterruptible;
+import com.oracle.svm.core.jdk.StackTraceUtils;
 import com.oracle.svm.core.snippets.KnownIntrinsics;
 import com.oracle.svm.core.stack.StackFrameVisitor;
 import com.oracle.svm.util.ReflectionUtil;
 
+import jdk.compiler.graal.api.directives.GraalDirectives;
+import jdk.compiler.graal.core.common.SuppressFBWarnings;
+import jdk.compiler.graal.replacements.ReplacementsUtil;
+
 /**
  * Implements operations on {@linkplain Target_java_lang_Thread Java threads}, which are on a higher
  * abstraction level than {@link IsolateThread}s. This class distinguishes these types of threads:
@@ -65,10 +67,6 @@
  * Methods with <em>platform</em> or <em>carrier</em> in their names must be called <em>only</em>
  * for that type of thread. Methods without that designation distinguish between the thread types
  * and choose the appropriate action.
- *
- * @see VirtualThreads
- * @see <a href="https://openjdk.java.net/projects/loom/">Wiki and source code of Project Loom on
- *      which concepts of virtual threads, carrier threads, etc. are modeled</a>
  */
 public final class JavaThreads {
     /** For Thread.nextThreadID(). */
@@ -139,62 +137,43 @@ public static boolean isInterrupted(Thread thread) {
         return toTarget(thread).interrupted;
     }
 
-    static boolean getAndClearInterrupt(Thread thread) {
-        if (supportsVirtual() && isVirtual(thread)) {
-            return VirtualThreads.singleton().getAndClearInterrupt(thread);
-        }
-        /*
-         * As we don't use a lock, it is possible to observe any kinds of races with other threads
-         * that try to set the interrupted status to true. However, those races don't cause any
-         * correctness issues as we only reset it to false if we observed that it was true earlier.
-         * There also can't be any problematic races with other calls to check the interrupt status
-         * because it is cleared only by the current thread.
-         */
-        if (!isInterrupted(thread)) {
-            return false;
-        }
-        toTarget(thread).interrupted = false;
-        return true;
-    }
-
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public static long getParentThreadId(Thread thread) {
         return toTarget(thread).parentThreadId;
     }
 
-    @Fold
-    static boolean supportsVirtual() {
-        return VirtualThreads.isSupported();
-    }
-
+    /**
+     * Indicates whether a thread is <em>truly</em> virtual, whereas {@link Thread#isVirtual()} also
+     * returns {@code true} for platform threads of type {@code BoundVirtualThread}.
+     */
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public static boolean isVirtual(Thread thread) {
-        return supportsVirtual() && VirtualThreads.singleton().isVirtual(thread);
+        return Target_java_lang_VirtualThread.class.isInstance(thread);
     }
 
-    /** @see PlatformThreads#setCurrentThread */
+    /** @see #isVirtual */
     public static boolean isCurrentThreadVirtual() {
-        if (!supportsVirtual()) {
-            return false;
-        }
         Thread thread = PlatformThreads.currentThread.get();
         return thread != null && toTarget(thread).vthread != null;
     }
 
+    /**
+     * Indicates whether the current thread is <em>truly</em> virtual (see {@link #isVirtual}) and
+     * currently pinned to its carrier thread.
+     */
+    public static boolean isCurrentThreadVirtualAndPinned() {
+        Target_java_lang_Thread carrier = JavaThreads.toTarget(Target_java_lang_Thread.currentCarrierThread());
+        return carrier != null && carrier.vthread != null && Target_jdk_internal_vm_Continuation.isPinned(carrier.cont.getScope());
+    }
+
     @SuppressFBWarnings(value = "BC", justification = "Cast for @TargetClass")
     static Target_java_lang_ThreadGroup toTarget(ThreadGroup threadGroup) {
         return Target_java_lang_ThreadGroup.class.cast(threadGroup);
     }
 
-    static void join(Thread thread, long millis) throws InterruptedException {
-        if (millis < 0) {
-            throw new IllegalArgumentException("Timeout value is negative");
-        }
-        if (supportsVirtual() && isVirtual(thread)) {
-            VirtualThreads.singleton().join(thread, millis);
-        } else {
-            PlatformThreads.join(thread, millis);
-        }
+    @SuppressFBWarnings(value = "BC", justification = "Cast for @TargetClass")
+    private static Target_java_lang_VirtualThread toVirtualTarget(Thread thread) {
+        return Target_java_lang_VirtualThread.class.cast(thread);
     }
 
     @NeverInline("Starting a stack walk in the caller frame")
@@ -206,10 +185,55 @@ public static StackTraceElement[] getStackTrace(boolean filterExceptions, Thread
          */
         Pointer callerSP = KnownIntrinsics.readCallerStackPointer();
 
-        if (supportsVirtual()) { // NOTE: also for platform threads!
-            return VirtualThreads.singleton().getVirtualOrPlatformThreadStackTrace(filterExceptions, thread, callerSP);
+        if (isVirtual(thread)) {
+            if (thread == Thread.currentThread()) {
+                return getMountedVirtualThreadStackTrace(filterExceptions, thread, callerSP);
+            }
+            assert !filterExceptions : "exception stack traces can be taken only for the current thread";
+            return asyncGetVirtualThreadStackTrace(toVirtualTarget(thread));
+        } else {
+            return PlatformThreads.getStackTrace(filterExceptions, thread, callerSP);
+        }
+    }
+
+    private static StackTraceElement[] getMountedVirtualThreadStackTrace(boolean filterExceptions, Thread thread, Pointer callerSP) {
+        Thread carrier = toVirtualTarget(thread).carrierThread;
+        if (carrier == null) {
+            return null;
+        }
+        Pointer endSP = PlatformThreads.getCarrierSPOrElse(carrier, WordFactory.nullPointer());
+        if (endSP.isNull()) {
+            return null;
+        }
+        if (carrier == PlatformThreads.currentThread.get()) {
+            return StackTraceUtils.getStackTrace(filterExceptions, callerSP, endSP);
+        }
+        assert VMOperation.isInProgressAtSafepoint();
+        return StackTraceUtils.getThreadStackTraceAtSafepoint(PlatformThreads.getIsolateThread(carrier), endSP);
+    }
+
+    public static StackTraceElement[] getStackTraceAtSafepoint(Thread thread, Pointer callerSP) {
+        if (isVirtual(thread)) {
+            return getMountedVirtualThreadStackTrace(false, thread, callerSP);
+        } else {
+            return PlatformThreads.getStackTraceAtSafepoint(thread, callerSP);
         }
-        return PlatformThreads.getStackTrace(filterExceptions, thread, callerSP);
+    }
+
+    /** Adapted from {@code VirtualThread.asyncGetStackTrace()}. */
+    private static StackTraceElement[] asyncGetVirtualThreadStackTrace(Target_java_lang_VirtualThread thread) {
+        StackTraceElement[] stackTrace;
+        do {
+            if (thread.carrierThread != null) {
+                stackTrace = StackTraceUtils.asyncGetStackTrace(SubstrateUtil.cast(thread, Thread.class));
+            } else {
+                stackTrace = thread.tryGetStackTrace();
+            }
+            if (stackTrace == null) {
+                Thread.yield();
+            }
+        } while (stackTrace == null);
+        return stackTrace;
     }
 
     @NeverInline("Starting a stack walk in the caller frame")
@@ -221,13 +245,23 @@ public static void visitCurrentStackFrames(StackFrameVisitor visitor) {
          */
         Pointer callerSP = KnownIntrinsics.readCallerStackPointer();
 
-        if (supportsVirtual()) { // NOTE: also for platform threads!
-            VirtualThreads.singleton().visitCurrentVirtualOrPlatformThreadStackFrames(callerSP, visitor);
+        if (isVirtual(Thread.currentThread())) {
+            visitCurrentVirtualThreadStackFrames(callerSP, visitor);
         } else {
             PlatformThreads.visitCurrentStackFrames(callerSP, visitor);
         }
     }
 
+    private static void visitCurrentVirtualThreadStackFrames(Pointer callerSP, StackFrameVisitor visitor) {
+        Thread carrier = toVirtualTarget(Thread.currentThread()).carrierThread;
+        if (carrier != null) {
+            Pointer endSP = PlatformThreads.getCarrierSPOrElse(carrier, WordFactory.nullPointer());
+            if (endSP.isNonNull()) {
+                StackTraceUtils.visitCurrentThreadStackFrames(callerSP, endSP, visitor);
+            }
+        }
+    }
+
     /** If there is an uncaught exception handler, call it. */
     public static void dispatchUncaughtException(Thread thread, Throwable throwable) {
         /* Get the uncaught exception handler for the Thread, or the default one. */
@@ -297,9 +331,7 @@ static void initializeNewThread(
 
         initThreadFields(tjlt, group, target, stackSize, priority, daemon);
 
-        if (!VirtualThreads.isSupported() || !VirtualThreads.singleton().isVirtual(fromTarget(tjlt))) {
-            PlatformThreads.setThreadStatus(fromTarget(tjlt), ThreadStatus.NEW);
-        }
+        PlatformThreads.setThreadStatus(fromTarget(tjlt), ThreadStatus.NEW);
 
         tjlt.inheritedAccessControlContext = acc != null ? acc : AccessController.getContext();
 
@@ -328,25 +360,18 @@ static void initNewThreadLocalsAndLoader(Target_java_lang_Thread tjlt, boolean i
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public static void setCurrentThreadLockHelper(Object helper) {
-        if (supportsVirtual()) {
-            toTarget(Thread.currentThread()).lockHelper = helper;
-        } else {
-            PlatformThreads.lockHelper.set(helper);
-        }
+        toTarget(Thread.currentThread()).lockHelper = helper;
     }
 
     @AlwaysInline("Locking fast path.")
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public static Object getCurrentThreadLockHelper() {
-        if (supportsVirtual()) {
-            return toTarget(Thread.currentThread()).lockHelper;
-        }
-        return PlatformThreads.lockHelper.get();
+        return toTarget(Thread.currentThread()).lockHelper;
     }
 
-    public static void blockedOn(Target_sun_nio_ch_Interruptible b) {
-        if (supportsVirtual() && isCurrentThreadVirtual()) {
-            VirtualThreads.singleton().blockedOn(b);
+    static void blockedOn(Target_sun_nio_ch_Interruptible b) {
+        if (isCurrentThreadVirtual()) {
+            VirtualThreadHelper.blockedOn(b);
         } else {
             PlatformThreads.blockedOn(b);
         }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomSupport.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomSupport.java
deleted file mode 100644
index 3de9625cec5a..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomSupport.java
+++ /dev/null
@@ -1,52 +0,0 @@
-/*
- * Copyright (c) 2021, 2022, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.thread;
-
-import jdk.compiler.graal.api.replacements.Fold;
-import org.graalvm.nativeimage.ImageSingletons;
-
-import com.oracle.svm.core.Uninterruptible;
-import com.oracle.svm.core.util.VMError;
-
-public final class LoomSupport {
-    @Fold
-    public static boolean isEnabled() {
-        VMError.guarantee(ImageSingletons.lookup(ContinuationsFeature.class).hasFinishedRegistration());
-        return ImageSingletons.contains(LoomVirtualThreads.class);
-    }
-
-    // See JDK native enum freeze_result
-    static final int FREEZE_OK = 0;
-    static final int FREEZE_PINNED_CS = 2; // critical section
-    static final int FREEZE_PINNED_NATIVE = 3;
-
-    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static Continuation getInternalContinuation(Target_jdk_internal_vm_Continuation cont) {
-        return cont.internal;
-    }
-
-    private LoomSupport() {
-    }
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomVirtualThreads.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomVirtualThreads.java
deleted file mode 100644
index 7c80d9334135..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/LoomVirtualThreads.java
+++ /dev/null
@@ -1,230 +0,0 @@
-/*
- * Copyright (c) 2021, 2021, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.thread;
-
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
-
-import java.util.concurrent.Executor;
-import java.util.concurrent.ThreadFactory;
-
-import jdk.compiler.graal.core.common.SuppressFBWarnings;
-import org.graalvm.nativeimage.CurrentIsolate;
-import org.graalvm.nativeimage.IsolateThread;
-import org.graalvm.nativeimage.c.function.CodePointer;
-import org.graalvm.word.Pointer;
-import org.graalvm.word.WordFactory;
-
-import com.oracle.svm.core.FrameAccess;
-import com.oracle.svm.core.SubstrateUtil;
-import com.oracle.svm.core.Uninterruptible;
-import com.oracle.svm.core.jdk.StackTraceUtils;
-import com.oracle.svm.core.stack.StackFrameVisitor;
-
-/**
- * In a JDK that supports Project Loom virtual threads (JEP 425, starting with JDK 19 as preview
- * feature), code specific to virtual threads is part of {@link Thread} methods, e.g. {@code yield}
- * or {@code sleep}, and the implementation for platform threads is generally in methods named
- * {@code yield0} or {@code sleep0}, so we only substitute that platform thread code in
- * {@link Target_java_lang_Thread}, and do not expect several methods here to be reachable.
- *
- * @see <a href="https://openjdk.java.net/projects/loom/">Project Loom (Wiki, code, etc.)</a>
- */
-final class LoomVirtualThreads implements VirtualThreads {
-    private static Target_java_lang_VirtualThread cast(Thread thread) {
-        return SubstrateUtil.cast(thread, Target_java_lang_VirtualThread.class);
-    }
-
-    @Override
-    public ThreadFactory createFactory() {
-        return SubstrateUtil.cast(Target_java_lang_Thread.ofVirtual(), Target_java_lang_Thread_Builder.class).factory();
-    }
-
-    @Override
-    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public boolean isVirtual(Thread thread) {
-        return Target_java_lang_VirtualThread.class.isInstance(thread);
-    }
-
-    @Override
-    public void join(Thread thread, long millis) throws InterruptedException {
-        if (thread.isAlive()) {
-            long nanos = MILLISECONDS.toNanos(millis);
-            cast(thread).joinNanos(nanos);
-        }
-    }
-
-    @Override
-    public boolean getAndClearInterrupt(Thread thread) {
-        return cast(thread).getAndClearInterrupt();
-    }
-
-    @Override
-    public void pinCurrent() {
-        Target_jdk_internal_vm_Continuation.pin();
-    }
-
-    @Override
-    public void unpinCurrent() {
-        Target_jdk_internal_vm_Continuation.unpin();
-    }
-
-    @Override
-    public boolean isCurrentPinned() {
-        Target_java_lang_Thread carrier = JavaThreads.toTarget(Target_java_lang_Thread.currentCarrierThread());
-        Target_jdk_internal_vm_ContinuationScope scope = carrier.cont.getScope();
-        return Target_jdk_internal_vm_Continuation.isPinned(scope);
-    }
-
-    @Override
-    public Executor getScheduler(Thread thread) {
-        return cast(thread).scheduler;
-    }
-
-    @Override
-    public void blockedOn(Target_sun_nio_ch_Interruptible b) {
-        VirtualThreadHelper.blockedOn(b);
-    }
-
-    @Override
-    public StackTraceElement[] getVirtualOrPlatformThreadStackTrace(boolean filterExceptions, Thread thread, Pointer callerSP) {
-        if (!isVirtual(thread)) {
-            return getPlatformThreadStackTrace(filterExceptions, thread, callerSP);
-        }
-        if (thread == Thread.currentThread()) {
-            return getVirtualThreadStackTrace(filterExceptions, thread, callerSP);
-        }
-        assert !filterExceptions : "exception stack traces can be taken only for the current thread";
-        return asyncGetStackTrace(cast(thread));
-    }
-
-    @Override
-    public void visitCurrentVirtualOrPlatformThreadStackFrames(Pointer callerSP, StackFrameVisitor visitor) {
-        if (!isVirtual(Thread.currentThread())) {
-            visitCurrentPlatformThreadStackFrames(callerSP, visitor);
-            return;
-        }
-        visitCurrentVirtualThreadStackFrames(callerSP, visitor);
-    }
-
-    @Override
-    public StackTraceElement[] getVirtualOrPlatformThreadStackTraceAtSafepoint(Thread thread, Pointer callerSP) {
-        if (!isVirtual(thread)) {
-            return getPlatformThreadStackTraceAtSafepoint(thread, callerSP);
-        }
-        return getVirtualThreadStackTrace(false, thread, callerSP);
-    }
-
-    private static StackTraceElement[] getVirtualThreadStackTrace(boolean filterExceptions, Thread thread, Pointer callerSP) {
-        Thread carrier = cast(thread).carrierThread;
-        if (carrier == null) {
-            return null;
-        }
-        Pointer endSP = getCarrierSPOrElse(carrier, WordFactory.nullPointer());
-        if (endSP.isNull()) {
-            return null;
-        }
-        if (carrier == PlatformThreads.currentThread.get()) {
-            return StackTraceUtils.getStackTrace(filterExceptions, callerSP, endSP);
-        }
-        assert VMOperation.isInProgressAtSafepoint();
-        return StackTraceUtils.getThreadStackTraceAtSafepoint(PlatformThreads.getIsolateThread(carrier), endSP);
-    }
-
-    private static void visitCurrentVirtualThreadStackFrames(Pointer callerSP, StackFrameVisitor visitor) {
-        Thread carrier = cast(Thread.currentThread()).carrierThread;
-        if (carrier == null) {
-            return;
-        }
-        Pointer endSP = getCarrierSPOrElse(carrier, WordFactory.nullPointer());
-        if (endSP.isNull()) {
-            return;
-        }
-        StackTraceUtils.visitCurrentThreadStackFrames(callerSP, endSP, visitor);
-    }
-
-    private static Pointer getCarrierSPOrElse(Thread carrier, Pointer other) {
-        Target_jdk_internal_vm_Continuation cont = JavaThreads.toTarget(carrier).cont;
-        while (cont != null) {
-            if (cont.getScope() == Target_java_lang_VirtualThread.VTHREAD_SCOPE) {
-                return cont.internal.getBaseSP();
-            }
-            cont = cont.getParent();
-        }
-        return other;
-    }
-
-    /** Adapted from {@code VirtualThread.asyncGetStackTrace()}. */
-    private static StackTraceElement[] asyncGetStackTrace(Target_java_lang_VirtualThread thread) {
-        StackTraceElement[] stackTrace;
-        do {
-            if (thread.carrierThread != null) {
-                stackTrace = asyncMountedGetStackTrace(thread);
-            } else {
-                stackTrace = thread.tryGetStackTrace();
-            }
-            if (stackTrace == null) {
-                Thread.yield();
-            }
-        } while (stackTrace == null);
-        return stackTrace;
-    }
-
-    @SuppressFBWarnings(value = "BC_IMPOSSIBLE_CAST", justification = "substitution hides acual type")
-    private static StackTraceElement[] asyncMountedGetStackTrace(Target_java_lang_VirtualThread thread) {
-        return StackTraceUtils.asyncGetStackTrace(SubstrateUtil.cast(thread, Thread.class));
-    }
-
-    private static StackTraceElement[] getPlatformThreadStackTrace(boolean filterExceptions, Thread thread, Pointer callerSP) {
-        if (thread == PlatformThreads.currentThread.get()) {
-            Pointer startSP = getCarrierSPOrElse(thread, callerSP);
-            return StackTraceUtils.getStackTrace(filterExceptions, startSP, WordFactory.nullPointer());
-        }
-        assert !filterExceptions : "exception stack traces can be taken only for the current thread";
-        return StackTraceUtils.asyncGetStackTrace(thread);
-    }
-
-    private static void visitCurrentPlatformThreadStackFrames(Pointer callerSP, StackFrameVisitor visitor) {
-        Pointer startSP = getCarrierSPOrElse(Thread.currentThread(), callerSP);
-        StackTraceUtils.visitCurrentThreadStackFrames(startSP, WordFactory.nullPointer(), visitor);
-    }
-
-    private static StackTraceElement[] getPlatformThreadStackTraceAtSafepoint(Thread thread, Pointer callerSP) {
-        Pointer carrierSP = getCarrierSPOrElse(thread, WordFactory.nullPointer());
-        IsolateThread isolateThread = PlatformThreads.getIsolateThread(thread);
-        if (isolateThread == CurrentIsolate.getCurrentThread()) {
-            Pointer startSP = carrierSP.isNonNull() ? carrierSP : callerSP;
-            /*
-             * Internal frames from the VMOperation handling show up in the stack traces, but we are
-             * OK with that.
-             */
-            return StackTraceUtils.getStackTrace(false, startSP, WordFactory.nullPointer());
-        }
-        if (carrierSP.isNonNull()) { // mounted virtual thread, skip its frames
-            CodePointer carrierIP = FrameAccess.singleton().readReturnAddress(carrierSP);
-            return StackTraceUtils.getThreadStackTraceAtSafepoint(carrierSP, WordFactory.nullPointer(), carrierIP);
-        }
-        return StackTraceUtils.getThreadStackTraceAtSafepoint(isolateThread, WordFactory.nullPointer());
-    }
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/PlatformThreads.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/PlatformThreads.java
index 12e36ec2727c..f3f63534f739 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/PlatformThreads.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/PlatformThreads.java
@@ -45,7 +45,6 @@
 import java.util.concurrent.ForkJoinWorkerThread;
 import java.util.concurrent.ScheduledThreadPoolExecutor;
 import java.util.concurrent.ThreadPoolExecutor;
-import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 
@@ -63,8 +62,8 @@
 import org.graalvm.nativeimage.UnmanagedMemory;
 import org.graalvm.nativeimage.c.function.CEntryPoint;
 import org.graalvm.nativeimage.c.function.CFunctionPointer;
+import org.graalvm.nativeimage.c.function.CodePointer;
 import org.graalvm.nativeimage.c.struct.RawField;
-import org.graalvm.nativeimage.c.struct.RawPointerTo;
 import org.graalvm.nativeimage.c.struct.RawStructure;
 import org.graalvm.nativeimage.c.type.WordPointer;
 import org.graalvm.word.ComparableWord;
@@ -73,6 +72,7 @@
 import org.graalvm.word.WordBase;
 import org.graalvm.word.WordFactory;
 
+import com.oracle.svm.core.FrameAccess;
 import com.oracle.svm.core.NeverInline;
 import com.oracle.svm.core.SubstrateDiagnostics;
 import com.oracle.svm.core.SubstrateOptions;
@@ -137,12 +137,6 @@ public static PlatformThreads singleton() {
      */
     static final FastThreadLocalLong currentVThreadId = FastThreadLocalFactory.createLong("PlatformThreads.currentVThreadId").setMaxOffset(FastThreadLocal.BYTE_OFFSET);
 
-    /**
-     * A thread-local helper object for locking. Use only if each {@link Thread} corresponds to an
-     * {@link IsolateThread}, otherwise use {@link Target_java_lang_Thread#lockHelper}.
-     */
-    static final FastThreadLocalObject<Object> lockHelper = FastThreadLocalFactory.createObject(Object.class, "PlatformThreads.lockHelper").setMaxOffset(FastThreadLocal.BYTE_OFFSET);
-
     /**
      * The number of running non-daemon threads. The initial value accounts for the main thread,
      * which is implicitly running when the isolate is created.
@@ -316,27 +310,6 @@ static void afterThreadExit(IsolateThread thread) {
         }
     }
 
-    static void join(Thread thread, long millis) throws InterruptedException {
-        assert !isVirtual(thread);
-        // Checkstyle: allow synchronization
-        synchronized (thread) {
-            if (millis > 0) {
-                if (thread.isAlive()) {
-                    final long startTime = System.nanoTime();
-                    long delay = millis;
-                    do {
-                        thread.wait(delay);
-                    } while (thread.isAlive() && (delay = millis - TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime)) > 0);
-                }
-            } else {
-                while (thread.isAlive()) {
-                    thread.wait(0);
-                }
-            }
-        }
-        // Checkstyle: disallow synchronization
-    }
-
     /**
      * Joins all non-daemon threads. If the current thread is itself a non-daemon thread, it does
      * not attempt to join itself.
@@ -389,7 +362,7 @@ public static long getRequestedStackSize(Thread thread) {
         long stackSize;
         Target_java_lang_Thread tjlt = toTarget(thread);
         long threadSpecificStackSize = tjlt.holder.stackSize;
-        if (threadSpecificStackSize != 0) {
+        if (threadSpecificStackSize > 0) {
             /* If the user set a thread stack size at thread creation, then use that. */
             stackSize = threadSpecificStackSize;
         } else {
@@ -490,7 +463,7 @@ private static void assignCurrent0(Thread thread) {
     @Uninterruptible(reason = "Ensure consistency of vthread and cached vthread id.")
     static void setCurrentThread(Thread carrier, Thread thread) {
         assert carrier == currentThread.get();
-        assert thread == carrier || (VirtualThreads.isSupported() && VirtualThreads.singleton().isVirtual(thread));
+        assert thread == carrier || isVirtual(thread);
         toTarget(carrier).vthread = (thread != carrier) ? thread : null;
         currentVThreadId.set(JavaThreads.getThreadId(thread));
     }
@@ -865,7 +838,8 @@ protected static void wakeUpVMConditionWaiters(Thread thread) {
     static StackTraceElement[] getStackTrace(boolean filterExceptions, Thread thread, Pointer callerSP) {
         assert !isVirtual(thread);
         if (thread == currentThread.get()) {
-            return StackTraceUtils.getStackTrace(filterExceptions, callerSP, WordFactory.nullPointer());
+            Pointer startSP = getCarrierSPOrElse(thread, callerSP);
+            return StackTraceUtils.getStackTrace(filterExceptions, startSP, WordFactory.nullPointer());
         }
         assert !filterExceptions : "exception stack traces can be taken only for the current thread";
         return StackTraceUtils.asyncGetStackTrace(thread);
@@ -873,22 +847,40 @@ static StackTraceElement[] getStackTrace(boolean filterExceptions, Thread thread
 
     static void visitCurrentStackFrames(Pointer callerSP, StackFrameVisitor visitor) {
         assert !isVirtual(Thread.currentThread());
-        StackTraceUtils.visitCurrentThreadStackFrames(callerSP, WordFactory.nullPointer(), visitor);
+        Pointer startSP = getCarrierSPOrElse(Thread.currentThread(), callerSP);
+        StackTraceUtils.visitCurrentThreadStackFrames(startSP, WordFactory.nullPointer(), visitor);
     }
 
-    public static StackTraceElement[] getStackTraceAtSafepoint(Thread thread, Pointer callerSP) {
+    static StackTraceElement[] getStackTraceAtSafepoint(Thread thread, Pointer callerSP) {
         assert !isVirtual(thread);
+        Pointer carrierSP = getCarrierSPOrElse(thread, WordFactory.nullPointer());
         IsolateThread isolateThread = getIsolateThread(thread);
         if (isolateThread == CurrentIsolate.getCurrentThread()) {
+            Pointer startSP = carrierSP.isNonNull() ? carrierSP : callerSP;
             /*
              * Internal frames from the VMOperation handling show up in the stack traces, but we are
              * OK with that.
              */
-            return StackTraceUtils.getStackTrace(false, callerSP, WordFactory.nullPointer());
+            return StackTraceUtils.getStackTrace(false, startSP, WordFactory.nullPointer());
+        }
+        if (carrierSP.isNonNull()) { // mounted virtual thread, skip its frames
+            CodePointer carrierIP = FrameAccess.singleton().readReturnAddress(carrierSP);
+            return StackTraceUtils.getThreadStackTraceAtSafepoint(carrierSP, WordFactory.nullPointer(), carrierIP);
         }
         return StackTraceUtils.getThreadStackTraceAtSafepoint(isolateThread, WordFactory.nullPointer());
     }
 
+    static Pointer getCarrierSPOrElse(Thread carrier, Pointer other) {
+        Target_jdk_internal_vm_Continuation cont = toTarget(carrier).cont;
+        while (cont != null) {
+            if (cont.getScope() == Target_java_lang_VirtualThread.VTHREAD_SCOPE) {
+                return cont.internal.getBaseSP();
+            }
+            cont = cont.getParent();
+        }
+        return other;
+    }
+
     static Map<Thread, StackTraceElement[]> getAllStackTraces() {
         GetAllStackTracesOperation vmOp = new GetAllStackTracesOperation();
         vmOp.enqueue();
@@ -1096,7 +1088,9 @@ private static class GetAllStackTracesOperation extends JavaVMOperation {
         protected void operate() {
             for (IsolateThread cur = VMThreads.firstThread(); cur.isNonNull(); cur = VMThreads.nextThread(cur)) {
                 Thread thread = PlatformThreads.fromVMThread(cur);
-                result.put(thread, StackTraceUtils.getStackTraceAtSafepoint(thread));
+                if (!thread.isVirtual()) { // filter BoundVirtualThread
+                    result.put(thread, StackTraceUtils.getStackTraceAtSafepoint(thread));
+                }
             }
         }
     }
@@ -1113,7 +1107,7 @@ private static class GetAllThreadsOperation extends JavaVMOperation {
         protected void operate() {
             for (IsolateThread cur = VMThreads.firstThread(); cur.isNonNull(); cur = VMThreads.nextThread(cur)) {
                 Thread thread = PlatformThreads.fromVMThread(cur);
-                if (thread != null) {
+                if (thread != null && !thread.isVirtual()) { // filter BoundVirtualThread
                     result.add(thread);
                 }
             }
@@ -1228,13 +1222,6 @@ static void blockedOn(Target_sun_nio_ch_Interruptible b) {
     public interface OSThreadHandle extends PointerBase {
     }
 
-    @RawPointerTo(OSThreadHandle.class)
-    public interface OSThreadHandlePointer extends PointerBase {
-        void write(int index, OSThreadHandle value);
-
-        OSThreadHandle read(int index);
-    }
-
     public interface ThreadLocalKey extends ComparableWord {
     }
 }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Safepoint.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Safepoint.java
index a9a4071ae09d..fe382844546e 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Safepoint.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Safepoint.java
@@ -443,7 +443,7 @@ public static void slowPathSafepointCheck() throws Throwable {
     @Uninterruptible(reason = "Must not contain safepoint checks")
     private static void exitSlowPathCheck() {
         if (ActionOnExitSafepointSupport.isActionPending()) {
-            if (LoomSupport.isEnabled() && ActionOnExitSafepointSupport.isSwitchStackPending()) {
+            if (ActionOnExitSafepointSupport.isSwitchStackPending()) {
                 ActionOnExitSafepointSupport.clearActions();
                 KnownIntrinsics.farReturn(0, ActionOnExitSafepointSupport.getSwitchStackSP(), ActionOnExitSafepointSupport.getSwitchStackIP(), false);
             } else {
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_Thread.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_Thread.java
index 51b19b2ebe52..a3b5ae23f6fc 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_Thread.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_Thread.java
@@ -30,7 +30,6 @@
 import java.security.AccessControlContext;
 import java.util.Map;
 import java.util.Objects;
-import java.util.concurrent.ThreadFactory;
 
 import jdk.compiler.graal.api.directives.GraalDirectives;
 import jdk.compiler.graal.replacements.ReplacementsUtil;
@@ -49,13 +48,8 @@
 import com.oracle.svm.core.annotate.Substitute;
 import com.oracle.svm.core.annotate.TargetClass;
 import com.oracle.svm.core.annotate.TargetElement;
-import com.oracle.svm.core.deopt.DeoptimizationSupport;
-import com.oracle.svm.core.jdk.ContinuationsNotSupported;
-import com.oracle.svm.core.jdk.ContinuationsSupported;
 import com.oracle.svm.core.jdk.JDK21OrEarlier;
 import com.oracle.svm.core.jdk.JDK22OrLater;
-import com.oracle.svm.core.jdk.LoomJDK;
-import com.oracle.svm.core.jdk.NotLoomJDK;
 import com.oracle.svm.core.monitor.MonitorSupport;
 import com.oracle.svm.core.util.VMError;
 
@@ -131,7 +125,6 @@ public final class Target_java_lang_Thread {
 
     /** @see JavaThreads#setCurrentThreadLockHelper */
     @Inject //
-    @TargetElement(onlyWith = ContinuationsSupported.class) //
     @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.Reset) //
     Object lockHelper;
 
@@ -189,19 +182,6 @@ public long getId() {
     @AnnotateOriginal
     public native boolean isDaemon();
 
-    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    @Substitute
-    @TargetElement(onlyWith = ContinuationsNotSupported.class)
-    static Thread currentThread() {
-        Thread thread = PlatformThreads.currentThread.get();
-        if (GraalDirectives.inIntrinsic()) {
-            ReplacementsUtil.dynamicAssert(thread != null, "Thread has not been set yet");
-        } else {
-            assert thread != null : "Thread has not been set yet";
-        }
-        return thread;
-    }
-
     @Substitute
     static Thread currentCarrierThread() {
         Thread thread = PlatformThreads.currentThread.get();
@@ -211,14 +191,12 @@ static Thread currentCarrierThread() {
 
     /** On HotSpot, a field in C++ class {@code JavaThread}. Loads and stores are unordered. */
     @Inject //
-    @TargetElement(onlyWith = ContinuationsSupported.class)//
     @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.Reset)//
     Thread vthread = null;
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     @Substitute
-    @TargetElement(name = "currentThread", onlyWith = ContinuationsSupported.class)
-    static Thread currentVThread() {
+    static Thread currentThread() {
         Thread thread = PlatformThreads.getCurrentThreadOrNull();
         if (GraalDirectives.inIntrinsic()) {
             ReplacementsUtil.dynamicAssert(thread != null, "Thread has not been set yet");
@@ -264,7 +242,9 @@ static String genThreadName() {
     /** This constructor is called only by {@code VirtualThread}. */
     @Substitute
     private Target_java_lang_Thread(String name, int characteristics, boolean bound) {
-        VMError.guarantee(!bound, "Bound virtual threads are not supported");
+        if (bound) {
+            this.threadData = new ThreadData();
+        }
 
         /* Non-0 instance field initialization. */
         this.interruptLock = new Object();
@@ -277,6 +257,14 @@ private Target_java_lang_Thread(String name, int characteristics, boolean bound)
         JavaThreads.initNewThreadLocalsAndLoader(this, inheritThreadLocals, Thread.currentThread());
 
         this.scopedValueBindings = NEW_THREAD_BINDINGS;
+
+        if (bound) {
+            ThreadGroup g = Target_java_lang_Thread_Constants.VTHREAD_GROUP;
+            int pri = Thread.NORM_PRIORITY;
+            JavaThreads.initThreadFields(this, g, null, -1, pri, true);
+
+            PlatformThreads.setThreadStatus(JavaThreads.fromTarget(this), ThreadStatus.NEW);
+        }
     }
 
     @SuppressWarnings("hiding")
@@ -325,11 +313,6 @@ public boolean isInterrupted() {
         return JavaThreads.isInterrupted(JavaThreads.fromTarget(this));
     }
 
-    @Substitute
-    public static boolean interrupted() {
-        return JavaThreads.getAndClearInterrupt(Thread.currentThread());
-    }
-
     /**
      * Marks the thread as interrupted and wakes it up.
      *
@@ -411,12 +394,6 @@ private static void sleepNanos0(long nanos) throws InterruptedException {
         PlatformThreads.sleep(nanos);
     }
 
-    @Substitute
-    @TargetElement
-    public void join(long millis) throws InterruptedException {
-        JavaThreads.join(JavaThreads.fromTarget(this), millis);
-    }
-
     /**
      * Returns <tt>true</tt> if and only if the current thread holds the monitor lock on the
      * specified object.
@@ -470,37 +447,8 @@ private static void clearInterruptEvent() {
 
     /** Carrier threads only: the current innermost continuation. */
     @Alias //
-    @TargetElement(onlyWith = LoomJDK.class) //
     Target_jdk_internal_vm_Continuation cont;
 
-    @Alias
-    @TargetElement(onlyWith = LoomJDK.class)
-    public static native Target_java_lang_Thread_Builder_OfVirtual ofVirtual();
-
-    @Substitute
-    @TargetElement(name = "ofVirtual", onlyWith = NotLoomJDK.class)
-    public static Target_java_lang_Thread_Builder_OfVirtual ofVirtualWithoutLoom() {
-        if (Target_jdk_internal_misc_PreviewFeatures.isEnabled()) {
-            if (DeoptimizationSupport.enabled()) {
-                throw new UnsupportedOperationException("Virtual threads are not supported together with Truffle JIT compilation.");
-            }
-            if (SubstrateOptions.useLLVMBackend()) {
-                throw new UnsupportedOperationException("Virtual threads are not supported together with the LLVM backend.");
-            }
-        } else {
-            Target_jdk_internal_misc_PreviewFeatures.ensureEnabled(); // throws
-        }
-        throw VMError.shouldNotReachHereSubstitution();
-    }
-
-    @Substitute
-    @TargetElement(name = "startVirtualThread", onlyWith = NotLoomJDK.class)
-    static Thread startVirtualThreadWithoutLoom(Runnable task) {
-        Objects.requireNonNull(task);
-        ofVirtualWithoutLoom(); // throws
-        throw VMError.shouldNotReachHereSubstitution();
-    }
-
     @Substitute
     static Object[] scopedValueCache() {
         return JavaThreads.toTarget(currentCarrierThread()).scopedValueCache;
@@ -537,7 +485,7 @@ static void setScopedValueCache(Object[] cache) {
     @Uninterruptible(reason = "Must not call other methods which can trigger a stack overflow.", callerMustBe = true)
     static void setScopedValueBindings(Object bindings) {
         Target_java_lang_Thread thread = SubstrateUtil.cast(PlatformThreads.currentThread.get(), Target_java_lang_Thread.class);
-        if (LoomSupport.isEnabled() && thread.vthread != null) {
+        if (thread.vthread != null) {
             thread = SubstrateUtil.cast(thread.vthread, Target_java_lang_Thread.class);
         }
         thread.scopedValueBindings = bindings;
@@ -593,21 +541,13 @@ boolean isTerminated() {
     static native long getNextThreadIdOffset();
 }
 
-@TargetClass(value = Thread.class, innerClass = "Builder")
-interface Target_java_lang_Thread_Builder {
-    @Alias
-    ThreadFactory factory();
-}
-
-@TargetClass(value = Thread.class, innerClass = {"Builder", "OfVirtual"})
-interface Target_java_lang_Thread_Builder_OfVirtual {
-}
-
 @TargetClass(value = Thread.class, innerClass = "Constants")
 final class Target_java_lang_Thread_Constants {
     // Checkstyle: stop
     @SuppressWarnings("removal") //
     @Alias static AccessControlContext NO_PERMISSIONS_ACC;
+
+    @Alias static ThreadGroup VTHREAD_GROUP;
     // Checkstyle: resume
 }
 
@@ -638,7 +578,7 @@ final class Target_java_lang_Thread_FieldHolder {
 }
 
 @Substitute//
-@TargetClass(value = Thread.class, innerClass = "ThreadIdentifiers", onlyWith = LoomJDK.class)
+@TargetClass(value = Thread.class, innerClass = "ThreadIdentifiers")
 final class Target_java_lang_Thread_ThreadIdentifiers {
     @Substitute//
     static long next() {
@@ -651,12 +591,3 @@ interface Target_sun_nio_ch_Interruptible {
     @Alias
     void interrupt(Thread t);
 }
-
-@TargetClass(className = "jdk.internal.misc.PreviewFeatures")
-final class Target_jdk_internal_misc_PreviewFeatures {
-    @Alias
-    static native boolean isEnabled();
-
-    @Alias
-    static native void ensureEnabled();
-}
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_VirtualThread.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_VirtualThread.java
index 4d82d085c9e3..3072bcdba5f1 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_VirtualThread.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_java_lang_VirtualThread.java
@@ -28,7 +28,6 @@
 import static com.oracle.svm.core.thread.VirtualThreadHelper.asThread;
 
 import java.util.Locale;
-import java.util.concurrent.Executor;
 
 import jdk.compiler.graal.serviceprovider.JavaVersionUtil;
 
@@ -41,14 +40,13 @@
 import com.oracle.svm.core.annotate.TargetClass;
 import com.oracle.svm.core.annotate.TargetElement;
 import com.oracle.svm.core.jdk.JDK21OrEarlier;
-import com.oracle.svm.core.jdk.LoomJDK;
 import com.oracle.svm.core.jfr.HasJfrSupport;
 import com.oracle.svm.core.jfr.SubstrateJVM;
 import com.oracle.svm.core.monitor.MonitorInflationCause;
 import com.oracle.svm.core.monitor.MonitorSupport;
 import com.oracle.svm.core.util.VMError;
 
-@TargetClass(className = "java.lang.VirtualThread", onlyWith = LoomJDK.class)
+@TargetClass(className = "java.lang.VirtualThread")
 public final class Target_java_lang_VirtualThread {
     // Checkstyle: stop
     @Alias static int NEW;
@@ -103,8 +101,6 @@ private void notifyJvmtiHideFrames(boolean hide) {
         // unimplemented (GR-45392)
     }
 
-    @Alias Executor scheduler;
-
     @Alias volatile Thread carrierThread;
 
     @Alias volatile Target_sun_nio_ch_Interruptible nioBlocker;
@@ -114,9 +110,6 @@ private void notifyJvmtiHideFrames(boolean hide) {
     @Alias
     public static native Target_jdk_internal_vm_ContinuationScope continuationScope();
 
-    @Alias
-    native boolean joinNanos(long nanos) throws InterruptedException;
-
     @Delete
     native StackTraceElement[] asyncGetStackTrace();
 
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_misc_Unsafe_JavaThreads.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_misc_Unsafe_JavaThreads.java
index e0787296b4f1..296702660329 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_misc_Unsafe_JavaThreads.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_misc_Unsafe_JavaThreads.java
@@ -77,10 +77,7 @@ void unpark(Object threadObj) {
             if (!(threadObj instanceof Thread)) {
                 throw new IllegalArgumentException("Unsafe.unpark(!(thread instanceof Thread))");
             }
-            Thread thread = (Thread) threadObj;
-            if (!VirtualThreads.isSupported() || !VirtualThreads.singleton().isVirtual(thread)) {
-                PlatformThreads.unpark(thread);
-            }
+            PlatformThreads.unpark((Thread) threadObj);
         }
     }
 }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_Continuation.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_Continuation.java
index 406fb1ee935e..85297c2e9ab1 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_Continuation.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_Continuation.java
@@ -33,33 +33,10 @@
 import com.oracle.svm.core.annotate.Substitute;
 import com.oracle.svm.core.annotate.TargetClass;
 import com.oracle.svm.core.jdk.InternalVMMethod;
-import com.oracle.svm.core.jdk.LoomJDK;
-import com.oracle.svm.core.jdk.NotLoomJDK;
 import com.oracle.svm.core.stack.JavaFrameAnchor;
 import com.oracle.svm.core.stack.JavaFrameAnchors;
-import com.oracle.svm.core.util.VMError;
 
-@TargetClass(className = "jdk.internal.vm.Continuation", onlyWith = NotLoomJDK.class)
-@Substitute
-@SuppressWarnings("unused")
-final class Target_jdk_internal_vm_Continuation__WithoutLoom {
-    @Substitute
-    static boolean yield(Target_jdk_internal_vm_ContinuationScope scope) {
-        throw VMError.shouldNotReachHereAtRuntime();
-    }
-
-    @Substitute
-    static void pin() {
-        throw VMError.shouldNotReachHereAtRuntime();
-    }
-
-    @Substitute
-    static void unpin() {
-        throw VMError.shouldNotReachHereAtRuntime();
-    }
-}
-
-@TargetClass(className = "jdk.internal.vm.Continuation", onlyWith = LoomJDK.class)
+@TargetClass(className = "jdk.internal.vm.Continuation")
 public final class Target_jdk_internal_vm_Continuation {
     @Substitute
     private static void registerNatives() {
@@ -69,7 +46,7 @@ private static void registerNatives() {
     Runnable target;
 
     @Inject @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.Reset)//
-    Continuation internal;
+    public Continuation internal;
 
     /** Treated as unsigned, located in native class {@code ContinuationEntry} in JDK code. */
     @Inject//
@@ -97,7 +74,7 @@ private static int isPinned0(Target_jdk_internal_vm_ContinuationScope scope) {
         if (cont != null) {
             while (true) {
                 if (cont.pinCount != 0) {
-                    return LoomSupport.FREEZE_PINNED_CS;
+                    return ContinuationSupport.FREEZE_PINNED_CS;
                 }
                 if (cont.getParent() == null) {
                     break;
@@ -109,10 +86,10 @@ private static int isPinned0(Target_jdk_internal_vm_ContinuationScope scope) {
             }
             JavaFrameAnchor anchor = JavaFrameAnchors.getFrameAnchor(CurrentIsolate.getCurrentThread());
             if (anchor.isNonNull() && cont.internal.getBaseSP().aboveThan(anchor.getLastJavaSP())) {
-                return LoomSupport.FREEZE_PINNED_NATIVE;
+                return ContinuationSupport.FREEZE_PINNED_NATIVE;
             }
         }
-        return LoomSupport.FREEZE_OK;
+        return ContinuationSupport.FREEZE_OK;
     }
 
     @Substitute
@@ -182,7 +159,7 @@ private void enter0() {
     }
 
     @Substitute
-    static void pin() {
+    public static void pin() {
         Target_java_lang_Thread carrier = JavaThreads.toTarget(Target_java_lang_Thread.currentCarrierThread());
         if (carrier.cont != null) {
             if (carrier.cont.pinCount + 1 == 0) { // unsigned arithmetic
@@ -193,7 +170,7 @@ static void pin() {
     }
 
     @Substitute
-    static void unpin() {
+    public static void unpin() {
         Target_java_lang_Thread carrier = JavaThreads.toTarget(Target_java_lang_Thread.currentCarrierThread());
         if (carrier.cont != null) {
             if (carrier.cont.pinCount == 0) {
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuations.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_ContinuationSupport.java
similarity index 57%
rename from substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuations.java
rename to substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_ContinuationSupport.java
index 12abecca827b..6c4226d983e5 100644
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Continuations.java
+++ b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Target_jdk_internal_vm_ContinuationSupport.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2023, 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
@@ -24,13 +24,24 @@
  */
 package com.oracle.svm.core.thread;
 
-import java.util.concurrent.ThreadFactory;
+import org.graalvm.nativeimage.Platform;
+import org.graalvm.nativeimage.Platforms;
+import org.graalvm.nativeimage.hosted.FieldValueTransformer;
 
-public final class Continuations {
-    public static ThreadFactory virtualThreadFactory() {
-        return VirtualThreads.singleton().createFactory();
-    }
+import com.oracle.svm.core.annotate.Alias;
+import com.oracle.svm.core.annotate.RecomputeFieldValue;
+import com.oracle.svm.core.annotate.TargetClass;
+
+@TargetClass(className = "jdk.internal.vm.ContinuationSupport")
+final class Target_jdk_internal_vm_ContinuationSupport {
+    @Alias @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.Custom, declClass = ComputeContinuationsSupported.class, isFinal = true) //
+    static boolean SUPPORTED;
+}
 
-    private Continuations() {
+@Platforms(Platform.HOSTED_ONLY.class)
+final class ComputeContinuationsSupported implements FieldValueTransformer {
+    @Override
+    public Object transform(Object receiver, Object originalValue) {
+        return ContinuationsFeature.isSupported();
     }
 }
diff --git a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/VirtualThreads.java b/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/VirtualThreads.java
deleted file mode 100644
index 0019093facfe..000000000000
--- a/substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/VirtualThreads.java
+++ /dev/null
@@ -1,76 +0,0 @@
-/*
- * Copyright (c) 2021, 2021, 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.  Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * 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 com.oracle.svm.core.thread;
-
-import java.util.concurrent.Executor;
-import java.util.concurrent.ThreadFactory;
-
-import jdk.compiler.graal.api.replacements.Fold;
-import org.graalvm.nativeimage.ImageSingletons;
-import org.graalvm.word.Pointer;
-
-import com.oracle.svm.core.stack.StackFrameVisitor;
-
-/** Operations on virtual threads. */
-public interface VirtualThreads {
-    @Fold
-    static VirtualThreads singleton() {
-        ContinuationsFeature.abortIfUnsupported();
-        return ImageSingletons.lookup(VirtualThreads.class);
-    }
-
-    @Fold
-    static boolean isSupported() {
-        return ImageSingletons.contains(VirtualThreads.class);
-    }
-
-    ThreadFactory createFactory();
-
-    boolean isVirtual(Thread thread);
-
-    boolean getAndClearInterrupt(Thread thread);
-
-    void join(Thread thread, long millis) throws InterruptedException;
-
-    void pinCurrent();
-
-    void unpinCurrent();
-
-    boolean isCurrentPinned();
-
-    Executor getScheduler(Thread thread);
-
-    void blockedOn(Target_sun_nio_ch_Interruptible b);
-
-    /**
-     * Virtual thread support must be able to support virtual thread stack frames from its carrier
-     * thread, therefore this method is also responsible for taking platform thread stack traces.
-     */
-    StackTraceElement[] getVirtualOrPlatformThreadStackTrace(boolean filterExceptions, Thread thread, Pointer callerSP);
-
-    void visitCurrentVirtualOrPlatformThreadStackFrames(Pointer callerSP, StackFrameVisitor visitor);
-
-    StackTraceElement[] getVirtualOrPlatformThreadStackTraceAtSafepoint(Thread thread, Pointer callerSP);
-}
diff --git a/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/SVMHost.java b/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/SVMHost.java
index b273ee4a5818..703c6c83cc89 100644
--- a/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/SVMHost.java
+++ b/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/SVMHost.java
@@ -118,7 +118,7 @@
 import com.oracle.svm.core.jdk.LambdaFormHiddenMethod;
 import com.oracle.svm.core.option.HostedOptionKey;
 import com.oracle.svm.core.option.SubstrateOptionsParser;
-import com.oracle.svm.core.thread.Continuation;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.util.HostedStringDeduplication;
 import com.oracle.svm.core.util.VMError;
 import com.oracle.svm.hosted.analysis.CustomTypeFieldHandler;
@@ -513,7 +513,7 @@ private static int computeHubType(AnalysisType type) {
                 return HubType.REFERENCE_INSTANCE;
             } else if (PodSupport.isPresent() && PodSupport.singleton().isPodClass(type.getJavaClass())) {
                 return HubType.POD_INSTANCE;
-            } else if (Continuation.isSupported() && type.getJavaClass() == StoredContinuation.class) {
+            } else if (ContinuationSupport.isSupported() && type.getJavaClass() == StoredContinuation.class) {
                 return HubType.STORED_CONTINUATION_INSTANCE;
             }
             assert !Target_java_lang_ref_Reference.class.isAssignableFrom(type.getJavaClass()) : "should not see substitution type here";
diff --git a/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/thread/HostedContinuationsFeature.java b/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/thread/HostedContinuationsFeature.java
index 8aafd2f8f18e..27c849ad7829 100644
--- a/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/thread/HostedContinuationsFeature.java
+++ b/substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/thread/HostedContinuationsFeature.java
@@ -31,6 +31,7 @@
 import com.oracle.svm.core.feature.AutomaticallyRegisteredFeature;
 import com.oracle.svm.core.feature.InternalFeature;
 import com.oracle.svm.core.thread.Continuation;
+import com.oracle.svm.core.thread.ContinuationSupport;
 import com.oracle.svm.core.thread.ContinuationsFeature;
 import com.oracle.svm.hosted.FeatureImpl;
 import com.oracle.svm.util.ReflectionUtil;
@@ -45,7 +46,7 @@ public List<Class<? extends Feature>> getRequiredFeatures() {
 
     @Override
     public void beforeAnalysis(BeforeAnalysisAccess access) {
-        if (Continuation.isSupported()) {
+        if (ContinuationSupport.isSupported()) {
             // limit the analysis optimizations performed on continuation return location
             ((FeatureImpl.BeforeAnalysisAccessImpl) access).registerOpaqueMethodReturn(ReflectionUtil.lookupMethod(Continuation.class, "enter1", boolean.class));
         }
diff --git a/substratevm/src/com.oracle.svm.test/src/com/oracle/svm/test/jfr/TestJavaLevelVirtualThreadEvents.java b/substratevm/src/com.oracle.svm.test/src/com/oracle/svm/test/jfr/TestJavaLevelVirtualThreadEvents.java
index 514ad614fca1..1810859671ab 100644
--- a/substratevm/src/com.oracle.svm.test/src/com/oracle/svm/test/jfr/TestJavaLevelVirtualThreadEvents.java
+++ b/substratevm/src/com.oracle.svm.test/src/com/oracle/svm/test/jfr/TestJavaLevelVirtualThreadEvents.java
@@ -38,7 +38,7 @@
 
 import org.junit.Test;
 
-import com.oracle.svm.core.thread.VirtualThreads;
+import com.oracle.svm.core.thread.Target_jdk_internal_vm_Continuation;
 import com.oracle.svm.test.jfr.events.StringEvent;
 
 import jdk.jfr.Recording;
@@ -65,7 +65,7 @@ public void test() throws Throwable {
                  * Pinning the current thread will result in a VirtualThreadPinned event when it
                  * attempts to yield at the subsequent Thread.sleep() call.
                  */
-                VirtualThreads.singleton().pinCurrent();
+                Target_jdk_internal_vm_Continuation.pin();
                 Thread.sleep(50);
 
                 com.oracle.svm.test.jfr.events.StringEvent stringEvent = new StringEvent();