8304919: Implementation of Virtual Threads

Reviewed-by: lmesnik, cjplummer, psandoz, mchung, sspitsyn, jpai

src/hotspot/share/classfile/javaClasses.cpp

@@ -1498,11 +1498,9 @@ JavaThreadStatus java_lang_Thread_FieldHolder::get_thread_status(oop holder) {
 
 
 int java_lang_Thread_Constants::_static_VTHREAD_GROUP_offset = 0;
-int java_lang_Thread_Constants::_static_NOT_SUPPORTED_CLASSLOADER_offset = 0;
 
 #define THREAD_CONSTANTS_STATIC_FIELDS_DO(macro) \
-  macro(_static_VTHREAD_GROUP_offset,             k, "VTHREAD_GROUP",             threadgroup_signature, true); \
-  macro(_static_NOT_SUPPORTED_CLASSLOADER_offset, k, "NOT_SUPPORTED_CLASSLOADER", classloader_signature, true);
+  macro(_static_VTHREAD_GROUP_offset,             k, "VTHREAD_GROUP",             threadgroup_signature, true);
 
 void java_lang_Thread_Constants::compute_offsets() {
   assert(_static_VTHREAD_GROUP_offset == 0, "offsets should be initialized only once");
@@ -1523,11 +1521,6 @@ oop java_lang_Thread_Constants::get_VTHREAD_GROUP() {
   return base->obj_field(_static_VTHREAD_GROUP_offset);
 }
 
-oop java_lang_Thread_Constants::get_NOT_SUPPORTED_CLASSLOADER() {
-  InstanceKlass* k = vmClasses::Thread_Constants_klass();
-  oop base = k->static_field_base_raw();
-  return base->obj_field(_static_NOT_SUPPORTED_CLASSLOADER_offset);
-}
 
 int java_lang_Thread::_holder_offset;
 int java_lang_Thread::_name_offset;

src/hotspot/share/classfile/javaClasses.hpp

@@ -475,7 +475,6 @@ class java_lang_Thread_Constants : AllStatic {
 
  public:
   static oop get_VTHREAD_GROUP();
-  static oop get_NOT_SUPPORTED_CLASSLOADER();
 
   friend class JavaClasses;
 };

src/hotspot/share/prims/jni.cpp

@@ -102,7 +102,7 @@
 #include "jfr/jfr.hpp"
 #endif
 
-static jint CurrentVersion = JNI_VERSION_20;
+static jint CurrentVersion = JNI_VERSION_21;
 
 #if defined(_WIN32) && !defined(USE_VECTORED_EXCEPTION_HANDLING)
 extern LONG WINAPI topLevelExceptionFilter(_EXCEPTION_POINTERS* );

src/hotspot/share/prims/jvmti.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="ISO-8859-1"?>
 <?xml-stylesheet type="text/xsl" href="jvmti.xsl"?>
 <!--
- Copyright (c) 2002, 2022, Oracle and/or its affiliates. All rights reserved.
+ Copyright (c) 2002, 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
@@ -1724,13 +1724,9 @@ jvmtiEnv *jvmti;
       </errors>
     </function>
 
-    <function id="SuspendAllVirtualThreads" num="118" since="19">
+    <function id="SuspendAllVirtualThreads" num="118" since="21">
       <synopsis>Suspend All Virtual Threads</synopsis>
       <description>
-        <b> SuspendAllVirtualThreads is a preview API of the Java platform. </b>
-        <i>Preview features may be removed in a future release, or upgraded to
-        permanent features of the Java platform.</i>
-        <p/>
         Suspend all virtual threads except those in the exception list.
         Virtual threads that are currently suspended do not change state.
         Virtual threads may be resumed with
@@ -1850,13 +1846,9 @@ jvmtiEnv *jvmti;
       </errors>
     </function>
 
-   <function id="ResumeAllVirtualThreads" num="119" since="19">
+   <function id="ResumeAllVirtualThreads" num="119" since="21">
       <synopsis>Resume All Virtual Threads</synopsis>
       <description>
-        <b> ResumeAllVirtualThreads is a preview API of the Java platform. </b>
-        <i>Preview features may be removed in a future release, or upgraded to
-        permanent features of the Java platform.</i>
-        <p/>
         Resume all virtual threads except those in the exception list.
         Virtual threads that are currently resumed do not change state.
         Virtual threads may be suspended with
@@ -10650,12 +10642,8 @@ myInit() {
           called and <eventlink id="SampledObjectAlloc"></eventlink> events can be generated.
         </description>
       </capabilityfield>
-      <capabilityfield id="can_support_virtual_threads" since="19">
+      <capabilityfield id="can_support_virtual_threads" since="21">
         <description>
-          <b> can_support_virtual_threads is a preview API of the Java platform. </b>
-          <i>Preview features may be removed in a future release, or upgraded to
-          permanent features of the Java platform.</i>
-          <p/>
           Can support virtual threads.
           If this capability is enabled then the following functions can be called:
           <functionlink id="SuspendAllVirtualThreads"></functionlink>,
@@ -13038,12 +13026,8 @@ myInit() {
   </event>
 
  <event label="Virtual Thread Start"
-         id="VirtualThreadStart" const="JVMTI_EVENT_VIRTUAL_THREAD_START" filtered="thread" num="87" phase="start" since="19">
+         id="VirtualThreadStart" const="JVMTI_EVENT_VIRTUAL_THREAD_START" filtered="thread" num="87" phase="start" since="21">
     <description>
-      <b> VirtualThreadStart is a preview API of the Java platform. </b>
-      <i>Preview features may be removed in a future release, or upgraded to
-      permanent features of the Java platform.</i>
-      <p/>
       A virtual thread start event is generated before its initial method executes.
       <p/>
       The event is sent on the newly started <paramlink id="virtual_thread"></paramlink>.
@@ -13071,12 +13055,8 @@ myInit() {
   </event>
 
   <event label="Virtual Thread End"
-         id="VirtualThreadEnd" const="JVMTI_EVENT_VIRTUAL_THREAD_END" filtered="thread" num="88" phase="start" since="19">
+         id="VirtualThreadEnd" const="JVMTI_EVENT_VIRTUAL_THREAD_END" filtered="thread" num="88" phase="start" since="21">
     <description>
-      <b> VirtualThreadEnd is a preview API of the Java platform. </b>
-      <i>Preview features may be removed in a future release, or upgraded to
-      permanent features of the Java platform.</i>
-      <p/>
       A virtual thread end event is generated after its initial method has finished execution.
       <p/>
       The event is sent on the terminating <paramlink id="virtual_thread"></paramlink>.

src/hotspot/share/prims/jvmtiEnv.cpp

@@ -1311,13 +1311,6 @@ JvmtiEnv::GetThreadInfo(jthread thread, jvmtiThreadInfo* info_ptr) {
   }
 
   oop loader = java_lang_Thread::context_class_loader(thread_obj());
-  if (loader != nullptr) {
-    // Do the same as Thread.getContextClassLoader and set context_class_loader to be
-    // the system class loader when the field value is the "not supported" placeholder.
-    if (loader == java_lang_Thread_Constants::get_NOT_SUPPORTED_CLASSLOADER()) {
-      loader = SystemDictionary::java_system_loader();
-    }
-  }
   context_class_loader = Handle(current_thread, loader);
 
   { const char *n;

src/hotspot/share/prims/jvmtiH.xsl

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!--
- Copyright (c) 2002, 2020, Oracle and/or its affiliates. All rights reserved.
+ Copyright (c) 2002, 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
@@ -116,6 +116,7 @@ enum {
     JVMTI_VERSION_9   = 0x30090000,
     JVMTI_VERSION_11  = 0x300B0000,
     JVMTI_VERSION_19  = 0x30130000,
+    JVMTI_VERSION_21  = 0x30150000,
 
     JVMTI_VERSION = 0x30000000 + (</xsl:text>
   <xsl:value-of select="$majorversion"/>

src/hotspot/share/prims/jvmtiTagMap.cpp

@@ -1141,7 +1141,6 @@ void JvmtiTagMap::iterate_through_heap(jint heap_filter,
                                        const void* user_data)
 {
   // EA based optimizations on tagged objects are already reverted.
-  // disabled if vritual threads are enabled with --enable-preview
   EscapeBarrier eb(!(heap_filter & JVMTI_HEAP_FILTER_UNTAGGED), JavaThread::current());
   eb.deoptimize_objects_all_threads();
 

src/hotspot/share/prims/stackwalk.cpp

@@ -173,6 +173,12 @@ int StackWalk::fill_in_frames(jlong mode, BaseFrameStream& stream,
 
   int frames_decoded = 0;
   for (; !stream.at_end(); stream.next()) {
+    if (stream.continuation() != nullptr && stream.continuation() != stream.reg_map()->cont()) {
+      // The code in StackStreamFactory.java has failed to set the continuation because frameBuffer.isAtBottom()
+      // returns false if the end of a continuation falls precisely at the end of the batch.
+      // By breaking here, we're signalling the Java code to set the continuation to the parent.
+      break;
+    }
     assert(stream.continuation() == nullptr || stream.continuation() == stream.reg_map()->cont(), "");
     Method* method = stream.method();
 
@@ -190,6 +196,8 @@ int StackWalk::fill_in_frames(jlong mode, BaseFrameStream& stream,
           method->print_short_name(&ls);
           ls.cr();
         }
+        // We end a batch on continuation bottom to let the Java side skip top frames of the next one
+        if (stream.continuation() != nullptr && method->intrinsic_id() == vmIntrinsics::_Continuation_enter) break;
         continue;
       }
     }
@@ -576,7 +584,7 @@ jint StackWalk::fetchNextBatch(Handle stackStream, jlong mode, jlong magic,
     if (!stream.at_end()) {
       int n = fill_in_frames(mode, stream, frame_count, start_index,
                              frames_array, end_index, CHECK_0);
-      if (n < 1) {
+      if (n < 1 && !skip_hidden_frames(mode)) {
         THROW_MSG_(vmSymbols::java_lang_InternalError(), "doStackWalk: later decode failed", 0L);
       }
       return end_index;

src/hotspot/share/runtime/threads.cpp

@@ -1159,6 +1159,7 @@ jboolean Threads::is_supported_jni_version(jint version) {
   if (version == JNI_VERSION_10) return JNI_TRUE;
   if (version == JNI_VERSION_19) return JNI_TRUE;
   if (version == JNI_VERSION_20) return JNI_TRUE;
+  if (version == JNI_VERSION_21) return JNI_TRUE;
   return JNI_FALSE;
 }
 

src/java.base/share/classes/java/lang/System.java

@@ -89,7 +89,6 @@
 import jdk.internal.vm.annotation.ForceInline;
 import jdk.internal.vm.annotation.IntrinsicCandidate;
 import jdk.internal.vm.annotation.Stable;
-import jdk.internal.vm.annotation.ChangesCurrentThread;
 import sun.nio.fs.DefaultFileSystemProvider;
 import sun.reflect.annotation.AnnotationType;
 import sun.nio.ch.Interruptible;
@@ -2567,17 +2566,9 @@ public Thread currentCarrierThread() {
                 return Thread.currentCarrierThread();
             }
 
-            @ChangesCurrentThread
             public <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
-                Thread thread = Thread.currentThread();
-                if (thread.isVirtual()) {
-                    Thread carrier = Thread.currentCarrierThread();
-                    carrier.setCurrentThread(carrier);
-                    try {
-                        return task.call();
-                    } finally {
-                        carrier.setCurrentThread(thread);
-                    }
+                if (Thread.currentThread() instanceof VirtualThread vthread) {
+                    return vthread.executeOnCarrierThread(task);
                 } else {
                     return task.call();
                 }