changeset 52311:274ba8fbd96d

8212958: Allow Klass::_subklass and _next_sibling to have unloaded classes Summary: Don't return unloaded klasses. Make sure access is protected by Compile_lock. Reviewed-by: eosterlund, dlong
author coleenp
date Mon, 29 Oct 2018 10:21:34 -0400
parents a8e43293b4c4
children 5b9c8d77a9fe
files src/hotspot/share/ci/ciInstanceKlass.cpp src/hotspot/share/ci/ciInstanceKlass.hpp src/hotspot/share/jfr/jni/jfrGetAllEventClasses.cpp src/hotspot/share/jvmci/jvmciCompilerToVM.cpp src/hotspot/share/memory/universe.cpp src/hotspot/share/memory/universe.hpp src/hotspot/share/oops/instanceKlass.cpp src/hotspot/share/oops/instanceKlass.hpp src/hotspot/share/oops/klass.cpp src/hotspot/share/oops/klass.hpp src/hotspot/share/runtime/mutex.cpp src/hotspot/share/utilities/vmError.cpp test/hotspot/jtreg/runtime/ClassUnload/UnloadInterfaceTest.java test/hotspot/jtreg/runtime/ClassUnload/test/ImplementorClass.java test/hotspot/jtreg/runtime/ClassUnload/test/Interface.java test/hotspot/jtreg/runtime/testlibrary/ClassUnloadCommon.java
diffstat 16 files changed, 325 insertions(+), 97 deletions(-) [+]
line wrap: on
line diff
--- a/src/hotspot/share/ci/ciInstanceKlass.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/ci/ciInstanceKlass.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -57,7 +57,7 @@
   AccessFlags access_flags = ik->access_flags();
   _flags = ciFlags(access_flags);
   _has_finalizer = access_flags.has_finalizer();
-  _has_subklass = ik->subklass() != NULL;
+  _has_subklass = flags().is_final() ? subklass_false : subklass_unknown;
   _init_state = ik->init_state();
   _nonstatic_field_size = ik->nonstatic_field_size();
   _has_nonstatic_fields = ik->has_nonstatic_fields();
@@ -146,9 +146,10 @@
 // ciInstanceKlass::compute_shared_has_subklass
 bool ciInstanceKlass::compute_shared_has_subklass() {
   GUARDED_VM_ENTRY(
+    MutexLocker ml(Compile_lock);
     InstanceKlass* ik = get_instanceKlass();
-    _has_subklass = ik->subklass() != NULL;
-    return _has_subklass;
+    _has_subklass = ik->subklass() != NULL ? subklass_true : subklass_false;
+    return _has_subklass == subklass_true;
   )
 }
 
@@ -374,6 +375,7 @@
   if (!is_abstract())   return NULL; // Only applies to abstract classes.
   if (!has_subklass())  return NULL; // Must have at least one subklass.
   VM_ENTRY_MARK;
+  MutexLocker ml(Compile_lock);
   InstanceKlass* ik = get_instanceKlass();
   Klass* up = ik->up_cast_abstract();
   assert(up->is_instance_klass(), "must be InstanceKlass");
@@ -388,6 +390,7 @@
 bool ciInstanceKlass::has_finalizable_subclass() {
   if (!is_loaded())     return true;
   VM_ENTRY_MARK;
+  MutexLocker ml(Compile_lock);
   return Dependencies::find_finalizable_subclass(get_instanceKlass()) != NULL;
 }
 
@@ -577,7 +580,7 @@
   if (is_shared()) {
     return is_final();  // approximately correct
   } else {
-    return !_has_subklass && (nof_implementors() == 0);
+    return !has_subklass() && (nof_implementors() == 0);
   }
 }
 
--- a/src/hotspot/share/ci/ciInstanceKlass.hpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/ci/ciInstanceKlass.hpp	Mon Oct 29 10:21:34 2018 -0400
@@ -44,13 +44,15 @@
   friend class ciField;
 
 private:
+  enum SubklassValue { subklass_unknown, subklass_false, subklass_true };
+
   jobject                _loader;
   jobject                _protection_domain;
 
   InstanceKlass::ClassState _init_state;           // state of class
   bool                   _is_shared;
   bool                   _has_finalizer;
-  bool                   _has_subklass;
+  SubklassValue          _has_subklass;
   bool                   _has_nonstatic_fields;
   bool                   _has_nonstatic_concrete_methods;
   bool                   _is_unsafe_anonymous;
@@ -139,14 +141,15 @@
     return _has_finalizer; }
   bool                   has_subklass()   {
     assert(is_loaded(), "must be loaded");
-    if (_is_shared && !_has_subklass) {
+    if (_has_subklass == subklass_unknown ||
+        (_is_shared && _has_subklass == subklass_false)) {
       if (flags().is_final()) {
         return false;
       } else {
         return compute_shared_has_subklass();
       }
     }
-    return _has_subklass;
+    return _has_subklass == subklass_true;
   }
   jint                   size_helper()  {
     return (Klass::layout_helper_size_in_bytes(layout_helper())
--- a/src/hotspot/share/jfr/jni/jfrGetAllEventClasses.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/jfr/jni/jfrGetAllEventClasses.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -90,7 +90,6 @@
   DEBUG_ONLY(JfrJavaSupport::check_java_thread_in_vm(thread));
 
   Stack<const Klass*, mtTracing> mark_stack;
-  MutexLocker ml(Compile_lock, thread);
   mark_stack.push(event_klass->subklass());
 
   while (!mark_stack.is_empty()) {
@@ -146,16 +145,19 @@
   assert(klass != NULL, "invariant");
   assert(JdkJfrEvent::is(klass), "invariant");
 
-  if (klass->subklass() == NULL) {
-    return empty_java_util_arraylist;
-  }
-
   ResourceMark rm(THREAD);
   GrowableArray<const void*> event_subklasses(THREAD, initial_size_growable_array);
-  fill_klasses(event_subklasses, klass, THREAD);
+  {
+    MutexLocker cl(Compile_lock);
+    if (klass->subklass() == NULL) {
+      return empty_java_util_arraylist;
+    }
 
-  if (event_subklasses.is_empty()) {
-    return empty_java_util_arraylist;
+    fill_klasses(event_subklasses, klass, THREAD);
+
+    if (event_subklasses.is_empty()) {
+      return empty_java_util_arraylist;
+    }
   }
 
   transform_klasses_to_local_jni_handles(event_subklasses, THREAD);
--- a/src/hotspot/share/jvmci/jvmciCompilerToVM.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/jvmci/jvmciCompilerToVM.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -627,6 +627,7 @@
 C2V_VMENTRY(jboolean, hasFinalizableSubclass,(JNIEnv *, jobject, jobject jvmci_type))
   Klass* klass = CompilerToVM::asKlass(jvmci_type);
   assert(klass != NULL, "method must not be called for primitive types");
+  MutexLocker ml(Compile_lock);
   return Dependencies::find_finalizable_subclass(klass) != NULL;
 C2V_END
 
--- a/src/hotspot/share/memory/universe.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/memory/universe.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -531,10 +531,6 @@
 #undef assert_pll_locked
 #undef assert_pll_ownership
 
-// initialize_vtable could cause gc if
-// 1) we specified true to initialize_vtable and
-// 2) this ran after gc was enabled
-// In case those ever change we use handles for oops
 void Universe::reinitialize_vtable_of(Klass* ko, TRAPS) {
   // init vtable of k and all subclasses
   ko->vtable().initialize_vtable(false, CHECK);
@@ -547,6 +543,16 @@
   }
 }
 
+void Universe::reinitialize_vtables(TRAPS) {
+  // The vtables are initialized by starting at java.lang.Object and
+  // initializing through the subclass links, so that the super
+  // classes are always initialized first.  The subclass links
+  // require the Compile_lock.
+  MutexLocker cl(Compile_lock);
+  Klass* ok = SystemDictionary::Object_klass();
+  Universe::reinitialize_vtable_of(ok, THREAD);
+}
+
 
 void initialize_itable_for_klass(InstanceKlass* k, TRAPS) {
   k->itable().initialize_itable(false, CHECK);
@@ -964,9 +970,7 @@
   { ResourceMark rm;
     Interpreter::initialize();      // needed for interpreter entry points
     if (!UseSharedSpaces) {
-      HandleMark hm(THREAD);
-      Klass* ok = SystemDictionary::Object_klass();
-      Universe::reinitialize_vtable_of(ok, CHECK_false);
+      Universe::reinitialize_vtables(CHECK_false);
       Universe::reinitialize_itables(CHECK_false);
     }
   }
--- a/src/hotspot/share/memory/universe.hpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/memory/universe.hpp	Mon Oct 29 10:21:34 2018 -0400
@@ -219,6 +219,7 @@
   static void fixup_mirrors(TRAPS);
 
   static void reinitialize_vtable_of(Klass* k, TRAPS);
+  static void reinitialize_vtables(TRAPS);
   static void reinitialize_itables(TRAPS);
   static void compute_base_vtable_size();             // compute vtable size of class Object
 
--- a/src/hotspot/share/oops/instanceKlass.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/oops/instanceKlass.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -1054,16 +1054,28 @@
   }
 }
 
-Klass* InstanceKlass::implementor() const {
+Klass* InstanceKlass::implementor(bool log) const {
   assert_locked_or_safepoint(Compile_lock);
   Klass** k = adr_implementor();
   if (k == NULL) {
     return NULL;
   } else {
-    return *k;
+    Klass* kls = *k;
+    if (kls != NULL && !kls->is_loader_alive()) {
+      if (log) {
+        if (log_is_enabled(Trace, class, unload)) {
+          ResourceMark rm;
+          log_trace(class, unload)("unlinking class (implementor): %s", kls->external_name());
+        }
+      }
+      return NULL;  // don't return unloaded class
+    } else {
+      return kls;
+    }
   }
 }
 
+
 void InstanceKlass::set_implementor(Klass* k) {
   assert_lock_strong(Compile_lock);
   assert(is_interface(), "not interface");
@@ -2139,20 +2151,15 @@
 }
 
 void InstanceKlass::clean_implementors_list() {
+  assert_locked_or_safepoint(Compile_lock);
   assert(is_loader_alive(), "this klass should be live");
   if (is_interface()) {
-    if (ClassUnloading) {
-      Klass* impl = implementor();
-      if (impl != NULL) {
-        if (!impl->is_loader_alive()) {
-          // remove this guy
-          Klass** klass = adr_implementor();
-          assert(klass != NULL, "null klass");
-          if (klass != NULL) {
-            *klass = NULL;
-          }
-        }
-      }
+    assert (ClassUnloading, "only called for ClassUnloading");
+    Klass* impl = implementor(true);
+    if (impl == NULL) {
+      // NULL this field, might be an unloaded klass or NULL
+      Klass** klass = adr_implementor();
+      *klass = NULL;
     }
   }
 }
@@ -3080,28 +3087,29 @@
   st->print(BULLET"name:              "); name()->print_value_on(st);             st->cr();
   st->print(BULLET"super:             "); Metadata::print_value_on_maybe_null(st, super()); st->cr();
   st->print(BULLET"sub:               ");
-  Klass* sub = subklass();
-  int n;
-  for (n = 0; sub != NULL; n++, sub = sub->next_sibling()) {
-    if (n < MaxSubklassPrintSize) {
-      sub->print_value_on(st);
-      st->print("   ");
+  {
+    MutexLocker ml(Compile_lock);
+    Klass* sub = subklass();
+    int n;
+    for (n = 0; sub != NULL; n++, sub = sub->next_sibling()) {
+      if (n < MaxSubklassPrintSize) {
+        sub->print_value_on(st);
+        st->print("   ");
+      }
+    }
+    if (n >= MaxSubklassPrintSize) st->print("(" INTX_FORMAT " more klasses...)", n - MaxSubklassPrintSize);
+    st->cr();
+
+    if (is_interface()) {
+      st->print_cr(BULLET"nof implementors:  %d", nof_implementors());
+      if (nof_implementors() == 1) {
+        st->print_cr(BULLET"implementor:    ");
+        st->print("   ");
+        implementor()->print_value_on(st);
+        st->cr();
+      }
     }
   }
-  if (n >= MaxSubklassPrintSize) st->print("(" INTX_FORMAT " more klasses...)", n - MaxSubklassPrintSize);
-  st->cr();
-
-  if (is_interface()) {
-    MutexLocker ml(Compile_lock);
-    st->print_cr(BULLET"nof implementors:  %d", nof_implementors());
-    if (nof_implementors() == 1) {
-      st->print_cr(BULLET"implementor:    ");
-      st->print("   ");
-      implementor()->print_value_on(st);
-      st->cr();
-    }
-  }
-
   st->print(BULLET"arrays:            "); Metadata::print_value_on_maybe_null(st, array_klasses()); st->cr();
   st->print(BULLET"methods:           "); methods()->print_value_on(st);                  st->cr();
   if (Verbose || WizardMode) {
@@ -3483,26 +3491,30 @@
     vtable().verify(st);
   }
 
-  // Verify first subklass
-  if (subklass() != NULL) {
-    guarantee(subklass()->is_klass(), "should be klass");
+  // This is called from add_to_hierarchy when the Compile_lock is owned.
+  {
+    MutexLockerEx ml(Compile_lock->owned_by_self() ? NULL : Compile_lock);
+    // Verify first subklass
+    if (subklass() != NULL) {
+      guarantee(subklass()->is_klass(), "should be klass");
+    }
+
+    // Verify siblings
+    Klass* super = this->super();
+    Klass* sib = next_sibling();
+    if (sib != NULL) {
+      if (sib == this) {
+        fatal("subclass points to itself " PTR_FORMAT, p2i(sib));
+      }
+
+      guarantee(sib->is_klass(), "should be klass");
+      guarantee(sib->super() == super, "siblings should have same superklass");
+    }
+
+    // Verify implementor fields requires the Compile_lock,
+    // but this is sometimes called inside a safepoint, so don't verify.
   }
 
-  // Verify siblings
-  Klass* super = this->super();
-  Klass* sib = next_sibling();
-  if (sib != NULL) {
-    if (sib == this) {
-      fatal("subclass points to itself " PTR_FORMAT, p2i(sib));
-    }
-
-    guarantee(sib->is_klass(), "should be klass");
-    guarantee(sib->super() == super, "siblings should have same superklass");
-  }
-
-  // Verify implementor fields requires the Compile_lock, but this is sometimes
-  // called inside a safepoint, so don't verify.
-
   // Verify local interfaces
   if (local_interfaces()) {
     Array<InstanceKlass*>* local_interfaces = this->local_interfaces();
--- a/src/hotspot/share/oops/instanceKlass.hpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/oops/instanceKlass.hpp	Mon Oct 29 10:21:34 2018 -0400
@@ -1007,7 +1007,7 @@
 #endif
 
   // Access to the implementor of an interface.
-  Klass* implementor() const;
+  Klass* implementor(bool log = false) const;
   void set_implementor(Klass* k);
   int  nof_implementors() const;
   void add_implementor(Klass* k);  // k is a new class that implements this interface
--- a/src/hotspot/share/oops/klass.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/oops/klass.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -117,7 +117,7 @@
   Klass *r = this;
   while( r->is_abstract() ) {   // Receiver is abstract?
     Klass *s = r->subklass();   // Check for exactly 1 subklass
-    if( !s || s->next_sibling() ) // Oops; wrong count; give up
+    if (s == NULL || s->next_sibling() != NULL) // Oops; wrong count; give up
       return this;              // Return 'this' as a no-progress flag
     r = s;                    // Loop till find concrete class
   }
@@ -358,11 +358,49 @@
 }
 
 
+// superklass links
 InstanceKlass* Klass::superklass() const {
   assert(super() == NULL || super()->is_instance_klass(), "must be instance klass");
   return _super == NULL ? NULL : InstanceKlass::cast(_super);
 }
 
+// subklass links.  Used by the compiler (and vtable initialization)
+// May be cleaned concurrently, so must use the Compile_lock.
+// The log parameter is for clean_weak_klass_links to report unlinked classes.
+Klass* Klass::subklass(bool log) const {
+  assert_locked_or_safepoint(Compile_lock);
+  for (Klass* chain = _subklass; chain != NULL;
+       chain = chain->_next_sibling) {
+    if (chain->is_loader_alive()) {
+      return chain;
+    } else if (log) {
+      if (log_is_enabled(Trace, class, unload)) {
+        ResourceMark rm;
+        log_trace(class, unload)("unlinking class (subclass): %s", chain->external_name());
+      }
+    }
+  }
+  return NULL;
+}
+
+Klass* Klass::next_sibling(bool log) const {
+  assert_locked_or_safepoint(Compile_lock);
+  for (Klass* chain = _next_sibling; chain != NULL;
+       chain = chain->_next_sibling) {
+    // Only return alive klass, there may be stale klass
+    // in this chain if cleaned concurrently.
+    if (chain->is_loader_alive()) {
+      return chain;
+    } else if (log) {
+      if (log_is_enabled(Trace, class, unload)) {
+        ResourceMark rm;
+        log_trace(class, unload)("unlinking class (sibling): %s", chain->external_name());
+      }
+    }
+  }
+  return NULL;
+}
+
 void Klass::set_subklass(Klass* s) {
   assert(s != this, "sanity check");
   _subklass = s;
@@ -374,6 +412,7 @@
 }
 
 void Klass::append_to_sibling_list() {
+  assert_locked_or_safepoint(Compile_lock);
   debug_only(verify();)
   // add ourselves to superklass' subklass list
   InstanceKlass* super = superklass();
@@ -381,6 +420,7 @@
   assert((!super->is_interface()    // interfaces cannot be supers
           && (super->superklass() == NULL || !is_interface())),
          "an interface can only be a subklass of Object");
+
   Klass* prev_first_subklass = super->subklass();
   if (prev_first_subklass != NULL) {
     // set our sibling to be the superklass' previous first subklass
@@ -396,6 +436,7 @@
 }
 
 void Klass::clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses) {
+  assert_locked_or_safepoint(Compile_lock);
   if (!ClassUnloading || !unloading_occurred) {
     return;
   }
@@ -410,30 +451,14 @@
     assert(current->is_loader_alive(), "just checking, this should be live");
 
     // Find and set the first alive subklass
-    Klass* sub = current->subklass();
-    while (sub != NULL && !sub->is_loader_alive()) {
-#ifndef PRODUCT
-      if (log_is_enabled(Trace, class, unload)) {
-        ResourceMark rm;
-        log_trace(class, unload)("unlinking class (subclass): %s", sub->external_name());
-      }
-#endif
-      sub = sub->next_sibling();
-    }
+    Klass* sub = current->subklass(true);
     current->set_subklass(sub);
     if (sub != NULL) {
       stack.push(sub);
     }
 
     // Find and set the first alive sibling
-    Klass* sibling = current->next_sibling();
-    while (sibling != NULL && !sibling->is_loader_alive()) {
-      if (log_is_enabled(Trace, class, unload)) {
-        ResourceMark rm;
-        log_trace(class, unload)("[Unlinking class (sibling) %s]", sibling->external_name());
-      }
-      sibling = sibling->next_sibling();
-    }
+    Klass* sibling = current->next_sibling(true);
     current->set_next_sibling(sibling);
     if (sibling != NULL) {
       stack.push(sibling);
--- a/src/hotspot/share/oops/klass.hpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/oops/klass.hpp	Mon Oct 29 10:21:34 2018 -0400
@@ -284,8 +284,9 @@
   // Use InstanceKlass::contains_field_offset to classify field offsets.
 
   // sub/superklass links
-  Klass* subklass() const              { return _subklass; }
-  Klass* next_sibling() const          { return _next_sibling; }
+  Klass* subklass(bool log = false) const;
+  Klass* next_sibling(bool log = false) const;
+
   InstanceKlass* superklass() const;
   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
 
--- a/src/hotspot/share/runtime/mutex.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/runtime/mutex.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -876,7 +876,7 @@
 #endif // CHECK_UNHANDLED_OOPS
 
   debug_only(check_prelock_state(Self, StrictSafepointChecks));
-  assert(_owner != Self, "invariant");
+  assert(_owner != Self, "this lock %s is already held by this thread", name());
   assert(_OnDeck != Self->_MutexEvent, "invariant");
 
   if (TryFast()) {
--- a/src/hotspot/share/utilities/vmError.cpp	Mon Oct 29 08:38:59 2018 -0400
+++ b/src/hotspot/share/utilities/vmError.cpp	Mon Oct 29 10:21:34 2018 -0400
@@ -1467,6 +1467,8 @@
     log.set_fd(-1);
   }
 
+  // Error handling generates replay data without the compile lock.
+  NOT_PRODUCT(FlagSetting fs(IgnoreLockingAssertions, true));
   static bool skip_replay = ReplayCompiles; // Do not overwrite file during replay
   if (DumpReplayDataOnError && _thread && _thread->is_Compiler_thread() && !skip_replay) {
     skip_replay = true;
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/runtime/ClassUnload/UnloadInterfaceTest.java	Mon Oct 29 10:21:34 2018 -0400
@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2018, 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.
+ *
+ * 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.
+ */
+
+/*
+ * @test UnloadInterfaceTest
+ * @requires vm.opt.final.ClassUnloading
+ * @modules java.base/jdk.internal.misc
+ * @library /runtime/testlibrary /test/lib
+ * @compile test/Interface.java
+ * @compile test/ImplementorClass.java
+ * @build sun.hotspot.WhiteBox
+ * @run driver ClassFileInstaller sun.hotspot.WhiteBox
+ *                              sun.hotspot.WhiteBox$WhiteBoxPermission
+ * @run main/othervm -Xbootclasspath/a:. -Xmn8m -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -Xlog:class+unload=trace UnloadInterfaceTest
+ */
+import sun.hotspot.WhiteBox;
+import test.Interface;
+import java.lang.ClassLoader;
+
+/**
+ * Test that verifies that class unloaded removes the implementor from its the interface that it implements
+ * via logging.
+ * [1.364s][info][class,unload] unloading class test.ImplementorClass 0x00000008000a2840
+ * [1.366s][trace][class,unload] unlinking class (subclass): test.ImplementorClass
+ * [1.366s][trace][class,unload] unlinking class (implementor): test.ImplementorClass
+ */
+public class UnloadInterfaceTest {
+    private static String className = "test.ImplementorClass";
+    private static String interfaceName = "test.Interface";
+
+    static class LoaderToUnload extends ClassLoader {
+       ClassLoader myParent;
+        public Class loadClass(String name) throws ClassNotFoundException {
+            if (name.contains(className)) {
+              System.out.println("className found " + className);
+              byte[] data = ClassUnloadCommon.getClassData(name);
+              return defineClass(name, data, 0, data.length);
+            } else {
+              return myParent.loadClass(name);
+            }
+        }
+        public LoaderToUnload(ClassLoader parent) {
+            super();
+            myParent = parent;
+        }
+    }
+
+    public static void main(String... args) throws Exception {
+       run();
+    }
+
+    private static void run() throws Exception {
+        final WhiteBox wb = WhiteBox.getWhiteBox();
+
+        ClassUnloadCommon.failIf(wb.isClassAlive(className), "is not expected to be alive yet");
+
+        // Load interface Class with one class loader.
+        ClassLoader icl = ClassUnloadCommon.newClassLoader();
+        Class<?> ic = icl.loadClass(interfaceName);
+
+        ClassLoader cl = new LoaderToUnload(icl);
+        Class<?> c = cl.loadClass(className);
+        Object o = c.newInstance();
+
+        ClassUnloadCommon.failIf(!wb.isClassAlive(className), "should be live here");
+        ClassUnloadCommon.failIf(!wb.isClassAlive(interfaceName), "should be live here");
+
+        cl = null; c = null; o = null;
+        ClassUnloadCommon.triggerUnloading();
+        ClassUnloadCommon.failIf(wb.isClassAlive(className), "should have been unloaded");
+        ClassUnloadCommon.failIf(!wb.isClassAlive(interfaceName), "should be live here");
+        System.out.println("We still have Interface referenced" + ic);
+    }
+}
+
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/runtime/ClassUnload/test/ImplementorClass.java	Mon Oct 29 10:21:34 2018 -0400
@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2018, 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.
+ *
+ * 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 test;
+
+public class ImplementorClass implements Interface {
+  public void foo() { System.out.println("foo implemented!"); }
+}
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/runtime/ClassUnload/test/Interface.java	Mon Oct 29 10:21:34 2018 -0400
@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2018, 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.
+ *
+ * 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 test;
+
+public interface Interface {
+  public void foo();
+}
--- a/test/hotspot/jtreg/runtime/testlibrary/ClassUnloadCommon.java	Mon Oct 29 08:38:59 2018 -0400
+++ b/test/hotspot/jtreg/runtime/testlibrary/ClassUnloadCommon.java	Mon Oct 29 10:21:34 2018 -0400
@@ -27,7 +27,10 @@
  * for an example.
  */
 
+
 import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLClassLoader;
@@ -104,4 +107,22 @@
             throw new RuntimeException(e);
         }
     }
+
+    // Get data for pre-compiled class file to load.
+    public static byte[] getClassData(String name) {
+        try {
+           String TempName = name.replaceAll("\\.", "/");
+           String currentDir = System.getProperty("test.classes");
+           String filename = currentDir + File.separator + TempName + ".class";
+           System.out.println("filename is " + filename);
+           FileInputStream fis = new FileInputStream(filename);
+           byte[] b = new byte[5000];
+           int cnt = fis.read(b, 0, 5000);
+           byte[] c = new byte[cnt];
+           for (int i=0; i<cnt; i++) c[i] = b[i];
+              return c;
+        } catch (IOException e) {
+           return null;
+        }
+    }
 }