diff -r 8b6cc0bb93d0 -r 9186be5c78ba src/hotspot/share/gc/shenandoah/shenandoahUnload.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shenandoah/shenandoahUnload.cpp	Wed Nov 27 11:52:57 2019 -0500
@@ -0,0 +1,186 @@
+/*
+ * Copyright (c) 2019, Red Hat, Inc. All rights reserved.
+ *
+ * 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.
+ *
+ */
+
+#include "precompiled.hpp"
+
+#include "classfile/classLoaderDataGraph.hpp"
+#include "classfile/systemDictionary.hpp"
+#include "code/codeBehaviours.hpp"
+#include "code/codeCache.hpp"
+#include "code/dependencyContext.hpp"
+#include "gc/shared/gcBehaviours.hpp"
+#include "gc/shared/suspendibleThreadSet.hpp"
+#include "gc/shenandoah/shenandoahClosures.inline.hpp"
+#include "gc/shenandoah/shenandoahCodeRoots.hpp"
+#include "gc/shenandoah/shenandoahConcurrentRoots.hpp"
+#include "gc/shenandoah/shenandoahNMethod.inline.hpp"
+#include "gc/shenandoah/shenandoahLock.hpp"
+#include "gc/shenandoah/shenandoahRootProcessor.hpp"
+#include "gc/shenandoah/shenandoahUnload.hpp"
+#include "gc/shenandoah/shenandoahVerifier.hpp"
+#include "memory/iterator.hpp"
+#include "memory/resourceArea.hpp"
+#include "oops/access.inline.hpp"
+
+class ShenandoahIsUnloadingOopClosure : public OopClosure {
+private:
+  ShenandoahMarkingContext*    _marking_context;
+  bool                         _is_unloading;
+
+public:
+  ShenandoahIsUnloadingOopClosure() :
+    _marking_context(ShenandoahHeap::heap()->marking_context()),
+    _is_unloading(false) {
+  }
+
+  virtual void do_oop(oop* p) {
+    if (_is_unloading) {
+      return;
+    }
+
+    const oop o = RawAccess<>::oop_load(p);
+    if (!CompressedOops::is_null(o) &&
+        _marking_context->is_complete() &&
+        !_marking_context->is_marked(o)) {
+      _is_unloading = true;
+    }
+  }
+
+  virtual void do_oop(narrowOop* p) {
+    ShouldNotReachHere();
+  }
+
+  bool is_unloading() const {
+    return _is_unloading;
+  }
+};
+
+class ShenandoahIsUnloadingBehaviour : public IsUnloadingBehaviour {
+public:
+  virtual bool is_unloading(CompiledMethod* method) const {
+    nmethod* const nm = method->as_nmethod();
+    guarantee(ShenandoahHeap::heap()->is_evacuation_in_progress(), "Only this phase");
+    ShenandoahNMethod* data = ShenandoahNMethod::gc_data(nm);
+    ShenandoahReentrantLocker locker(data->lock());
+    ShenandoahIsUnloadingOopClosure cl;
+    data->oops_do(&cl);
+    return  cl.is_unloading();
+  }
+};
+
+class ShenandoahCompiledICProtectionBehaviour : public CompiledICProtectionBehaviour {
+public:
+  virtual bool lock(CompiledMethod* method) {
+    nmethod* const nm = method->as_nmethod();
+    ShenandoahReentrantLock* const lock = ShenandoahNMethod::lock_for_nmethod(nm);
+    assert(lock != NULL, "Not yet registered?");
+    lock->lock();
+    return true;
+  }
+
+  virtual void unlock(CompiledMethod* method) {
+    nmethod* const nm = method->as_nmethod();
+    ShenandoahReentrantLock* const lock = ShenandoahNMethod::lock_for_nmethod(nm);
+    assert(lock != NULL, "Not yet registered?");
+    lock->unlock();
+  }
+
+  virtual bool is_safe(CompiledMethod* method) {
+    if (SafepointSynchronize::is_at_safepoint()) {
+      return true;
+    }
+
+    nmethod* const nm = method->as_nmethod();
+    ShenandoahReentrantLock* const lock = ShenandoahNMethod::lock_for_nmethod(nm);
+    assert(lock != NULL, "Not yet registered?");
+    return lock->owned_by_self();
+  }
+};
+
+ShenandoahUnload::ShenandoahUnload() {
+  if (ShenandoahConcurrentRoots::can_do_concurrent_class_unloading()) {
+    static ShenandoahIsUnloadingBehaviour is_unloading_behaviour;
+    IsUnloadingBehaviour::set_current(&is_unloading_behaviour);
+
+    static ShenandoahCompiledICProtectionBehaviour ic_protection_behaviour;
+    CompiledICProtectionBehaviour::set_current(&ic_protection_behaviour);
+  }
+}
+
+void ShenandoahUnload::prepare() {
+  assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
+  assert(ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(), "Sanity");
+  CodeCache::increment_unloading_cycle();
+  DependencyContext::cleaning_start();
+}
+
+void ShenandoahUnload::unlink() {
+  SuspendibleThreadSetJoiner sts;
+  bool unloading_occurred;
+  ShenandoahHeap* const heap = ShenandoahHeap::heap();
+  {
+    MutexLocker cldg_ml(ClassLoaderDataGraph_lock);
+    unloading_occurred = SystemDictionary::do_unloading(heap->gc_timer());
+  }
+
+  Klass::clean_weak_klass_links(unloading_occurred);
+  ShenandoahCodeRoots::unlink(ShenandoahHeap::heap()->workers(), unloading_occurred);
+  DependencyContext::cleaning_end();
+}
+
+void ShenandoahUnload::purge() {
+  {
+    SuspendibleThreadSetJoiner sts;
+    ShenandoahCodeRoots::purge(ShenandoahHeap::heap()->workers());
+  }
+
+  ClassLoaderDataGraph::purge();
+  CodeCache::purge_exception_caches();
+}
+
+class ShenandoahUnloadRendezvousClosure : public ThreadClosure {
+public:
+  void do_thread(Thread* thread) {}
+};
+
+void ShenandoahUnload::unload() {
+  assert(ShenandoahConcurrentRoots::can_do_concurrent_class_unloading(), "Why we here?");
+  if (!ShenandoahHeap::heap()->is_evacuation_in_progress()) {
+    return;
+  }
+
+  // Unlink stale metadata and nmethods
+  unlink();
+
+  // Make sure stale metadata and nmethods are no longer observable
+  ShenandoahUnloadRendezvousClosure cl;
+  Handshake::execute(&cl);
+
+  // Purge stale metadata and nmethods that were unlinked
+  purge();
+}
+
+void ShenandoahUnload::finish() {
+  MetaspaceGC::compute_new_size();
+  MetaspaceUtils::verify_metrics();
+}