--- /dev/null	2020-01-17 11:46:19.065201212 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahCodeRoots.cpp	2020-01-17 17:09:55.901131262 +0100
@@ -0,0 +1,332 @@
+/*
+ * Copyright (c) 2017, 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 "code/codeCache.hpp"
+#include "code/nmethod.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
+#include "gc/shenandoah/shenandoahCodeRoots.hpp"
+#include "gc/shenandoah/shenandoahUtils.hpp"
+#include "memory/resourceArea.hpp"
+
+ShenandoahParallelCodeCacheIterator::ShenandoahParallelCodeCacheIterator(const GrowableArray<CodeHeap*>* heaps) {
+  _length = heaps->length();
+  _iters = NEW_C_HEAP_ARRAY(ShenandoahParallelCodeHeapIterator, _length, mtGC);
+  for (int h = 0; h < _length; h++) {
+    _iters[h] = ShenandoahParallelCodeHeapIterator(heaps->at(h));
+  }
+}
+
+ShenandoahParallelCodeCacheIterator::~ShenandoahParallelCodeCacheIterator() {
+  FREE_C_HEAP_ARRAY(ParallelCodeHeapIterator, _iters);
+}
+
+void ShenandoahParallelCodeCacheIterator::parallel_blobs_do(CodeBlobClosure* f) {
+  for (int c = 0; c < _length; c++) {
+    _iters[c].parallel_blobs_do(f);
+  }
+}
+
+ShenandoahParallelCodeHeapIterator::ShenandoahParallelCodeHeapIterator(CodeHeap* heap) :
+        _heap(heap), _claimed_idx(0), _finished(false) {
+}
+
+void ShenandoahParallelCodeHeapIterator::parallel_blobs_do(CodeBlobClosure* f) {
+  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
+
+  /*
+   * Parallel code heap walk.
+   *
+   * This code makes all threads scan all code heaps, but only one thread would execute the
+   * closure on given blob. This is achieved by recording the "claimed" blocks: if a thread
+   * had claimed the block, it can process all blobs in it. Others have to fast-forward to
+   * next attempt without processing.
+   *
+   * Late threads would return immediately if iterator is finished.
+   */
+
+  if (_finished) {
+    return;
+  }
+
+  int stride = 256; // educated guess
+  int stride_mask = stride - 1;
+  assert (is_power_of_2(stride), "sanity");
+
+  int count = 0;
+  bool process_block = true;
+
+  for (CodeBlob *cb = CodeCache::first_blob(_heap); cb != NULL; cb = CodeCache::next_blob(_heap, cb)) {
+    int current = count++;
+    if ((current & stride_mask) == 0) {
+      process_block = (current >= _claimed_idx) &&
+                      (Atomic::cmpxchg(current + stride, &_claimed_idx, current) == current);
+    }
+    if (process_block) {
+      if (cb->is_alive()) {
+        f->do_code_blob(cb);
+#ifdef ASSERT
+        if (cb->is_nmethod())
+          Universe::heap()->verify_nmethod((nmethod*)cb);
+#endif
+      }
+    }
+  }
+
+  _finished = true;
+}
+
+class ShenandoahNMethodOopDetector : public OopClosure {
+private:
+  ResourceMark rm; // For growable array allocation below.
+  GrowableArray<oop*> _oops;
+
+public:
+  ShenandoahNMethodOopDetector() : _oops(10) {};
+
+  void do_oop(oop* o) {
+    _oops.append(o);
+  }
+  void do_oop(narrowOop* o) {
+    fatal("NMethods should not have compressed oops embedded.");
+  }
+
+  GrowableArray<oop*>* oops() {
+    return &_oops;
+  }
+
+  bool has_oops() {
+    return !_oops.is_empty();
+  }
+};
+
+GrowableArray<ShenandoahNMethod*>* ShenandoahCodeRoots::_recorded_nms;
+ShenandoahLock                     ShenandoahCodeRoots::_recorded_nms_lock;
+
+void ShenandoahCodeRoots::initialize() {
+  _recorded_nms = new (ResourceObj::C_HEAP, mtGC) GrowableArray<ShenandoahNMethod*>(100, true, mtGC);
+}
+
+void ShenandoahCodeRoots::add_nmethod(nmethod* nm) {
+  switch (ShenandoahCodeRootsStyle) {
+    case 0:
+    case 1:
+      break;
+    case 2: {
+      assert_locked_or_safepoint(CodeCache_lock);
+      ShenandoahLocker locker(CodeCache_lock->owned_by_self() ? NULL : &_recorded_nms_lock);
+
+      ShenandoahNMethodOopDetector detector;
+      nm->oops_do(&detector);
+
+      if (detector.has_oops()) {
+        ShenandoahNMethod* nmr = new ShenandoahNMethod(nm, detector.oops());
+        nmr->assert_alive_and_correct();
+        int idx = _recorded_nms->find(nm, ShenandoahNMethod::find_with_nmethod);
+        if (idx != -1) {
+          ShenandoahNMethod* old = _recorded_nms->at(idx);
+          _recorded_nms->at_put(idx, nmr);
+          delete old;
+        } else {
+          _recorded_nms->append(nmr);
+        }
+      }
+      break;
+    }
+    default:
+      ShouldNotReachHere();
+  }
+};
+
+void ShenandoahCodeRoots::remove_nmethod(nmethod* nm) {
+  switch (ShenandoahCodeRootsStyle) {
+    case 0:
+    case 1: {
+      break;
+    }
+    case 2: {
+      assert_locked_or_safepoint(CodeCache_lock);
+      ShenandoahLocker locker(CodeCache_lock->owned_by_self() ? NULL : &_recorded_nms_lock);
+
+      ShenandoahNMethodOopDetector detector;
+      nm->oops_do(&detector, /* allow_zombie = */ true);
+
+      if (detector.has_oops()) {
+        int idx = _recorded_nms->find(nm, ShenandoahNMethod::find_with_nmethod);
+        assert(idx != -1, "nmethod " PTR_FORMAT " should be registered", p2i(nm));
+        ShenandoahNMethod* old = _recorded_nms->at(idx);
+        old->assert_same_oops(detector.oops());
+        _recorded_nms->delete_at(idx);
+        delete old;
+      }
+      break;
+    }
+    default:
+      ShouldNotReachHere();
+  }
+}
+
+ShenandoahCodeRootsIterator::ShenandoahCodeRootsIterator() :
+        _heap(ShenandoahHeap::heap()),
+        _par_iterator(CodeCache::heaps()),
+        _claimed(0) {
+  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
+  assert(!Thread::current()->is_Worker_thread(), "Should not be acquired by workers");
+  switch (ShenandoahCodeRootsStyle) {
+    case 0:
+    case 1: {
+      // No need to do anything here
+      break;
+    }
+    case 2: {
+      CodeCache_lock->lock_without_safepoint_check();
+      break;
+    }
+    default:
+      ShouldNotReachHere();
+  }
+}
+
+ShenandoahCodeRootsIterator::~ShenandoahCodeRootsIterator() {
+  switch (ShenandoahCodeRootsStyle) {
+    case 0:
+    case 1: {
+      // No need to do anything here
+      break;
+    }
+    case 2: {
+      CodeCache_lock->unlock();
+      break;
+    }
+    default:
+      ShouldNotReachHere();
+  }
+}
+
+template<bool CSET_FILTER>
+void ShenandoahCodeRootsIterator::dispatch_parallel_blobs_do(CodeBlobClosure *f) {
+  switch (ShenandoahCodeRootsStyle) {
+    case 0: {
+      if (_seq_claimed.try_set()) {
+        CodeCache::blobs_do(f);
+      }
+      break;
+    }
+    case 1: {
+      _par_iterator.parallel_blobs_do(f);
+      break;
+    }
+    case 2: {
+      ShenandoahCodeRootsIterator::fast_parallel_blobs_do<CSET_FILTER>(f);
+      break;
+    }
+    default:
+      ShouldNotReachHere();
+  }
+}
+
+void ShenandoahAllCodeRootsIterator::possibly_parallel_blobs_do(CodeBlobClosure *f) {
+  ShenandoahCodeRootsIterator::dispatch_parallel_blobs_do<false>(f);
+}
+
+void ShenandoahCsetCodeRootsIterator::possibly_parallel_blobs_do(CodeBlobClosure *f) {
+  ShenandoahCodeRootsIterator::dispatch_parallel_blobs_do<true>(f);
+}
+
+template <bool CSET_FILTER>
+void ShenandoahCodeRootsIterator::fast_parallel_blobs_do(CodeBlobClosure *f) {
+  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
+
+  size_t stride = 256; // educated guess
+
+  GrowableArray<ShenandoahNMethod*>* list = ShenandoahCodeRoots::_recorded_nms;
+
+  size_t max = (size_t)list->length();
+  while (_claimed < max) {
+    size_t cur = Atomic::add(stride, &_claimed) - stride;
+    size_t start = cur;
+    size_t end = MIN2(cur + stride, max);
+    if (start >= max) break;
+
+    for (size_t idx = start; idx < end; idx++) {
+      ShenandoahNMethod* nmr = list->at((int) idx);
+      nmr->assert_alive_and_correct();
+
+      if (CSET_FILTER && !nmr->has_cset_oops(_heap)) {
+        continue;
+      }
+
+      f->do_code_blob(nmr->nm());
+    }
+  }
+}
+
+ShenandoahNMethod::ShenandoahNMethod(nmethod* nm, GrowableArray<oop*>* oops) {
+  _nm = nm;
+  _oops = NEW_C_HEAP_ARRAY(oop*, oops->length(), mtGC);
+  _oops_count = oops->length();
+  for (int c = 0; c < _oops_count; c++) {
+    _oops[c] = oops->at(c);
+  }
+}
+
+ShenandoahNMethod::~ShenandoahNMethod() {
+  if (_oops != NULL) {
+    FREE_C_HEAP_ARRAY(oop*, _oops);
+  }
+}
+
+bool ShenandoahNMethod::has_cset_oops(ShenandoahHeap *heap) {
+  for (int c = 0; c < _oops_count; c++) {
+    oop o = RawAccess<>::oop_load(_oops[c]);
+    if (heap->in_collection_set(o)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+#ifdef ASSERT
+void ShenandoahNMethod::assert_alive_and_correct() {
+  assert(_nm->is_alive(), "only alive nmethods here");
+  assert(_oops_count > 0, "should have filtered nmethods without oops before");
+  ShenandoahHeap* heap = ShenandoahHeap::heap();
+  for (int c = 0; c < _oops_count; c++) {
+    oop *loc = _oops[c];
+    assert(_nm->code_contains((address) loc) || _nm->oops_contains(loc), "nmethod should contain the oop*");
+    oop o = RawAccess<>::oop_load(loc);
+    shenandoah_assert_correct_except(loc, o,
+             o == NULL ||
+             heap->is_full_gc_move_in_progress() ||
+             (VMThread::vm_operation() != NULL) && (VMThread::vm_operation()->type() == VM_Operation::VMOp_HeapWalkOperation)
+    );
+  }
+}
+
+void ShenandoahNMethod::assert_same_oops(GrowableArray<oop*>* oops) {
+  assert(_oops_count == oops->length(), "should have the same number of oop*");
+  for (int c = 0; c < _oops_count; c++) {
+    assert(_oops[c] == oops->at(c), "should be the same oop*");
+  }
+}
+#endif