--- /dev/null	2018-11-30 10:10:44.238550338 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahCodeRoots.hpp	2018-11-30 21:08:05.211404604 +0100
@@ -0,0 +1,200 @@
+/*
+ * Copyright (c) 2017, 2018, 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.
+ *
+ */
+
+#ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHCODEROOTS_HPP
+#define SHARE_VM_GC_SHENANDOAH_SHENANDOAHCODEROOTS_HPP
+
+#include "code/codeCache.hpp"
+#include "gc/shenandoah/shenandoahSharedVariables.hpp"
+#include "memory/allocation.hpp"
+#include "memory/iterator.hpp"
+
+class ShenandoahHeap;
+class ShenandoahHeapRegion;
+class ShenandoahCodeRootsLock;
+
+class ShenandoahParallelCodeHeapIterator {
+  friend class CodeCache;
+private:
+  CodeHeap*     _heap;
+  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
+  volatile int  _claimed_idx;
+  volatile bool _finished;
+  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);
+public:
+  ShenandoahParallelCodeHeapIterator(CodeHeap* heap);
+  void parallel_blobs_do(CodeBlobClosure* f);
+};
+
+class ShenandoahParallelCodeCacheIterator {
+  friend class CodeCache;
+private:
+  ShenandoahParallelCodeHeapIterator* _iters;
+  int                       _length;
+public:
+  ShenandoahParallelCodeCacheIterator(const GrowableArray<CodeHeap*>* heaps);
+  ~ShenandoahParallelCodeCacheIterator();
+  void parallel_blobs_do(CodeBlobClosure* f);
+};
+
+// ShenandoahNMethod tuple records the internal locations of oop slots within the nmethod.
+// This allows us to quickly scan the oops without doing the nmethod-internal scans, that
+// sometimes involves parsing the machine code. Note it does not record the oops themselves,
+// because it would then require handling these tuples as the new class of roots.
+class ShenandoahNMethod : public CHeapObj<mtGC> {
+private:
+  nmethod* _nm;
+  oop**    _oops;
+  int      _oops_count;
+
+public:
+  ShenandoahNMethod(nmethod *nm, GrowableArray<oop*>* oops);
+  ~ShenandoahNMethod();
+
+  nmethod* nm() {
+    return _nm;
+  }
+
+  bool has_cset_oops(ShenandoahHeap* heap);
+
+  void assert_alive_and_correct() PRODUCT_RETURN;
+  void assert_same_oops(GrowableArray<oop*>* oops) PRODUCT_RETURN;
+
+  static bool find_with_nmethod(void* nm, ShenandoahNMethod* other) {
+    return other->_nm == nm;
+  }
+};
+
+class ShenandoahCodeRootsIterator {
+  friend class ShenandoahCodeRoots;
+protected:
+  ShenandoahHeap* _heap;
+  ShenandoahParallelCodeCacheIterator _par_iterator;
+  ShenandoahSharedFlag _seq_claimed;
+  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile size_t));
+  volatile size_t _claimed;
+  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);
+protected:
+  ShenandoahCodeRootsIterator();
+  ~ShenandoahCodeRootsIterator();
+
+  template<bool CSET_FILTER>
+  void dispatch_parallel_blobs_do(CodeBlobClosure *f);
+
+  template<bool CSET_FILTER>
+  void fast_parallel_blobs_do(CodeBlobClosure *f);
+};
+
+class ShenandoahAllCodeRootsIterator : public ShenandoahCodeRootsIterator {
+public:
+  ShenandoahAllCodeRootsIterator() : ShenandoahCodeRootsIterator() {};
+  void possibly_parallel_blobs_do(CodeBlobClosure *f);
+};
+
+class ShenandoahCsetCodeRootsIterator : public ShenandoahCodeRootsIterator {
+public:
+  ShenandoahCsetCodeRootsIterator() : ShenandoahCodeRootsIterator() {};
+  void possibly_parallel_blobs_do(CodeBlobClosure* f);
+};
+
+class ShenandoahCodeRoots : public CHeapObj<mtGC> {
+  friend class ShenandoahHeap;
+  friend class ShenandoahCodeRootsLock;
+  friend class ShenandoahCodeRootsIterator;
+
+public:
+  static void initialize();
+  static void add_nmethod(nmethod* nm);
+  static void remove_nmethod(nmethod* nm);
+
+  /**
+   * Provides the iterator over all nmethods in the code cache that have oops.
+   * @return
+   */
+  static ShenandoahAllCodeRootsIterator iterator();
+
+  /**
+   * Provides the iterator over nmethods that have at least one oop in collection set.
+   * @return
+   */
+  static ShenandoahCsetCodeRootsIterator cset_iterator();
+
+private:
+  struct PaddedLock {
+    DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
+    volatile int _lock;
+    DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);
+  };
+
+  static PaddedLock _recorded_nms_lock;
+  static GrowableArray<ShenandoahNMethod*>* _recorded_nms;
+
+  static void acquire_lock(bool write) {
+    volatile int* loc = &_recorded_nms_lock._lock;
+    if (write) {
+      while ((OrderAccess::load_acquire(loc) != 0) ||
+             Atomic::cmpxchg(-1, loc, 0) != 0) {
+        SpinPause();
+      }
+      assert (*loc == -1, "acquired for write");
+    } else {
+      while (true) {
+        int cur = OrderAccess::load_acquire(loc);
+        if (cur >= 0) {
+          if (Atomic::cmpxchg(cur + 1, loc, cur) == cur) {
+            // Success!
+            assert (*loc > 0, "acquired for read");
+            return;
+          }
+        }
+        SpinPause();
+      }
+    }
+  }
+
+  static void release_lock(bool write) {
+    volatile int* loc = &ShenandoahCodeRoots::_recorded_nms_lock._lock;
+    if (write) {
+      OrderAccess::release_store_fence(loc, 0);
+    } else {
+      Atomic::dec(loc);
+    }
+  }
+};
+
+// Very simple unranked read-write lock
+class ShenandoahCodeRootsLock : public StackObj {
+  friend class ShenandoahCodeRoots;
+private:
+  const bool _write;
+public:
+  ShenandoahCodeRootsLock(bool write) : _write(write) {
+    ShenandoahCodeRoots::acquire_lock(write);
+  }
+
+  ~ShenandoahCodeRootsLock() {
+    ShenandoahCodeRoots::release_lock(_write);
+  }
+};
+
+#endif //SHARE_VM_GC_SHENANDOAH_SHENANDOAHCODEROOTS_HPP