diff -r a1aaf68b119d -r 2e91d927e00c src/hotspot/share/gc/shared/ptrQueue.hpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shared/ptrQueue.hpp	Sat Aug 18 13:59:25 2018 -0400
@@ -0,0 +1,371 @@
+/*
+ * Copyright (c) 2001, 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.
+ *
+ */
+
+#ifndef SHARE_GC_SHARED_PTRQUEUE_HPP
+#define SHARE_GC_SHARED_PTRQUEUE_HPP
+
+#include "utilities/align.hpp"
+#include "utilities/sizes.hpp"
+
+// There are various techniques that require threads to be able to log
+// addresses.  For example, a generational write barrier might log
+// the addresses of modified old-generation objects.  This type supports
+// this operation.
+
+class BufferNode;
+class PtrQueueSet;
+class PtrQueue {
+  friend class VMStructs;
+
+  // Noncopyable - not defined.
+  PtrQueue(const PtrQueue&);
+  PtrQueue& operator=(const PtrQueue&);
+
+  // The ptr queue set to which this queue belongs.
+  PtrQueueSet* const _qset;
+
+  // Whether updates should be logged.
+  bool _active;
+
+  // If true, the queue is permanent, and doesn't need to deallocate
+  // its buffer in the destructor (since that obtains a lock which may not
+  // be legally locked by then.
+  const bool _permanent;
+
+  // The (byte) index at which an object was last enqueued.  Starts at
+  // capacity_in_bytes (indicating an empty buffer) and goes towards zero.
+  // Value is always pointer-size aligned.
+  size_t _index;
+
+  // Size of the current buffer, in bytes.
+  // Value is always pointer-size aligned.
+  size_t _capacity_in_bytes;
+
+  static const size_t _element_size = sizeof(void*);
+
+  // Get the capacity, in bytes.  The capacity must have been set.
+  size_t capacity_in_bytes() const {
+    assert(_capacity_in_bytes > 0, "capacity not set");
+    return _capacity_in_bytes;
+  }
+
+  void set_capacity(size_t entries) {
+    size_t byte_capacity = index_to_byte_index(entries);
+    assert(_capacity_in_bytes == 0 || _capacity_in_bytes == byte_capacity,
+           "changing capacity " SIZE_FORMAT " -> " SIZE_FORMAT,
+           _capacity_in_bytes, byte_capacity);
+    _capacity_in_bytes = byte_capacity;
+  }
+
+  static size_t byte_index_to_index(size_t ind) {
+    assert(is_aligned(ind, _element_size), "precondition");
+    return ind / _element_size;
+  }
+
+  static size_t index_to_byte_index(size_t ind) {
+    return ind * _element_size;
+  }
+
+protected:
+  // The buffer.
+  void** _buf;
+
+  size_t index() const {
+    return byte_index_to_index(_index);
+  }
+
+  void set_index(size_t new_index) {
+    size_t byte_index = index_to_byte_index(new_index);
+    assert(byte_index <= capacity_in_bytes(), "precondition");
+    _index = byte_index;
+  }
+
+  size_t capacity() const {
+    return byte_index_to_index(capacity_in_bytes());
+  }
+
+  // If there is a lock associated with this buffer, this is that lock.
+  Mutex* _lock;
+
+  PtrQueueSet* qset() { return _qset; }
+  bool is_permanent() const { return _permanent; }
+
+  // Process queue entries and release resources.
+  void flush_impl();
+
+  // Initialize this queue to contain a null buffer, and be part of the
+  // given PtrQueueSet.
+  PtrQueue(PtrQueueSet* qset, bool permanent = false, bool active = false);
+
+  // Requires queue flushed or permanent.
+  ~PtrQueue();
+
+public:
+
+  // Associate a lock with a ptr queue.
+  void set_lock(Mutex* lock) { _lock = lock; }
+
+  // Forcibly set empty.
+  void reset() {
+    if (_buf != NULL) {
+      _index = capacity_in_bytes();
+    }
+  }
+
+  void enqueue(volatile void* ptr) {
+    enqueue((void*)(ptr));
+  }
+
+  // Enqueues the given "obj".
+  void enqueue(void* ptr) {
+    if (!_active) return;
+    else enqueue_known_active(ptr);
+  }
+
+  // This method is called when we're doing the zero index handling
+  // and gives a chance to the queues to do any pre-enqueueing
+  // processing they might want to do on the buffer. It should return
+  // true if the buffer should be enqueued, or false if enough
+  // entries were cleared from it so that it can be re-used. It should
+  // not return false if the buffer is still full (otherwise we can
+  // get into an infinite loop).
+  virtual bool should_enqueue_buffer() { return true; }
+  void handle_zero_index();
+  void locking_enqueue_completed_buffer(BufferNode* node);
+
+  void enqueue_known_active(void* ptr);
+
+  // Return the size of the in-use region.
+  size_t size() const {
+    size_t result = 0;
+    if (_buf != NULL) {
+      assert(_index <= capacity_in_bytes(), "Invariant");
+      result = byte_index_to_index(capacity_in_bytes() - _index);
+    }
+    return result;
+  }
+
+  bool is_empty() const {
+    return _buf == NULL || capacity_in_bytes() == _index;
+  }
+
+  // Set the "active" property of the queue to "b".  An enqueue to an
+  // inactive thread is a no-op.  Setting a queue to inactive resets its
+  // log to the empty state.
+  void set_active(bool b) {
+    _active = b;
+    if (!b && _buf != NULL) {
+      reset();
+    } else if (b && _buf != NULL) {
+      assert(index() == capacity(),
+             "invariant: queues are empty when activated.");
+    }
+  }
+
+  bool is_active() const { return _active; }
+
+  // To support compiler.
+
+protected:
+  template<typename Derived>
+  static ByteSize byte_offset_of_index() {
+    return byte_offset_of(Derived, _index);
+  }
+
+  static ByteSize byte_width_of_index() { return in_ByteSize(sizeof(size_t)); }
+
+  template<typename Derived>
+  static ByteSize byte_offset_of_buf() {
+    return byte_offset_of(Derived, _buf);
+  }
+
+  static ByteSize byte_width_of_buf() { return in_ByteSize(_element_size); }
+
+  template<typename Derived>
+  static ByteSize byte_offset_of_active() {
+    return byte_offset_of(Derived, _active);
+  }
+
+  static ByteSize byte_width_of_active() { return in_ByteSize(sizeof(bool)); }
+
+};
+
+class BufferNode {
+  size_t _index;
+  BufferNode* _next;
+  void* _buffer[1];             // Pseudo flexible array member.
+
+  BufferNode() : _index(0), _next(NULL) { }
+  ~BufferNode() { }
+
+  static size_t buffer_offset() {
+    return offset_of(BufferNode, _buffer);
+  }
+
+public:
+  BufferNode* next() const     { return _next;  }
+  void set_next(BufferNode* n) { _next = n;     }
+  size_t index() const         { return _index; }
+  void set_index(size_t i)     { _index = i; }
+
+  // Allocate a new BufferNode with the "buffer" having size elements.
+  static BufferNode* allocate(size_t size);
+
+  // Free a BufferNode.
+  static void deallocate(BufferNode* node);
+
+  // Return the BufferNode containing the buffer, after setting its index.
+  static BufferNode* make_node_from_buffer(void** buffer, size_t index) {
+    BufferNode* node =
+      reinterpret_cast<BufferNode*>(
+        reinterpret_cast<char*>(buffer) - buffer_offset());
+    node->set_index(index);
+    return node;
+  }
+
+  // Return the buffer for node.
+  static void** make_buffer_from_node(BufferNode *node) {
+    // &_buffer[0] might lead to index out of bounds warnings.
+    return reinterpret_cast<void**>(
+      reinterpret_cast<char*>(node) + buffer_offset());
+  }
+};
+
+// A PtrQueueSet represents resources common to a set of pointer queues.
+// In particular, the individual queues allocate buffers from this shared
+// set, and return completed buffers to the set.
+// All these variables are are protected by the TLOQ_CBL_mon. XXX ???
+class PtrQueueSet {
+  // The size of all buffers in the set.
+  size_t _buffer_size;
+
+protected:
+  Monitor* _cbl_mon;  // Protects the fields below.
+  BufferNode* _completed_buffers_head;
+  BufferNode* _completed_buffers_tail;
+  size_t _n_completed_buffers;
+  int _process_completed_threshold;
+  volatile bool _process_completed;
+
+  // This (and the interpretation of the first element as a "next"
+  // pointer) are protected by the TLOQ_FL_lock.
+  Mutex* _fl_lock;
+  BufferNode* _buf_free_list;
+  size_t _buf_free_list_sz;
+  // Queue set can share a freelist. The _fl_owner variable
+  // specifies the owner. It is set to "this" by default.
+  PtrQueueSet* _fl_owner;
+
+  bool _all_active;
+
+  // If true, notify_all on _cbl_mon when the threshold is reached.
+  bool _notify_when_complete;
+
+  // Maximum number of elements allowed on completed queue: after that,
+  // enqueuer does the work itself.  Zero indicates no maximum.
+  int _max_completed_queue;
+  size_t _completed_queue_padding;
+
+  size_t completed_buffers_list_length();
+  void assert_completed_buffer_list_len_correct_locked();
+  void assert_completed_buffer_list_len_correct();
+
+protected:
+  // A mutator thread does the the work of processing a buffer.
+  // Returns "true" iff the work is complete (and the buffer may be
+  // deallocated).
+  virtual bool mut_process_buffer(BufferNode* node) {
+    ShouldNotReachHere();
+    return false;
+  }
+
+  // Create an empty ptr queue set.
+  PtrQueueSet(bool notify_when_complete = false);
+  ~PtrQueueSet();
+
+  // Because of init-order concerns, we can't pass these as constructor
+  // arguments.
+  void initialize(Monitor* cbl_mon,
+                  Mutex* fl_lock,
+                  int process_completed_threshold,
+                  int max_completed_queue,
+                  PtrQueueSet *fl_owner = NULL);
+
+public:
+
+  // Return the buffer for a BufferNode of size buffer_size().
+  void** allocate_buffer();
+
+  // Return an empty buffer to the free list.  The node is required
+  // to have been allocated with a size of buffer_size().
+  void deallocate_buffer(BufferNode* node);
+
+  // Declares that "buf" is a complete buffer.
+  void enqueue_complete_buffer(BufferNode* node);
+
+  // To be invoked by the mutator.
+  bool process_or_enqueue_complete_buffer(BufferNode* node);
+
+  bool completed_buffers_exist_dirty() {
+    return _n_completed_buffers > 0;
+  }
+
+  bool process_completed_buffers() { return _process_completed; }
+  void set_process_completed(bool x) { _process_completed = x; }
+
+  bool is_active() { return _all_active; }
+
+  // Set the buffer size.  Should be called before any "enqueue" operation
+  // can be called.  And should only be called once.
+  void set_buffer_size(size_t sz);
+
+  // Get the buffer size.  Must have been set.
+  size_t buffer_size() const {
+    assert(_buffer_size > 0, "buffer size not set");
+    return _buffer_size;
+  }
+
+  // Get/Set the number of completed buffers that triggers log processing.
+  void set_process_completed_threshold(int sz) { _process_completed_threshold = sz; }
+  int process_completed_threshold() const { return _process_completed_threshold; }
+
+  // Must only be called at a safe point.  Indicates that the buffer free
+  // list size may be reduced, if that is deemed desirable.
+  void reduce_free_list();
+
+  size_t completed_buffers_num() { return _n_completed_buffers; }
+
+  void merge_bufferlists(PtrQueueSet* src);
+
+  void set_max_completed_queue(int m) { _max_completed_queue = m; }
+  int max_completed_queue() { return _max_completed_queue; }
+
+  void set_completed_queue_padding(size_t padding) { _completed_queue_padding = padding; }
+  size_t completed_queue_padding() { return _completed_queue_padding; }
+
+  // Notify the consumer if the number of buffers crossed the threshold
+  void notify_if_necessary();
+};
+
+#endif // SHARE_GC_SHARED_PTRQUEUE_HPP