--- /dev/null	2018-11-30 10:10:44.238550338 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahStrDedupQueue.cpp	2018-11-30 10:22:56.660302544 +0100
@@ -0,0 +1,246 @@
+/*
+ * 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.
+ *
+ */
+
+#include "precompiled.hpp"
+
+#include "gc/shared/stringdedup/stringDedup.hpp"
+#include "gc/shared/stringdedup/stringDedupThread.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
+#include "gc/shenandoah/shenandoahStrDedupQueue.hpp"
+#include "gc/shenandoah/shenandoahStrDedupQueue.inline.hpp"
+#include "gc/shenandoah/shenandoahStringDedup.hpp"
+#include "logging/log.hpp"
+#include "runtime/mutex.hpp"
+#include "runtime/mutexLocker.hpp"
+
+ShenandoahStrDedupQueue::ShenandoahStrDedupQueue() :
+  _consumer_queue(NULL),
+  _num_producer_queue(ShenandoahHeap::heap()->max_workers()),
+  _published_queues(NULL),
+  _free_list(NULL),
+  _num_free_buffer(0),
+  _max_free_buffer(ShenandoahHeap::heap()->max_workers() * 2),
+  _cancel(false),
+  _total_buffers(0) {
+  _producer_queues = NEW_C_HEAP_ARRAY(ShenandoahQueueBuffer*, _num_producer_queue, mtGC);
+  for (size_t index = 0; index < _num_producer_queue; index ++) {
+    _producer_queues[index] = NULL;
+  }
+}
+
+ShenandoahStrDedupQueue::~ShenandoahStrDedupQueue() {
+  MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+  for (size_t index = 0; index < num_queues(); index ++) {
+    release_buffers(queue_at(index));
+  }
+
+  release_buffers(_free_list);
+  FREE_C_HEAP_ARRAY(ShenandoahQueueBuffer*, _producer_queues);
+}
+
+void ShenandoahStrDedupQueue::wait_impl() {
+  MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+  while (_consumer_queue == NULL && !_cancel) {
+    ml.wait(Mutex::_no_safepoint_check_flag);
+    assert(_consumer_queue == NULL, "Why wait?");
+    _consumer_queue = _published_queues;
+    _published_queues = NULL;
+  }
+}
+
+void ShenandoahStrDedupQueue::cancel_wait_impl() {
+  MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+  _cancel = true;
+  ml.notify();
+}
+
+void ShenandoahStrDedupQueue::unlink_or_oops_do_impl(StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
+  ShenandoahQueueBuffer* q = queue_at(queue);
+  while (q != NULL) {
+    q->unlink_or_oops_do(cl);
+    q = q->next();
+  }
+}
+
+ShenandoahQueueBuffer* ShenandoahStrDedupQueue::queue_at(size_t queue_id) const {
+  assert(queue_id <= num_queues(), "Invalid queue id");
+  if (queue_id < _num_producer_queue) {
+    return _producer_queues[queue_id];
+  } else if (queue_id == _num_producer_queue) {
+    return _consumer_queue;
+  } else {
+    assert(queue_id == _num_producer_queue + 1, "Must be");
+    return _published_queues;
+  }
+}
+
+void ShenandoahStrDedupQueue::set_producer_buffer(ShenandoahQueueBuffer* buf, size_t queue_id) {
+  assert(queue_id < _num_producer_queue, "Not a producer queue id");
+  _producer_queues[queue_id] = buf;
+}
+
+void ShenandoahStrDedupQueue::push_impl(uint worker_id, oop string_oop) {
+  assert(worker_id < _num_producer_queue, "Invalid queue id. Can only push to producer queue");
+  assert(ShenandoahStringDedup::is_candidate(string_oop), "Not a candidate");
+
+  ShenandoahQueueBuffer* buf = queue_at((size_t)worker_id);
+
+  if (buf == NULL) {
+    MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+    buf = new_buffer();
+    set_producer_buffer(buf, worker_id);
+  } else if (buf->is_full()) {
+    MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+    buf->set_next(_published_queues);
+    _published_queues = buf;
+    buf = new_buffer();
+    set_producer_buffer(buf, worker_id);
+    ml.notify();
+  }
+
+  assert(!buf->is_full(), "Sanity");
+  buf->push(string_oop);
+}
+
+oop ShenandoahStrDedupQueue::pop_impl() {
+  assert(Thread::current() == StringDedupThread::thread(), "Must be dedup thread");
+  while (true) {
+    if (_consumer_queue == NULL) {
+      MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+      _consumer_queue = _published_queues;
+      _published_queues = NULL;
+    }
+
+    // there is nothing
+    if (_consumer_queue == NULL) {
+      return NULL;
+    }
+
+    oop obj = NULL;
+    if (pop_candidate(obj)) {
+      assert(ShenandoahStringDedup::is_candidate(obj), "Must be a candidate");
+      return obj;
+    }
+    assert(obj == NULL, "No more candidate");
+  }
+}
+
+bool ShenandoahStrDedupQueue::pop_candidate(oop& obj) {
+  ShenandoahQueueBuffer* to_release = NULL;
+  bool suc = true;
+  do {
+    if (_consumer_queue->is_empty()) {
+      ShenandoahQueueBuffer* buf = _consumer_queue;
+      _consumer_queue = _consumer_queue->next();
+      buf->set_next(to_release);
+      to_release = buf;
+
+      if (_consumer_queue == NULL) {
+        suc = false;
+        break;
+      }
+    }
+    obj = _consumer_queue->pop();
+  } while (obj == NULL);
+
+  if (to_release != NULL) {
+    MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
+    release_buffers(to_release);
+  }
+
+  return suc;
+}
+
+ShenandoahQueueBuffer* ShenandoahStrDedupQueue::new_buffer() {
+  assert_lock_strong(StringDedupQueue_lock);
+  if (_free_list != NULL) {
+    assert(_num_free_buffer > 0, "Sanity");
+    ShenandoahQueueBuffer* buf = _free_list;
+    _free_list = _free_list->next();
+    _num_free_buffer --;
+    buf->reset();
+    return buf;
+  } else {
+    assert(_num_free_buffer == 0, "Sanity");
+    _total_buffers ++;
+    return new ShenandoahQueueBuffer;
+  }
+}
+
+void ShenandoahStrDedupQueue::release_buffers(ShenandoahQueueBuffer* list) {
+  assert_lock_strong(StringDedupQueue_lock);
+  while (list != NULL) {
+    ShenandoahQueueBuffer* tmp = list;
+    list = list->next();
+    if (_num_free_buffer < _max_free_buffer) {
+      tmp->set_next(_free_list);
+      _free_list = tmp;
+      _num_free_buffer ++;
+    } else {
+      _total_buffers --;
+      delete tmp;
+    }
+  }
+}
+
+void ShenandoahStrDedupQueue::print_statistics_impl() {
+  Log(gc, stringdedup) log;
+  log.debug("  Queue:");
+  log.debug("    Total buffers: " SIZE_FORMAT " (" SIZE_FORMAT " K). " SIZE_FORMAT " buffers are on free list",
+    _total_buffers, (_total_buffers * sizeof(ShenandoahQueueBuffer) / K), _num_free_buffer);
+}
+
+class VerifyQueueClosure : public OopClosure {
+private:
+  ShenandoahHeap* _heap;
+public:
+  VerifyQueueClosure();
+
+  void do_oop(oop* o);
+  void do_oop(narrowOop* o) {
+    ShouldNotCallThis();
+  }
+};
+
+VerifyQueueClosure::VerifyQueueClosure() :
+  _heap(ShenandoahHeap::heap()) {
+}
+
+void VerifyQueueClosure::do_oop(oop* o) {
+  if (*o != NULL) {
+    oop obj = *o;
+    shenandoah_assert_correct(o, obj);
+    assert(java_lang_String::is_instance(obj), "Object must be a String");
+  }
+}
+
+void ShenandoahStrDedupQueue::verify_impl() {
+  VerifyQueueClosure vcl;
+  for (size_t index = 0; index < num_queues(); index ++) {
+    ShenandoahQueueBuffer* buf = queue_at(index);
+    while (buf != NULL) {
+      buf->oops_do(&vcl);
+      buf = buf->next();
+    }
+  }
+}