--- /dev/null	2018-12-03 11:58:50.256341286 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahTaskqueue.cpp	2018-12-03 17:47:47.777262133 +0100
@@ -0,0 +1,229 @@
+/*
+ * Copyright (c) 2016, 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/shenandoah/shenandoahHeap.hpp"
+#include "gc/shenandoah/shenandoahTaskqueue.hpp"
+#include "logging/log.hpp"
+#include "logging/logStream.hpp"
+
+void ShenandoahObjToScanQueueSet::clear() {
+  uint size = GenericTaskQueueSet<ShenandoahObjToScanQueue, mtGC>::size();
+  for (uint index = 0; index < size; index ++) {
+    ShenandoahObjToScanQueue* q = queue(index);
+    assert(q != NULL, "Sanity");
+    q->clear();
+  }
+}
+
+bool ShenandoahObjToScanQueueSet::is_empty() {
+  uint size = GenericTaskQueueSet<ShenandoahObjToScanQueue, mtGC>::size();
+  for (uint index = 0; index < size; index ++) {
+    ShenandoahObjToScanQueue* q = queue(index);
+    assert(q != NULL, "Sanity");
+    if (!q->is_empty()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool ShenandoahTaskTerminator::offer_termination(ShenandoahTerminatorTerminator* terminator) {
+  assert(_n_threads > 0, "Initialization is incorrect");
+  assert(_offered_termination < _n_threads, "Invariant");
+  assert(_blocker != NULL, "Invariant");
+
+  // single worker, done
+  if (_n_threads == 1) {
+    return true;
+  }
+
+  _blocker->lock_without_safepoint_check();
+  // all arrived, done
+  if (++ _offered_termination == _n_threads) {
+    _blocker->notify_all();
+    _blocker->unlock();
+    return true;
+  }
+
+  Thread* the_thread = Thread::current();
+  while (true) {
+    if (_spin_master == NULL) {
+      _spin_master = the_thread;
+
+      _blocker->unlock();
+
+      if (do_spin_master_work(terminator)) {
+        assert(_offered_termination == _n_threads, "termination condition");
+        return true;
+      } else {
+        _blocker->lock_without_safepoint_check();
+      }
+    } else {
+      _blocker->wait(true, WorkStealingSleepMillis);
+
+      if (_offered_termination == _n_threads) {
+        _blocker->unlock();
+        return true;
+      }
+    }
+
+    bool force = (terminator != NULL) && terminator->should_force_termination();
+    bool exit  = (terminator != NULL) && terminator->should_exit_termination();
+    if ((!force && peek_in_queue_set()) || exit) {
+      _offered_termination --;
+      _blocker->unlock();
+      return false;
+    }
+  }
+}
+
+#if TASKQUEUE_STATS
+void ShenandoahObjToScanQueueSet::print_taskqueue_stats_hdr(outputStream* const st) {
+  st->print_raw_cr("GC Task Stats");
+  st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
+  st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
+}
+
+void ShenandoahObjToScanQueueSet::print_taskqueue_stats() const {
+  if (!log_develop_is_enabled(Trace, gc, task, stats)) {
+    return;
+  }
+  Log(gc, task, stats) log;
+  ResourceMark rm;
+  LogStream ls(log.trace());
+  outputStream* st = &ls;
+  print_taskqueue_stats_hdr(st);
+
+  ShenandoahObjToScanQueueSet* queues = const_cast<ShenandoahObjToScanQueueSet*>(this);
+  TaskQueueStats totals;
+  const uint n = size();
+  for (uint i = 0; i < n; ++i) {
+    st->print(UINT32_FORMAT_W(3), i);
+    queues->queue(i)->stats.print(st);
+    st->cr();
+    totals += queues->queue(i)->stats;
+  }
+  st->print("tot "); totals.print(st); st->cr();
+  DEBUG_ONLY(totals.verify());
+
+}
+
+void ShenandoahObjToScanQueueSet::reset_taskqueue_stats() {
+  const uint n = size();
+  for (uint i = 0; i < n; ++i) {
+    queue(i)->stats.reset();
+  }
+}
+#endif // TASKQUEUE_STATS
+
+bool ShenandoahTaskTerminator::do_spin_master_work(ShenandoahTerminatorTerminator* terminator) {
+  uint yield_count = 0;
+  // Number of hard spin loops done since last yield
+  uint hard_spin_count = 0;
+  // Number of iterations in the hard spin loop.
+  uint hard_spin_limit = WorkStealingHardSpins;
+
+  // If WorkStealingSpinToYieldRatio is 0, no hard spinning is done.
+  // If it is greater than 0, then start with a small number
+  // of spins and increase number with each turn at spinning until
+  // the count of hard spins exceeds WorkStealingSpinToYieldRatio.
+  // Then do a yield() call and start spinning afresh.
+  if (WorkStealingSpinToYieldRatio > 0) {
+    hard_spin_limit = WorkStealingHardSpins >> WorkStealingSpinToYieldRatio;
+    hard_spin_limit = MAX2(hard_spin_limit, 1U);
+  }
+  // Remember the initial spin limit.
+  uint hard_spin_start = hard_spin_limit;
+
+  // Loop waiting for all threads to offer termination or
+  // more work.
+  while (true) {
+    // Look for more work.
+    // Periodically sleep() instead of yield() to give threads
+    // waiting on the cores the chance to grab this code
+    if (yield_count <= WorkStealingYieldsBeforeSleep) {
+      // Do a yield or hardspin.  For purposes of deciding whether
+      // to sleep, count this as a yield.
+      yield_count++;
+
+      // Periodically call yield() instead spinning
+      // After WorkStealingSpinToYieldRatio spins, do a yield() call
+      // and reset the counts and starting limit.
+      if (hard_spin_count > WorkStealingSpinToYieldRatio) {
+        yield();
+        hard_spin_count = 0;
+        hard_spin_limit = hard_spin_start;
+#ifdef TRACESPINNING
+        _total_yields++;
+#endif
+      } else {
+        // Hard spin this time
+        // Increase the hard spinning period but only up to a limit.
+        hard_spin_limit = MIN2(2*hard_spin_limit,
+                               (uint) WorkStealingHardSpins);
+        for (uint j = 0; j < hard_spin_limit; j++) {
+          SpinPause();
+        }
+        hard_spin_count++;
+#ifdef TRACESPINNING
+        _total_spins++;
+#endif
+      }
+    } else {
+      log_develop_trace(gc, task)("ShenanddoahTaskTerminator::do_spin_master_work() thread " PTR_FORMAT " sleeps after %u yields",
+                                  p2i(Thread::current()), yield_count);
+      yield_count = 0;
+
+      MonitorLockerEx locker(_blocker, Mutex::_no_safepoint_check_flag);   // no safepoint check
+      _spin_master = NULL;
+      locker.wait(Mutex::_no_safepoint_check_flag, WorkStealingSleepMillis);
+      if (_spin_master == NULL) {
+        _spin_master = Thread::current();
+      } else {
+        return false;
+      }
+    }
+
+#ifdef TRACESPINNING
+      _total_peeks++;
+#endif
+    size_t tasks = tasks_in_queue_set();
+    if (tasks > 0 && (terminator == NULL || ! terminator->should_force_termination())) {
+      MonitorLockerEx locker(_blocker, Mutex::_no_safepoint_check_flag);   // no safepoint check
+
+      if (tasks >= _offered_termination - 1) {
+        locker.notify_all();
+      } else {
+        for (; tasks > 1; tasks --) {
+          locker.notify();
+        }
+      }
+      _spin_master = NULL;
+      return false;
+    } else if (_offered_termination == _n_threads) {
+      return true;
+    }
+  }
+}