--- a/src/hotspot/share/gc/g1/g1BarrierSet.cpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/g1/g1BarrierSet.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -58,7 +58,8 @@
   _satb_mark_queue_buffer_allocator("SATB Buffer Allocator", G1SATBBufferSize),
   _dirty_card_queue_buffer_allocator("DC Buffer Allocator", G1UpdateBufferSize),
   _satb_mark_queue_set(),
-  _dirty_card_queue_set()
+  _dirty_card_queue_set(),
+  _shared_dirty_card_queue(&_dirty_card_queue_set)
 {}
 
 void G1BarrierSet::enqueue(oop pre_val) {

--- a/src/hotspot/share/gc/g1/g1BarrierSet.hpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/g1/g1BarrierSet.hpp	Fri Mar 22 15:42:43 2019 -0400
@@ -27,6 +27,7 @@
 
 #include "gc/g1/g1DirtyCardQueue.hpp"
 #include "gc/g1/g1SATBMarkQueueSet.hpp"
+#include "gc/g1/g1SharedDirtyCardQueue.hpp"
 #include "gc/shared/cardTable.hpp"
 #include "gc/shared/cardTableBarrierSet.hpp"
 
@@ -42,6 +43,7 @@
   BufferNode::Allocator _dirty_card_queue_buffer_allocator;
   G1SATBMarkQueueSet _satb_mark_queue_set;
   G1DirtyCardQueueSet _dirty_card_queue_set;
+  G1SharedDirtyCardQueue _shared_dirty_card_queue;
 
   static G1BarrierSet* g1_barrier_set() {
     return barrier_set_cast<G1BarrierSet>(BarrierSet::barrier_set());
@@ -91,6 +93,10 @@
     return g1_barrier_set()->_dirty_card_queue_set;
   }
 
+  static G1SharedDirtyCardQueue& shared_dirty_card_queue() {
+    return g1_barrier_set()->_shared_dirty_card_queue;
+  }
+
   // Callbacks for runtime accesses.
   template <DecoratorSet decorators, typename BarrierSetT = G1BarrierSet>
   class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {

--- a/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -1682,12 +1682,10 @@
   // later, based on the concurrent refinement object.
   G1BarrierSet::dirty_card_queue_set().initialize(DirtyCardQ_CBL_mon,
                                                   &bs->dirty_card_queue_buffer_allocator(),
-                                                  Shared_DirtyCardQ_lock,
                                                   true); // init_free_ids
 
   dirty_card_queue_set().initialize(DirtyCardQ_CBL_mon,
-                                    &bs->dirty_card_queue_buffer_allocator(),
-                                    Shared_DirtyCardQ_lock);
+                                    &bs->dirty_card_queue_buffer_allocator());
 
   // Create the hot card cache.
   _hot_card_cache = new G1HotCardCache(this);

--- a/src/hotspot/share/gc/g1/g1DirtyCardQueue.cpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/g1/g1DirtyCardQueue.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -56,21 +56,18 @@
   }
 };
 
-G1DirtyCardQueue::G1DirtyCardQueue(G1DirtyCardQueueSet* qset, bool permanent) :
+G1DirtyCardQueue::G1DirtyCardQueue(G1DirtyCardQueueSet* qset) :
   // Dirty card queues are always active, so we create them with their
   // active field set to true.
-  PtrQueue(qset, permanent, true /* active */)
+  PtrQueue(qset, true /* active */)
 { }
 
 G1DirtyCardQueue::~G1DirtyCardQueue() {
-  if (!is_permanent()) {
-    flush();
-  }
+  flush();
 }
 
 G1DirtyCardQueueSet::G1DirtyCardQueueSet(bool notify_when_complete) :
   PtrQueueSet(notify_when_complete),
-  _shared_dirty_card_queue(this, true /* permanent */),
   _free_ids(NULL),
   _processed_buffers_mut(0),
   _processed_buffers_rs_thread(0),
@@ -90,10 +87,8 @@
 
 void G1DirtyCardQueueSet::initialize(Monitor* cbl_mon,
                                      BufferNode::Allocator* allocator,
-                                     Mutex* lock,
                                      bool init_free_ids) {
   PtrQueueSet::initialize(cbl_mon, allocator);
-  _shared_dirty_card_queue.set_lock(lock);
   if (init_free_ids) {
     _free_ids = new G1FreeIdSet(0, num_par_ids());
   }
@@ -217,13 +212,7 @@
   } closure;
   Threads::threads_do(&closure);
 
-  shared_dirty_card_queue()->reset();
-}
-
-void G1DirtyCardQueueSet::concatenate_log(G1DirtyCardQueue& dcq) {
-  if (!dcq.is_empty()) {
-    dcq.flush();
-  }
+  G1BarrierSet::shared_dirty_card_queue().reset();
 }
 
 void G1DirtyCardQueueSet::concatenate_logs() {
@@ -234,16 +223,16 @@
   size_t old_limit = max_completed_buffers();
   set_max_completed_buffers(MaxCompletedBuffersUnlimited);
 
-  class ConcatenateThreadLogClosure : public ThreadClosure {
-    G1DirtyCardQueueSet* _qset;
-  public:
-    ConcatenateThreadLogClosure(G1DirtyCardQueueSet* qset) : _qset(qset) {}
+  struct ConcatenateThreadLogClosure : public ThreadClosure {
     virtual void do_thread(Thread* t) {
-      _qset->concatenate_log(G1ThreadLocalData::dirty_card_queue(t));
+      G1DirtyCardQueue& dcq = G1ThreadLocalData::dirty_card_queue(t);
+      if (!dcq.is_empty()) {
+        dcq.flush();
+      }
     }
-  } closure(this);
+  } closure;
   Threads::threads_do(&closure);
 
-  concatenate_log(_shared_dirty_card_queue);
+  G1BarrierSet::shared_dirty_card_queue().flush();
   set_max_completed_buffers(old_limit);
 }

--- a/src/hotspot/share/gc/g1/g1DirtyCardQueue.hpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/g1/g1DirtyCardQueue.hpp	Fri Mar 22 15:42:43 2019 -0400
@@ -48,7 +48,7 @@
 // A ptrQueue whose elements are "oops", pointers to object heads.
 class G1DirtyCardQueue: public PtrQueue {
 public:
-  G1DirtyCardQueue(G1DirtyCardQueueSet* qset, bool permanent = false);
+  G1DirtyCardQueue(G1DirtyCardQueueSet* qset);
 
   // Flush before destroying; queue may be used to capture pending work while
   // doing something else, with auto-flush on completion.
@@ -70,11 +70,7 @@
 
 };
 
-
-
 class G1DirtyCardQueueSet: public PtrQueueSet {
-  G1DirtyCardQueue _shared_dirty_card_queue;
-
   // Apply the closure to the elements of "node" from it's index to
   // buffer_size.  If all closure applications return true, then
   // returns true.  Stops processing after the first closure
@@ -116,15 +112,12 @@
   // Current buffer node used for parallel iteration.
   BufferNode* volatile _cur_par_buffer_node;
 
-  void concatenate_log(G1DirtyCardQueue& dcq);
-
 public:
   G1DirtyCardQueueSet(bool notify_when_complete = true);
   ~G1DirtyCardQueueSet();
 
   void initialize(Monitor* cbl_mon,
                   BufferNode::Allocator* allocator,
-                  Mutex* lock,
                   bool init_free_ids = false);
 
   // The number of parallel ids that can be claimed to allow collector or
@@ -147,10 +140,6 @@
   // by reset_for_par_iteration.
   void par_apply_closure_to_all_completed_buffers(G1CardTableEntryClosure* cl);
 
-  G1DirtyCardQueue* shared_dirty_card_queue() {
-    return &_shared_dirty_card_queue;
-  }
-
   // If a full collection is happening, reset partial logs, and ignore
   // completed ones: the full collection will make them all irrelevant.
   void abandon_logs();

--- a/src/hotspot/share/gc/g1/g1RemSet.cpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/g1/g1RemSet.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -35,6 +35,7 @@
 #include "gc/g1/g1OopClosures.inline.hpp"
 #include "gc/g1/g1RootClosures.hpp"
 #include "gc/g1/g1RemSet.hpp"
+#include "gc/g1/g1SharedDirtyCardQueue.hpp"
 #include "gc/g1/heapRegion.inline.hpp"
 #include "gc/g1/heapRegionManager.inline.hpp"
 #include "gc/g1/heapRegionRemSet.hpp"
@@ -519,9 +520,7 @@
 }
 
 void G1RemSet::prepare_for_oops_into_collection_set_do() {
-  G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
-  dcqs.concatenate_logs();
-
+  G1BarrierSet::dirty_card_queue_set().concatenate_logs();
   _scan_state->reset();
 }
 
@@ -660,29 +659,30 @@
   assert(!dirty_region.is_empty(), "sanity");
 
   G1ConcurrentRefineOopClosure conc_refine_cl(_g1h, worker_i);
-
-  bool card_processed =
-    r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl);
+  if (r->oops_on_card_seq_iterate_careful<false>(dirty_region, &conc_refine_cl)) {
+    _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
+    return;
+  }
 
   // If unable to process the card then we encountered an unparsable
-  // part of the heap (e.g. a partially allocated object) while
-  // processing a stale card.  Despite the card being stale, redirty
-  // and re-enqueue, because we've already cleaned the card.  Without
-  // this we could incorrectly discard a non-stale card.
-  if (!card_processed) {
-    // The card might have gotten re-dirtied and re-enqueued while we
-    // worked.  (In fact, it's pretty likely.)
-    if (*card_ptr != G1CardTable::dirty_card_val()) {
-      *card_ptr = G1CardTable::dirty_card_val();
-      MutexLockerEx x(Shared_DirtyCardQ_lock,
-                      Mutex::_no_safepoint_check_flag);
-      G1DirtyCardQueue* sdcq =
-        G1BarrierSet::dirty_card_queue_set().shared_dirty_card_queue();
-      sdcq->enqueue(card_ptr);
-    }
-  } else {
-    _num_conc_refined_cards++; // Unsynchronized update, only used for logging.
+  // part of the heap (e.g. a partially allocated object, so only
+  // temporarily a problem) while processing a stale card.  Despite
+  // the card being stale, we can't simply ignore it, because we've
+  // already marked the card cleaned, so taken responsibility for
+  // ensuring the card gets scanned.
+  //
+  // However, the card might have gotten re-dirtied and re-enqueued
+  // while we worked.  (In fact, it's pretty likely.)
+  if (*card_ptr == G1CardTable::dirty_card_val()) {
+    return;
   }
+
+  // Re-dirty the card and enqueue in the *shared* queue.  Can't use
+  // the thread-local queue, because that might be the queue that is
+  // being processed by us; we could be a Java thread conscripted to
+  // perform refinement on our queue's current buffer.
+  *card_ptr = G1CardTable::dirty_card_val();
+  G1BarrierSet::shared_dirty_card_queue().enqueue(card_ptr);
 }
 
 bool G1RemSet::refine_card_during_gc(CardValue* card_ptr,

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/g1/g1SharedDirtyCardQueue.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2019, 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.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc/g1/g1DirtyCardQueue.hpp"
+#include "gc/g1/g1SharedDirtyCardQueue.hpp"
+#include "gc/shared/ptrQueue.hpp"
+#include "runtime/mutex.hpp"
+#include "runtime/mutexLocker.hpp"
+
+G1SharedDirtyCardQueue::G1SharedDirtyCardQueue(G1DirtyCardQueueSet* qset) :
+  _qset(qset),
+  _buffer(NULL),
+  _index(0)
+{}
+
+G1SharedDirtyCardQueue::~G1SharedDirtyCardQueue() {
+  flush();
+}
+
+void G1SharedDirtyCardQueue::enqueue(void* card_ptr) {
+  MutexLockerEx ml(Shared_DirtyCardQ_lock, Mutex::_no_safepoint_check_flag);
+  if (_index == 0) {
+    flush();
+    _buffer = _qset->allocate_buffer();
+    _index = _qset->buffer_size();
+    assert(_index != 0, "invariant");
+  }
+  _buffer[--_index] = card_ptr;
+}
+
+void G1SharedDirtyCardQueue::flush() {
+  if (_buffer != NULL) {
+    BufferNode* node = BufferNode::make_node_from_buffer(_buffer, _index);
+    _buffer = NULL;
+    _index = 0;
+    if (node->index() == _qset->buffer_size()) {
+      _qset->deallocate_buffer(node);
+    } else {
+      _qset->enqueue_completed_buffer(node);
+    }
+  }
+  assert(_index == 0, "invariant");
+}
+
+void G1SharedDirtyCardQueue::reset() {
+  if (_buffer == NULL) {
+    _index = 0;
+  } else {
+    _index = _qset->buffer_size();
+  }
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/g1/g1SharedDirtyCardQueue.hpp	Fri Mar 22 15:42:43 2019 -0400
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2019, 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_G1_G1SHAREDDIRTYCARDQUEUE_HPP
+#define SHARE_GC_G1_G1SHAREDDIRTYCARDQUEUE_HPP
+
+#include "utilities/globalDefinitions.hpp"
+
+class G1DirtyCardQueueSet;
+
+// A dirty card queue providing thread-safe enqueue.  A shared global
+// instance can be used for cases where a thread-local dirty card can't
+// be used.
+class G1SharedDirtyCardQueue {
+  G1DirtyCardQueueSet* const _qset;
+  void** _buffer;
+  size_t _index;
+
+  // Noncopyable
+  G1SharedDirtyCardQueue(const G1SharedDirtyCardQueue&);
+  G1SharedDirtyCardQueue& operator=(const G1SharedDirtyCardQueue&);
+
+public:
+  G1SharedDirtyCardQueue(G1DirtyCardQueueSet* qset);
+  ~G1SharedDirtyCardQueue();    // flushes the queue.
+
+  // Thread-safe addition to shared logging buffer.
+  void enqueue(void* card_ptr);
+
+  // Flush any pending entries to the qset and remove the buffer.
+  // Not thread-safe.
+  void flush();
+
+  // Discard any pending entries.
+  // Not thread-safe.
+  void reset();
+};
+
+#endif // SHARE_GC_G1_G1SHAREDDIRTYCARDQUEUE_HPP

--- a/src/hotspot/share/gc/shared/ptrQueue.cpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/shared/ptrQueue.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -36,18 +36,16 @@
 
 #include <new>
 
-PtrQueue::PtrQueue(PtrQueueSet* qset, bool permanent, bool active) :
+PtrQueue::PtrQueue(PtrQueueSet* qset, bool active) :
   _qset(qset),
   _active(active),
-  _permanent(permanent),
   _index(0),
   _capacity_in_bytes(0),
-  _buf(NULL),
-  _lock(NULL)
+  _buf(NULL)
 {}
 
 PtrQueue::~PtrQueue() {
-  assert(_permanent || (_buf == NULL), "queue must be flushed before delete");
+  assert(_buf == NULL, "queue must be flushed before delete");
 }
 
 void PtrQueue::flush_impl() {
@@ -271,23 +269,13 @@
       return;
     }
 
-    if (_lock) {
-      assert(_lock->owned_by_self(), "Required.");
-
-      BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
-      _buf = NULL;         // clear shared _buf field
-
-      qset()->enqueue_completed_buffer(node);
-      assert(_buf == NULL, "multiple enqueuers appear to be racing");
-    } else {
-      BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
-      if (qset()->process_or_enqueue_completed_buffer(node)) {
-        // Recycle the buffer. No allocation.
-        assert(_buf == BufferNode::make_buffer_from_node(node), "invariant");
-        assert(capacity() == qset()->buffer_size(), "invariant");
-        reset();
-        return;
-      }
+    BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
+    if (qset()->process_or_enqueue_completed_buffer(node)) {
+      // Recycle the buffer. No allocation.
+      assert(_buf == BufferNode::make_buffer_from_node(node), "invariant");
+      assert(capacity() == qset()->buffer_size(), "invariant");
+      reset();
+      return;
     }
   }
   // Set capacity in case this is the first allocation.

--- a/src/hotspot/share/gc/shared/ptrQueue.hpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/shared/ptrQueue.hpp	Fri Mar 22 15:42:43 2019 -0400
@@ -54,11 +54,6 @@
   // 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.
@@ -111,27 +106,20 @@
     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);
+  PtrQueue(PtrQueueSet* qset, bool active = false);
 
-  // Requires queue flushed or permanent.
+  // Requires queue flushed.
   ~PtrQueue();
 
 public:
 
-  // Associate a lock with a ptr queue.
-  void set_lock(Mutex* lock) { _lock = lock; }
-
   // Forcibly set empty.
   void reset() {
     if (_buf != NULL) {

--- a/src/hotspot/share/gc/shared/satbMarkQueue.cpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/shared/satbMarkQueue.cpp	Fri Mar 22 15:42:43 2019 -0400
@@ -35,14 +35,14 @@
 #include "runtime/threadSMR.hpp"
 #include "runtime/vmThread.hpp"
 
-SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
+SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset) :
   // SATB queues are only active during marking cycles. We create
   // them with their active field set to false. If a thread is
   // created during a cycle and its SATB queue needs to be activated
   // before the thread starts running, we'll need to set its active
   // field to true. This must be done in the collector-specific
   // BarrierSet thread attachment protocol.
-  PtrQueue(qset, permanent, false /* active */)
+  PtrQueue(qset, false /* active */)
 { }
 
 void SATBMarkQueue::flush() {

--- a/src/hotspot/share/gc/shared/satbMarkQueue.hpp	Fri Mar 22 16:16:10 2019 -0400
+++ b/src/hotspot/share/gc/shared/satbMarkQueue.hpp	Fri Mar 22 15:42:43 2019 -0400
@@ -55,7 +55,7 @@
   inline void apply_filter(Filter filter_out);
 
 public:
-  SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent = false);
+  SATBMarkQueue(SATBMarkQueueSet* qset);
 
   // Process queue entries and free resources.
   void flush();