--- /dev/null	2020-01-17 11:46:19.065201212 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahSATBMarkQueue.cpp	2020-01-17 17:10:35.801129063 +0100
@@ -0,0 +1,347 @@
+/*
+ * Copyright (c) 2001, 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 "jvm.h"
+#include "gc/shared/collectedHeap.hpp"
+#include "memory/allocation.inline.hpp"
+#include "oops/oop.inline.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/safepoint.hpp"
+#include "runtime/thread.hpp"
+#include "runtime/threadSMR.hpp"
+#include "runtime/vmThread.hpp"
+#include "utilities/macros.hpp"
+#include "gc/shenandoah/shenandoahHeap.inline.hpp"
+#include "gc/shenandoah/shenandoahSATBMarkQueue.hpp"
+#include "gc/shenandoah/shenandoahThreadLocalData.hpp"
+
+ShenandoahSATBMarkQueue::ShenandoahSATBMarkQueue(ShenandoahSATBMarkQueueSet* qset, bool permanent) :
+  // 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 is done in G1SBarrierSet::on_thread_attach().
+  PtrQueue(qset, permanent, false /* active */)
+{ }
+
+void ShenandoahSATBMarkQueue::flush() {
+  // Filter now to possibly save work later.  If filtering empties the
+  // buffer then flush_impl can deallocate the buffer.
+  filter();
+  flush_impl();
+}
+
+// Return true if a SATB buffer entry refers to an object that
+// requires marking.
+//
+// The entry must point into the Shenandoah heap.  In particular, it must not
+// be a NULL pointer.  NULL pointers are pre-filtered and never
+// inserted into a SATB buffer.
+//
+// An entry that is below the NTAMS pointer for the containing heap
+// region requires marking. Such an entry must point to a valid object.
+//
+// An entry that is at least the NTAMS pointer for the containing heap
+// region might be any of the following, none of which should be marked.
+//
+// * A reference to an object allocated since marking started.
+//   According to SATB, such objects are implicitly kept live and do
+//   not need to be dealt with via SATB buffer processing.
+//
+// * A reference to a young generation object. Young objects are
+//   handled separately and are not marked by concurrent marking.
+//
+// * A stale reference to a young generation object. If a young
+//   generation object reference is recorded and not filtered out
+//   before being moved by a young collection, the reference becomes
+//   stale.
+//
+// * A stale reference to an eagerly reclaimed humongous object.  If a
+//   humongous object is recorded and then reclaimed, the reference
+//   becomes stale.
+//
+// The stale reference cases are implicitly handled by the NTAMS
+// comparison. Because of the possibility of stale references, buffer
+// processing must be somewhat circumspect and not assume entries
+// in an unfiltered buffer refer to valid objects.
+
+inline bool retain_entry(const void* entry, ShenandoahHeap* heap) {
+  return heap->requires_marking(entry);
+}
+
+// This method removes entries from a SATB buffer that will not be
+// useful to the concurrent marking threads.  Entries are retained if
+// they require marking and are not already marked. Retained entries
+// are compacted toward the top of the buffer.
+
+void ShenandoahSATBMarkQueue::filter() {
+  ShenandoahHeap* heap = ShenandoahHeap::heap();
+  void** buf = _buf;
+
+  if (buf == NULL) {
+    // nothing to do
+    return;
+  }
+
+  // Two-fingered compaction toward the end.
+  void** src = &buf[index()];
+  void** dst = &buf[capacity()];
+  assert(src <= dst, "invariant");
+  for ( ; src < dst; ++src) {
+    // Search low to high for an entry to keep.
+    void* entry = *src;
+    if (retain_entry(entry, heap)) {
+      // Found keeper.  Search high to low for an entry to discard.
+      while (src < --dst) {
+        if (!retain_entry(*dst, heap)) {
+          *dst = entry;         // Replace discard with keeper.
+          break;
+        }
+      }
+      // If discard search failed (src == dst), the outer loop will also end.
+    }
+  }
+  // dst points to the lowest retained entry, or the end of the buffer
+  // if all the entries were filtered out.
+  set_index(dst - buf);
+}
+
+// This method will first apply the above filtering to the buffer. If
+// post-filtering a large enough chunk of the buffer has been cleared
+// we can re-use the buffer (instead of enqueueing it) and we can just
+// allow the mutator to carry on executing using the same buffer
+// instead of replacing it.
+
+bool ShenandoahSATBMarkQueue::should_enqueue_buffer() {
+  assert(_lock == NULL || _lock->owned_by_self(),
+         "we should have taken the lock before calling this");
+
+  // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
+
+  // This method should only be called if there is a non-NULL buffer
+  // that is full.
+  assert(index() == 0, "pre-condition");
+  assert(_buf != NULL, "pre-condition");
+
+  filter();
+
+  size_t cap = capacity();
+  size_t percent_used = ((cap - index()) * 100) / cap;
+  bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
+
+  Thread* t = Thread::current();
+  if (ShenandoahThreadLocalData::is_force_satb_flush(t)) {
+    if (!should_enqueue && cap != index()) {
+      // Non-empty buffer is compacted, and we decided not to enqueue it.
+      // We still want to know about leftover work in that buffer eventually.
+      // This avoid dealing with these leftovers during the final-mark, after
+      // the buffers are drained completely. See JDK-8205353 for more discussion.
+      should_enqueue = true;
+    }
+    ShenandoahThreadLocalData::set_force_satb_flush(t, false);
+  }
+  return should_enqueue;
+}
+
+void ShenandoahSATBMarkQueue::apply_closure_and_empty(ShenandoahSATBBufferClosure* cl) {
+  assert(SafepointSynchronize::is_at_safepoint(),
+         "SATB queues must only be processed at safepoints");
+  if (_buf != NULL) {
+    cl->do_buffer(&_buf[index()], size());
+    reset();
+  }
+}
+
+#ifndef PRODUCT
+// Helpful for debugging
+
+static void print_satb_buffer(const char* name,
+                              void** buf,
+                              size_t index,
+                              size_t capacity) {
+  tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
+                " capacity: " SIZE_FORMAT,
+                name, p2i(buf), index, capacity);
+}
+
+void ShenandoahSATBMarkQueue::print(const char* name) {
+  print_satb_buffer(name, _buf, index(), capacity());
+}
+
+#endif // PRODUCT
+
+ShenandoahSATBMarkQueueSet::ShenandoahSATBMarkQueueSet() :
+  PtrQueueSet(),
+  _shared_satb_queue(this, true /* permanent */) { }
+
+void ShenandoahSATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
+                                            int process_completed_threshold,
+                                            Mutex* lock) {
+  PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
+  _shared_satb_queue.set_lock(lock);
+}
+
+#ifdef ASSERT
+void ShenandoahSATBMarkQueueSet::dump_active_states(bool expected_active) {
+  log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
+  log_error(gc, verify)("Actual SATB active states:");
+  log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
+  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
+    log_error(gc, verify)("  Thread \"%s\" queue: %s", t->name(), satb_queue_for_thread(t).is_active() ? "ACTIVE" : "INACTIVE");
+  }
+  log_error(gc, verify)("  Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
+}
+
+void ShenandoahSATBMarkQueueSet::verify_active_states(bool expected_active) {
+  // Verify queue set state
+  if (is_active() != expected_active) {
+    dump_active_states(expected_active);
+    guarantee(false, "SATB queue set has an unexpected active state");
+  }
+
+  // Verify thread queue states
+  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
+    if (satb_queue_for_thread(t).is_active() != expected_active) {
+      dump_active_states(expected_active);
+      guarantee(false, "Thread SATB queue has an unexpected active state");
+    }
+  }
+
+  // Verify shared queue state
+  if (shared_satb_queue()->is_active() != expected_active) {
+    dump_active_states(expected_active);
+    guarantee(false, "Shared SATB queue has an unexpected active state");
+  }
+}
+#endif // ASSERT
+
+void ShenandoahSATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
+  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
+#ifdef ASSERT
+  verify_active_states(expected_active);
+#endif // ASSERT
+  _all_active = active;
+  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
+    satb_queue_for_thread(t).set_active(active);
+  }
+  shared_satb_queue()->set_active(active);
+}
+
+void ShenandoahSATBMarkQueueSet::filter_thread_buffers() {
+  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
+    satb_queue_for_thread(t).filter();
+  }
+  shared_satb_queue()->filter();
+}
+
+bool ShenandoahSATBMarkQueueSet::apply_closure_to_completed_buffer(ShenandoahSATBBufferClosure* cl) {
+  BufferNode* nd = NULL;
+  {
+    MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
+    if (_completed_buffers_head != NULL) {
+      nd = _completed_buffers_head;
+      _completed_buffers_head = nd->next();
+      if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
+      _n_completed_buffers--;
+      if (_n_completed_buffers == 0) _process_completed = false;
+    }
+  }
+  if (nd != NULL) {
+    void **buf = BufferNode::make_buffer_from_node(nd);
+    size_t index = nd->index();
+    size_t size = buffer_size();
+    assert(index <= size, "invariant");
+    cl->do_buffer(buf + index, size - index);
+    deallocate_buffer(nd);
+    return true;
+  } else {
+    return false;
+  }
+}
+
+#ifndef PRODUCT
+// Helpful for debugging
+
+#define SATB_PRINTER_BUFFER_SIZE 256
+
+void ShenandoahSATBMarkQueueSet::print_all(const char* msg) {
+  char buffer[SATB_PRINTER_BUFFER_SIZE];
+  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
+
+  tty->cr();
+  tty->print_cr("SATB BUFFERS [%s]", msg);
+
+  BufferNode* nd = _completed_buffers_head;
+  int i = 0;
+  while (nd != NULL) {
+    void** buf = BufferNode::make_buffer_from_node(nd);
+    jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
+    print_satb_buffer(buffer, buf, nd->index(), buffer_size());
+    nd = nd->next();
+    i += 1;
+  }
+
+  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
+    jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
+    satb_queue_for_thread(t).print(buffer);
+  }
+
+  shared_satb_queue()->print("Shared");
+
+  tty->cr();
+}
+#endif // PRODUCT
+
+void ShenandoahSATBMarkQueueSet::abandon_partial_marking() {
+  BufferNode* buffers_to_delete = NULL;
+  {
+    MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
+    while (_completed_buffers_head != NULL) {
+      BufferNode* nd = _completed_buffers_head;
+      _completed_buffers_head = nd->next();
+      nd->set_next(buffers_to_delete);
+      buffers_to_delete = nd;
+    }
+    _completed_buffers_tail = NULL;
+    _n_completed_buffers = 0;
+    DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
+  }
+  while (buffers_to_delete != NULL) {
+    BufferNode* nd = buffers_to_delete;
+    buffers_to_delete = nd->next();
+    deallocate_buffer(nd);
+  }
+  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
+  // So we can safely manipulate these queues.
+  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
+    satb_queue_for_thread(t).reset();
+  }
+  shared_satb_queue()->reset();
+}
+
+ShenandoahSATBMarkQueue& ShenandoahSATBMarkQueueSet::satb_queue_for_thread(Thread* t) {
+  return ShenandoahThreadLocalData::satb_mark_queue(t);
+}
+