diff -r 04f4e983c2f7 -r 767cdb97f103 src/hotspot/share/gc/z/zReferenceProcessor.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/z/zReferenceProcessor.cpp	Tue Jun 12 17:40:28 2018 +0200
@@ -0,0 +1,429 @@
+/*
+ * Copyright (c) 2015, 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.
+ */
+
+#include "precompiled.hpp"
+#include "classfile/javaClasses.inline.hpp"
+#include "gc/shared/referencePolicy.hpp"
+#include "gc/shared/referenceProcessorStats.hpp"
+#include "gc/z/zHeap.inline.hpp"
+#include "gc/z/zOopClosures.inline.hpp"
+#include "gc/z/zReferenceProcessor.hpp"
+#include "gc/z/zStat.hpp"
+#include "gc/z/zTask.hpp"
+#include "gc/z/zTracer.inline.hpp"
+#include "gc/z/zUtils.inline.hpp"
+#include "memory/universe.hpp"
+#include "runtime/mutexLocker.hpp"
+#include "runtime/os.hpp"
+
+static const ZStatSubPhase ZSubPhaseConcurrentReferencesProcess("Concurrent References Process");
+static const ZStatSubPhase ZSubPhaseConcurrentReferencesEnqueue("Concurrent References Enqueue");
+
+ZReferenceProcessor::ZReferenceProcessor(ZWorkers* workers) :
+    _workers(workers),
+    _soft_reference_policy(NULL),
+    _encountered_count(),
+    _discovered_count(),
+    _enqueued_count(),
+    _discovered_list(NULL),
+    _pending_list(NULL),
+    _pending_list_tail(_pending_list.addr()) {}
+
+void ZReferenceProcessor::set_soft_reference_policy(bool clear) {
+  static AlwaysClearPolicy always_clear_policy;
+  static LRUMaxHeapPolicy lru_max_heap_policy;
+
+  if (clear) {
+    log_info(gc, ref)("Clearing All Soft References");
+    _soft_reference_policy = &always_clear_policy;
+  } else {
+    _soft_reference_policy = &lru_max_heap_policy;
+  }
+
+  _soft_reference_policy->setup();
+}
+
+void ZReferenceProcessor::update_soft_reference_clock() const {
+  const jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
+  java_lang_ref_SoftReference::set_clock(now);
+}
+
+bool ZReferenceProcessor::is_reference_inactive(oop obj) const {
+  // A non-null next field means the reference is inactive
+  return java_lang_ref_Reference::next(obj) != NULL;
+}
+
+ReferenceType ZReferenceProcessor::reference_type(oop obj) const {
+  return InstanceKlass::cast(obj->klass())->reference_type();
+}
+
+const char* ZReferenceProcessor::reference_type_name(ReferenceType type) const {
+  switch (type) {
+  case REF_SOFT:
+    return "Soft";
+
+  case REF_WEAK:
+    return "Weak";
+
+  case REF_FINAL:
+    return "Final";
+
+  case REF_PHANTOM:
+    return "Phantom";
+
+  default:
+    ShouldNotReachHere();
+    return NULL;
+  }
+}
+
+volatile oop* ZReferenceProcessor::reference_referent_addr(oop obj) const {
+  return (volatile oop*)java_lang_ref_Reference::referent_addr_raw(obj);
+}
+
+oop ZReferenceProcessor::reference_referent(oop obj) const {
+  return *reference_referent_addr(obj);
+}
+
+bool ZReferenceProcessor::is_referent_alive_or_null(oop obj, ReferenceType type) const {
+  volatile oop* const p = reference_referent_addr(obj);
+
+  // Check if the referent is alive or null, in which case we don't want to discover
+  // the reference. It can only be null if the application called Reference.enqueue()
+  // or Reference.clear().
+  if (type == REF_PHANTOM) {
+    const oop o = ZBarrier::weak_load_barrier_on_phantom_oop_field(p);
+    return o == NULL || ZHeap::heap()->is_object_live(ZOop::to_address(o));
+  } else {
+    const oop o = ZBarrier::weak_load_barrier_on_weak_oop_field(p);
+    return o == NULL || ZHeap::heap()->is_object_strongly_live(ZOop::to_address(o));
+  }
+}
+
+bool ZReferenceProcessor::is_referent_softly_alive(oop obj, ReferenceType type) const {
+  if (type != REF_SOFT) {
+    // Not a soft reference
+    return false;
+  }
+
+  // Ask soft reference policy
+  const jlong clock = java_lang_ref_SoftReference::clock();
+  assert(clock != 0, "Clock not initialized");
+  assert(_soft_reference_policy != NULL, "Policy not initialized");
+  return !_soft_reference_policy->should_clear_reference(obj, clock);
+}
+
+bool ZReferenceProcessor::should_drop_reference(oop obj, ReferenceType type) const {
+  // This check is racing with a call to Reference.clear() from the application.
+  // If the application clears the reference after this check it will still end
+  // up on the pending list, and there's nothing we can do about that without
+  // changing the Reference.clear() API. This check is also racing with a call
+  // to Reference.enqueue() from the application, which is unproblematic, since
+  // the application wants the reference to be enqueued anyway.
+  const oop o = reference_referent(obj);
+  if (o == NULL) {
+    // Reference has been cleared, by a call to Reference.enqueue()
+    // or Reference.clear() from the application, which means we
+    // should drop the reference.
+    return true;
+  }
+
+  // Check if the referent is still alive, in which case we should
+  // drop the reference.
+  if (type == REF_PHANTOM) {
+    return ZBarrier::is_alive_barrier_on_phantom_oop(o);
+  } else {
+    return ZBarrier::is_alive_barrier_on_weak_oop(o);
+  }
+}
+
+bool ZReferenceProcessor::should_mark_referent(ReferenceType type) const {
+  // Referents of final references (and its reachable sub graph) are
+  // always marked finalizable during discovery. This avoids the problem
+  // of later having to mark those objects if the referent is still final
+  // reachable during processing.
+  return type == REF_FINAL;
+}
+
+bool ZReferenceProcessor::should_clear_referent(ReferenceType type) const {
+  // Referents that were not marked must be cleared
+  return !should_mark_referent(type);
+}
+
+void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const {
+  volatile oop* const p = reference_referent_addr(obj);
+  if (type == REF_PHANTOM) {
+    ZBarrier::keep_alive_barrier_on_phantom_oop_field(p);
+  } else {
+    ZBarrier::keep_alive_barrier_on_weak_oop_field(p);
+  }
+}
+
+bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {
+  if (!RegisterReferences) {
+    // Reference processing disabled
+    return false;
+  }
+
+  log_trace(gc, ref)("Encountered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
+
+  // Update statistics
+  _encountered_count.get()[type]++;
+
+  if (is_reference_inactive(obj) ||
+      is_referent_alive_or_null(obj, type) ||
+      is_referent_softly_alive(obj, type)) {
+    // Not discovered
+    return false;
+  }
+
+  discover(obj, type);
+
+  // Discovered
+  return true;
+}
+
+void ZReferenceProcessor::discover(oop obj, ReferenceType type) {
+  log_trace(gc, ref)("Discovered Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
+
+  // Update statistics
+  _discovered_count.get()[type]++;
+
+  // Mark referent finalizable
+  if (should_mark_referent(type)) {
+    oop* const referent_addr = (oop*)java_lang_ref_Reference::referent_addr_raw(obj);
+    ZBarrier::mark_barrier_on_oop_field(referent_addr, true /* finalizable */);
+  }
+
+  // Add reference to discovered list
+  assert(java_lang_ref_Reference::discovered(obj) == NULL, "Already discovered");
+  oop* const list = _discovered_list.addr();
+  java_lang_ref_Reference::set_discovered(obj, *list);
+  *list = obj;
+}
+
+oop ZReferenceProcessor::drop(oop obj, ReferenceType type) {
+  log_trace(gc, ref)("Dropped Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
+
+  // Keep referent alive
+  keep_referent_alive(obj, type);
+
+  // Unlink and return next in list
+  const oop next = java_lang_ref_Reference::discovered(obj);
+  java_lang_ref_Reference::set_discovered(obj, NULL);
+  return next;
+}
+
+oop* ZReferenceProcessor::keep(oop obj, ReferenceType type) {
+  log_trace(gc, ref)("Enqueued Reference: " PTR_FORMAT " (%s)", p2i(obj), reference_type_name(type));
+
+  // Update statistics
+  _enqueued_count.get()[type]++;
+
+  // Clear referent
+  if (should_clear_referent(type)) {
+    java_lang_ref_Reference::set_referent(obj, NULL);
+  }
+
+  // Make reference inactive by self-looping the next field. We could be racing with a
+  // call to Reference.enqueue() from the application, which is why we are using a CAS
+  // to make sure we change the next field only if it is NULL. A failing CAS means the
+  // reference has already been enqueued. However, we don't check the result of the CAS,
+  // since we still have no option other than keeping the reference on the pending list.
+  // It's ok to have the reference both on the pending list and enqueued at the same
+  // time (the pending list is linked through the discovered field, while the reference
+  // queue is linked through the next field). When the ReferenceHandler thread later
+  // calls Reference.enqueue() we detect that it has already been enqueued and drop it.
+  oop* const next_addr = (oop*)java_lang_ref_Reference::next_addr_raw(obj);
+  Atomic::cmpxchg(obj, next_addr, oop(NULL));
+
+  // Return next in list
+  return (oop*)java_lang_ref_Reference::discovered_addr_raw(obj);
+}
+
+void ZReferenceProcessor::work() {
+  // Process discovered references
+  oop* const list = _discovered_list.addr();
+  oop* p = list;
+
+  while (*p != NULL) {
+    const oop obj = *p;
+    const ReferenceType type = reference_type(obj);
+
+    if (should_drop_reference(obj, type)) {
+      *p = drop(obj, type);
+    } else {
+      p = keep(obj, type);
+    }
+  }
+
+  // Prepend discovered references to internal pending list
+  if (*list != NULL) {
+    *p = Atomic::xchg(*list, _pending_list.addr());
+    if (*p == NULL) {
+      // First to prepend to list, record tail
+      _pending_list_tail = p;
+    }
+
+    // Clear discovered list
+    *list = NULL;
+  }
+}
+
+bool ZReferenceProcessor::is_empty() const {
+  ZPerWorkerConstIterator<oop> iter(&_discovered_list);
+  for (const oop* list; iter.next(&list);) {
+    if (*list != NULL) {
+      return false;
+    }
+  }
+
+  if (_pending_list.get() != NULL) {
+    return false;
+  }
+
+  return true;
+}
+
+void ZReferenceProcessor::reset_statistics() {
+  assert(is_empty(), "Should be empty");
+
+  // Reset encountered
+  ZPerWorkerIterator<Counters> iter_encountered(&_encountered_count);
+  for (Counters* counters; iter_encountered.next(&counters);) {
+    for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
+      (*counters)[i] = 0;
+    }
+  }
+
+  // Reset discovered
+  ZPerWorkerIterator<Counters> iter_discovered(&_discovered_count);
+  for (Counters* counters; iter_discovered.next(&counters);) {
+    for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
+      (*counters)[i] = 0;
+    }
+  }
+
+  // Reset enqueued
+  ZPerWorkerIterator<Counters> iter_enqueued(&_enqueued_count);
+  for (Counters* counters; iter_enqueued.next(&counters);) {
+    for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
+      (*counters)[i] = 0;
+    }
+  }
+}
+
+void ZReferenceProcessor::collect_statistics() {
+  Counters encountered = {};
+  Counters discovered = {};
+  Counters enqueued = {};
+
+  // Sum encountered
+  ZPerWorkerConstIterator<Counters> iter_encountered(&_encountered_count);
+  for (const Counters* counters; iter_encountered.next(&counters);) {
+    for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
+      encountered[i] += (*counters)[i];
+    }
+  }
+
+  // Sum discovered
+  ZPerWorkerConstIterator<Counters> iter_discovered(&_discovered_count);
+  for (const Counters* counters; iter_discovered.next(&counters);) {
+    for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
+      discovered[i] += (*counters)[i];
+    }
+  }
+
+  // Sum enqueued
+  ZPerWorkerConstIterator<Counters> iter_enqueued(&_enqueued_count);
+  for (const Counters* counters; iter_enqueued.next(&counters);) {
+    for (int i = REF_SOFT; i <= REF_PHANTOM; i++) {
+      enqueued[i] += (*counters)[i];
+    }
+  }
+
+  // Update statistics
+  ZStatReferences::set_soft(encountered[REF_SOFT], discovered[REF_SOFT], enqueued[REF_SOFT]);
+  ZStatReferences::set_weak(encountered[REF_WEAK], discovered[REF_WEAK], enqueued[REF_WEAK]);
+  ZStatReferences::set_final(encountered[REF_FINAL], discovered[REF_FINAL], enqueued[REF_FINAL]);
+  ZStatReferences::set_phantom(encountered[REF_PHANTOM], discovered[REF_PHANTOM], enqueued[REF_PHANTOM]);
+
+  // Trace statistics
+  const ReferenceProcessorStats stats(discovered[REF_SOFT],
+                                      discovered[REF_WEAK],
+                                      discovered[REF_FINAL],
+                                      discovered[REF_PHANTOM]);
+  ZTracer::tracer()->report_gc_reference_stats(stats);
+}
+
+class ZReferenceProcessorTask : public ZTask {
+private:
+  ZReferenceProcessor* const _reference_processor;
+
+public:
+  ZReferenceProcessorTask(ZReferenceProcessor* reference_processor) :
+      ZTask("ZReferenceProcessorTask"),
+      _reference_processor(reference_processor) {}
+
+  virtual void work() {
+    _reference_processor->work();
+  }
+};
+
+void ZReferenceProcessor::process_references() {
+  ZStatTimer timer(ZSubPhaseConcurrentReferencesProcess);
+
+  // Process discovered lists
+  ZReferenceProcessorTask task(this);
+  _workers->run_concurrent(&task);
+
+  // Update soft reference clock
+  update_soft_reference_clock();
+
+  // Collect, log and trace statistics
+  collect_statistics();
+}
+
+void ZReferenceProcessor::enqueue_references() {
+  ZStatTimer timer(ZSubPhaseConcurrentReferencesEnqueue);
+
+  if (_pending_list.get() == NULL) {
+    // Nothing to enqueue
+    return;
+  }
+
+  {
+    // Heap_lock protects external pending list
+    MonitorLockerEx ml(Heap_lock);
+
+    // Prepend internal pending list to external pending list
+    *_pending_list_tail = Universe::swap_reference_pending_list(_pending_list.get());
+
+    // Notify ReferenceHandler thread
+    ml.notify_all();
+  }
+
+  // Reset internal pending list
+  _pending_list.set(NULL);
+  _pending_list_tail = _pending_list.addr();
+}