/*

 * 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();

}