/*

 * Copyright (c) 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/shared/gcCause.hpp"

#include "gc/shenandoah/shenandoahBrooksPointer.hpp"

#include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"

#include "gc/shenandoah/shenandoahCollectorPolicy.hpp"

#include "gc/shenandoah/shenandoahHeap.inline.hpp"

#include "gc/shenandoah/shenandoahHeapRegion.hpp"

#include "gc/shenandoah/shenandoahHeuristics.hpp"

#include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"

#include "logging/log.hpp"

#include "logging/logTag.hpp"

int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {

  if (a._garbage > b._garbage)

    return -1;

  else if (a._garbage < b._garbage)

    return 1;

  else return 0;

}

int ShenandoahHeuristics::compare_by_garbage_then_alloc_seq_ascending(RegionData a, RegionData b) {

  int r = compare_by_garbage(a, b);

  if (r != 0) {

    return r;

  }

  return compare_by_alloc_seq_ascending(a, b);

}

int ShenandoahHeuristics::compare_by_alloc_seq_ascending(RegionData a, RegionData b) {

  if (a._seqnum_last_alloc == b._seqnum_last_alloc)

    return 0;

  else if (a._seqnum_last_alloc < b._seqnum_last_alloc)

    return -1;

  else return 1;

}

int ShenandoahHeuristics::compare_by_alloc_seq_descending(RegionData a, RegionData b) {

  return -compare_by_alloc_seq_ascending(a, b);

}

ShenandoahHeuristics::ShenandoahHeuristics() :

  _update_refs_early(false),

  _update_refs_adaptive(false),

  _region_data(NULL),

  _region_data_size(0),

  _degenerated_cycles_in_a_row(0),

  _successful_cycles_in_a_row(0),

  _bytes_in_cset(0),

  _cycle_start(os::elapsedTime()),

  _last_cycle_end(0),

  _gc_times_learned(0),

  _gc_time_penalties(0),

  _gc_time_history(new TruncatedSeq(5)),

  _metaspace_oom()

{

  if (strcmp(ShenandoahUpdateRefsEarly, "on") == 0 ||

      strcmp(ShenandoahUpdateRefsEarly, "true") == 0 ) {

    _update_refs_early = true;

  } else if (strcmp(ShenandoahUpdateRefsEarly, "off") == 0 ||

             strcmp(ShenandoahUpdateRefsEarly, "false") == 0 ) {

    _update_refs_early = false;

  } else if (strcmp(ShenandoahUpdateRefsEarly, "adaptive") == 0) {

    _update_refs_adaptive = true;

    _update_refs_early = true;

  } else {

    vm_exit_during_initialization("Unknown -XX:ShenandoahUpdateRefsEarly option: %s", ShenandoahUpdateRefsEarly);

  }

  // No unloading during concurrent mark? Communicate that to heuristics

  if (!ClassUnloadingWithConcurrentMark) {

    FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);

  }

}

ShenandoahHeuristics::~ShenandoahHeuristics() {

  if (_region_data != NULL) {

    FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);

  }

}

ShenandoahHeuristics::RegionData* ShenandoahHeuristics::get_region_data_cache(size_t num) {

  RegionData* res = _region_data;

  if (res == NULL) {

    res = NEW_C_HEAP_ARRAY(RegionData, num, mtGC);

    _region_data = res;

    _region_data_size = num;

  } else if (_region_data_size < num) {

    res = REALLOC_C_HEAP_ARRAY(RegionData, _region_data, num, mtGC);

    _region_data = res;

    _region_data_size = num;

  }

  return res;

}

void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {

  assert(collection_set->count() == 0, "Must be empty");

  ShenandoahHeap* heap = ShenandoahHeap::heap();

  // Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.

  size_t num_regions = heap->num_regions();

  RegionData* candidates = get_region_data_cache(num_regions);

  size_t cand_idx = 0;

  size_t total_garbage = 0;

  size_t immediate_garbage = 0;

  size_t immediate_regions = 0;

  size_t free = 0;

  size_t free_regions = 0;

  ShenandoahMarkingContext* const ctx = heap->complete_marking_context();

  for (size_t i = 0; i < num_regions; i++) {

    ShenandoahHeapRegion* region = heap->get_region(i);

    size_t garbage = region->garbage();

    total_garbage += garbage;

    if (region->is_empty()) {

      free_regions++;

      free += ShenandoahHeapRegion::region_size_bytes();

    } else if (region->is_regular()) {

      if (!region->has_live()) {

        // We can recycle it right away and put it in the free set.

        immediate_regions++;

        immediate_garbage += garbage;

        region->make_trash_immediate();

      } else {

        // This is our candidate for later consideration.

        candidates[cand_idx]._region = region;

        candidates[cand_idx]._garbage = garbage;

        cand_idx++;

      }

    } else if (region->is_humongous_start()) {

      // Reclaim humongous regions here, and count them as the immediate garbage

#ifdef ASSERT

      bool reg_live = region->has_live();

      bool bm_live = ctx->is_marked(oop(region->bottom() + ShenandoahBrooksPointer::word_size()));

      assert(reg_live == bm_live,

             "Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,

             BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());

#endif

      if (!region->has_live()) {

        heap->trash_humongous_region_at(region);

        // Count only the start. Continuations would be counted on "trash" path

        immediate_regions++;

        immediate_garbage += garbage;

      }

    } else if (region->is_trash()) {

      // Count in just trashed collection set, during coalesced CM-with-UR

      immediate_regions++;

      immediate_garbage += garbage;

    }

  }

  // Step 2. Look back at garbage statistics, and decide if we want to collect anything,

  // given the amount of immediately reclaimable garbage. If we do, figure out the collection set.

  assert (immediate_garbage <= total_garbage,

          "Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "M vs " SIZE_FORMAT "M",

          immediate_garbage / M, total_garbage / M);

  size_t immediate_percent = total_garbage == 0 ? 0 : (immediate_garbage * 100 / total_garbage);

  if (immediate_percent <= ShenandoahImmediateThreshold) {

    choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);

    collection_set->update_region_status();

    size_t cset_percent = total_garbage == 0 ? 0 : (collection_set->garbage() * 100 / total_garbage);

    log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "M (" SIZE_FORMAT "%% of total), " SIZE_FORMAT "M CSet, " SIZE_FORMAT " CSet regions",

                       collection_set->garbage() / M, cset_percent, collection_set->live_data() / M, collection_set->count());

  }

  log_info(gc, ergo)("Immediate Garbage: " SIZE_FORMAT "M (" SIZE_FORMAT "%% of total), " SIZE_FORMAT " regions",

                     immediate_garbage / M, immediate_percent, immediate_regions);

}

void ShenandoahHeuristics::record_gc_start() {

  // Do nothing

}

void ShenandoahHeuristics::record_gc_end() {

  // Do nothing

}

void ShenandoahHeuristics::record_cycle_start() {

  _cycle_start = os::elapsedTime();

}

void ShenandoahHeuristics::record_cycle_end() {

  _last_cycle_end = os::elapsedTime();

}

void ShenandoahHeuristics::record_phase_time(ShenandoahPhaseTimings::Phase phase, double secs) {

  // Do nothing

}

bool ShenandoahHeuristics::should_start_update_refs() {

  return _update_refs_early;

}

bool ShenandoahHeuristics::should_start_normal_gc() const {

  // Perform GC to cleanup metaspace

  if (has_metaspace_oom()) {

    // Some of vmTestbase/metaspace tests depend on following line to count GC cycles

    log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));

    return true;

  }

  double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;

  bool periodic_gc = (last_time_ms > ShenandoahGuaranteedGCInterval);

  if (periodic_gc) {

    log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",

                  last_time_ms, ShenandoahGuaranteedGCInterval);

  }

  return periodic_gc;

}

bool ShenandoahHeuristics::should_start_traversal_gc() {

  return false;

}

bool ShenandoahHeuristics::can_do_traversal_gc() {

  return false;

}

bool ShenandoahHeuristics::should_degenerate_cycle() {

  return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;

}

void ShenandoahHeuristics::record_success_concurrent() {

  _degenerated_cycles_in_a_row = 0;

  _successful_cycles_in_a_row++;

  _gc_time_history->add(time_since_last_gc());

  _gc_times_learned++;

  _gc_time_penalties -= MIN2<size_t>(_gc_time_penalties, Concurrent_Adjust);

}

void ShenandoahHeuristics::record_success_degenerated() {

  _degenerated_cycles_in_a_row++;

  _successful_cycles_in_a_row = 0;

  _gc_time_penalties += Degenerated_Penalty;

}

void ShenandoahHeuristics::record_success_full() {

  _degenerated_cycles_in_a_row = 0;

  _successful_cycles_in_a_row++;

  _gc_time_penalties += Full_Penalty;

}

void ShenandoahHeuristics::record_allocation_failure_gc() {

  _bytes_in_cset = 0;

}

void ShenandoahHeuristics::record_requested_gc() {

  _bytes_in_cset = 0;

  // Assume users call System.gc() when external state changes significantly,

  // which forces us to re-learn the GC timings and allocation rates.

  _gc_times_learned = 0;

}

bool ShenandoahHeuristics::can_process_references() {

  if (ShenandoahRefProcFrequency == 0) return false;

  return true;

}

bool ShenandoahHeuristics::should_process_references() {

  if (!can_process_references()) return false;

  size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();

  // Process references every Nth GC cycle.

  return cycle % ShenandoahRefProcFrequency == 0;

}

bool ShenandoahHeuristics::can_unload_classes() {

  if (!ClassUnloading) return false;

  return true;

}

bool ShenandoahHeuristics::can_unload_classes_normal() {

  if (!can_unload_classes()) return false;

  if (has_metaspace_oom()) return true;

  if (!ClassUnloadingWithConcurrentMark) return false;

  if (ShenandoahUnloadClassesFrequency == 0) return false;

  return true;

}

bool ShenandoahHeuristics::should_unload_classes() {

  if (!can_unload_classes_normal()) return false;

  if (has_metaspace_oom()) return true;

  size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();

  // Unload classes every Nth GC cycle.

  // This should not happen in the same cycle as process_references to amortize costs.

  // Offsetting by one is enough to break the rendezvous when periods are equal.

  // When periods are not equal, offsetting by one is just as good as any other guess.

  return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;

}

void ShenandoahHeuristics::initialize() {

  // Nothing to do by default.

}

double ShenandoahHeuristics::time_since_last_gc() const {

  return os::elapsedTime() - _cycle_start;

}