src/hotspot/share/gc/g1/g1CollectedHeap.cpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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#include "classfile/classLoaderDataGraph.hpp"
#include "classfile/metadataOnStackMark.hpp"
#include "classfile/systemDictionary.hpp"
#include "code/codeCache.hpp"
#include "compiler/oopMap.hpp"
#include "gc/g1/g1Allocator.inline.hpp"
#include "gc/g1/g1Arguments.hpp"
#include "gc/g1/g1BarrierSet.hpp"
#include "gc/g1/g1BatchedTask.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1CollectionSet.hpp"
#include "gc/g1/g1CollectionSetCandidates.hpp"
#include "gc/g1/g1CollectorState.hpp"
#include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
#include "gc/g1/g1ConcurrentRefine.hpp"
#include "gc/g1/g1ConcurrentRefineThread.hpp"
#include "gc/g1/g1DirtyCardQueue.hpp"
#include "gc/g1/g1EvacStats.inline.hpp"
#include "gc/g1/g1FullCollector.hpp"
#include "gc/g1/g1GCCounters.hpp"
#include "gc/g1/g1GCParPhaseTimesTracker.hpp"
#include "gc/g1/g1GCPauseType.hpp"
#include "gc/g1/g1GCPhaseTimes.hpp"
#include "gc/g1/g1HeapRegion.inline.hpp"
#include "gc/g1/g1HeapRegionPrinter.hpp"
#include "gc/g1/g1HeapRegionRemSet.inline.hpp"
#include "gc/g1/g1HeapRegionSet.inline.hpp"
#include "gc/g1/g1HeapSizingPolicy.hpp"
#include "gc/g1/g1HeapTransition.hpp"
#include "gc/g1/g1HeapVerifier.hpp"
#include "gc/g1/g1InitLogger.hpp"
#include "gc/g1/g1MemoryPool.hpp"
#include "gc/g1/g1MonotonicArenaFreeMemoryTask.hpp"
#include "gc/g1/g1OopClosures.inline.hpp"
#include "gc/g1/g1ParallelCleaning.hpp"
#include "gc/g1/g1ParScanThreadState.inline.hpp"
#include "gc/g1/g1PeriodicGCTask.hpp"
#include "gc/g1/g1Policy.hpp"
#include "gc/g1/g1RedirtyCardsQueue.hpp"
#include "gc/g1/g1RegionPinCache.inline.hpp"
#include "gc/g1/g1RegionToSpaceMapper.hpp"
#include "gc/g1/g1RemSet.hpp"
#include "gc/g1/g1RootClosures.hpp"
#include "gc/g1/g1RootProcessor.hpp"
#include "gc/g1/g1SATBMarkQueueSet.hpp"
#include "gc/g1/g1ServiceThread.hpp"
#include "gc/g1/g1ThreadLocalData.hpp"
#include "gc/g1/g1Trace.hpp"
#include "gc/g1/g1UncommitRegionTask.hpp"
#include "gc/g1/g1VMOperations.hpp"
#include "gc/g1/g1YoungCollector.hpp"
#include "gc/g1/g1YoungGCAllocationFailureInjector.hpp"
#include "gc/shared/classUnloadingContext.hpp"
#include "gc/shared/concurrentGCBreakpoints.hpp"
#include "gc/shared/fullGCForwarding.hpp"
#include "gc/shared/gcBehaviours.hpp"
#include "gc/shared/gcHeapSummary.hpp"
#include "gc/shared/gcId.hpp"
#include "gc/shared/gcTimer.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
#include "gc/shared/isGCActiveMark.hpp"
#include "gc/shared/locationPrinter.inline.hpp"
#include "gc/shared/oopStorageParState.hpp"
#include "gc/shared/partialArrayState.hpp"
#include "gc/shared/referenceProcessor.inline.hpp"
#include "gc/shared/suspendibleThreadSet.hpp"
#include "gc/shared/taskqueue.inline.hpp"
#include "gc/shared/taskTerminator.hpp"
#include "gc/shared/tlab_globals.hpp"
#include "gc/shared/weakProcessor.inline.hpp"
#include "gc/shared/workerPolicy.hpp"
#include "logging/log.hpp"
#include "memory/allocation.hpp"
#include "memory/heapInspection.hpp"
#include "memory/iterator.hpp"
#include "memory/memoryReserver.hpp"
#include "memory/metaspaceUtils.hpp"
#include "memory/resourceArea.hpp"
#include "memory/universe.hpp"
#include "oops/access.inline.hpp"
#include "oops/compressedOops.inline.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/atomic.hpp"
#include "runtime/cpuTimeCounters.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/init.hpp"
#include "runtime/java.hpp"
#include "runtime/orderAccess.hpp"
#include "runtime/threadSMR.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/align.hpp"
#include "utilities/autoRestore.hpp"
#include "utilities/bitMap.inline.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/stack.inline.hpp"

size_t G1CollectedHeap::_humongous_object_threshold_in_words = 0;

// INVARIANTS/NOTES
//
// All allocation activity covered by the G1CollectedHeap interface is
// serialized by acquiring the HeapLock.  This happens in mem_allocate
// and allocate_new_tlab, which are the "entry" points to the
// allocation code from the rest of the JVM.  (Note that this does not
// apply to TLAB allocation, which is not part of this interface: it
// is done by clients of this interface.)

void G1RegionMappingChangedListener::reset_from_card_cache(uint start_idx, size_t num_regions) {
  G1HeapRegionRemSet::invalidate_from_card_cache(start_idx, num_regions);
}

void G1RegionMappingChangedListener::on_commit(uint start_idx, size_t num_regions, bool zero_filled) {
  // The from card cache is not the memory that is actually committed. So we cannot
  // take advantage of the zero_filled parameter.
  reset_from_card_cache(start_idx, num_regions);
}

void G1CollectedHeap::run_batch_task(G1BatchedTask* cl) {
  uint num_workers = MAX2(1u, MIN2(cl->num_workers_estimate(), workers()->active_workers()));
  cl->set_max_workers(num_workers);
  workers()->run_task(cl, num_workers);
}

uint G1CollectedHeap::get_chunks_per_region() {
  uint log_region_size = G1HeapRegion::LogOfHRGrainBytes;
  // Limit the expected input values to current known possible values of the
  // (log) region size. Adjust as necessary after testing if changing the permissible
  // values for region size.
  assert(log_region_size >= 20 && log_region_size <= 29,
         "expected value in [20,29], but got %u", log_region_size);
  return 1u << (log_region_size / 2 - 4);
}

G1HeapRegion* G1CollectedHeap::new_heap_region(uint hrs_index,
                                               MemRegion mr) {
  return new G1HeapRegion(hrs_index, bot(), mr, &_card_set_config);
}

// Private methods.

G1HeapRegion* G1CollectedHeap::new_region(size_t word_size,
                                          G1HeapRegionType type,
                                          bool do_expand,
                                          uint node_index) {
  assert(!is_humongous(word_size) || word_size <= G1HeapRegion::GrainWords,
         "the only time we use this to allocate a humongous region is "
         "when we are allocating a single humongous region");

  G1HeapRegion* res = _hrm.allocate_free_region(type, node_index);

  if (res == nullptr && do_expand) {
    // Currently, only attempts to allocate GC alloc regions set
    // do_expand to true. So, we should only reach here during a
    // safepoint.
    assert(SafepointSynchronize::is_at_safepoint(), "invariant");

    log_debug(gc, ergo, heap)("Attempt heap expansion (region allocation request failed). Allocation request: %zuB",
                              word_size * HeapWordSize);

    assert(word_size * HeapWordSize < G1HeapRegion::GrainBytes,
           "This kind of expansion should never be more than one region. Size: %zu",
           word_size * HeapWordSize);
    if (expand_single_region(node_index)) {
      // Given that expand_single_region() succeeded in expanding the heap, and we
      // always expand the heap by an amount aligned to the heap
      // region size, the free list should in theory not be empty.
      // In either case allocate_free_region() will check for null.
      res = _hrm.allocate_free_region(type, node_index);
    }
  }
  return res;
}

void G1CollectedHeap::set_humongous_metadata(G1HeapRegion* first_hr,
                                             uint num_regions,
                                             size_t word_size,
                                             bool update_remsets) {
  // Calculate the new top of the humongous object.
  HeapWord* obj_top = first_hr->bottom() + word_size;
  // The word size sum of all the regions used
  size_t word_size_sum = num_regions * G1HeapRegion::GrainWords;
  assert(word_size <= word_size_sum, "sanity");

  // How many words memory we "waste" which cannot hold a filler object.
  size_t words_not_fillable = 0;

  // Pad out the unused tail of the last region with filler
  // objects, for improved usage accounting.

  // How many words can we use for filler objects.
  size_t words_fillable = word_size_sum - word_size;

  if (words_fillable >= G1CollectedHeap::min_fill_size()) {
    G1CollectedHeap::fill_with_objects(obj_top, words_fillable);
  } else {
    // We have space to fill, but we cannot fit an object there.
    words_not_fillable = words_fillable;
    words_fillable = 0;
  }

  // We will set up the first region as "starts humongous". This
  // will also update the BOT covering all the regions to reflect
  // that there is a single object that starts at the bottom of the
  // first region.
  first_hr->hr_clear(false /* clear_space */);
  first_hr->set_starts_humongous(obj_top, words_fillable);

  if (update_remsets) {
    _policy->remset_tracker()->update_at_allocate(first_hr);
  }

  // Indices of first and last regions in the series.
  uint first = first_hr->hrm_index();
  uint last = first + num_regions - 1;

  G1HeapRegion* hr = nullptr;
  for (uint i = first + 1; i <= last; ++i) {
    hr = region_at(i);
    hr->hr_clear(false /* clear_space */);
    hr->set_continues_humongous(first_hr);
    if (update_remsets) {
      _policy->remset_tracker()->update_at_allocate(hr);
    }
  }

  // Up to this point no concurrent thread would have been able to
  // do any scanning on any region in this series. All the top
  // fields still point to bottom, so the intersection between
  // [bottom,top] and [card_start,card_end] will be empty. Before we
  // update the top fields, we'll do a storestore to make sure that
  // no thread sees the update to top before the zeroing of the
  // object header and the BOT initialization.
  OrderAccess::storestore();

  // Now, we will update the top fields of the "continues humongous"
  // regions except the last one.
  for (uint i = first; i < last; ++i) {
    hr = region_at(i);
    hr->set_top(hr->end());
  }

  hr = region_at(last);
  // If we cannot fit a filler object, we must set top to the end
  // of the humongous object, otherwise we cannot iterate the heap
  // and the BOT will not be complete.
  hr->set_top(hr->end() - words_not_fillable);

  assert(hr->bottom() < obj_top && obj_top <= hr->end(),
         "obj_top should be in last region");

  assert(words_not_fillable == 0 ||
         first_hr->bottom() + word_size_sum - words_not_fillable == hr->top(),
         "Miscalculation in humongous allocation");
}

HeapWord*
G1CollectedHeap::humongous_obj_allocate_initialize_regions(G1HeapRegion* first_hr,
                                                           uint num_regions,
                                                           size_t word_size) {
  assert(first_hr != nullptr, "pre-condition");
  assert(is_humongous(word_size), "word_size should be humongous");
  assert(num_regions * G1HeapRegion::GrainWords >= word_size, "pre-condition");

  // Index of last region in the series.
  uint first = first_hr->hrm_index();
  uint last = first + num_regions - 1;

  // We need to initialize the region(s) we just discovered. This is
  // a bit tricky given that it can happen concurrently with
  // refinement threads refining cards on these regions and
  // potentially wanting to refine the BOT as they are scanning
  // those cards (this can happen shortly after a cleanup; see CR
  // 6991377). So we have to set up the region(s) carefully and in
  // a specific order.

  // The passed in hr will be the "starts humongous" region. The header
  // of the new object will be placed at the bottom of this region.
  HeapWord* new_obj = first_hr->bottom();

  // First, we need to zero the header of the space that we will be
  // allocating. When we update top further down, some refinement
  // threads might try to scan the region. By zeroing the header we
  // ensure that any thread that will try to scan the region will
  // come across the zero klass word and bail out.
  //
  // NOTE: It would not have been correct to have used
  // CollectedHeap::fill_with_object() and make the space look like
  // an int array. The thread that is doing the allocation will
  // later update the object header to a potentially different array
  // type and, for a very short period of time, the klass and length
  // fields will be inconsistent. This could cause a refinement
  // thread to calculate the object size incorrectly.
  Copy::fill_to_words(new_obj, oopDesc::header_size(), 0);

  // Next, update the metadata for the regions.
  set_humongous_metadata(first_hr, num_regions, word_size, true);

  G1HeapRegion* last_hr = region_at(last);
  size_t used = byte_size(first_hr->bottom(), last_hr->top());

  increase_used(used);

  for (uint i = first; i <= last; ++i) {
    G1HeapRegion *hr = region_at(i);
    _humongous_set.add(hr);
    G1HeapRegionPrinter::alloc(hr);
  }

  return new_obj;
}

size_t G1CollectedHeap::humongous_obj_size_in_regions(size_t word_size) {
  assert(is_humongous(word_size), "Object of size %zu must be humongous here", word_size);
  return align_up(word_size, G1HeapRegion::GrainWords) / G1HeapRegion::GrainWords;
}

// If could fit into free regions w/o expansion, try.
// Otherwise, if can expand, do so.
// Otherwise, if using ex regions might help, try with ex given back.
HeapWord* G1CollectedHeap::humongous_obj_allocate(size_t word_size) {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);

  _verifier->verify_region_sets_optional();

  uint obj_regions = (uint) humongous_obj_size_in_regions(word_size);

  // Policy: First try to allocate a humongous object in the free list.
  G1HeapRegion* humongous_start = _hrm.allocate_humongous(obj_regions);
  if (humongous_start == nullptr) {
    // Policy: We could not find enough regions for the humongous object in the
    // free list. Look through the heap to find a mix of free and uncommitted regions.
    // If so, expand the heap and allocate the humongous object.
    humongous_start = _hrm.expand_and_allocate_humongous(obj_regions);
    if (humongous_start != nullptr) {
      // We managed to find a region by expanding the heap.
      log_debug(gc, ergo, heap)("Heap expansion (humongous allocation request). Allocation request: %zuB",
                                word_size * HeapWordSize);
      policy()->record_new_heap_size(num_committed_regions());
    } else {
      // Policy: Potentially trigger a defragmentation GC.
    }
  }

  HeapWord* result = nullptr;
  if (humongous_start != nullptr) {
    result = humongous_obj_allocate_initialize_regions(humongous_start, obj_regions, word_size);
    assert(result != nullptr, "it should always return a valid result");

    // A successful humongous object allocation changes the used space
    // information of the old generation so we need to recalculate the
    // sizes and update the jstat counters here.
    monitoring_support()->update_sizes();
  }

  _verifier->verify_region_sets_optional();

  return result;
}

HeapWord* G1CollectedHeap::allocate_new_tlab(size_t min_size,
                                             size_t requested_size,
                                             size_t* actual_size) {
  assert_heap_not_locked_and_not_at_safepoint();
  assert(!is_humongous(requested_size), "we do not allow humongous TLABs");

  return attempt_allocation(min_size, requested_size, actual_size);
}

HeapWord*
G1CollectedHeap::mem_allocate(size_t word_size,
                              bool*  gc_overhead_limit_was_exceeded) {
  assert_heap_not_locked_and_not_at_safepoint();

  if (is_humongous(word_size)) {
    return attempt_allocation_humongous(word_size);
  }
  size_t dummy = 0;
  return attempt_allocation(word_size, word_size, &dummy);
}

HeapWord* G1CollectedHeap::attempt_allocation_slow(uint node_index, size_t word_size) {
  ResourceMark rm; // For retrieving the thread names in log messages.

  // Make sure you read the note in attempt_allocation_humongous().

  assert_heap_not_locked_and_not_at_safepoint();
  assert(!is_humongous(word_size), "attempt_allocation_slow() should not "
         "be called for humongous allocation requests");

  // We should only get here after the first-level allocation attempt
  // (attempt_allocation()) failed to allocate.

  // We will loop until a) we manage to successfully perform the allocation or b)
  // successfully schedule a collection which fails to perform the allocation.
  // Case b) is the only case when we'll return null.
  HeapWord* result = nullptr;
  for (uint try_count = 1; /* we'll return */; try_count++) {
    uint gc_count_before;

    {
      MutexLocker x(Heap_lock);

      // Now that we have the lock, we first retry the allocation in case another
      // thread changed the region while we were waiting to acquire the lock.
      result = _allocator->attempt_allocation_locked(node_index, word_size);
      if (result != nullptr) {
        return result;
      }

      // Read the GC count while still holding the Heap_lock.
      gc_count_before = total_collections();
    }

    bool succeeded;
    result = do_collection_pause(word_size, gc_count_before, &succeeded, GCCause::_g1_inc_collection_pause);
    if (succeeded) {
      log_trace(gc, alloc)("%s: Successfully scheduled collection returning " PTR_FORMAT,
                           Thread::current()->name(), p2i(result));
      return result;
    }

    log_trace(gc, alloc)("%s: Unsuccessfully scheduled collection allocating %zu words",
                         Thread::current()->name(), word_size);

    // We can reach here if we were unsuccessful in scheduling a collection (because
    // another thread beat us to it). In this case immeditealy retry the allocation
    // attempt because another thread successfully performed a collection and possibly
    // reclaimed enough space. The first attempt (without holding the Heap_lock) is
    // here and the follow-on attempt will be at the start of the next loop
    // iteration (after taking the Heap_lock).
    size_t dummy = 0;
    result = _allocator->attempt_allocation(node_index, word_size, word_size, &dummy);
    if (result != nullptr) {
      return result;
    }

    // Give a warning if we seem to be looping forever.
    if ((QueuedAllocationWarningCount > 0) &&
        (try_count % QueuedAllocationWarningCount == 0)) {
      log_warning(gc, alloc)("%s:  Retried allocation %u times for %zu words",
                             Thread::current()->name(), try_count, word_size);
    }
  }

  ShouldNotReachHere();
  return nullptr;
}

template <typename Func>
void G1CollectedHeap::iterate_regions_in_range(MemRegion range, const Func& func) {
  // Mark each G1 region touched by the range as old, add it to
  // the old set, and set top.
  G1HeapRegion* curr_region = _hrm.addr_to_region(range.start());
  G1HeapRegion* end_region = _hrm.addr_to_region(range.last());

  while (curr_region != nullptr) {
    bool is_last = curr_region == end_region;
    G1HeapRegion* next_region = is_last ? nullptr : _hrm.next_region_in_heap(curr_region);

    func(curr_region, is_last);

    curr_region = next_region;
  }
}

HeapWord* G1CollectedHeap::alloc_archive_region(size_t word_size, HeapWord* preferred_addr) {
  assert(!is_init_completed(), "Expect to be called at JVM init time");
  MutexLocker x(Heap_lock);

  MemRegion reserved = _hrm.reserved();

  if (reserved.word_size() <= word_size) {
    log_info(gc, heap)("Unable to allocate regions as archive heap is too large; size requested = %zu"
                       " bytes, heap = %zu bytes", word_size, reserved.word_size());
    return nullptr;
  }

  // Temporarily disable pretouching of heap pages. This interface is used
  // when mmap'ing archived heap data in, so pre-touching is wasted.
  FlagSetting fs(AlwaysPreTouch, false);

  size_t commits = 0;
  // Attempt to allocate towards the end of the heap.
  HeapWord* start_addr = reserved.end() - align_up(word_size, G1HeapRegion::GrainWords);
  MemRegion range = MemRegion(start_addr, word_size);
  HeapWord* last_address = range.last();
  if (!_hrm.allocate_containing_regions(range, &commits, workers())) {
    return nullptr;
  }
  increase_used(word_size * HeapWordSize);
  if (commits != 0) {
    log_debug(gc, ergo, heap)("Attempt heap expansion (allocate archive regions). Total size: %zuB",
                              G1HeapRegion::GrainWords * HeapWordSize * commits);
  }

  // Mark each G1 region touched by the range as old, add it to
  // the old set, and set top.
  auto set_region_to_old = [&] (G1HeapRegion* r, bool is_last) {
    assert(r->is_empty(), "Region already in use (%u)", r->hrm_index());

    HeapWord* top = is_last ? last_address + 1 : r->end();
    r->set_top(top);

    r->set_old();
    G1HeapRegionPrinter::alloc(r);
    _old_set.add(r);
  };

  iterate_regions_in_range(range, set_region_to_old);
  return start_addr;
}

void G1CollectedHeap::populate_archive_regions_bot(MemRegion range) {
  assert(!is_init_completed(), "Expect to be called at JVM init time");

  iterate_regions_in_range(range,
                           [&] (G1HeapRegion* r, bool is_last) {
                             r->update_bot();
                           });
}

void G1CollectedHeap::dealloc_archive_regions(MemRegion range) {
  assert(!is_init_completed(), "Expect to be called at JVM init time");
  MemRegion reserved = _hrm.reserved();
  size_t size_used = 0;

  // Free the G1 regions that are within the specified range.
  MutexLocker x(Heap_lock);
  HeapWord* start_address = range.start();
  HeapWord* last_address = range.last();

  assert(reserved.contains(start_address) && reserved.contains(last_address),
         "MemRegion outside of heap [" PTR_FORMAT ", " PTR_FORMAT "]",
         p2i(start_address), p2i(last_address));
  size_used += range.byte_size();

  uint max_shrink_count = 0;
  if (capacity() > MinHeapSize) {
    size_t max_shrink_bytes = capacity() - MinHeapSize;
    max_shrink_count = (uint)(max_shrink_bytes / G1HeapRegion::GrainBytes);
  }

  uint shrink_count = 0;
  // Free, empty and uncommit regions with CDS archive content.
  auto dealloc_archive_region = [&] (G1HeapRegion* r, bool is_last) {
    guarantee(r->is_old(), "Expected old region at index %u", r->hrm_index());
    _old_set.remove(r);
    r->set_free();
    r->set_top(r->bottom());
    if (shrink_count < max_shrink_count) {
      _hrm.shrink_at(r->hrm_index(), 1);
      shrink_count++;
    } else {
      _hrm.insert_into_free_list(r);
    }
  };

  iterate_regions_in_range(range, dealloc_archive_region);

  if (shrink_count != 0) {
    log_debug(gc, ergo, heap)("Attempt heap shrinking (CDS archive regions). Total size: %zuB (%u Regions)",
                              G1HeapRegion::GrainWords * HeapWordSize * shrink_count, shrink_count);
    // Explicit uncommit.
    uncommit_regions(shrink_count);
  }
  decrease_used(size_used);
}

inline HeapWord* G1CollectedHeap::attempt_allocation(size_t min_word_size,
                                                     size_t desired_word_size,
                                                     size_t* actual_word_size) {
  assert_heap_not_locked_and_not_at_safepoint();
  assert(!is_humongous(desired_word_size), "attempt_allocation() should not "
         "be called for humongous allocation requests");

  // Fix NUMA node association for the duration of this allocation
  const uint node_index = _allocator->current_node_index();

  HeapWord* result = _allocator->attempt_allocation(node_index, min_word_size, desired_word_size, actual_word_size);

  if (result == nullptr) {
    *actual_word_size = desired_word_size;
    result = attempt_allocation_slow(node_index, desired_word_size);
  }

  assert_heap_not_locked();
  if (result != nullptr) {
    assert(*actual_word_size != 0, "Actual size must have been set here");
    dirty_young_block(result, *actual_word_size);
  } else {
    *actual_word_size = 0;
  }

  return result;
}

HeapWord* G1CollectedHeap::attempt_allocation_humongous(size_t word_size) {
  ResourceMark rm; // For retrieving the thread names in log messages.

  // The structure of this method has a lot of similarities to
  // attempt_allocation_slow(). The reason these two were not merged
  // into a single one is that such a method would require several "if
  // allocation is not humongous do this, otherwise do that"
  // conditional paths which would obscure its flow. In fact, an early
  // version of this code did use a unified method which was harder to
  // follow and, as a result, it had subtle bugs that were hard to
  // track down. So keeping these two methods separate allows each to
  // be more readable. It will be good to keep these two in sync as
  // much as possible.

  assert_heap_not_locked_and_not_at_safepoint();
  assert(is_humongous(word_size), "attempt_allocation_humongous() "
         "should only be called for humongous allocations");

  // Humongous objects can exhaust the heap quickly, so we should check if we
  // need to start a marking cycle at each humongous object allocation. We do
  // the check before we do the actual allocation. The reason for doing it
  // before the allocation is that we avoid having to keep track of the newly
  // allocated memory while we do a GC.
  if (policy()->need_to_start_conc_mark("concurrent humongous allocation",
                                        word_size)) {
    collect(GCCause::_g1_humongous_allocation);
  }

  // We will loop until a) we manage to successfully perform the allocation or b)
  // successfully schedule a collection which fails to perform the allocation.
  // Case b) is the only case when we'll return null.
  HeapWord* result = nullptr;
  for (uint try_count = 1; /* we'll return */; try_count++) {
    uint gc_count_before;


    {
      MutexLocker x(Heap_lock);

      size_t size_in_regions = humongous_obj_size_in_regions(word_size);
      // Given that humongous objects are not allocated in young
      // regions, we'll first try to do the allocation without doing a
      // collection hoping that there's enough space in the heap.
      result = humongous_obj_allocate(word_size);
      if (result != nullptr) {
        policy()->old_gen_alloc_tracker()->
          add_allocated_humongous_bytes_since_last_gc(size_in_regions * G1HeapRegion::GrainBytes);
        return result;
      }

      // Read the GC count while still holding the Heap_lock.
      gc_count_before = total_collections();
    }

    bool succeeded;
    result = do_collection_pause(word_size, gc_count_before, &succeeded, GCCause::_g1_humongous_allocation);
    if (succeeded) {
      log_trace(gc, alloc)("%s: Successfully scheduled collection returning " PTR_FORMAT,
                           Thread::current()->name(), p2i(result));
      if (result != nullptr) {
        size_t size_in_regions = humongous_obj_size_in_regions(word_size);
        policy()->old_gen_alloc_tracker()->
          record_collection_pause_humongous_allocation(size_in_regions * G1HeapRegion::GrainBytes);
      }
      return result;
    }

    log_trace(gc, alloc)("%s: Unsuccessfully scheduled collection allocating %zu",
                         Thread::current()->name(), word_size);

    // We can reach here if we were unsuccessful in scheduling a collection (because
    // another thread beat us to it).
    // Humongous object allocation always needs a lock, so we wait for the retry
    // in the next iteration of the loop, unlike for the regular iteration case.
    // Give a warning if we seem to be looping forever.

    if ((QueuedAllocationWarningCount > 0) &&
        (try_count % QueuedAllocationWarningCount == 0)) {
      log_warning(gc, alloc)("%s: Retried allocation %u times for %zu words",
                             Thread::current()->name(), try_count, word_size);
    }
  }

  ShouldNotReachHere();
  return nullptr;
}

HeapWord* G1CollectedHeap::attempt_allocation_at_safepoint(size_t word_size,
                                                           bool expect_null_mutator_alloc_region) {
  assert_at_safepoint_on_vm_thread();
  assert(!_allocator->has_mutator_alloc_region() || !expect_null_mutator_alloc_region,
         "the current alloc region was unexpectedly found to be non-null");

  // Fix NUMA node association for the duration of this allocation
  const uint node_index = _allocator->current_node_index();

  if (!is_humongous(word_size)) {
    return _allocator->attempt_allocation_locked(node_index, word_size);
  } else {
    HeapWord* result = humongous_obj_allocate(word_size);
    if (result != nullptr && policy()->need_to_start_conc_mark("STW humongous allocation")) {
      collector_state()->set_initiate_conc_mark_if_possible(true);
    }
    return result;
  }

  ShouldNotReachHere();
}

class PostCompactionPrinterClosure: public G1HeapRegionClosure {
public:
  bool do_heap_region(G1HeapRegion* hr) {
    assert(!hr->is_young(), "not expecting to find young regions");
    G1HeapRegionPrinter::post_compaction(hr);
    return false;
  }
};

void G1CollectedHeap::print_heap_after_full_collection() {
  // Post collection region logging.
  // We should do this after we potentially resize the heap so
  // that all the COMMIT / UNCOMMIT events are generated before
  // the compaction events.
  if (G1HeapRegionPrinter::is_active()) {
    PostCompactionPrinterClosure cl;
    heap_region_iterate(&cl);
  }
}

bool G1CollectedHeap::abort_concurrent_cycle() {
  // Disable discovery and empty the discovered lists
  // for the CM ref processor.
  _ref_processor_cm->disable_discovery();
  _ref_processor_cm->abandon_partial_discovery();
  _ref_processor_cm->verify_no_references_recorded();

  // Abandon current iterations of concurrent marking and concurrent
  // refinement, if any are in progress.
  return concurrent_mark()->concurrent_cycle_abort();
}

void G1CollectedHeap::prepare_heap_for_full_collection() {
  // Make sure we'll choose a new allocation region afterwards.
  _allocator->release_mutator_alloc_regions();
  _allocator->abandon_gc_alloc_regions();

  // We may have added regions to the current incremental collection
  // set between the last GC or pause and now. We need to clear the
  // incremental collection set and then start rebuilding it afresh
  // after this full GC.
  abandon_collection_set(collection_set());

  _hrm.remove_all_free_regions();
}

void G1CollectedHeap::verify_before_full_collection() {
  assert_used_and_recalculate_used_equal(this);
  if (!VerifyBeforeGC) {
    return;
  }
  if (!G1HeapVerifier::should_verify(G1HeapVerifier::G1VerifyFull)) {
    return;
  }
  _verifier->verify_region_sets_optional();
  _verifier->verify_before_gc();
  _verifier->verify_bitmap_clear(true /* above_tams_only */);
}

void G1CollectedHeap::prepare_for_mutator_after_full_collection(size_t allocation_word_size) {
  // Prepare heap for normal collections.
  assert(num_free_regions() == 0, "we should not have added any free regions");
  rebuild_region_sets(false /* free_list_only */);
  abort_refinement();
  resize_heap_if_necessary(allocation_word_size);
  uncommit_regions_if_necessary();

  // Rebuild the code root lists for each region
  rebuild_code_roots();

  start_new_collection_set();
  _allocator->init_mutator_alloc_regions();

  // Post collection state updates.
  MetaspaceGC::compute_new_size();
}

void G1CollectedHeap::abort_refinement() {
  // Discard all remembered set updates and reset refinement statistics.
  G1BarrierSet::dirty_card_queue_set().abandon_logs_and_stats();
  assert(G1BarrierSet::dirty_card_queue_set().num_cards() == 0,
         "DCQS should be empty");
  concurrent_refine()->get_and_reset_refinement_stats();
}

void G1CollectedHeap::verify_after_full_collection() {
  if (!VerifyAfterGC) {
    return;
  }
  if (!G1HeapVerifier::should_verify(G1HeapVerifier::G1VerifyFull)) {
    return;
  }
  _hrm.verify_optional();
  _verifier->verify_region_sets_optional();
  _verifier->verify_after_gc();
  _verifier->verify_bitmap_clear(false /* above_tams_only */);

  // At this point there should be no regions in the
  // entire heap tagged as young.
  assert(check_young_list_empty(), "young list should be empty at this point");

  // Note: since we've just done a full GC, concurrent
  // marking is no longer active. Therefore we need not
  // re-enable reference discovery for the CM ref processor.
  // That will be done at the start of the next marking cycle.
  // We also know that the STW processor should no longer
  // discover any new references.
  assert(!_ref_processor_stw->discovery_enabled(), "Postcondition");
  assert(!_ref_processor_cm->discovery_enabled(), "Postcondition");
  _ref_processor_stw->verify_no_references_recorded();
  _ref_processor_cm->verify_no_references_recorded();
}

void G1CollectedHeap::do_full_collection(bool clear_all_soft_refs,
                                         bool do_maximal_compaction,
                                         size_t allocation_word_size) {
  assert_at_safepoint_on_vm_thread();

  const bool do_clear_all_soft_refs = clear_all_soft_refs ||
      soft_ref_policy()->should_clear_all_soft_refs();

  G1FullGCMark gc_mark;
  GCTraceTime(Info, gc) tm("Pause Full", nullptr, gc_cause(), true);
  G1FullCollector collector(this, do_clear_all_soft_refs, do_maximal_compaction, gc_mark.tracer());

  collector.prepare_collection();
  collector.collect();
  collector.complete_collection(allocation_word_size);
}

void G1CollectedHeap::do_full_collection(bool clear_all_soft_refs) {
  // Currently, there is no facility in the do_full_collection(bool) API to notify
  // the caller that the collection did not succeed (e.g., because it was locked
  // out by the GC locker). So, right now, we'll ignore the return value.

  do_full_collection(clear_all_soft_refs,
                     false /* do_maximal_compaction */,
                     size_t(0) /* allocation_word_size */);
}

void G1CollectedHeap::upgrade_to_full_collection() {
  GCCauseSetter compaction(this, GCCause::_g1_compaction_pause);
  log_info(gc, ergo)("Attempting full compaction clearing soft references");
  do_full_collection(true  /* clear_all_soft_refs */,
                     false /* do_maximal_compaction */,
                     size_t(0) /* allocation_word_size */);
}

void G1CollectedHeap::resize_heap_if_necessary(size_t allocation_word_size) {
  assert_at_safepoint_on_vm_thread();

  bool should_expand;
  size_t resize_amount = _heap_sizing_policy->full_collection_resize_amount(should_expand, allocation_word_size);

  if (resize_amount == 0) {
    return;
  } else if (should_expand) {
    expand(resize_amount, _workers);
  } else {
    shrink(resize_amount);
  }
}

HeapWord* G1CollectedHeap::satisfy_failed_allocation_helper(size_t word_size,
                                                            bool do_gc,
                                                            bool maximal_compaction,
                                                            bool expect_null_mutator_alloc_region) {
  // Let's attempt the allocation first.
  HeapWord* result =
    attempt_allocation_at_safepoint(word_size,
                                    expect_null_mutator_alloc_region);
  if (result != nullptr) {
    return result;
  }

  // In a G1 heap, we're supposed to keep allocation from failing by
  // incremental pauses.  Therefore, at least for now, we'll favor
  // expansion over collection.  (This might change in the future if we can
  // do something smarter than full collection to satisfy a failed alloc.)
  result = expand_and_allocate(word_size);
  if (result != nullptr) {
    return result;
  }

  if (do_gc) {
    GCCauseSetter compaction(this, GCCause::_g1_compaction_pause);
    // Expansion didn't work, we'll try to do a Full GC.
    // If maximal_compaction is set we clear all soft references and don't
    // allow any dead wood to be left on the heap.
    if (maximal_compaction) {
      log_info(gc, ergo)("Attempting maximal full compaction clearing soft references");
    } else {
      log_info(gc, ergo)("Attempting full compaction");
    }
    do_full_collection(maximal_compaction /* clear_all_soft_refs */,
                       maximal_compaction /* do_maximal_compaction */,
                       word_size /* allocation_word_size */);
  }

  return nullptr;
}

HeapWord* G1CollectedHeap::satisfy_failed_allocation(size_t word_size) {
  assert_at_safepoint_on_vm_thread();

  // Attempts to allocate followed by Full GC.
  HeapWord* result =
    satisfy_failed_allocation_helper(word_size,
                                     true,  /* do_gc */
                                     false, /* maximum_collection */
                                     false /* expect_null_mutator_alloc_region */);

  if (result != nullptr) {
    return result;
  }

  // Attempts to allocate followed by Full GC that will collect all soft references.
  result = satisfy_failed_allocation_helper(word_size,
                                            true, /* do_gc */
                                            true, /* maximum_collection */
                                            true /* expect_null_mutator_alloc_region */);

  if (result != nullptr) {
    return result;
  }

  // Attempts to allocate, no GC
  result = satisfy_failed_allocation_helper(word_size,
                                            false, /* do_gc */
                                            false, /* maximum_collection */
                                            true  /* expect_null_mutator_alloc_region */);

  if (result != nullptr) {
    return result;
  }

  assert(!soft_ref_policy()->should_clear_all_soft_refs(),
         "Flag should have been handled and cleared prior to this point");

  // What else?  We might try synchronous finalization later.  If the total
  // space available is large enough for the allocation, then a more
  // complete compaction phase than we've tried so far might be
  // appropriate.
  return nullptr;
}

// Attempting to expand the heap sufficiently
// to support an allocation of the given "word_size".  If
// successful, perform the allocation and return the address of the
// allocated block, or else null.

HeapWord* G1CollectedHeap::expand_and_allocate(size_t word_size) {
  assert_at_safepoint_on_vm_thread();

  _verifier->verify_region_sets_optional();

  size_t expand_bytes = MAX2(word_size * HeapWordSize, MinHeapDeltaBytes);
  log_debug(gc, ergo, heap)("Attempt heap expansion (allocation request failed). Allocation request: %zuB",
                            word_size * HeapWordSize);


  if (expand(expand_bytes, _workers)) {
    _hrm.verify_optional();
    _verifier->verify_region_sets_optional();
    return attempt_allocation_at_safepoint(word_size,
                                           false /* expect_null_mutator_alloc_region */);
  }
  return nullptr;
}

bool G1CollectedHeap::expand(size_t expand_bytes, WorkerThreads* pretouch_workers, double* expand_time_ms) {
  size_t aligned_expand_bytes = os::align_up_vm_page_size(expand_bytes);
  aligned_expand_bytes = align_up(aligned_expand_bytes, G1HeapRegion::GrainBytes);

  log_debug(gc, ergo, heap)("Expand the heap. requested expansion amount: %zuB expansion amount: %zuB",
                            expand_bytes, aligned_expand_bytes);

  if (num_inactive_regions() == 0) {
    log_debug(gc, ergo, heap)("Did not expand the heap (heap already fully expanded)");
    return false;
  }

  double expand_heap_start_time_sec = os::elapsedTime();
  uint regions_to_expand = (uint)(aligned_expand_bytes / G1HeapRegion::GrainBytes);
  assert(regions_to_expand > 0, "Must expand by at least one region");

  uint expanded_by = _hrm.expand_by(regions_to_expand, pretouch_workers);
  if (expand_time_ms != nullptr) {
    *expand_time_ms = (os::elapsedTime() - expand_heap_start_time_sec) * MILLIUNITS;
  }

  assert(expanded_by > 0, "must have failed during commit.");

  size_t actual_expand_bytes = expanded_by * G1HeapRegion::GrainBytes;
  assert(actual_expand_bytes <= aligned_expand_bytes, "post-condition");
  policy()->record_new_heap_size(num_committed_regions());

  return true;
}

bool G1CollectedHeap::expand_single_region(uint node_index) {
  uint expanded_by = _hrm.expand_on_preferred_node(node_index);

  if (expanded_by == 0) {
    assert(num_inactive_regions() == 0, "Should be no regions left, available: %u", num_inactive_regions());
    log_debug(gc, ergo, heap)("Did not expand the heap (heap already fully expanded)");
    return false;
  }

  policy()->record_new_heap_size(num_committed_regions());
  return true;
}

void G1CollectedHeap::shrink_helper(size_t shrink_bytes) {
  size_t aligned_shrink_bytes = os::align_down_vm_page_size(shrink_bytes);
  aligned_shrink_bytes = align_down(aligned_shrink_bytes, G1HeapRegion::GrainBytes);
  uint num_regions_to_remove = (uint)(shrink_bytes / G1HeapRegion::GrainBytes);

  uint num_regions_removed = _hrm.shrink_by(num_regions_to_remove);
  size_t shrunk_bytes = num_regions_removed * G1HeapRegion::GrainBytes;

  log_debug(gc, ergo, heap)("Shrink the heap. requested shrinking amount: %zuB aligned shrinking amount: %zuB actual amount shrunk: %zuB",
                            shrink_bytes, aligned_shrink_bytes, shrunk_bytes);
  if (num_regions_removed > 0) {
    log_debug(gc, heap)("Uncommittable regions after shrink: %u", num_regions_removed);
    policy()->record_new_heap_size(num_committed_regions());
  } else {
    log_debug(gc, ergo, heap)("Did not shrink the heap (heap shrinking operation failed)");
  }
}

void G1CollectedHeap::shrink(size_t shrink_bytes) {
  _verifier->verify_region_sets_optional();

  // We should only reach here at the end of a Full GC or during Remark which
  // means we should not not be holding to any GC alloc regions. The method
  // below will make sure of that and do any remaining clean up.
  _allocator->abandon_gc_alloc_regions();

  // Instead of tearing down / rebuilding the free lists here, we
  // could instead use the remove_all_pending() method on free_list to
  // remove only the ones that we need to remove.
  _hrm.remove_all_free_regions();
  shrink_helper(shrink_bytes);
  rebuild_region_sets(true /* free_list_only */);

  _hrm.verify_optional();
  _verifier->verify_region_sets_optional();
}

class OldRegionSetChecker : public G1HeapRegionSetChecker {
public:
  void check_mt_safety() {
    // Master Old Set MT safety protocol:
    // (a) If we're at a safepoint, operations on the master old set
    // should be invoked:
    // - by the VM thread (which will serialize them), or
    // - by the GC workers while holding the FreeList_lock, if we're
    //   at a safepoint for an evacuation pause (this lock is taken
    //   anyway when an GC alloc region is retired so that a new one
    //   is allocated from the free list), or
    // - by the GC workers while holding the OldSets_lock, if we're at a
    //   safepoint for a cleanup pause.
    // (b) If we're not at a safepoint, operations on the master old set
    // should be invoked while holding the Heap_lock.

    if (SafepointSynchronize::is_at_safepoint()) {
      guarantee(Thread::current()->is_VM_thread() ||
                FreeList_lock->owned_by_self() || OldSets_lock->owned_by_self(),
                "master old set MT safety protocol at a safepoint");
    } else {
      guarantee(Heap_lock->owned_by_self(), "master old set MT safety protocol outside a safepoint");
    }
  }
  bool is_correct_type(G1HeapRegion* hr) { return hr->is_old(); }
  const char* get_description() { return "Old Regions"; }
};

class HumongousRegionSetChecker : public G1HeapRegionSetChecker {
public:
  void check_mt_safety() {
    // Humongous Set MT safety protocol:
    // (a) If we're at a safepoint, operations on the master humongous
    // set should be invoked by either the VM thread (which will
    // serialize them) or by the GC workers while holding the
    // OldSets_lock.
    // (b) If we're not at a safepoint, operations on the master
    // humongous set should be invoked while holding the Heap_lock.

    if (SafepointSynchronize::is_at_safepoint()) {
      guarantee(Thread::current()->is_VM_thread() ||
                OldSets_lock->owned_by_self(),
                "master humongous set MT safety protocol at a safepoint");
    } else {
      guarantee(Heap_lock->owned_by_self(),
                "master humongous set MT safety protocol outside a safepoint");
    }
  }
  bool is_correct_type(G1HeapRegion* hr) { return hr->is_humongous(); }
  const char* get_description() { return "Humongous Regions"; }
};

G1CollectedHeap::G1CollectedHeap() :
  CollectedHeap(),
  _service_thread(nullptr),
  _periodic_gc_task(nullptr),
  _free_arena_memory_task(nullptr),
  _workers(nullptr),
  _card_table(nullptr),
  _collection_pause_end(Ticks::now()),
  _old_set("Old Region Set", new OldRegionSetChecker()),
  _humongous_set("Humongous Region Set", new HumongousRegionSetChecker()),
  _bot(nullptr),
  _listener(),
  _numa(G1NUMA::create()),
  _hrm(),
  _allocator(nullptr),
  _allocation_failure_injector(),
  _verifier(nullptr),
  _summary_bytes_used(0),
  _bytes_used_during_gc(0),
  _survivor_evac_stats("Young", YoungPLABSize, PLABWeight),
  _old_evac_stats("Old", OldPLABSize, PLABWeight),
  _monitoring_support(nullptr),
  _num_humongous_objects(0),
  _num_humongous_reclaim_candidates(0),
  _collector_state(),
  _old_marking_cycles_started(0),
  _old_marking_cycles_completed(0),
  _eden(),
  _survivor(),
  _gc_timer_stw(new STWGCTimer()),
  _gc_tracer_stw(new G1NewTracer()),
  _policy(new G1Policy(_gc_timer_stw)),
  _heap_sizing_policy(nullptr),
  _collection_set(this, _policy),
  _rem_set(nullptr),
  _card_set_config(),
  _card_set_freelist_pool(G1CardSetConfiguration::num_mem_object_types()),
  _young_regions_cset_group(card_set_config(), &_card_set_freelist_pool, 1u /* group_id */),
  _cm(nullptr),
  _cm_thread(nullptr),
  _cr(nullptr),
  _task_queues(nullptr),
  _partial_array_state_manager(nullptr),
  _ref_processor_stw(nullptr),
  _is_alive_closure_stw(this),
  _is_subject_to_discovery_stw(this),
  _ref_processor_cm(nullptr),
  _is_alive_closure_cm(),
  _is_subject_to_discovery_cm(this),
  _region_attr() {

  _verifier = new G1HeapVerifier(this);

  _allocator = new G1Allocator(this);

  _heap_sizing_policy = G1HeapSizingPolicy::create(this, _policy->analytics());

  _humongous_object_threshold_in_words = humongous_threshold_for(G1HeapRegion::GrainWords);

  // Since filler arrays are never referenced, we can make them region sized.
  // This simplifies filling up the region in case we have some potentially
  // unreferenced (by Java code, but still in use by native code) pinned objects
  // in there.
  _filler_array_max_size = G1HeapRegion::GrainWords;

  // Override the default _stack_chunk_max_size so that no humongous stack chunks are created
  _stack_chunk_max_size = _humongous_object_threshold_in_words;

  uint n_queues = ParallelGCThreads;
  _task_queues = new G1ScannerTasksQueueSet(n_queues);

  for (uint i = 0; i < n_queues; i++) {
    G1ScannerTasksQueue* q = new G1ScannerTasksQueue();
    _task_queues->register_queue(i, q);
  }

  _partial_array_state_manager = new PartialArrayStateManager(n_queues);

  _gc_tracer_stw->initialize();
}

PartialArrayStateManager* G1CollectedHeap::partial_array_state_manager() const {
  return _partial_array_state_manager;
}

G1RegionToSpaceMapper* G1CollectedHeap::create_aux_memory_mapper(const char* description,
                                                                 size_t size,
                                                                 size_t translation_factor) {
  size_t preferred_page_size = os::page_size_for_region_unaligned(size, 1);

  // When a page size is given we don't want to mix large
  // and normal pages. If the size is not a multiple of the
  // page size it will be aligned up to achieve this.
  size_t alignment = os::vm_allocation_granularity();
  if (preferred_page_size != os::vm_page_size()) {
    alignment = MAX2(preferred_page_size, alignment);
    size = align_up(size, alignment);
  }

  // Allocate a new reserved space, preferring to use large pages.
  ReservedSpace rs = MemoryReserver::reserve(size,
                                             alignment,
                                             preferred_page_size,
                                             mtGC);

  size_t page_size = rs.page_size();
  G1RegionToSpaceMapper* result  =
    G1RegionToSpaceMapper::create_mapper(rs,
                                         size,
                                         page_size,
                                         G1HeapRegion::GrainBytes,
                                         translation_factor,
                                         mtGC);

  os::trace_page_sizes_for_requested_size(description,
                                          size,
                                          preferred_page_size,
                                          rs.base(),
                                          rs.size(),
                                          page_size);

  return result;
}

jint G1CollectedHeap::initialize_concurrent_refinement() {
  jint ecode = JNI_OK;
  _cr = G1ConcurrentRefine::create(policy(), &ecode);
  return ecode;
}

jint G1CollectedHeap::initialize_service_thread() {
  _service_thread = new G1ServiceThread();
  if (_service_thread->osthread() == nullptr) {
    vm_shutdown_during_initialization("Could not create G1ServiceThread");
    return JNI_ENOMEM;
  }
  return JNI_OK;
}

jint G1CollectedHeap::initialize() {

  // Necessary to satisfy locking discipline assertions.

  MutexLocker x(Heap_lock);

  // While there are no constraints in the GC code that HeapWordSize
  // be any particular value, there are multiple other areas in the
  // system which believe this to be true (e.g. oop->object_size in some
  // cases incorrectly returns the size in wordSize units rather than
  // HeapWordSize).
  guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");

  size_t init_byte_size = InitialHeapSize;
  size_t reserved_byte_size = G1Arguments::heap_reserved_size_bytes();

  // Ensure that the sizes are properly aligned.
  Universe::check_alignment(init_byte_size, G1HeapRegion::GrainBytes, "g1 heap");
  Universe::check_alignment(reserved_byte_size, G1HeapRegion::GrainBytes, "g1 heap");
  Universe::check_alignment(reserved_byte_size, HeapAlignment, "g1 heap");

  // Reserve the maximum.

  // When compressed oops are enabled, the preferred heap base
  // is calculated by subtracting the requested size from the
  // 32Gb boundary and using the result as the base address for
  // heap reservation. If the requested size is not aligned to
  // G1HeapRegion::GrainBytes (i.e. the alignment that is passed
  // into the ReservedHeapSpace constructor) then the actual
  // base of the reserved heap may end up differing from the
  // address that was requested (i.e. the preferred heap base).
  // If this happens then we could end up using a non-optimal
  // compressed oops mode.

  ReservedHeapSpace heap_rs = Universe::reserve_heap(reserved_byte_size,
                                                     HeapAlignment);

  initialize_reserved_region(heap_rs);

  // Create the barrier set for the entire reserved region.
  G1CardTable* ct = new G1CardTable(_reserved);
  G1BarrierSet* bs = new G1BarrierSet(ct);
  bs->initialize();
  assert(bs->is_a(BarrierSet::G1BarrierSet), "sanity");
  BarrierSet::set_barrier_set(bs);
  _card_table = ct;

  {
    G1SATBMarkQueueSet& satbqs = bs->satb_mark_queue_set();
    satbqs.set_process_completed_buffers_threshold(G1SATBProcessCompletedThreshold);
    satbqs.set_buffer_enqueue_threshold_percentage(G1SATBBufferEnqueueingThresholdPercent);
  }

  // Create space mappers.
  size_t page_size = heap_rs.page_size();
  G1RegionToSpaceMapper* heap_storage =
    G1RegionToSpaceMapper::create_mapper(heap_rs,
                                         heap_rs.size(),
                                         page_size,
                                         G1HeapRegion::GrainBytes,
                                         1,
                                         mtJavaHeap);
  if(heap_storage == nullptr) {
    vm_shutdown_during_initialization("Could not initialize G1 heap");
    return JNI_ERR;
  }

  os::trace_page_sizes("Heap",
                       MinHeapSize,
                       reserved_byte_size,
                       heap_rs.base(),
                       heap_rs.size(),
                       page_size);
  heap_storage->set_mapping_changed_listener(&_listener);

  // Create storage for the BOT, card table and the bitmap.
  G1RegionToSpaceMapper* bot_storage =
    create_aux_memory_mapper("Block Offset Table",
                             G1BlockOffsetTable::compute_size(heap_rs.size() / HeapWordSize),
                             G1BlockOffsetTable::heap_map_factor());

  G1RegionToSpaceMapper* cardtable_storage =
    create_aux_memory_mapper("Card Table",
                             G1CardTable::compute_size(heap_rs.size() / HeapWordSize),
                             G1CardTable::heap_map_factor());

  size_t bitmap_size = G1CMBitMap::compute_size(heap_rs.size());
  G1RegionToSpaceMapper* bitmap_storage =
    create_aux_memory_mapper("Mark Bitmap", bitmap_size, G1CMBitMap::heap_map_factor());

  _hrm.initialize(heap_storage, bitmap_storage, bot_storage, cardtable_storage);
  _card_table->initialize(cardtable_storage);

  // 6843694 - ensure that the maximum region index can fit
  // in the remembered set structures.
  const uint max_region_idx = (1U << (sizeof(RegionIdx_t)*BitsPerByte-1)) - 1;
  guarantee((max_num_regions() - 1) <= max_region_idx, "too many regions");

  // The G1FromCardCache reserves card with value 0 as "invalid", so the heap must not
  // start within the first card.
  guarantee((uintptr_t)(heap_rs.base()) >= G1CardTable::card_size(), "Java heap must not start within the first card.");
  G1FromCardCache::initialize(max_num_regions());
  // Also create a G1 rem set.
  _rem_set = new G1RemSet(this, _card_table);
  _rem_set->initialize(max_num_regions());

  size_t max_cards_per_region = ((size_t)1 << (sizeof(CardIdx_t)*BitsPerByte-1)) - 1;
  guarantee(G1HeapRegion::CardsPerRegion > 0, "make sure it's initialized");
  guarantee(G1HeapRegion::CardsPerRegion < max_cards_per_region,
            "too many cards per region");

  G1HeapRegionRemSet::initialize(_reserved);

  G1FreeRegionList::set_unrealistically_long_length(max_num_regions() + 1);

  _bot = new G1BlockOffsetTable(reserved(), bot_storage);

  {
    size_t granularity = G1HeapRegion::GrainBytes;

    _region_attr.initialize(reserved(), granularity);
  }

  _workers = new WorkerThreads("GC Thread", ParallelGCThreads);
  if (_workers == nullptr) {
    return JNI_ENOMEM;
  }
  _workers->initialize_workers();

  _numa->set_region_info(G1HeapRegion::GrainBytes, page_size);

  // Create the G1ConcurrentMark data structure and thread.
  // (Must do this late, so that "max_[reserved_]regions" is defined.)
  _cm = new G1ConcurrentMark(this, bitmap_storage);
  _cm_thread = _cm->cm_thread();

  // Now expand into the initial heap size.
  if (!expand(init_byte_size, _workers)) {
    vm_shutdown_during_initialization("Failed to allocate initial heap.");
    return JNI_ENOMEM;
  }

  // Perform any initialization actions delegated to the policy.
  policy()->init(this, &_collection_set);

  jint ecode = initialize_concurrent_refinement();
  if (ecode != JNI_OK) {
    return ecode;
  }

  ecode = initialize_service_thread();
  if (ecode != JNI_OK) {
    return ecode;
  }

  // Create and schedule the periodic gc task on the service thread.
  _periodic_gc_task = new G1PeriodicGCTask("Periodic GC Task");
  _service_thread->register_task(_periodic_gc_task);

  _free_arena_memory_task = new G1MonotonicArenaFreeMemoryTask("Card Set Free Memory Task");
  _service_thread->register_task(_free_arena_memory_task);

  // Here we allocate the dummy G1HeapRegion that is required by the
  // G1AllocRegion class.
  G1HeapRegion* dummy_region = _hrm.get_dummy_region();

  // We'll re-use the same region whether the alloc region will
  // require BOT updates or not and, if it doesn't, then a non-young
  // region will complain that it cannot support allocations without
  // BOT updates. So we'll tag the dummy region as eden to avoid that.
  dummy_region->set_eden();
  // Make sure it's full.
  dummy_region->set_top(dummy_region->end());
  G1AllocRegion::setup(this, dummy_region);

  _allocator->init_mutator_alloc_regions();

  // Do create of the monitoring and management support so that
  // values in the heap have been properly initialized.
  _monitoring_support = new G1MonitoringSupport(this);

  _collection_set.initialize(max_num_regions());

  allocation_failure_injector()->reset();

  CPUTimeCounters::create_counter(CPUTimeGroups::CPUTimeType::gc_parallel_workers);
  CPUTimeCounters::create_counter(CPUTimeGroups::CPUTimeType::gc_conc_mark);
  CPUTimeCounters::create_counter(CPUTimeGroups::CPUTimeType::gc_conc_refine);
  CPUTimeCounters::create_counter(CPUTimeGroups::CPUTimeType::gc_service);

  G1InitLogger::print();

  FullGCForwarding::initialize(_reserved);

  return JNI_OK;
}

bool G1CollectedHeap::concurrent_mark_is_terminating() const {
  return _cm_thread->should_terminate();
}

void G1CollectedHeap::stop() {
  // Stop all concurrent threads. We do this to make sure these threads
  // do not continue to execute and access resources (e.g. logging)
  // that are destroyed during shutdown.
  _cr->stop();
  _service_thread->stop();
  _cm_thread->stop();
}

void G1CollectedHeap::safepoint_synchronize_begin() {
  SuspendibleThreadSet::synchronize();
}

void G1CollectedHeap::safepoint_synchronize_end() {
  SuspendibleThreadSet::desynchronize();
}

void G1CollectedHeap::post_initialize() {
  CollectedHeap::post_initialize();
  ref_processing_init();
}

void G1CollectedHeap::ref_processing_init() {
  // Reference processing in G1 currently works as follows:
  //
  // * There are two reference processor instances. One is
  //   used to record and process discovered references
  //   during concurrent marking; the other is used to
  //   record and process references during STW pauses
  //   (both full and incremental).
  // * Both ref processors need to 'span' the entire heap as
  //   the regions in the collection set may be dotted around.
  //
  // * For the concurrent marking ref processor:
  //   * Reference discovery is enabled at concurrent start.
  //   * Reference discovery is disabled and the discovered
  //     references processed etc during remarking.
  //   * Reference discovery is MT (see below).
  //   * Reference discovery requires a barrier (see below).
  //   * Reference processing may or may not be MT
  //     (depending on the value of ParallelRefProcEnabled
  //     and ParallelGCThreads).
  //   * A full GC disables reference discovery by the CM
  //     ref processor and abandons any entries on it's
  //     discovered lists.
  //
  // * For the STW processor:
  //   * Non MT discovery is enabled at the start of a full GC.
  //   * Processing and enqueueing during a full GC is non-MT.
  //   * During a full GC, references are processed after marking.
  //
  //   * Discovery (may or may not be MT) is enabled at the start
  //     of an incremental evacuation pause.
  //   * References are processed near the end of a STW evacuation pause.
  //   * For both types of GC:
  //     * Discovery is atomic - i.e. not concurrent.
  //     * Reference discovery will not need a barrier.

  _is_alive_closure_cm.initialize(concurrent_mark());
  // Concurrent Mark ref processor
  _ref_processor_cm =
    new ReferenceProcessor(&_is_subject_to_discovery_cm,
                           ParallelGCThreads,                              // degree of mt processing
                           // We discover with the gc worker threads during Remark, so both
                           // thread counts must be considered for discovery.
                           MAX2(ParallelGCThreads, ConcGCThreads),         // degree of mt discovery
                           true,                                           // Reference discovery is concurrent
                           &_is_alive_closure_cm);                         // is alive closure

  // STW ref processor
  _ref_processor_stw =
    new ReferenceProcessor(&_is_subject_to_discovery_stw,
                           ParallelGCThreads,                    // degree of mt processing
                           ParallelGCThreads,                    // degree of mt discovery
                           false,                                // Reference discovery is not concurrent
                           &_is_alive_closure_stw);              // is alive closure
}

size_t G1CollectedHeap::capacity() const {
  return _hrm.num_committed_regions() * G1HeapRegion::GrainBytes;
}

size_t G1CollectedHeap::unused_committed_regions_in_bytes() const {
  return _hrm.total_free_bytes();
}

// Computes the sum of the storage used by the various regions.
size_t G1CollectedHeap::used() const {
  size_t result = _summary_bytes_used + _allocator->used_in_alloc_regions();
  return result;
}

size_t G1CollectedHeap::used_unlocked() const {
  return _summary_bytes_used;
}

class SumUsedClosure: public G1HeapRegionClosure {
  size_t _used;
public:
  SumUsedClosure() : _used(0) {}
  bool do_heap_region(G1HeapRegion* r) {
    _used += r->used();
    return false;
  }
  size_t result() { return _used; }
};

size_t G1CollectedHeap::recalculate_used() const {
  SumUsedClosure blk;
  heap_region_iterate(&blk);
  return blk.result();
}

bool  G1CollectedHeap::is_user_requested_concurrent_full_gc(GCCause::Cause cause) {
  return GCCause::is_user_requested_gc(cause) && ExplicitGCInvokesConcurrent;
}

bool G1CollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
  switch (cause) {
    case GCCause::_g1_humongous_allocation: return true;
    case GCCause::_g1_periodic_collection:  return G1PeriodicGCInvokesConcurrent;
    case GCCause::_wb_breakpoint:           return true;
    case GCCause::_codecache_GC_aggressive: return true;
    case GCCause::_codecache_GC_threshold:  return true;
    default:                                return is_user_requested_concurrent_full_gc(cause);
  }
}

void G1CollectedHeap::increment_old_marking_cycles_started() {
  assert(_old_marking_cycles_started == _old_marking_cycles_completed ||
         _old_marking_cycles_started == _old_marking_cycles_completed + 1,
         "Wrong marking cycle count (started: %d, completed: %d)",
         _old_marking_cycles_started, _old_marking_cycles_completed);

  _old_marking_cycles_started++;
}

void G1CollectedHeap::increment_old_marking_cycles_completed(bool concurrent,
                                                             bool whole_heap_examined) {
  MonitorLocker ml(G1OldGCCount_lock, Mutex::_no_safepoint_check_flag);

  // We assume that if concurrent == true, then the caller is a
  // concurrent thread that was joined the Suspendible Thread
  // Set. If there's ever a cheap way to check this, we should add an
  // assert here.

  // Given that this method is called at the end of a Full GC or of a
  // concurrent cycle, and those can be nested (i.e., a Full GC can
  // interrupt a concurrent cycle), the number of full collections
  // completed should be either one (in the case where there was no
  // nesting) or two (when a Full GC interrupted a concurrent cycle)
  // behind the number of full collections started.

  // This is the case for the inner caller, i.e. a Full GC.
  assert(concurrent ||
         (_old_marking_cycles_started == _old_marking_cycles_completed + 1) ||
         (_old_marking_cycles_started == _old_marking_cycles_completed + 2),
         "for inner caller (Full GC): _old_marking_cycles_started = %u "
         "is inconsistent with _old_marking_cycles_completed = %u",
         _old_marking_cycles_started, _old_marking_cycles_completed);

  // This is the case for the outer caller, i.e. the concurrent cycle.
  assert(!concurrent ||
         (_old_marking_cycles_started == _old_marking_cycles_completed + 1),
         "for outer caller (concurrent cycle): "
         "_old_marking_cycles_started = %u "
         "is inconsistent with _old_marking_cycles_completed = %u",
         _old_marking_cycles_started, _old_marking_cycles_completed);

  _old_marking_cycles_completed += 1;
  if (whole_heap_examined) {
    // Signal that we have completed a visit to all live objects.
    record_whole_heap_examined_timestamp();
  }

  // We need to clear the "in_progress" flag in the CM thread before
  // we wake up any waiters (especially when ExplicitInvokesConcurrent
  // is set) so that if a waiter requests another System.gc() it doesn't
  // incorrectly see that a marking cycle is still in progress.
  if (concurrent) {
    _cm_thread->set_idle();
  }

  // Notify threads waiting in System.gc() (with ExplicitGCInvokesConcurrent)
  // for a full GC to finish that their wait is over.
  ml.notify_all();
}

// Helper for collect().
static G1GCCounters collection_counters(G1CollectedHeap* g1h) {
  MutexLocker ml(Heap_lock);
  return G1GCCounters(g1h);
}

void G1CollectedHeap::collect(GCCause::Cause cause) {
  try_collect(cause, collection_counters(this));
}

// Return true if (x < y) with allowance for wraparound.
static bool gc_counter_less_than(uint x, uint y) {
  return (x - y) > (UINT_MAX/2);
}

// LOG_COLLECT_CONCURRENTLY(cause, msg, args...)
// Macro so msg printing is format-checked.
#define LOG_COLLECT_CONCURRENTLY(cause, ...)                            \
  do {                                                                  \
    LogTarget(Trace, gc) LOG_COLLECT_CONCURRENTLY_lt;                   \
    if (LOG_COLLECT_CONCURRENTLY_lt.is_enabled()) {                     \
      ResourceMark rm; /* For thread name. */                           \
      LogStream LOG_COLLECT_CONCURRENTLY_s(&LOG_COLLECT_CONCURRENTLY_lt); \
      LOG_COLLECT_CONCURRENTLY_s.print("%s: Try Collect Concurrently (%s): ", \
                                       Thread::current()->name(),       \
                                       GCCause::to_string(cause));      \
      LOG_COLLECT_CONCURRENTLY_s.print(__VA_ARGS__);                    \
    }                                                                   \
  } while (0)

#define LOG_COLLECT_CONCURRENTLY_COMPLETE(cause, result) \
  LOG_COLLECT_CONCURRENTLY(cause, "complete %s", BOOL_TO_STR(result))

bool G1CollectedHeap::wait_full_mark_finished(GCCause::Cause cause,
                                              uint old_marking_started_before,
                                              uint old_marking_started_after,
                                              uint old_marking_completed_after) {
  // Request is finished if a full collection (concurrent or stw)
  // was started after this request and has completed, e.g.
  // started_before < completed_after.
  if (gc_counter_less_than(old_marking_started_before,
                           old_marking_completed_after)) {
    LOG_COLLECT_CONCURRENTLY_COMPLETE(cause, true);
    return true;
  }

  if (old_marking_started_after != old_marking_completed_after) {
    // If there is an in-progress cycle (possibly started by us), then
    // wait for that cycle to complete, e.g.
    // while completed_now < started_after.
    LOG_COLLECT_CONCURRENTLY(cause, "wait");
    MonitorLocker ml(G1OldGCCount_lock);
    while (gc_counter_less_than(_old_marking_cycles_completed,
                                old_marking_started_after)) {
      ml.wait();
    }
    // Request is finished if the collection we just waited for was
    // started after this request.
    if (old_marking_started_before != old_marking_started_after) {
      LOG_COLLECT_CONCURRENTLY(cause, "complete after wait");
      return true;
    }
  }
  return false;
}

// After calling wait_full_mark_finished(), this method determines whether we
// previously failed for ordinary reasons (concurrent cycle in progress, whitebox
// has control). Returns if this has been such an ordinary reason.
static bool should_retry_vm_op(GCCause::Cause cause,
                               VM_G1TryInitiateConcMark* op) {
  if (op->cycle_already_in_progress()) {
    // If VMOp failed because a cycle was already in progress, it
    // is now complete.  But it didn't finish this user-requested
    // GC, so try again.
    LOG_COLLECT_CONCURRENTLY(cause, "retry after in-progress");
    return true;
  } else if (op->whitebox_attached()) {
    // If WhiteBox wants control, wait for notification of a state
    // change in the controller, then try again.  Don't wait for
    // release of control, since collections may complete while in
    // control.  Note: This won't recognize a STW full collection
    // while waiting; we can't wait on multiple monitors.
    LOG_COLLECT_CONCURRENTLY(cause, "whitebox control stall");
    MonitorLocker ml(ConcurrentGCBreakpoints::monitor());
    if (ConcurrentGCBreakpoints::is_controlled()) {
      ml.wait();
    }
    return true;
  }
  return false;
}

bool G1CollectedHeap::try_collect_concurrently(GCCause::Cause cause,
                                               uint gc_counter,
                                               uint old_marking_started_before) {
  assert_heap_not_locked();
  assert(should_do_concurrent_full_gc(cause),
         "Non-concurrent cause %s", GCCause::to_string(cause));

  for (uint i = 1; true; ++i) {
    // Try to schedule concurrent start evacuation pause that will
    // start a concurrent cycle.
    LOG_COLLECT_CONCURRENTLY(cause, "attempt %u", i);
    VM_G1TryInitiateConcMark op(gc_counter, cause);
    VMThread::execute(&op);

    // Request is trivially finished.
    if (cause == GCCause::_g1_periodic_collection) {
      LOG_COLLECT_CONCURRENTLY_COMPLETE(cause, op.gc_succeeded());
      return op.gc_succeeded();
    }

    // If VMOp skipped initiating concurrent marking cycle because
    // we're terminating, then we're done.
    if (op.terminating()) {
      LOG_COLLECT_CONCURRENTLY(cause, "skipped: terminating");
      return false;
    }

    // Lock to get consistent set of values.
    uint old_marking_started_after;
    uint old_marking_completed_after;
    {
      MutexLocker ml(Heap_lock);
      // Update gc_counter for retrying VMOp if needed. Captured here to be
      // consistent with the values we use below for termination tests.  If
      // a retry is needed after a possible wait, and another collection
      // occurs in the meantime, it will cause our retry to be skipped and
      // we'll recheck for termination with updated conditions from that
      // more recent collection.  That's what we want, rather than having
      // our retry possibly perform an unnecessary collection.
      gc_counter = total_collections();
      old_marking_started_after = _old_marking_cycles_started;
      old_marking_completed_after = _old_marking_cycles_completed;
    }

    if (cause == GCCause::_wb_breakpoint) {
      if (op.gc_succeeded()) {
        LOG_COLLECT_CONCURRENTLY_COMPLETE(cause, true);
        return true;
      }
      // When _wb_breakpoint there can't be another cycle or deferred.
      assert(!op.cycle_already_in_progress(), "invariant");
      assert(!op.whitebox_attached(), "invariant");
      // Concurrent cycle attempt might have been cancelled by some other
      // collection, so retry.  Unlike other cases below, we want to retry
      // even if cancelled by a STW full collection, because we really want
      // to start a concurrent cycle.
      if (old_marking_started_before != old_marking_started_after) {
        LOG_COLLECT_CONCURRENTLY(cause, "ignoring STW full GC");
        old_marking_started_before = old_marking_started_after;
      }
    } else if (GCCause::is_codecache_requested_gc(cause)) {
      // For a CodeCache requested GC, before marking, progress is ensured as the
      // following Remark pause unloads code (and signals the requester such).
      // Otherwise we must ensure that it is restarted.
      //
      // For a CodeCache requested GC, a successful GC operation means that
      // (1) marking is in progress. I.e. the VMOp started the marking or a
      //     Remark pause is pending from a different VM op; we will potentially
      //     abort a mixed phase if needed.
      // (2) a new cycle was started (by this thread or some other), or
      // (3) a Full GC was performed.
      //
      // Cases (2) and (3) are detected together by a change to
      // _old_marking_cycles_started.
      //
      // Compared to other "automatic" GCs (see below), we do not consider being
      // in whitebox as sufficient too because we might be anywhere within that
      // cycle and we need to make progress.
      if (op.mark_in_progress() ||
          (old_marking_started_before != old_marking_started_after)) {
        LOG_COLLECT_CONCURRENTLY_COMPLETE(cause, true);
        return true;
      }

      if (wait_full_mark_finished(cause,
                                  old_marking_started_before,
                                  old_marking_started_after,
                                  old_marking_completed_after)) {
        return true;
      }

      if (should_retry_vm_op(cause, &op)) {
        continue;
      }
    } else if (!GCCause::is_user_requested_gc(cause)) {
      assert(cause == GCCause::_g1_humongous_allocation ||
             cause == GCCause::_g1_periodic_collection,
             "Unsupported cause %s", GCCause::to_string(cause));

      // For an "automatic" (not user-requested) collection, we just need to
      // ensure that progress is made.
      //
      // Request is finished if any of
      // (1) the VMOp successfully performed a GC,
      // (2) a concurrent cycle was already in progress,
      // (3) whitebox is controlling concurrent cycles,
      // (4) a new cycle was started (by this thread or some other), or
      // (5) a Full GC was performed.
      // Cases (4) and (5) are detected together by a change to
      // _old_marking_cycles_started.
      if (op.gc_succeeded() ||
          op.cycle_already_in_progress() ||
          op.whitebox_attached() ||
          (old_marking_started_before != old_marking_started_after)) {
        LOG_COLLECT_CONCURRENTLY_COMPLETE(cause, true);
        return true;
      }
    } else {                    // User-requested GC.
      // For a user-requested collection, we want to ensure that a complete
      // full collection has been performed before returning, but without
      // waiting for more than needed.

      // For user-requested GCs (unlike non-UR), a successful VMOp implies a
      // new cycle was started.  That's good, because it's not clear what we
      // should do otherwise.  Trying again just does back to back GCs.
      // Can't wait for someone else to start a cycle.  And returning fails
      // to meet the goal of ensuring a full collection was performed.
      assert(!op.gc_succeeded() ||
             (old_marking_started_before != old_marking_started_after),
             "invariant: succeeded %s, started before %u, started after %u",
             BOOL_TO_STR(op.gc_succeeded()),
             old_marking_started_before, old_marking_started_after);

      if (wait_full_mark_finished(cause,
                                  old_marking_started_before,
                                  old_marking_started_after,
                                  old_marking_completed_after)) {
        return true;
      }

      // If VMOp was successful then it started a new cycle that the above
      // wait &etc should have recognized as finishing this request.  This
      // differs from a non-user-request, where gc_succeeded does not imply
      // a new cycle was started.
      assert(!op.gc_succeeded(), "invariant");

      if (should_retry_vm_op(cause, &op)) {
        continue;
      }
    }

    // Collection failed and should be retried.
    assert(op.transient_failure(), "invariant");

    LOG_COLLECT_CONCURRENTLY(cause, "retry");
  }
}

bool G1CollectedHeap::try_collect(GCCause::Cause cause,
                                  const G1GCCounters& counters_before) {
  if (should_do_concurrent_full_gc(cause)) {
    return try_collect_concurrently(cause,
                                    counters_before.total_collections(),
                                    counters_before.old_marking_cycles_started());
  } else if (cause == GCCause::_wb_young_gc
             DEBUG_ONLY(|| cause == GCCause::_scavenge_alot)) {

    // Schedule a standard evacuation pause. We're setting word_size
    // to 0 which means that we are not requesting a post-GC allocation.
    VM_G1CollectForAllocation op(0,     /* word_size */
                                 counters_before.total_collections(),
                                 cause);
    VMThread::execute(&op);
    return op.gc_succeeded();
  } else {
    // Schedule a Full GC.
    VM_G1CollectFull op(counters_before.total_collections(),
                        counters_before.total_full_collections(),
                        cause);
    VMThread::execute(&op);
    return op.gc_succeeded();
  }
}

void G1CollectedHeap::start_concurrent_gc_for_metadata_allocation(GCCause::Cause gc_cause) {
  GCCauseSetter x(this, gc_cause);

  // At this point we are supposed to start a concurrent cycle. We
  // will do so if one is not already in progress.
  bool should_start = policy()->force_concurrent_start_if_outside_cycle(gc_cause);
  if (should_start) {
    do_collection_pause_at_safepoint();
  }
}

bool G1CollectedHeap::is_in(const void* p) const {
  return is_in_reserved(p) && _hrm.is_available(addr_to_region(p));
}

// Iteration functions.

// Iterates an ObjectClosure over all objects within a G1HeapRegion.

class IterateObjectClosureRegionClosure: public G1HeapRegionClosure {
  ObjectClosure* _cl;
public:
  IterateObjectClosureRegionClosure(ObjectClosure* cl) : _cl(cl) {}
  bool do_heap_region(G1HeapRegion* r) {
    if (!r->is_continues_humongous()) {
      r->object_iterate(_cl);
    }
    return false;
  }
};

void G1CollectedHeap::object_iterate(ObjectClosure* cl) {
  IterateObjectClosureRegionClosure blk(cl);
  heap_region_iterate(&blk);
}

class G1ParallelObjectIterator : public ParallelObjectIteratorImpl {
private:
  G1CollectedHeap*  _heap;
  G1HeapRegionClaimer _claimer;

public:
  G1ParallelObjectIterator(uint thread_num) :
      _heap(G1CollectedHeap::heap()),
      _claimer(thread_num == 0 ? G1CollectedHeap::heap()->workers()->active_workers() : thread_num) {}

  virtual void object_iterate(ObjectClosure* cl, uint worker_id) {
    _heap->object_iterate_parallel(cl, worker_id, &_claimer);
  }
};

ParallelObjectIteratorImpl* G1CollectedHeap::parallel_object_iterator(uint thread_num) {
  return new G1ParallelObjectIterator(thread_num);
}

void G1CollectedHeap::object_iterate_parallel(ObjectClosure* cl, uint worker_id, G1HeapRegionClaimer* claimer) {
  IterateObjectClosureRegionClosure blk(cl);
  heap_region_par_iterate_from_worker_offset(&blk, claimer, worker_id);
}

void G1CollectedHeap::keep_alive(oop obj) {
  G1BarrierSet::enqueue_preloaded(obj);
}

void G1CollectedHeap::heap_region_iterate(G1HeapRegionClosure* cl) const {
  _hrm.iterate(cl);
}

void G1CollectedHeap::heap_region_iterate(G1HeapRegionIndexClosure* cl) const {
  _hrm.iterate(cl);
}

void G1CollectedHeap::heap_region_par_iterate_from_worker_offset(G1HeapRegionClosure* cl,
                                                                 G1HeapRegionClaimer *hrclaimer,
                                                                 uint worker_id) const {
  _hrm.par_iterate(cl, hrclaimer, hrclaimer->offset_for_worker(worker_id));
}

void G1CollectedHeap::heap_region_par_iterate_from_start(G1HeapRegionClosure* cl,
                                                         G1HeapRegionClaimer *hrclaimer) const {
  _hrm.par_iterate(cl, hrclaimer, 0);
}

void G1CollectedHeap::collection_set_iterate_all(G1HeapRegionClosure* cl) {
  _collection_set.iterate(cl);
}

void G1CollectedHeap::collection_set_par_iterate_all(G1HeapRegionClosure* cl,
                                                     G1HeapRegionClaimer* hr_claimer,
                                                     uint worker_id) {
  _collection_set.par_iterate(cl, hr_claimer, worker_id);
}

void G1CollectedHeap::collection_set_iterate_increment_from(G1HeapRegionClosure *cl,
                                                            G1HeapRegionClaimer* hr_claimer,
                                                            uint worker_id) {
  _collection_set.iterate_incremental_part_from(cl, hr_claimer, worker_id);
}

void G1CollectedHeap::par_iterate_regions_array(G1HeapRegionClosure* cl,
                                                G1HeapRegionClaimer* hr_claimer,
                                                const uint regions[],
                                                size_t length,
                                                uint worker_id) const {
  assert_at_safepoint();
  if (length == 0) {
    return;
  }
  uint total_workers = workers()->active_workers();

  size_t start_pos = (worker_id * length) / total_workers;
  size_t cur_pos = start_pos;

  do {
    uint region_idx = regions[cur_pos];
    if (hr_claimer == nullptr || hr_claimer->claim_region(region_idx)) {
      G1HeapRegion* r = region_at(region_idx);
      bool result = cl->do_heap_region(r);
      guarantee(!result, "Must not cancel iteration");
    }

    cur_pos++;
    if (cur_pos == length) {
      cur_pos = 0;
    }
  } while (cur_pos != start_pos);
}

HeapWord* G1CollectedHeap::block_start(const void* addr) const {
  G1HeapRegion* hr = heap_region_containing(addr);
  // The CollectedHeap API requires us to not fail for any given address within
  // the heap. G1HeapRegion::block_start() has been optimized to not accept addresses
  // outside of the allocated area.
  if (addr >= hr->top()) {
    return nullptr;
  }
  return hr->block_start(addr);
}

bool G1CollectedHeap::block_is_obj(const HeapWord* addr) const {
  G1HeapRegion* hr = heap_region_containing(addr);
  return hr->block_is_obj(addr, hr->parsable_bottom_acquire());
}

size_t G1CollectedHeap::tlab_capacity(Thread* ignored) const {
  return (_policy->young_list_target_length() - _survivor.length()) * G1HeapRegion::GrainBytes;
}

size_t G1CollectedHeap::tlab_used(Thread* ignored) const {
  return _eden.length() * G1HeapRegion::GrainBytes;
}

// For G1 TLABs should not contain humongous objects, so the maximum TLAB size
// must be equal to the humongous object limit.
size_t G1CollectedHeap::max_tlab_size() const {
  return align_down(_humongous_object_threshold_in_words, MinObjAlignment);
}

size_t G1CollectedHeap::unsafe_max_tlab_alloc(Thread* ignored) const {
  return _allocator->unsafe_max_tlab_alloc();
}

size_t G1CollectedHeap::max_capacity() const {
  return max_num_regions() * G1HeapRegion::GrainBytes;
}

void G1CollectedHeap::prepare_for_verify() {
  _verifier->prepare_for_verify();
}

void G1CollectedHeap::verify(VerifyOption vo) {
  _verifier->verify(vo);
}

bool G1CollectedHeap::supports_concurrent_gc_breakpoints() const {
  return true;
}

class G1PrintRegionClosure: public G1HeapRegionClosure {
  outputStream* _st;
public:
  G1PrintRegionClosure(outputStream* st) : _st(st) {}
  bool do_heap_region(G1HeapRegion* r) {
    r->print_on(_st);
    return false;
  }
};

bool G1CollectedHeap::is_obj_dead_cond(const oop obj,
                                       const G1HeapRegion* hr,
                                       const VerifyOption vo) const {
  switch (vo) {
    case VerifyOption::G1UseConcMarking: return is_obj_dead(obj, hr);
    case VerifyOption::G1UseFullMarking: return is_obj_dead_full(obj, hr);
    default:                             ShouldNotReachHere();
  }
  return false; // keep some compilers happy
}

bool G1CollectedHeap::is_obj_dead_cond(const oop obj,
                                       const VerifyOption vo) const {
  switch (vo) {
    case VerifyOption::G1UseConcMarking: return is_obj_dead(obj);
    case VerifyOption::G1UseFullMarking: return is_obj_dead_full(obj);
    default:                             ShouldNotReachHere();
  }
  return false; // keep some compilers happy
}

void G1CollectedHeap::print_heap_regions() const {
  LogTarget(Trace, gc, heap, region) lt;
  if (lt.is_enabled()) {
    LogStream ls(lt);
    print_regions_on(&ls);
  }
}

void G1CollectedHeap::print_heap_on(outputStream* st) const {
  size_t heap_used = Heap_lock->owned_by_self() ? used() : used_unlocked();
  st->print("%-20s", "garbage-first heap");
  st->print(" total reserved %zuK, committed %zuK, used %zuK",
            _hrm.reserved().byte_size()/K, capacity()/K, heap_used/K);
  st->print(" [" PTR_FORMAT ", " PTR_FORMAT ")",
            p2i(_hrm.reserved().start()),
            p2i(_hrm.reserved().end()));
  st->cr();

  StreamIndentor si(st, 1);
  st->print("region size %zuK, ", G1HeapRegion::GrainBytes / K);
  uint young_regions = young_regions_count();
  st->print("%u young (%zuK), ", young_regions,
            (size_t) young_regions * G1HeapRegion::GrainBytes / K);
  uint survivor_regions = survivor_regions_count();
  st->print("%u survivors (%zuK)", survivor_regions,
            (size_t) survivor_regions * G1HeapRegion::GrainBytes / K);
  st->cr();
  if (_numa->is_enabled()) {
    uint num_nodes = _numa->num_active_nodes();
    st->print("remaining free region(s) on each NUMA node: ");
    const uint* node_ids = _numa->node_ids();
    for (uint node_index = 0; node_index < num_nodes; node_index++) {
      uint num_free_regions = _hrm.num_free_regions(node_index);
      st->print("%u=%u ", node_ids[node_index], num_free_regions);
    }
    st->cr();
  }
}

void G1CollectedHeap::print_regions_on(outputStream* st) const {
  st->print_cr("Heap Regions: E=young(eden), S=young(survivor), O=old, "
               "HS=humongous(starts), HC=humongous(continues), "
               "CS=collection set, F=free, "
               "TAMS=top-at-mark-start, "
               "PB=parsable bottom");
  G1PrintRegionClosure blk(st);
  heap_region_iterate(&blk);
}

void G1CollectedHeap::print_extended_on(outputStream* st) const {
  print_heap_on(st);

  // Print the per-region information.
  st->cr();
  print_regions_on(st);
}

void G1CollectedHeap::print_gc_on(outputStream* st) const {
  // Print the per-region information.
  print_regions_on(st);
  st->cr();

  BarrierSet* bs = BarrierSet::barrier_set();
  if (bs != nullptr) {
    bs->print_on(st);
  }

  if (_cm != nullptr) {
    st->cr();
    _cm->print_on(st);
  }
}

void G1CollectedHeap::gc_threads_do(ThreadClosure* tc) const {
  workers()->threads_do(tc);
  tc->do_thread(_cm_thread);
  _cm->threads_do(tc);
  _cr->threads_do(tc);
  tc->do_thread(_service_thread);
}

void G1CollectedHeap::print_tracing_info() const {
  rem_set()->print_summary_info();
  concurrent_mark()->print_summary_info();
}

bool G1CollectedHeap::print_location(outputStream* st, void* addr) const {
  return BlockLocationPrinter<G1CollectedHeap>::print_location(st, addr);
}

G1HeapSummary G1CollectedHeap::create_g1_heap_summary() {

  size_t eden_used_bytes = _monitoring_support->eden_space_used();
  size_t survivor_used_bytes = _monitoring_support->survivor_space_used();
  size_t old_gen_used_bytes = _monitoring_support->old_gen_used();
  size_t heap_used = Heap_lock->owned_by_self() ? used() : used_unlocked();

  size_t eden_capacity_bytes =
    (policy()->young_list_target_length() * G1HeapRegion::GrainBytes) - survivor_used_bytes;

  VirtualSpaceSummary heap_summary = create_heap_space_summary();
  return G1HeapSummary(heap_summary, heap_used, eden_used_bytes, eden_capacity_bytes,
                       survivor_used_bytes, old_gen_used_bytes, num_committed_regions());
}

G1EvacSummary G1CollectedHeap::create_g1_evac_summary(G1EvacStats* stats) {
  return G1EvacSummary(stats->allocated(), stats->wasted(), stats->undo_wasted(),
                       stats->unused(), stats->used(), stats->region_end_waste(),
                       stats->regions_filled(), stats->num_plab_filled(),
                       stats->direct_allocated(), stats->num_direct_allocated(),
                       stats->failure_used(), stats->failure_waste());
}

void G1CollectedHeap::trace_heap(GCWhen::Type when, const GCTracer* gc_tracer) {
  const G1HeapSummary& heap_summary = create_g1_heap_summary();
  gc_tracer->report_gc_heap_summary(when, heap_summary);

  const MetaspaceSummary& metaspace_summary = create_metaspace_summary();
  gc_tracer->report_metaspace_summary(when, metaspace_summary);
}

void G1CollectedHeap::gc_prologue(bool full) {
  // Update common counters.
  increment_total_collections(full /* full gc */);
  if (full || collector_state()->in_concurrent_start_gc()) {
    increment_old_marking_cycles_started();
  }
}

void G1CollectedHeap::gc_epilogue(bool full) {
  // Update common counters.
  if (full) {
    // Update the number of full collections that have been completed.
    increment_old_marking_cycles_completed(false /* concurrent */, true /* liveness_completed */);
  }

#if COMPILER2_OR_JVMCI
  assert(DerivedPointerTable::is_empty(), "derived pointer present");
#endif

  // We have just completed a GC. Update the soft reference
  // policy with the new heap occupancy
  Universe::heap()->update_capacity_and_used_at_gc();

  _collection_pause_end = Ticks::now();

  _free_arena_memory_task->notify_new_stats(&_young_gen_card_set_stats,
                                            &_collection_set_candidates_card_set_stats);

  update_parallel_gc_threads_cpu_time();
}

uint G1CollectedHeap::uncommit_regions(uint region_limit) {
  return _hrm.uncommit_inactive_regions(region_limit);
}

bool G1CollectedHeap::has_uncommittable_regions() {
  return _hrm.has_inactive_regions();
}

void G1CollectedHeap::uncommit_regions_if_necessary() {
  if (has_uncommittable_regions()) {
    G1UncommitRegionTask::enqueue();
  }
}

void G1CollectedHeap::verify_numa_regions(const char* desc) {
  LogTarget(Trace, gc, heap, verify) lt;

  if (lt.is_enabled()) {
    LogStream ls(lt);
    // Iterate all heap regions to print matching between preferred numa id and actual numa id.
    G1NodeIndexCheckClosure cl(desc, _numa, &ls);
    heap_region_iterate(&cl);
  }
}

HeapWord* G1CollectedHeap::do_collection_pause(size_t word_size,
                                               uint gc_count_before,
                                               bool* succeeded,
                                               GCCause::Cause gc_cause) {
  assert_heap_not_locked_and_not_at_safepoint();
  VM_G1CollectForAllocation op(word_size, gc_count_before, gc_cause);
  VMThread::execute(&op);

  HeapWord* result = op.result();
  *succeeded = op.gc_succeeded();
  assert(result == nullptr || *succeeded,
         "the result should be null if the VM did not succeed");

  assert_heap_not_locked();
  return result;
}

void G1CollectedHeap::start_concurrent_cycle(bool concurrent_operation_is_full_mark) {
  assert(!_cm_thread->in_progress(), "Can not start concurrent operation while in progress");

  MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
  if (concurrent_operation_is_full_mark) {
    _cm->post_concurrent_mark_start();
    _cm_thread->start_full_mark();
  } else {
    _cm->post_concurrent_undo_start();
    _cm_thread->start_undo_mark();
  }
  CGC_lock->notify();
}

bool G1CollectedHeap::is_potential_eager_reclaim_candidate(G1HeapRegion* r) const {
  // We don't nominate objects with many remembered set entries, on
  // the assumption that such objects are likely still live.
  G1HeapRegionRemSet* rem_set = r->rem_set();

  return rem_set->occupancy_less_or_equal_than(G1EagerReclaimRemSetThreshold);
}

#ifndef PRODUCT
void G1CollectedHeap::verify_region_attr_remset_is_tracked() {
  class VerifyRegionAttrRemSet : public G1HeapRegionClosure {
  public:
    virtual bool do_heap_region(G1HeapRegion* r) {
      G1CollectedHeap* g1h = G1CollectedHeap::heap();
      bool const remset_is_tracked = g1h->region_attr(r->bottom()).remset_is_tracked();
      assert(r->rem_set()->is_tracked() == remset_is_tracked,
             "Region %u remset tracking status (%s) different to region attribute (%s)",
             r->hrm_index(), BOOL_TO_STR(r->rem_set()->is_tracked()), BOOL_TO_STR(remset_is_tracked));
      return false;
    }
  } cl;
  heap_region_iterate(&cl);
}
#endif

void G1CollectedHeap::update_parallel_gc_threads_cpu_time() {
  assert(Thread::current()->is_VM_thread(),
         "Must be called from VM thread to avoid races");
  if (!UsePerfData || !os::is_thread_cpu_time_supported()) {
    return;
  }

  // Ensure ThreadTotalCPUTimeClosure destructor is called before publishing gc
  // time.
  {
    ThreadTotalCPUTimeClosure tttc(CPUTimeGroups::CPUTimeType::gc_parallel_workers);
    // Currently parallel worker threads never terminate (JDK-8081682), so it is
    // safe for VMThread to read their CPU times. However, if JDK-8087340 is
    // resolved so they terminate, we should rethink if it is still safe.
    workers()->threads_do(&tttc);
  }

  CPUTimeCounters::publish_gc_total_cpu_time();
}

void G1CollectedHeap::start_new_collection_set() {
  collection_set()->start_incremental_building();

  clear_region_attr();

  guarantee(_eden.length() == 0, "eden should have been cleared");
  policy()->transfer_survivors_to_cset(survivor());

  // We redo the verification but now wrt to the new CSet which
  // has just got initialized after the previous CSet was freed.
  _cm->verify_no_collection_set_oops();
}

void G1CollectedHeap::verify_before_young_collection(G1HeapVerifier::G1VerifyType type) {
  if (!VerifyBeforeGC) {
    return;
  }
  if (!G1HeapVerifier::should_verify(type)) {
    return;
  }
  Ticks start = Ticks::now();
  _verifier->prepare_for_verify();
  _verifier->verify_region_sets_optional();
  _verifier->verify_dirty_young_regions();
  _verifier->verify_before_gc();
  verify_numa_regions("GC Start");
  phase_times()->record_verify_before_time_ms((Ticks::now() - start).seconds() * MILLIUNITS);
}

void G1CollectedHeap::verify_after_young_collection(G1HeapVerifier::G1VerifyType type) {
  if (!VerifyAfterGC) {
    return;
  }
  if (!G1HeapVerifier::should_verify(type)) {
    return;
  }
  Ticks start = Ticks::now();
  _verifier->verify_after_gc();
  verify_numa_regions("GC End");
  _verifier->verify_region_sets_optional();

  if (collector_state()->in_concurrent_start_gc()) {
    log_debug(gc, verify)("Marking state");
    _verifier->verify_marking_state();
  }

  phase_times()->record_verify_after_time_ms((Ticks::now() - start).seconds() * MILLIUNITS);
}

void G1CollectedHeap::expand_heap_after_young_collection(){
  size_t expand_bytes = _heap_sizing_policy->young_collection_expansion_amount();
  if (expand_bytes > 0) {
    // No need for an ergo logging here,
    // expansion_amount() does this when it returns a value > 0.
    double expand_ms = 0.0;
    if (!expand(expand_bytes, _workers, &expand_ms)) {
      // We failed to expand the heap. Cannot do anything about it.
    }
    phase_times()->record_expand_heap_time(expand_ms);
  }
}

void G1CollectedHeap::do_collection_pause_at_safepoint() {
  assert_at_safepoint_on_vm_thread();
  guarantee(!is_stw_gc_active(), "collection is not reentrant");

  do_collection_pause_at_safepoint_helper();
}

G1HeapPrinterMark::G1HeapPrinterMark(G1CollectedHeap* g1h) : _g1h(g1h), _heap_transition(g1h) {
  // This summary needs to be printed before incrementing total collections.
  _g1h->rem_set()->print_periodic_summary_info("Before GC RS summary",
                                               _g1h->total_collections(),
                                               true /* show_thread_times */);
  _g1h->print_before_gc();
  _g1h->print_heap_regions();
}

G1HeapPrinterMark::~G1HeapPrinterMark() {
  _g1h->policy()->print_age_table();
  _g1h->rem_set()->print_coarsen_stats();
  // We are at the end of the GC. Total collections has already been increased.
  _g1h->rem_set()->print_periodic_summary_info("After GC RS summary",
                                               _g1h->total_collections() - 1,
                                               false /* show_thread_times */);

  _heap_transition.print();
  _g1h->print_heap_regions();
  _g1h->print_after_gc();
  // Print NUMA statistics.
  _g1h->numa()->print_statistics();
}

G1JFRTracerMark::G1JFRTracerMark(STWGCTimer* timer, GCTracer* tracer) :
  _timer(timer), _tracer(tracer) {

  _timer->register_gc_start();
  _tracer->report_gc_start(G1CollectedHeap::heap()->gc_cause(), _timer->gc_start());
  G1CollectedHeap::heap()->trace_heap_before_gc(_tracer);
}

G1JFRTracerMark::~G1JFRTracerMark() {
  G1CollectedHeap::heap()->trace_heap_after_gc(_tracer);
  _timer->register_gc_end();
  _tracer->report_gc_end(_timer->gc_end(), _timer->time_partitions());
}

void G1CollectedHeap::prepare_for_mutator_after_young_collection() {
  Ticks start = Ticks::now();

  _survivor_evac_stats.adjust_desired_plab_size();
  _old_evac_stats.adjust_desired_plab_size();

  // Start a new incremental collection set for the mutator phase.
  start_new_collection_set();
  _allocator->init_mutator_alloc_regions();

  phase_times()->record_prepare_for_mutator_time_ms((Ticks::now() - start).seconds() * 1000.0);
}

void G1CollectedHeap::retire_tlabs() {
  ensure_parsability(true);
}

void G1CollectedHeap::flush_region_pin_cache() {
  for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
    G1ThreadLocalData::pin_count_cache(thread).flush();
  }
}

void G1CollectedHeap::do_collection_pause_at_safepoint_helper() {
  ResourceMark rm;

  IsSTWGCActiveMark active_gc_mark;
  GCIdMark gc_id_mark;
  SvcGCMarker sgcm(SvcGCMarker::MINOR);

  GCTraceCPUTime tcpu(_gc_tracer_stw);

  _bytes_used_during_gc = 0;

  policy()->decide_on_concurrent_start_pause();
  // Record whether this pause may need to trigger a concurrent operation. Later,
  // when we signal the G1ConcurrentMarkThread, the collector state has already
  // been reset for the next pause.
  bool should_start_concurrent_mark_operation = collector_state()->in_concurrent_start_gc();

  // Perform the collection.
  G1YoungCollector collector(gc_cause());
  collector.collect();

  // It should now be safe to tell the concurrent mark thread to start
  // without its logging output interfering with the logging output
  // that came from the pause.
  if (should_start_concurrent_mark_operation) {
    verifier()->verify_bitmap_clear(true /* above_tams_only */);
    // CAUTION: after the start_concurrent_cycle() call below, the concurrent marking
    // thread(s) could be running concurrently with us. Make sure that anything
    // after this point does not assume that we are the only GC thread running.
    // Note: of course, the actual marking work will not start until the safepoint
    // itself is released in SuspendibleThreadSet::desynchronize().
    start_concurrent_cycle(collector.concurrent_operation_is_full_mark());
    ConcurrentGCBreakpoints::notify_idle_to_active();
  }
}

void G1CollectedHeap::complete_cleaning(bool class_unloading_occurred) {
  uint num_workers = workers()->active_workers();
  G1ParallelCleaningTask unlink_task(num_workers, class_unloading_occurred);
  workers()->run_task(&unlink_task);
}

void G1CollectedHeap::unload_classes_and_code(const char* description, BoolObjectClosure* is_alive, GCTimer* timer) {
  GCTraceTime(Debug, gc, phases) debug(description, timer);

  ClassUnloadingContext ctx(workers()->active_workers(),
                            false /* unregister_nmethods_during_purge */,
                            false /* lock_nmethod_free_separately */);
  {
    CodeCache::UnlinkingScope scope(is_alive);
    bool unloading_occurred = SystemDictionary::do_unloading(timer);
    GCTraceTime(Debug, gc, phases) t("G1 Complete Cleaning", timer);
    complete_cleaning(unloading_occurred);
  }
  {
    GCTraceTime(Debug, gc, phases) t("Purge Unlinked NMethods", timer);
    ctx.purge_nmethods();
  }
  {
    GCTraceTime(Debug, gc, phases) ur("Unregister NMethods", timer);
    G1CollectedHeap::heap()->bulk_unregister_nmethods();
  }
  {
    GCTraceTime(Debug, gc, phases) t("Free Code Blobs", timer);
    ctx.free_nmethods();
  }
  {
    GCTraceTime(Debug, gc, phases) t("Purge Class Loader Data", timer);
    ClassLoaderDataGraph::purge(true /* at_safepoint */);
    DEBUG_ONLY(MetaspaceUtils::verify();)
  }
}

class G1BulkUnregisterNMethodTask : public WorkerTask {
  G1HeapRegionClaimer _hrclaimer;

  class UnregisterNMethodsHeapRegionClosure : public G1HeapRegionClosure {
  public:

    bool do_heap_region(G1HeapRegion* hr) {
      hr->rem_set()->bulk_remove_code_roots();
      return false;
    }
  } _cl;

public:
  G1BulkUnregisterNMethodTask(uint num_workers)
  : WorkerTask("G1 Remove Unlinked NMethods From Code Root Set Task"),
    _hrclaimer(num_workers) { }

  void work(uint worker_id) {
    G1CollectedHeap::heap()->heap_region_par_iterate_from_worker_offset(&_cl, &_hrclaimer, worker_id);
  }
};

void G1CollectedHeap::bulk_unregister_nmethods() {
  uint num_workers = workers()->active_workers();
  G1BulkUnregisterNMethodTask t(num_workers);
  workers()->run_task(&t);
}

bool G1STWSubjectToDiscoveryClosure::do_object_b(oop obj) {
  assert(obj != nullptr, "must not be null");
  assert(_g1h->is_in_reserved(obj), "Trying to discover obj " PTR_FORMAT " not in heap", p2i(obj));
  // The areas the CM and STW ref processor manage must be disjoint. The is_in_cset() below
  // may falsely indicate that this is not the case here: however the collection set only
  // contains old regions when concurrent mark is not running.
  return _g1h->is_in_cset(obj) || _g1h->heap_region_containing(obj)->is_survivor();
}

void G1CollectedHeap::make_pending_list_reachable() {
  if (collector_state()->in_concurrent_start_gc()) {
    oop pll_head = Universe::reference_pending_list();
    if (pll_head != nullptr) {
      // Any valid worker id is fine here as we are in the VM thread and single-threaded.
      _cm->mark_in_bitmap(0 /* worker_id */, pll_head);
    }
  }
}

void G1CollectedHeap::set_humongous_stats(uint num_humongous_total, uint num_humongous_candidates) {
  _num_humongous_objects = num_humongous_total;
  _num_humongous_reclaim_candidates = num_humongous_candidates;
}

bool G1CollectedHeap::should_sample_collection_set_candidates() const {
  const G1CollectionSetCandidates* candidates = collection_set()->candidates();
  return !candidates->is_empty();
}

void G1CollectedHeap::set_collection_set_candidates_stats(G1MonotonicArenaMemoryStats& stats) {
  _collection_set_candidates_card_set_stats = stats;
}

void G1CollectedHeap::set_young_gen_card_set_stats(const G1MonotonicArenaMemoryStats& stats) {
  _young_gen_card_set_stats = stats;
}

void G1CollectedHeap::record_obj_copy_mem_stats() {
  size_t total_old_allocated = _old_evac_stats.allocated() + _old_evac_stats.direct_allocated();
  policy()->old_gen_alloc_tracker()->
    add_allocated_bytes_since_last_gc(total_old_allocated * HeapWordSize);

  _gc_tracer_stw->report_evacuation_statistics(create_g1_evac_summary(&_survivor_evac_stats),
                                               create_g1_evac_summary(&_old_evac_stats));
}

void G1CollectedHeap::clear_bitmap_for_region(G1HeapRegion* hr) {
  concurrent_mark()->clear_bitmap_for_region(hr);
}

void G1CollectedHeap::free_region(G1HeapRegion* hr, G1FreeRegionList* free_list) {
  assert(!hr->is_free(), "the region should not be free");
  assert(!hr->is_empty(), "the region should not be empty");
  assert(_hrm.is_available(hr->hrm_index()), "region should be committed");
  assert(!hr->has_pinned_objects(),
         "must not free a region which contains pinned objects");

  // Reset region metadata to allow reuse.
  hr->hr_clear(true /* clear_space */);
  _policy->remset_tracker()->update_at_free(hr);

  if (free_list != nullptr) {
    free_list->add_ordered(hr);
  }
}

void G1CollectedHeap::retain_region(G1HeapRegion* hr) {
  MutexLocker x(G1RareEvent_lock, Mutex::_no_safepoint_check_flag);
  collection_set()->candidates()->add_retained_region_unsorted(hr);
}

void G1CollectedHeap::free_humongous_region(G1HeapRegion* hr,
                                            G1FreeRegionList* free_list) {
  assert(hr->is_humongous(), "this is only for humongous regions");
  hr->clear_humongous();
  free_region(hr, free_list);
}

void G1CollectedHeap::remove_from_old_gen_sets(const uint old_regions_removed,
                                               const uint humongous_regions_removed) {
  if (old_regions_removed > 0 || humongous_regions_removed > 0) {
    MutexLocker x(OldSets_lock, Mutex::_no_safepoint_check_flag);
    _old_set.bulk_remove(old_regions_removed);
    _humongous_set.bulk_remove(humongous_regions_removed);
  }

}

void G1CollectedHeap::prepend_to_freelist(G1FreeRegionList* list) {
  assert(list != nullptr, "list can't be null");
  if (!list->is_empty()) {
    MutexLocker x(FreeList_lock, Mutex::_no_safepoint_check_flag);
    _hrm.insert_list_into_free_list(list);
  }
}

void G1CollectedHeap::decrement_summary_bytes(size_t bytes) {
  decrease_used(bytes);
}

void G1CollectedHeap::clear_eden() {
  _eden.clear();
}

void G1CollectedHeap::clear_collection_set() {
  collection_set()->clear();
}

void G1CollectedHeap::rebuild_free_region_list() {
  Ticks start = Ticks::now();
  _hrm.rebuild_free_list(workers());
  phase_times()->record_total_rebuild_freelist_time_ms((Ticks::now() - start).seconds() * 1000.0);
}

class G1AbandonCollectionSetClosure : public G1HeapRegionClosure {
public:
  virtual bool do_heap_region(G1HeapRegion* r) {
    assert(r->in_collection_set(), "Region %u must have been in collection set", r->hrm_index());
    G1CollectedHeap::heap()->clear_region_attr(r);
    r->clear_young_index_in_cset();
    return false;
  }
};

void G1CollectedHeap::abandon_collection_set(G1CollectionSet* collection_set) {
  G1AbandonCollectionSetClosure cl;
  collection_set_iterate_all(&cl);

  collection_set->clear();
  collection_set->stop_incremental_building();
}

bool G1CollectedHeap::is_old_gc_alloc_region(G1HeapRegion* hr) {
  return _allocator->is_retained_old_region(hr);
}

void G1CollectedHeap::set_region_short_lived_locked(G1HeapRegion* hr) {
  _eden.add(hr);
  _policy->set_region_eden(hr);
  young_regions_cset_group()->add(hr);
}

#ifdef ASSERT

class NoYoungRegionsClosure: public G1HeapRegionClosure {
private:
  bool _success;
public:
  NoYoungRegionsClosure() : _success(true) { }
  bool do_heap_region(G1HeapRegion* r) {
    if (r->is_young()) {
      log_error(gc, verify)("Region [" PTR_FORMAT ", " PTR_FORMAT ") tagged as young",
                            p2i(r->bottom()), p2i(r->end()));
      _success = false;
    }
    return false;
  }
  bool success() { return _success; }
};

bool G1CollectedHeap::check_young_list_empty() {
  bool ret = (young_regions_count() == 0);

  NoYoungRegionsClosure closure;
  heap_region_iterate(&closure);
  ret = ret && closure.success();

  return ret;
}

#endif // ASSERT

// Remove the given G1HeapRegion from the appropriate region set.
void G1CollectedHeap::prepare_region_for_full_compaction(G1HeapRegion* hr) {
  if (hr->is_humongous()) {
    _humongous_set.remove(hr);
  } else if (hr->is_old()) {
    _old_set.remove(hr);
  } else if (hr->is_young()) {
    // Note that emptying the eden and survivor lists is postponed and instead
    // done as the first step when rebuilding the regions sets again. The reason
    // for this is that during a full GC string deduplication needs to know if
    // a collected region was young or old when the full GC was initiated.
    hr->uninstall_surv_rate_group();
  } else {
    // We ignore free regions, we'll empty the free list afterwards.
    assert(hr->is_free(), "it cannot be another type");
  }
}

void G1CollectedHeap::increase_used(size_t bytes) {
  _summary_bytes_used += bytes;
}

void G1CollectedHeap::decrease_used(size_t bytes) {
  assert(_summary_bytes_used >= bytes,
         "invariant: _summary_bytes_used: %zu should be >= bytes: %zu",
         _summary_bytes_used, bytes);
  _summary_bytes_used -= bytes;
}

void G1CollectedHeap::set_used(size_t bytes) {
  _summary_bytes_used = bytes;
}

class RebuildRegionSetsClosure : public G1HeapRegionClosure {
private:
  bool _free_list_only;

  G1HeapRegionSet* _old_set;
  G1HeapRegionSet* _humongous_set;

  G1HeapRegionManager* _hrm;

  size_t _total_used;

public:
  RebuildRegionSetsClosure(bool free_list_only,
                           G1HeapRegionSet* old_set,
                           G1HeapRegionSet* humongous_set,
                           G1HeapRegionManager* hrm) :
    _free_list_only(free_list_only), _old_set(old_set),
    _humongous_set(humongous_set), _hrm(hrm), _total_used(0) {
    assert(_hrm->num_free_regions() == 0, "pre-condition");
    if (!free_list_only) {
      assert(_old_set->is_empty(), "pre-condition");
      assert(_humongous_set->is_empty(), "pre-condition");
    }
  }

  bool do_heap_region(G1HeapRegion* r) {
    if (r->is_empty()) {
      assert(r->rem_set()->is_empty(), "Empty regions should have empty remembered sets.");
      // Add free regions to the free list
      r->set_free();
      _hrm->insert_into_free_list(r);
    } else if (!_free_list_only) {
      assert(r->rem_set()->is_empty(), "At this point remembered sets must have been cleared.");

      if (r->is_humongous()) {
        _humongous_set->add(r);
      } else {
        assert(r->is_young() || r->is_free() || r->is_old(), "invariant");
        // We now move all (non-humongous, non-old) regions to old gen,
        // and register them as such.
        r->move_to_old();
        _old_set->add(r);
      }
      _total_used += r->used();
    }

    return false;
  }

  size_t total_used() {
    return _total_used;
  }
};

void G1CollectedHeap::rebuild_region_sets(bool free_list_only) {
  assert_at_safepoint_on_vm_thread();

  if (!free_list_only) {
    _eden.clear();
    _survivor.clear();
  }

  RebuildRegionSetsClosure cl(free_list_only,
                              &_old_set, &_humongous_set,
                              &_hrm);
  heap_region_iterate(&cl);

  if (!free_list_only) {
    set_used(cl.total_used());
  }
  assert_used_and_recalculate_used_equal(this);
}

// Methods for the mutator alloc region

G1HeapRegion* G1CollectedHeap::new_mutator_alloc_region(size_t word_size,
                                                      uint node_index) {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);
  bool should_allocate = policy()->should_allocate_mutator_region();
  if (should_allocate) {
    G1HeapRegion* new_alloc_region = new_region(word_size,
                                                G1HeapRegionType::Eden,
                                                false /* do_expand */,
                                                node_index);
    if (new_alloc_region != nullptr) {
      set_region_short_lived_locked(new_alloc_region);
      G1HeapRegionPrinter::alloc(new_alloc_region);
      _policy->remset_tracker()->update_at_allocate(new_alloc_region);
      return new_alloc_region;
    }
  }
  return nullptr;
}

void G1CollectedHeap::retire_mutator_alloc_region(G1HeapRegion* alloc_region,
                                                  size_t allocated_bytes) {
  assert_heap_locked_or_at_safepoint(true /* should_be_vm_thread */);
  assert(alloc_region->is_eden(), "all mutator alloc regions should be eden");

  collection_set()->add_eden_region(alloc_region);
  increase_used(allocated_bytes);
  _eden.add_used_bytes(allocated_bytes);
  G1HeapRegionPrinter::retire(alloc_region);

  // We update the eden sizes here, when the region is retired,
  // instead of when it's allocated, since this is the point that its
  // used space has been recorded in _summary_bytes_used.
  monitoring_support()->update_eden_size();
}

// Methods for the GC alloc regions

bool G1CollectedHeap::has_more_regions(G1HeapRegionAttr dest) {
  if (dest.is_old()) {
    return true;
  } else {
    return survivor_regions_count() < policy()->max_survivor_regions();
  }
}

G1HeapRegion* G1CollectedHeap::new_gc_alloc_region(size_t word_size, G1HeapRegionAttr dest, uint node_index) {
  assert(FreeList_lock->owned_by_self(), "pre-condition");

  if (!has_more_regions(dest)) {
    return nullptr;
  }

  G1HeapRegionType type;
  if (dest.is_young()) {
    type = G1HeapRegionType::Survivor;
  } else {
    type = G1HeapRegionType::Old;
  }

  G1HeapRegion* new_alloc_region = new_region(word_size,
                                              type,
                                              true /* do_expand */,
                                              node_index);

  if (new_alloc_region != nullptr) {
    if (type.is_survivor()) {
      new_alloc_region->set_survivor();
      _survivor.add(new_alloc_region);
      register_new_survivor_region_with_region_attr(new_alloc_region);
      // Install the group cardset.
      young_regions_cset_group()->add(new_alloc_region);
    } else {
      new_alloc_region->set_old();
    }
    _policy->remset_tracker()->update_at_allocate(new_alloc_region);
    register_region_with_region_attr(new_alloc_region);
    G1HeapRegionPrinter::alloc(new_alloc_region);
    return new_alloc_region;
  }
  return nullptr;
}

void G1CollectedHeap::retire_gc_alloc_region(G1HeapRegion* alloc_region,
                                             size_t allocated_bytes,
                                             G1HeapRegionAttr dest) {
  _bytes_used_during_gc += allocated_bytes;
  if (dest.is_old()) {
    old_set_add(alloc_region);
  } else {
    assert(dest.is_young(), "Retiring alloc region should be young (%d)", dest.type());
    _survivor.add_used_bytes(allocated_bytes);
  }

  bool const during_im = collector_state()->in_concurrent_start_gc();
  if (during_im && allocated_bytes > 0) {
    _cm->add_root_region(alloc_region);
  }
  G1HeapRegionPrinter::retire(alloc_region);
}

void G1CollectedHeap::mark_evac_failure_object(uint worker_id, const oop obj, size_t obj_size) const {
  assert(!_cm->is_marked_in_bitmap(obj), "must be");

  _cm->raw_mark_in_bitmap(obj);
}

// Optimized nmethod scanning
class RegisterNMethodOopClosure: public OopClosure {
  G1CollectedHeap* _g1h;
  nmethod* _nm;

public:
  RegisterNMethodOopClosure(G1CollectedHeap* g1h, nmethod* nm) :
    _g1h(g1h), _nm(nm) {}

  void do_oop(oop* p) {
    oop heap_oop = RawAccess<>::oop_load(p);
    if (!CompressedOops::is_null(heap_oop)) {
      oop obj = CompressedOops::decode_not_null(heap_oop);
      G1HeapRegion* hr = _g1h->heap_region_containing(obj);
      assert(!hr->is_continues_humongous(),
             "trying to add code root " PTR_FORMAT " in continuation of humongous region " HR_FORMAT
             " starting at " HR_FORMAT,
             p2i(_nm), HR_FORMAT_PARAMS(hr), HR_FORMAT_PARAMS(hr->humongous_start_region()));

      hr->add_code_root(_nm);
    }
  }

  void do_oop(narrowOop* p) { ShouldNotReachHere(); }
};

void G1CollectedHeap::register_nmethod(nmethod* nm) {
  guarantee(nm != nullptr, "sanity");
  RegisterNMethodOopClosure reg_cl(this, nm);
  nm->oops_do(&reg_cl);
}

void G1CollectedHeap::unregister_nmethod(nmethod* nm) {
  // We always unregister nmethods in bulk during code unloading only.
  ShouldNotReachHere();
}

void G1CollectedHeap::update_used_after_gc(bool evacuation_failed) {
  if (evacuation_failed) {
    set_used(recalculate_used());
  } else {
    // The "used" of the collection set have already been subtracted
    // when they were freed.  Add in the bytes used.
    increase_used(_bytes_used_during_gc);
  }
}

class RebuildCodeRootClosure: public NMethodClosure {
  G1CollectedHeap* _g1h;

public:
  RebuildCodeRootClosure(G1CollectedHeap* g1h) :
    _g1h(g1h) {}

  void do_nmethod(nmethod* nm) {
    assert(nm != nullptr, "Sanity");
    _g1h->register_nmethod(nm);
  }
};

void G1CollectedHeap::rebuild_code_roots() {
  RebuildCodeRootClosure nmethod_cl(this);
  CodeCache::nmethods_do(&nmethod_cl);
}

void G1CollectedHeap::initialize_serviceability() {
  _monitoring_support->initialize_serviceability();
}

MemoryUsage G1CollectedHeap::memory_usage() {
  return _monitoring_support->memory_usage();
}

GrowableArray<GCMemoryManager*> G1CollectedHeap::memory_managers() {
  return _monitoring_support->memory_managers();
}

GrowableArray<MemoryPool*> G1CollectedHeap::memory_pools() {
  return _monitoring_support->memory_pools();
}

void G1CollectedHeap::fill_with_dummy_object(HeapWord* start, HeapWord* end, bool zap) {
  G1HeapRegion* region = heap_region_containing(start);
  region->fill_with_dummy_object(start, pointer_delta(end, start), zap);
}

void G1CollectedHeap::start_codecache_marking_cycle_if_inactive(bool concurrent_mark_start) {
  // We can reach here with an active code cache marking cycle either because the
  // previous G1 concurrent marking cycle was undone (if heap occupancy after the
  // concurrent start young collection was below the threshold) or aborted. See
  // CodeCache::on_gc_marking_cycle_finish() why this is.  We must not start a new code
  // cache cycle then. If we are about to start a new g1 concurrent marking cycle we
  // still have to arm all nmethod entry barriers. They are needed for adding oop
  // constants to the SATB snapshot. Full GC does not need nmethods to be armed.
  if (!CodeCache::is_gc_marking_cycle_active()) {
    CodeCache::on_gc_marking_cycle_start();
  }
  if (concurrent_mark_start) {
    CodeCache::arm_all_nmethods();
  }
}

void G1CollectedHeap::finish_codecache_marking_cycle() {
  CodeCache::on_gc_marking_cycle_finish();
  CodeCache::arm_all_nmethods();
}

void G1CollectedHeap::prepare_group_cardsets_for_scan() {
  young_regions_cardset()->reset_table_scanner_for_groups();

  collection_set()->prepare_groups_for_scan();
}