src/heap.cc

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "heap.h"

#include <sys/types.h>
#include <sys/wait.h>

#include <limits>
#include <vector>

#include "base/stl_util.h"
#include "cutils/sched_policy.h"
#include "debugger.h"
#include "gc/atomic_stack.h"
#include "gc/card_table.h"
#include "gc/card_table-inl.h"
#include "gc/heap_bitmap.h"
#include "gc/heap_bitmap-inl.h"
#include "gc/large_object_space.h"
#include "gc/mark_sweep.h"
#include "gc/mark_sweep-inl.h"
#include "gc/partial_mark_sweep.h"
#include "gc/space_bitmap-inl.h"
#include "gc/sticky_mark_sweep.h"
#include "gc/mod_union_table.h"
#include "gc/mod_union_table-inl.h"
#include "gc/space.h"
#include "image.h"
#include "invoke_arg_array_builder.h"
#include "mirror/class-inl.h"
#include "mirror/field-inl.h"
#include "mirror/object.h"
#include "mirror/object-inl.h"
#include "mirror/object_array-inl.h"
#include "object_utils.h"
#include "os.h"
#include "ScopedLocalRef.h"
#include "scoped_thread_state_change.h"
#include "sirt_ref.h"
#include "thread_list.h"
#include "UniquePtr.h"
#include "well_known_classes.h"

namespace art {

static const uint64_t kSlowGcThreshold = MsToNs(100);
static const uint64_t kLongGcPauseThreshold = MsToNs(5);
static const bool kDumpGcPerformanceOnShutdown = false;
const double Heap::kDefaultTargetUtilization = 0.5;

static bool GenerateImage(const std::string& image_file_name) {
  const std::string boot_class_path_string(Runtime::Current()->GetBootClassPathString());
  std::vector<std::string> boot_class_path;
  Split(boot_class_path_string, ':', boot_class_path);
  if (boot_class_path.empty()) {
    LOG(FATAL) << "Failed to generate image because no boot class path specified";
  }

  std::vector<char*> arg_vector;

  std::string dex2oat_string(GetAndroidRoot());
  dex2oat_string += (kIsDebugBuild ? "/bin/dex2oatd" : "/bin/dex2oat");
  const char* dex2oat = dex2oat_string.c_str();
  arg_vector.push_back(strdup(dex2oat));

  std::string image_option_string("--image=");
  image_option_string += image_file_name;
  const char* image_option = image_option_string.c_str();
  arg_vector.push_back(strdup(image_option));

  arg_vector.push_back(strdup("--runtime-arg"));
  arg_vector.push_back(strdup("-Xms64m"));

  arg_vector.push_back(strdup("--runtime-arg"));
  arg_vector.push_back(strdup("-Xmx64m"));

  for (size_t i = 0; i < boot_class_path.size(); i++) {
    std::string dex_file_option_string("--dex-file=");
    dex_file_option_string += boot_class_path[i];
    const char* dex_file_option = dex_file_option_string.c_str();
    arg_vector.push_back(strdup(dex_file_option));
  }

  std::string oat_file_option_string("--oat-file=");
  oat_file_option_string += image_file_name;
  oat_file_option_string.erase(oat_file_option_string.size() - 3);
  oat_file_option_string += "oat";
  const char* oat_file_option = oat_file_option_string.c_str();
  arg_vector.push_back(strdup(oat_file_option));

  std::string base_option_string(StringPrintf("--base=0x%x", ART_BASE_ADDRESS));
  arg_vector.push_back(strdup(base_option_string.c_str()));

  if (!kIsTargetBuild) {
    arg_vector.push_back(strdup("--host"));
  }

  std::string command_line(Join(arg_vector, ' '));
  LOG(INFO) << command_line;

  arg_vector.push_back(NULL);
  char** argv = &arg_vector[0];

  // fork and exec dex2oat
  pid_t pid = fork();
  if (pid == 0) {
    // no allocation allowed between fork and exec

    // change process groups, so we don't get reaped by ProcessManager
    setpgid(0, 0);

    execv(dex2oat, argv);

    PLOG(FATAL) << "execv(" << dex2oat << ") failed";
    return false;
  } else {
    STLDeleteElements(&arg_vector);

    // wait for dex2oat to finish
    int status;
    pid_t got_pid = TEMP_FAILURE_RETRY(waitpid(pid, &status, 0));
    if (got_pid != pid) {
      PLOG(ERROR) << "waitpid failed: wanted " << pid << ", got " << got_pid;
      return false;
    }
    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
      LOG(ERROR) << dex2oat << " failed: " << command_line;
      return false;
    }
  }
  return true;
}

void Heap::UnReserveOatFileAddressRange() {
  oat_file_map_.reset(NULL);
}

Heap::Heap(size_t initial_size, size_t growth_limit, size_t min_free, size_t max_free,
           double target_utilization, size_t capacity,
           const std::string& original_image_file_name, bool concurrent_gc)
    : alloc_space_(NULL),
      card_table_(NULL),
      concurrent_gc_(concurrent_gc),
      have_zygote_space_(false),
      is_gc_running_(false),
      last_gc_type_(kGcTypeNone),
      enforce_heap_growth_rate_(false),
      capacity_(capacity),
      growth_limit_(growth_limit),
      max_allowed_footprint_(initial_size),
      concurrent_start_size_(128 * KB),
      concurrent_min_free_(256 * KB),
      concurrent_start_bytes_(concurrent_gc ? initial_size - concurrent_start_size_ :
          std::numeric_limits<size_t>::max()),
      sticky_gc_count_(0),
      total_bytes_freed_(0),
      total_objects_freed_(0),
      large_object_threshold_(3 * kPageSize),
      num_bytes_allocated_(0),
      verify_missing_card_marks_(false),
      verify_system_weaks_(false),
      verify_pre_gc_heap_(false),
      verify_post_gc_heap_(false),
      verify_mod_union_table_(false),
      partial_gc_frequency_(10),
      min_alloc_space_size_for_sticky_gc_(2 * MB),
      min_remaining_space_for_sticky_gc_(1 * MB),
      last_trim_time_(0),
      allocation_rate_(0),
      max_allocation_stack_size_(MB),
      reference_referent_offset_(0),
      reference_queue_offset_(0),
      reference_queueNext_offset_(0),
      reference_pendingNext_offset_(0),
      finalizer_reference_zombie_offset_(0),
      min_free_(min_free),
      max_free_(max_free),
      target_utilization_(target_utilization),
      total_wait_time_(0),
      measure_allocation_time_(false),
      total_allocation_time_(0),
      verify_objects_(false) {
  if (VLOG_IS_ON(heap) || VLOG_IS_ON(startup)) {
    LOG(INFO) << "Heap() entering";
  }

  live_bitmap_.reset(new HeapBitmap(this));
  mark_bitmap_.reset(new HeapBitmap(this));

  // Requested begin for the alloc space, to follow the mapped image and oat files
  byte* requested_begin = NULL;
  std::string image_file_name(original_image_file_name);
  if (!image_file_name.empty()) {
    ImageSpace* image_space = NULL;

    if (OS::FileExists(image_file_name.c_str())) {
      // If the /system file exists, it should be up-to-date, don't try to generate
      image_space = ImageSpace::Create(image_file_name);
    } else {
      // If the /system file didn't exist, we need to use one from the art-cache.
      // If the cache file exists, try to open, but if it fails, regenerate.
      // If it does not exist, generate.
      image_file_name = GetArtCacheFilenameOrDie(image_file_name);
      if (OS::FileExists(image_file_name.c_str())) {
        image_space = ImageSpace::Create(image_file_name);
      }
      if (image_space == NULL) {
        CHECK(GenerateImage(image_file_name)) << "Failed to generate image: " << image_file_name;
        image_space = ImageSpace::Create(image_file_name);
      }
    }

    CHECK(image_space != NULL) << "Failed to create space from " << image_file_name;
    AddSpace(image_space);
    // Oat files referenced by image files immediately follow them in memory, ensure alloc space
    // isn't going to get in the middle
    byte* oat_file_end_addr = image_space->GetImageHeader().GetOatFileEnd();
    CHECK_GT(oat_file_end_addr, image_space->End());

    // Reserve address range from image_space->End() to image_space->GetImageHeader().GetOatEnd()
    uintptr_t reserve_begin = RoundUp(reinterpret_cast<uintptr_t>(image_space->End()), kPageSize);
    uintptr_t reserve_end = RoundUp(reinterpret_cast<uintptr_t>(oat_file_end_addr), kPageSize);
    oat_file_map_.reset(MemMap::MapAnonymous("oat file reserve",
                                             reinterpret_cast<byte*>(reserve_begin),
                                             reserve_end - reserve_begin, PROT_NONE));

    if (oat_file_end_addr > requested_begin) {
      requested_begin = reinterpret_cast<byte*>(RoundUp(reinterpret_cast<uintptr_t>(oat_file_end_addr),
                                                          kPageSize));
    }
  }

  // Allocate the large object space.
  large_object_space_.reset(FreeListSpace::Create("large object space", NULL, capacity));
  live_bitmap_->SetLargeObjects(large_object_space_->GetLiveObjects());
  mark_bitmap_->SetLargeObjects(large_object_space_->GetMarkObjects());

  UniquePtr<DlMallocSpace> alloc_space(DlMallocSpace::Create("alloc space", initial_size,
                                                             growth_limit, capacity,
                                                             requested_begin));
  alloc_space_ = alloc_space.release();
  CHECK(alloc_space_ != NULL) << "Failed to create alloc space";
  alloc_space_->SetFootprintLimit(alloc_space_->Capacity());
  AddSpace(alloc_space_);

  // Spaces are sorted in order of Begin().
  byte* heap_begin = spaces_.front()->Begin();
  size_t heap_capacity = spaces_.back()->End() - spaces_.front()->Begin();
  if (spaces_.back()->IsAllocSpace()) {
    heap_capacity += spaces_.back()->AsAllocSpace()->NonGrowthLimitCapacity();
  }

  // Mark image objects in the live bitmap
  // TODO: C++0x
  for (Spaces::iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    Space* space = *it;
    if (space->IsImageSpace()) {
      ImageSpace* image_space = space->AsImageSpace();
      image_space->RecordImageAllocations(image_space->GetLiveBitmap());
    }
  }

  // Allocate the card table.
  card_table_.reset(CardTable::Create(heap_begin, heap_capacity));
  CHECK(card_table_.get() != NULL) << "Failed to create card table";

  mod_union_table_.reset(new ModUnionTableToZygoteAllocspace<ModUnionTableReferenceCache>(this));
  CHECK(mod_union_table_.get() != NULL) << "Failed to create mod-union table";

  zygote_mod_union_table_.reset(new ModUnionTableCardCache(this));
  CHECK(zygote_mod_union_table_.get() != NULL) << "Failed to create Zygote mod-union table";

  // TODO: Count objects in the image space here.
  num_bytes_allocated_ = 0;

  // Default mark stack size in bytes.
  static const size_t default_mark_stack_size = 64 * KB;
  mark_stack_.reset(ObjectStack::Create("mark stack", default_mark_stack_size));
  allocation_stack_.reset(ObjectStack::Create("allocation stack",
                                              max_allocation_stack_size_));
  live_stack_.reset(ObjectStack::Create("live stack",
                                      max_allocation_stack_size_));

  // It's still too early to take a lock because there are no threads yet, but we can create locks
  // now. We don't create it earlier to make it clear that you can't use locks during heap
  // initialization.
  gc_complete_lock_ = new Mutex("GC complete lock");
  gc_complete_cond_.reset(new ConditionVariable("GC complete condition variable",
                                                *gc_complete_lock_));

  // Create the reference queue lock, this is required so for parrallel object scanning in the GC.
  reference_queue_lock_.reset(new Mutex("reference queue lock"));

  last_gc_time_ = NanoTime();
  last_gc_size_ = GetBytesAllocated();

  // Create our garbage collectors.
  for (size_t i = 0; i < 2; ++i) {
    const bool concurrent = i != 0;
    mark_sweep_collectors_.push_back(new MarkSweep(this, concurrent));
    mark_sweep_collectors_.push_back(new PartialMarkSweep(this, concurrent));
    mark_sweep_collectors_.push_back(new StickyMarkSweep(this, concurrent));
  }

  CHECK(max_allowed_footprint_ != 0);
  if (VLOG_IS_ON(heap) || VLOG_IS_ON(startup)) {
    LOG(INFO) << "Heap() exiting";
  }
}

void Heap::CreateThreadPool() {
  // TODO: Make sysconf(_SC_NPROCESSORS_CONF) be a helper function?
  // Use the number of processors - 1 since the thread doing the GC does work while its waiting for
  // workers to complete.
  thread_pool_.reset(new ThreadPool(sysconf(_SC_NPROCESSORS_CONF) - 1));
}

void Heap::DeleteThreadPool() {
  thread_pool_.reset(NULL);
}

// Sort spaces based on begin address
struct SpaceSorter {
  bool operator ()(const ContinuousSpace* a, const ContinuousSpace* b) const {
    return a->Begin() < b->Begin();
  }
};

void Heap::AddSpace(ContinuousSpace* space) {
  WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
  DCHECK(space != NULL);
  DCHECK(space->GetLiveBitmap() != NULL);
  live_bitmap_->AddSpaceBitmap(space->GetLiveBitmap());
  DCHECK(space->GetMarkBitmap() != NULL);
  mark_bitmap_->AddSpaceBitmap(space->GetMarkBitmap());
  spaces_.push_back(space);
  if (space->IsAllocSpace()) {
    alloc_space_ = space->AsAllocSpace();
  }

  // Ensure that spaces remain sorted in increasing order of start address (required for CMS finger)
  std::sort(spaces_.begin(), spaces_.end(), SpaceSorter());

  // Ensure that ImageSpaces < ZygoteSpaces < AllocSpaces so that we can do address based checks to
  // avoid redundant marking.
  bool seen_zygote = false, seen_alloc = false;
  for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    Space* space = *it;
    if (space->IsImageSpace()) {
      DCHECK(!seen_zygote);
      DCHECK(!seen_alloc);
    } else if (space->IsZygoteSpace()) {
      DCHECK(!seen_alloc);
      seen_zygote = true;
    } else if (space->IsAllocSpace()) {
      seen_alloc = true;
    }
  }
}

void Heap::DumpGcPerformanceInfo() {
  // Dump cumulative timings.
  LOG(INFO) << "Dumping cumulative Gc timings";
  uint64_t total_duration = 0;

  // Dump cumulative loggers for each GC type.
  // TODO: C++0x
  uint64_t total_paused_time = 0;
  for (Collectors::const_iterator it = mark_sweep_collectors_.begin();
       it != mark_sweep_collectors_.end(); ++it) {
    MarkSweep* collector = *it;
    CumulativeLogger& logger = collector->GetCumulativeTimings();
    if (logger.GetTotalNs() != 0) {
      LOG(INFO) << Dumpable<CumulativeLogger>(logger);
      const uint64_t total_ns = logger.GetTotalNs();
      const uint64_t total_pause_ns = (*it)->GetTotalPausedTime();
      double seconds = NsToMs(logger.GetTotalNs()) / 1000.0;
      const uint64_t freed_bytes = collector->GetTotalFreedBytes();
      const uint64_t freed_objects = collector->GetTotalFreedObjects();
      LOG(INFO)
          << collector->GetName() << " total time: " << PrettyDuration(total_ns) << "\n"
          << collector->GetName() << " paused time: " << PrettyDuration(total_pause_ns) << "\n"
          << collector->GetName() << " freed: " << freed_objects
          << " objects with total size " << PrettySize(freed_bytes) << "\n"
          << collector->GetName() << " throughput: " << freed_objects / seconds << "/s / "
          << PrettySize(freed_bytes / seconds) << "/s\n";
      total_duration += total_ns;
      total_paused_time += total_pause_ns;
    }
  }
  uint64_t allocation_time = static_cast<uint64_t>(total_allocation_time_) * kTimeAdjust;
  size_t total_objects_allocated = GetTotalObjectsAllocated();
  size_t total_bytes_allocated = GetTotalBytesAllocated();
  if (total_duration != 0) {
    const double total_seconds = double(total_duration / 1000) / 1000000.0;
    LOG(INFO) << "Total time spent in GC: " << PrettyDuration(total_duration);
    LOG(INFO) << "Mean GC size throughput: "
              << PrettySize(GetTotalBytesFreed() / total_seconds) << "/s";
    LOG(INFO) << "Mean GC object throughput: "
              << (GetTotalObjectsFreed() / total_seconds) << " objects/s";
  }
  LOG(INFO) << "Total number of allocations: " << total_objects_allocated;
  LOG(INFO) << "Total bytes allocated " << PrettySize(total_bytes_allocated);
  if (measure_allocation_time_) {
    LOG(INFO) << "Total time spent allocating: " << PrettyDuration(allocation_time);
    LOG(INFO) << "Mean allocation time: "
              << PrettyDuration(allocation_time / total_objects_allocated);
  }
  LOG(INFO) << "Total mutator paused time: " << PrettyDuration(total_paused_time);
  LOG(INFO) << "Total time waiting for GC to complete: " << PrettyDuration(total_wait_time_);
}

Heap::~Heap() {
  if (kDumpGcPerformanceOnShutdown) {
    DumpGcPerformanceInfo();
  }

  STLDeleteElements(&mark_sweep_collectors_);

  // If we don't reset then the mark stack complains in it's destructor.
  allocation_stack_->Reset();
  live_stack_->Reset();

  VLOG(heap) << "~Heap()";
  // We can't take the heap lock here because there might be a daemon thread suspended with the
  // heap lock held. We know though that no non-daemon threads are executing, and we know that
  // all daemon threads are suspended, and we also know that the threads list have been deleted, so
  // those threads can't resume. We're the only running thread, and we can do whatever we like...
  STLDeleteElements(&spaces_);
  delete gc_complete_lock_;
}

ContinuousSpace* Heap::FindSpaceFromObject(const mirror::Object* obj) const {
  // TODO: C++0x auto
  for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    if ((*it)->Contains(obj)) {
      return *it;
    }
  }
  LOG(FATAL) << "object " << reinterpret_cast<const void*>(obj) << " not inside any spaces!";
  return NULL;
}

ImageSpace* Heap::GetImageSpace() {
  // TODO: C++0x auto
  for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    if ((*it)->IsImageSpace()) {
      return (*it)->AsImageSpace();
    }
  }
  return NULL;
}

DlMallocSpace* Heap::GetAllocSpace() {
  return alloc_space_;
}

static void MSpaceChunkCallback(void* start, void* end, size_t used_bytes, void* arg) {
  size_t chunk_size = reinterpret_cast<uint8_t*>(end) - reinterpret_cast<uint8_t*>(start);
  if (used_bytes < chunk_size) {
    size_t chunk_free_bytes = chunk_size - used_bytes;
    size_t& max_contiguous_allocation = *reinterpret_cast<size_t*>(arg);
    max_contiguous_allocation = std::max(max_contiguous_allocation, chunk_free_bytes);
  }
}

mirror::Object* Heap::AllocObject(Thread* self, mirror::Class* c, size_t byte_count) {
  DCHECK(c == NULL || (c->IsClassClass() && byte_count >= sizeof(mirror::Class)) ||
         (c->IsVariableSize() || c->GetObjectSize() == byte_count) ||
         strlen(ClassHelper(c).GetDescriptor()) == 0);
  DCHECK_GE(byte_count, sizeof(mirror::Object));

  mirror::Object* obj = NULL;
  size_t size = 0;
  uint64_t allocation_start = 0;
  if (measure_allocation_time_) {
    allocation_start = NanoTime();
  }

  // We need to have a zygote space or else our newly allocated large object can end up in the
  // Zygote resulting in it being prematurely freed.
  // We can only do this for primive objects since large objects will not be within the card table
  // range. This also means that we rely on SetClass not dirtying the object's card.
  //
  // TODO: note "false && " to temporarily disable large object space
  // due to issues on occam and mantaray.  We were seeing objects in
  // the large object space with NULL klass_ fields.
  if (false && byte_count >= large_object_threshold_ && have_zygote_space_ && c->IsPrimitiveArray()) {
    size = RoundUp(byte_count, kPageSize);
    obj = Allocate(self, large_object_space_.get(), size);
    // Make sure that our large object didn't get placed anywhere within the space interval or else
    // it breaks the immune range.
    DCHECK(obj == NULL ||
           reinterpret_cast<byte*>(obj) < spaces_.front()->Begin() ||
           reinterpret_cast<byte*>(obj) >= spaces_.back()->End());
  } else {
    obj = Allocate(self, alloc_space_, byte_count);

    // Ensure that we did not allocate into a zygote space.
    DCHECK(obj == NULL || !have_zygote_space_ || !FindSpaceFromObject(obj)->IsZygoteSpace());
    size = alloc_space_->AllocationSize(obj);
  }

  if (LIKELY(obj != NULL)) {
    obj->SetClass(c);

    // Record allocation after since we want to use the atomic add for the atomic fence to guard
    // the SetClass since we do not want the class to appear NULL in another thread.
    RecordAllocation(size, obj);

    if (Dbg::IsAllocTrackingEnabled()) {
      Dbg::RecordAllocation(c, byte_count);
    }
    if (static_cast<size_t>(num_bytes_allocated_) >= concurrent_start_bytes_) {
      // We already have a request pending, no reason to start more until we update
      // concurrent_start_bytes_.
      concurrent_start_bytes_ = std::numeric_limits<size_t>::max();
      // The SirtRef is necessary since the calls in RequestConcurrentGC are a safepoint.
      SirtRef<mirror::Object> ref(self, obj);
      RequestConcurrentGC(self);
    }
    VerifyObject(obj);

    if (measure_allocation_time_) {
      total_allocation_time_ += (NanoTime() - allocation_start) / kTimeAdjust;
    }

    return obj;
  }
  std::ostringstream oss;
  int64_t total_bytes_free = GetFreeMemory();
  uint64_t alloc_space_size = alloc_space_->GetNumBytesAllocated();
  uint64_t large_object_size = large_object_space_->GetNumObjectsAllocated();
  oss << "Failed to allocate a " << byte_count << " byte allocation with " << total_bytes_free
      << " free bytes; allocation space size " << alloc_space_size
      << "; large object space size " << large_object_size;
  // If the allocation failed due to fragmentation, print out the largest continuous allocation.
  if (total_bytes_free >= byte_count) {
    size_t max_contiguous_allocation = 0;
    // TODO: C++0x auto
    for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
      if ((*it)->IsAllocSpace()) {
        (*it)->AsAllocSpace()->Walk(MSpaceChunkCallback, &max_contiguous_allocation);
      }
    }
    oss << "; failed due to fragmentation (largest possible contiguous allocation "
        <<  max_contiguous_allocation << " bytes)";
  }
  self->ThrowOutOfMemoryError(oss.str().c_str());
  return NULL;
}

bool Heap::IsHeapAddress(const mirror::Object* obj) {
  // Note: we deliberately don't take the lock here, and mustn't test anything that would
  // require taking the lock.
  if (obj == NULL) {
    return true;
  }
  if (!IsAligned<kObjectAlignment>(obj)) {
    return false;
  }
  for (size_t i = 0; i < spaces_.size(); ++i) {
    if (spaces_[i]->Contains(obj)) {
      return true;
    }
  }
  // Note: Doing this only works for the free list version of the large object space since the
  // multiple memory map version uses a lock to do the contains check.
  return large_object_space_->Contains(obj);
}

bool Heap::IsLiveObjectLocked(const mirror::Object* obj) {
  Locks::heap_bitmap_lock_->AssertReaderHeld(Thread::Current());
  return IsHeapAddress(obj) && GetLiveBitmap()->Test(obj);
}

#if VERIFY_OBJECT_ENABLED
void Heap::VerifyObject(const Object* obj) {
  if (obj == NULL || this == NULL || !verify_objects_ || Thread::Current() == NULL ||
      Runtime::Current()->GetThreadList()->GetLockOwner() == Thread::Current()->GetTid()) {
    return;
  }
  VerifyObjectBody(obj);
}
#endif

void Heap::DumpSpaces() {
  // TODO: C++0x auto
  for (Spaces::iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    ContinuousSpace* space = *it;
    SpaceBitmap* live_bitmap = space->GetLiveBitmap();
    SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
    LOG(INFO) << space << " " << *space << "\n"
              << live_bitmap << " " << *live_bitmap << "\n"
              << mark_bitmap << " " << *mark_bitmap;
  }
  if (large_object_space_.get() != NULL) {
    large_object_space_->Dump(LOG(INFO));
  }
}

void Heap::VerifyObjectBody(const mirror::Object* obj) {
  if (!IsAligned<kObjectAlignment>(obj)) {
    LOG(FATAL) << "Object isn't aligned: " << obj;
  }

  // TODO: the bitmap tests below are racy if VerifyObjectBody is called without the
  //       heap_bitmap_lock_.
  if (!GetLiveBitmap()->Test(obj)) {
    // Check the allocation stack / live stack.
    if (!std::binary_search(live_stack_->Begin(), live_stack_->End(), obj) &&
        std::find(allocation_stack_->Begin(), allocation_stack_->End(), obj) ==
            allocation_stack_->End()) {
      if (large_object_space_->GetLiveObjects()->Test(obj)) {
        DumpSpaces();
        LOG(FATAL) << "Object is dead: " << obj;
      }
    }
  }

  // Ignore early dawn of the universe verifications
  if (!VERIFY_OBJECT_FAST && GetObjectsAllocated() > 10) {
    const byte* raw_addr = reinterpret_cast<const byte*>(obj) +
        mirror::Object::ClassOffset().Int32Value();
    const mirror::Class* c = *reinterpret_cast<mirror::Class* const *>(raw_addr);
    if (c == NULL) {
      LOG(FATAL) << "Null class in object: " << obj;
    } else if (!IsAligned<kObjectAlignment>(c)) {
      LOG(FATAL) << "Class isn't aligned: " << c << " in object: " << obj;
    } else if (!GetLiveBitmap()->Test(c)) {
      LOG(FATAL) << "Class of object is dead: " << c << " in object: " << obj;
    }
    // Check obj.getClass().getClass() == obj.getClass().getClass().getClass()
    // Note: we don't use the accessors here as they have internal sanity checks
    // that we don't want to run
    raw_addr = reinterpret_cast<const byte*>(c) + mirror::Object::ClassOffset().Int32Value();
    const mirror::Class* c_c = *reinterpret_cast<mirror::Class* const *>(raw_addr);
    raw_addr = reinterpret_cast<const byte*>(c_c) + mirror::Object::ClassOffset().Int32Value();
    const mirror::Class* c_c_c = *reinterpret_cast<mirror::Class* const *>(raw_addr);
    CHECK_EQ(c_c, c_c_c);
  }
}

void Heap::VerificationCallback(mirror::Object* obj, void* arg) {
  DCHECK(obj != NULL);
  reinterpret_cast<Heap*>(arg)->VerifyObjectBody(obj);
}

void Heap::VerifyHeap() {
  ReaderMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
  GetLiveBitmap()->Walk(Heap::VerificationCallback, this);
}

void Heap::RecordAllocation(size_t size, mirror::Object* obj) {
  DCHECK(obj != NULL);
  DCHECK_GT(size, 0u);
  num_bytes_allocated_ += size;

  if (Runtime::Current()->HasStatsEnabled()) {
    RuntimeStats* thread_stats = Thread::Current()->GetStats();
    ++thread_stats->allocated_objects;
    thread_stats->allocated_bytes += size;

    // TODO: Update these atomically.
    RuntimeStats* global_stats = Runtime::Current()->GetStats();
    ++global_stats->allocated_objects;
    global_stats->allocated_bytes += size;
  }

  // This is safe to do since the GC will never free objects which are neither in the allocation
  // stack or the live bitmap.
  while (!allocation_stack_->AtomicPushBack(obj)) {
    CollectGarbageInternal(kGcTypeSticky, kGcCauseForAlloc, false);
  }
}

void Heap::RecordFree(size_t freed_objects, size_t freed_bytes) {
  DCHECK_LE(freed_bytes, static_cast<size_t>(num_bytes_allocated_));
  num_bytes_allocated_ -= freed_bytes;

  if (Runtime::Current()->HasStatsEnabled()) {
    RuntimeStats* thread_stats = Thread::Current()->GetStats();
    thread_stats->freed_objects += freed_objects;
    thread_stats->freed_bytes += freed_bytes;

    // TODO: Do this concurrently.
    RuntimeStats* global_stats = Runtime::Current()->GetStats();
    global_stats->freed_objects += freed_objects;
    global_stats->freed_bytes += freed_bytes;
  }
}

mirror::Object* Heap::TryToAllocate(Thread* self, AllocSpace* space, size_t alloc_size, bool grow) {
  // Should we try to use a CAS here and fix up num_bytes_allocated_ later with AllocationSize?
  if (num_bytes_allocated_ + alloc_size > max_allowed_footprint_) {
    // max_allowed_footprint_ <= growth_limit_ so it is safe to check in here.
    if (num_bytes_allocated_ + alloc_size > growth_limit_) {
      // Completely out of memory.
      return NULL;
    }

    if (enforce_heap_growth_rate_) {
      if (grow) {
        // Grow the heap by alloc_size extra bytes.
        max_allowed_footprint_ = std::min(max_allowed_footprint_ + alloc_size, growth_limit_);
        VLOG(gc) << "Grow heap to " << PrettySize(max_allowed_footprint_)
                 << " for a " << PrettySize(alloc_size) << " allocation";
      } else {
        return NULL;
      }
    }
  }

  return space->Alloc(self, alloc_size);
}

mirror::Object* Heap::Allocate(Thread* self, AllocSpace* space, size_t alloc_size) {
  // Since allocation can cause a GC which will need to SuspendAll, make sure all allocations are
  // done in the runnable state where suspension is expected.
  DCHECK_EQ(self->GetState(), kRunnable);
  self->AssertThreadSuspensionIsAllowable();

  mirror::Object* ptr = TryToAllocate(self, space, alloc_size, false);
  if (ptr != NULL) {
    return ptr;
  }

  // The allocation failed. If the GC is running, block until it completes, and then retry the
  // allocation.
  GcType last_gc = WaitForConcurrentGcToComplete(self);
  if (last_gc != kGcTypeNone) {
    // A GC was in progress and we blocked, retry allocation now that memory has been freed.
    ptr = TryToAllocate(self, space, alloc_size, false);
    if (ptr != NULL) {
      return ptr;
    }
  }

  // Loop through our different Gc types and try to Gc until we get enough free memory.
  for (size_t i = static_cast<size_t>(last_gc) + 1; i < static_cast<size_t>(kGcTypeMax); ++i) {
    bool run_gc = false;
    GcType gc_type = static_cast<GcType>(i);
    switch (gc_type) {
      case kGcTypeSticky: {
          const size_t alloc_space_size = alloc_space_->Size();
          run_gc = alloc_space_size > min_alloc_space_size_for_sticky_gc_ &&
              alloc_space_->Capacity() - alloc_space_size >= min_remaining_space_for_sticky_gc_;
          break;
        }
      case kGcTypePartial:
        run_gc = have_zygote_space_;
        break;
      case kGcTypeFull:
        run_gc = true;
        break;
      default:
        break;
    }

    if (run_gc) {
      // If we actually ran a different type of Gc than requested, we can skip the index forwards.
      GcType gc_type_ran = CollectGarbageInternal(gc_type, kGcCauseForAlloc, false);
      DCHECK_GE(static_cast<size_t>(gc_type_ran), i);
      i = static_cast<size_t>(gc_type_ran);

      // Did we free sufficient memory for the allocation to succeed?
      ptr = TryToAllocate(self, space, alloc_size, false);
      if (ptr != NULL) {
        return ptr;
      }
    }
  }

  // Allocations have failed after GCs;  this is an exceptional state.
  // Try harder, growing the heap if necessary.
  ptr = TryToAllocate(self, space, alloc_size, true);
  if (ptr != NULL) {
    return ptr;
  }

  // Most allocations should have succeeded by now, so the heap is really full, really fragmented,
  // or the requested size is really big. Do another GC, collecting SoftReferences this time. The
  // VM spec requires that all SoftReferences have been collected and cleared before throwing OOME.

  // OLD-TODO: wait for the finalizers from the previous GC to finish
  VLOG(gc) << "Forcing collection of SoftReferences for " << PrettySize(alloc_size)
           << " allocation";

  // We don't need a WaitForConcurrentGcToComplete here either.
  CollectGarbageInternal(kGcTypeFull, kGcCauseForAlloc, true);
  return TryToAllocate(self, space, alloc_size, true);
}

void Heap::SetTargetHeapUtilization(float target) {
  DCHECK_GT(target, 0.0f);  // asserted in Java code
  DCHECK_LT(target, 1.0f);
  target_utilization_ = target;
}

int64_t Heap::GetMaxMemory() const {
  return growth_limit_;
}

int64_t Heap::GetTotalMemory() const {
  return GetMaxMemory();
}

int64_t Heap::GetFreeMemory() const {
  return GetMaxMemory() - num_bytes_allocated_;
}

size_t Heap::GetTotalBytesFreed() const {
  return total_bytes_freed_;
}

size_t Heap::GetTotalObjectsFreed() const {
  return total_objects_freed_;
}

size_t Heap::GetTotalObjectsAllocated() const {
  size_t total = large_object_space_->GetTotalObjectsAllocated();
  for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    Space* space = *it;
    if (space->IsAllocSpace()) {
      total += space->AsAllocSpace()->GetTotalObjectsAllocated();
    }
  }
  return total;
}

size_t Heap::GetTotalBytesAllocated() const {
  size_t total = large_object_space_->GetTotalBytesAllocated();
  for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    Space* space = *it;
    if (space->IsAllocSpace()) {
      total += space->AsAllocSpace()->GetTotalBytesAllocated();
    }
  }
  return total;
}

class InstanceCounter {
 public:
  InstanceCounter(const std::vector<mirror::Class*>& classes, bool use_is_assignable_from, uint64_t* counts)
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
      : classes_(classes), use_is_assignable_from_(use_is_assignable_from), counts_(counts) {
  }

  void operator()(const mirror::Object* o) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    for (size_t i = 0; i < classes_.size(); ++i) {
      const mirror::Class* instance_class = o->GetClass();
      if (use_is_assignable_from_) {
        if (instance_class != NULL && classes_[i]->IsAssignableFrom(instance_class)) {
          ++counts_[i];
        }
      } else {
        if (instance_class == classes_[i]) {
          ++counts_[i];
        }
      }
    }
  }

 private:
  const std::vector<mirror::Class*>& classes_;
  bool use_is_assignable_from_;
  uint64_t* const counts_;

  DISALLOW_COPY_AND_ASSIGN(InstanceCounter);
};

void Heap::CountInstances(const std::vector<mirror::Class*>& classes, bool use_is_assignable_from,
                          uint64_t* counts) {
  // We only want reachable instances, so do a GC. This also ensures that the alloc stack
  // is empty, so the live bitmap is the only place we need to look.
  Thread* self = Thread::Current();
  self->TransitionFromRunnableToSuspended(kNative);
  CollectGarbage(false);
  self->TransitionFromSuspendedToRunnable();

  InstanceCounter counter(classes, use_is_assignable_from, counts);
  ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
  GetLiveBitmap()->Visit(counter);
}

class InstanceCollector {
 public:
  InstanceCollector(mirror::Class* c, int32_t max_count, std::vector<mirror::Object*>& instances)
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
      : class_(c), max_count_(max_count), instances_(instances) {
  }

  void operator()(const mirror::Object* o) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    const mirror::Class* instance_class = o->GetClass();
    if (instance_class == class_) {
      if (max_count_ == 0 || instances_.size() < max_count_) {
        instances_.push_back(const_cast<mirror::Object*>(o));
      }
    }
  }

 private:
  mirror::Class* class_;
  uint32_t max_count_;
  std::vector<mirror::Object*>& instances_;

  DISALLOW_COPY_AND_ASSIGN(InstanceCollector);
};

void Heap::GetInstances(mirror::Class* c, int32_t max_count,
                        std::vector<mirror::Object*>& instances) {
  // We only want reachable instances, so do a GC. This also ensures that the alloc stack
  // is empty, so the live bitmap is the only place we need to look.
  Thread* self = Thread::Current();
  self->TransitionFromRunnableToSuspended(kNative);
  CollectGarbage(false);
  self->TransitionFromSuspendedToRunnable();

  InstanceCollector collector(c, max_count, instances);
  ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
  GetLiveBitmap()->Visit(collector);
}

class ReferringObjectsFinder {
 public:
  ReferringObjectsFinder(mirror::Object* object, int32_t max_count,
                         std::vector<mirror::Object*>& referring_objects)
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
      : object_(object), max_count_(max_count), referring_objects_(referring_objects) {
  }

  // For bitmap Visit.
  // TODO: Fix lock analysis to not use NO_THREAD_SAFETY_ANALYSIS, requires support for
  // annotalysis on visitors.
  void operator()(const mirror::Object* o) const NO_THREAD_SAFETY_ANALYSIS {
    MarkSweep::VisitObjectReferences(o, *this);
  }

  // For MarkSweep::VisitObjectReferences.
  void operator ()(const mirror::Object* referrer, const mirror::Object* object,
                   const MemberOffset&, bool) const {
    if (object == object_ && (max_count_ == 0 || referring_objects_.size() < max_count_)) {
      referring_objects_.push_back(const_cast<mirror::Object*>(referrer));
    }
  }

 private:
  mirror::Object* object_;
  uint32_t max_count_;
  std::vector<mirror::Object*>& referring_objects_;

  DISALLOW_COPY_AND_ASSIGN(ReferringObjectsFinder);
};

void Heap::GetReferringObjects(mirror::Object* o, int32_t max_count,
                               std::vector<mirror::Object*>& referring_objects) {
  // We only want reachable instances, so do a GC. This also ensures that the alloc stack
  // is empty, so the live bitmap is the only place we need to look.
  Thread* self = Thread::Current();
  self->TransitionFromRunnableToSuspended(kNative);
  CollectGarbage(false);
  self->TransitionFromSuspendedToRunnable();

  ReferringObjectsFinder finder(o, max_count, referring_objects);
  ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
  GetLiveBitmap()->Visit(finder);
}

void Heap::CollectGarbage(bool clear_soft_references) {
  // Even if we waited for a GC we still need to do another GC since weaks allocated during the
  // last GC will not have necessarily been cleared.
  Thread* self = Thread::Current();
  WaitForConcurrentGcToComplete(self);
  CollectGarbageInternal(kGcTypeFull, kGcCauseExplicit, clear_soft_references);
}

void Heap::PreZygoteFork() {
  static Mutex zygote_creation_lock_("zygote creation lock", kZygoteCreationLock);
  // Do this before acquiring the zygote creation lock so that we don't get lock order violations.
  CollectGarbage(false);
  Thread* self = Thread::Current();
  MutexLock mu(self, zygote_creation_lock_);

  // Try to see if we have any Zygote spaces.
  if (have_zygote_space_) {
    return;
  }

  VLOG(heap) << "Starting PreZygoteFork with alloc space size " << PrettySize(alloc_space_->Size());

  {
    // Flush the alloc stack.
    WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
    FlushAllocStack();
  }

  // Replace the first alloc space we find with a zygote space.
  // TODO: C++0x auto
  for (Spaces::iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    if ((*it)->IsAllocSpace()) {
      DlMallocSpace* zygote_space = (*it)->AsAllocSpace();

      // Turns the current alloc space into a Zygote space and obtain the new alloc space composed
      // of the remaining available heap memory.
      alloc_space_ = zygote_space->CreateZygoteSpace();
      alloc_space_->SetFootprintLimit(alloc_space_->Capacity());

      // Change the GC retention policy of the zygote space to only collect when full.
      zygote_space->SetGcRetentionPolicy(kGcRetentionPolicyFullCollect);
      AddSpace(alloc_space_);
      have_zygote_space_ = true;
      break;
    }
  }

  // Reset the cumulative loggers since we now have a few additional timing phases.
  // TODO: C++0x
  for (Collectors::const_iterator it = mark_sweep_collectors_.begin();
        it != mark_sweep_collectors_.end(); ++it) {
    (*it)->ResetCumulativeStatistics();
  }
}

void Heap::FlushAllocStack() {
  MarkAllocStack(alloc_space_->GetLiveBitmap(), large_object_space_->GetLiveObjects(),
                 allocation_stack_.get());
  allocation_stack_->Reset();
}

size_t Heap::GetUsedMemorySize() const {
  return num_bytes_allocated_;
}

void Heap::MarkAllocStack(SpaceBitmap* bitmap, SpaceSetMap* large_objects, ObjectStack* stack) {
  mirror::Object** limit = stack->End();
  for (mirror::Object** it = stack->Begin(); it != limit; ++it) {
    const mirror::Object* obj = *it;
    DCHECK(obj != NULL);
    if (LIKELY(bitmap->HasAddress(obj))) {
      bitmap->Set(obj);
    } else {
      large_objects->Set(obj);
    }
  }
}

void Heap::UnMarkAllocStack(SpaceBitmap* bitmap, SpaceSetMap* large_objects, ObjectStack* stack) {
  mirror::Object** limit = stack->End();
  for (mirror::Object** it = stack->Begin(); it != limit; ++it) {
    const mirror::Object* obj = *it;
    DCHECK(obj != NULL);
    if (LIKELY(bitmap->HasAddress(obj))) {
      bitmap->Clear(obj);
    } else {
      large_objects->Clear(obj);
    }
  }
}

GcType Heap::CollectGarbageInternal(GcType gc_type, GcCause gc_cause, bool clear_soft_references) {
  Thread* self = Thread::Current();
  ScopedThreadStateChange tsc(self, kWaitingPerformingGc);
  Locks::mutator_lock_->AssertNotHeld(self);

  if (self->IsHandlingStackOverflow()) {
    LOG(WARNING) << "Performing GC on a thread that is handling a stack overflow.";
  }

  // Ensure there is only one GC at a time.
  bool start_collect = false;
  while (!start_collect) {
    {
      MutexLock mu(self, *gc_complete_lock_);
      if (!is_gc_running_) {
        is_gc_running_ = true;
        start_collect = true;
      }
    }
    if (!start_collect) {
      WaitForConcurrentGcToComplete(self);
      // TODO: if another thread beat this one to do the GC, perhaps we should just return here?
      //       Not doing at the moment to ensure soft references are cleared.
    }
  }
  gc_complete_lock_->AssertNotHeld(self);

  if (gc_cause == kGcCauseForAlloc && Runtime::Current()->HasStatsEnabled()) {
    ++Runtime::Current()->GetStats()->gc_for_alloc_count;
    ++Thread::Current()->GetStats()->gc_for_alloc_count;
  }

  // We need to do partial GCs every now and then to avoid the heap growing too much and
  // fragmenting.
  if (gc_type == kGcTypeSticky && ++sticky_gc_count_ > partial_gc_frequency_) {
    gc_type = have_zygote_space_ ? kGcTypePartial : kGcTypeFull;
  }
  if (gc_type != kGcTypeSticky) {
    sticky_gc_count_ = 0;
  }

  uint64_t gc_start_time = NanoTime();
  uint64_t gc_start_size = GetBytesAllocated();
  // Approximate allocation rate in bytes / second.
  if (UNLIKELY(gc_start_time == last_gc_time_)) {
    LOG(WARNING) << "Timers are broken (gc_start_time == last_gc_time_).";
  }
  uint64_t ms_delta = NsToMs(gc_start_time - last_gc_time_);
  if (ms_delta != 0) {
    allocation_rate_ = (gc_start_size - last_gc_size_) * 1000 / ms_delta;
    VLOG(heap) << "Allocation rate: " << PrettySize(allocation_rate_) << "/s";
  }

  DCHECK_LT(gc_type, kGcTypeMax);
  DCHECK_NE(gc_type, kGcTypeNone);
  MarkSweep* collector = NULL;
  for (Collectors::iterator it = mark_sweep_collectors_.begin();
      it != mark_sweep_collectors_.end(); ++it) {
    MarkSweep* cur_collector = *it;
    if (cur_collector->IsConcurrent() == concurrent_gc_ && cur_collector->GetGcType() == gc_type) {
      collector = cur_collector;
      break;
    }
  }
  CHECK(collector != NULL)
      << "Could not find garbage collector with concurrent=" << concurrent_gc_
      << " and type=" << gc_type;
  collector->clear_soft_references_ = clear_soft_references;
  collector->Run();
  total_objects_freed_ += collector->GetFreedObjects();
  total_bytes_freed_ += collector->GetFreedBytes();

  const size_t duration = collector->GetDuration();
  std::vector<uint64_t> pauses = collector->GetPauseTimes();
  bool was_slow = duration > kSlowGcThreshold ||
      (gc_cause == kGcCauseForAlloc && duration > kLongGcPauseThreshold);
  for (size_t i = 0; i < pauses.size(); ++i) {
    if (pauses[i] > kLongGcPauseThreshold) {
      was_slow = true;
    }
  }

  if (was_slow) {
    const size_t percent_free = GetPercentFree();
    const size_t current_heap_size = GetUsedMemorySize();
    const size_t total_memory = GetTotalMemory();
    std::ostringstream pause_string;
    for (size_t i = 0; i < pauses.size(); ++i) {
      pause_string << PrettyDuration((pauses[i] / 1000) * 1000)
                   << ((i != pauses.size() - 1) ? ", " : "");
    }
    LOG(INFO) << gc_cause << " " << collector->GetName()
              << "GC freed " << PrettySize(collector->GetFreedBytes()) << ", "
              << percent_free << "% free, " << PrettySize(current_heap_size) << "/"
              << PrettySize(total_memory) << ", " << "paused " << pause_string.str()
              << " total " << PrettyDuration((duration / 1000) * 1000);
    if (VLOG_IS_ON(heap)) {
      LOG(INFO) << Dumpable<TimingLogger>(collector->GetTimings());
    }
  }

  {
    MutexLock mu(self, *gc_complete_lock_);
    is_gc_running_ = false;
    last_gc_type_ = gc_type;
    // Wake anyone who may have been waiting for the GC to complete.
    gc_complete_cond_->Broadcast(self);
  }
  // Inform DDMS that a GC completed.
  Dbg::GcDidFinish();
  return gc_type;
}

void Heap::UpdateAndMarkModUnion(MarkSweep* mark_sweep, TimingLogger& timings, GcType gc_type) {
  if (gc_type == kGcTypeSticky) {
    // Don't need to do anything for mod union table in this case since we are only scanning dirty
    // cards.
    return;
  }

  // Update zygote mod union table.
  if (gc_type == kGcTypePartial) {
    zygote_mod_union_table_->Update();
    timings.AddSplit("UpdateZygoteModUnionTable");

    zygote_mod_union_table_->MarkReferences(mark_sweep);
    timings.AddSplit("ZygoteMarkReferences");
  }

  // Processes the cards we cleared earlier and adds their objects into the mod-union table.
  mod_union_table_->Update();
  timings.AddSplit("UpdateModUnionTable");

  // Scans all objects in the mod-union table.
  mod_union_table_->MarkReferences(mark_sweep);
  timings.AddSplit("MarkImageToAllocSpaceReferences");
}

void Heap::RootMatchesObjectVisitor(const mirror::Object* root, void* arg) {
  mirror::Object* obj = reinterpret_cast<mirror::Object*>(arg);
  if (root == obj) {
    LOG(INFO) << "Object " << obj << " is a root";
  }
}

class ScanVisitor {
 public:
  void operator ()(const mirror::Object* obj) const {
    LOG(INFO) << "Would have rescanned object " << obj;
  }
};

class VerifyReferenceVisitor {
 public:
  VerifyReferenceVisitor(Heap* heap, bool* failed)
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_,
                            Locks::heap_bitmap_lock_)
      : heap_(heap),
        failed_(failed) {
  }

  // TODO: Fix lock analysis to not use NO_THREAD_SAFETY_ANALYSIS, requires support for smarter
  // analysis.
  void operator ()(const mirror::Object* obj, const mirror::Object* ref,
                   const MemberOffset& /* offset */, bool /* is_static */) const
      NO_THREAD_SAFETY_ANALYSIS {
    // Verify that the reference is live.
    if (ref != NULL && !IsLive(ref)) {
      CardTable* card_table = heap_->GetCardTable();
      ObjectStack* alloc_stack = heap_->allocation_stack_.get();
      ObjectStack* live_stack = heap_->live_stack_.get();

      byte* card_addr = card_table->CardFromAddr(obj);
      LOG(ERROR) << "Object " << obj << " references dead object " << ref << "\n"
                 << "IsDirty = " << (*card_addr == CardTable::kCardDirty) << "\n"
                 << "Obj type " << PrettyTypeOf(obj) << "\n"
                 << "Ref type " << PrettyTypeOf(ref);
      card_table->CheckAddrIsInCardTable(reinterpret_cast<const byte*>(obj));
      void* cover_begin = card_table->AddrFromCard(card_addr);
      void* cover_end = reinterpret_cast<void*>(reinterpret_cast<size_t>(cover_begin) +
          CardTable::kCardSize);
      LOG(ERROR) << "Card " << reinterpret_cast<void*>(card_addr) << " covers " << cover_begin
                 << "-" << cover_end;
      SpaceBitmap* bitmap = heap_->GetLiveBitmap()->GetSpaceBitmap(obj);

      // Print out how the object is live.
      if (bitmap->Test(obj)) {
        LOG(ERROR) << "Object " << obj << " found in live bitmap";
      }
      if (std::binary_search(alloc_stack->Begin(), alloc_stack->End(), obj)) {
        LOG(ERROR) << "Object " << obj << " found in allocation stack";
      }
      if (std::binary_search(live_stack->Begin(), live_stack->End(), obj)) {
        LOG(ERROR) << "Object " << obj << " found in live stack";
      }
      if (std::binary_search(live_stack->Begin(), live_stack->End(), ref)) {
        LOG(ERROR) << "Reference " << ref << " found in live stack!";
      }

      // Attempt to see if the card table missed the reference.
      ScanVisitor scan_visitor;
      byte* byte_cover_begin = reinterpret_cast<byte*>(card_table->AddrFromCard(card_addr));
      card_table->Scan(bitmap, byte_cover_begin, byte_cover_begin + CardTable::kCardSize,
                       scan_visitor, VoidFunctor());

      // Search to see if any of the roots reference our object.
      void* arg = const_cast<void*>(reinterpret_cast<const void*>(obj));
      Runtime::Current()->VisitRoots(&Heap::RootMatchesObjectVisitor, arg);
      *failed_ = true;
    }
  }

  bool IsLive(const mirror::Object* obj) const NO_THREAD_SAFETY_ANALYSIS {
    if (heap_->GetLiveBitmap()->Test(obj)) {
      return true;
    }
    ObjectStack* alloc_stack = heap_->allocation_stack_.get();
    // At this point we need to search the allocation since things in the live stack may get swept.
    // If the object is not either in the live bitmap or allocation stack, so the object must be
    // dead.
    return std::binary_search(alloc_stack->Begin(), alloc_stack->End(), obj);
  }

 private:
  Heap* heap_;
  bool* failed_;
};

class VerifyObjectVisitor {
 public:
  VerifyObjectVisitor(Heap* heap)
      : heap_(heap),
        failed_(false) {

  }

  void operator ()(const mirror::Object* obj) const
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
    VerifyReferenceVisitor visitor(heap_, const_cast<bool*>(&failed_));
    MarkSweep::VisitObjectReferences(obj, visitor);
  }

  bool Failed() const {
    return failed_;
  }

 private:
  Heap* heap_;
  bool failed_;
};

// Must do this with mutators suspended since we are directly accessing the allocation stacks.
bool Heap::VerifyHeapReferences() {
  Locks::mutator_lock_->AssertExclusiveHeld(Thread::Current());
  // Lets sort our allocation stacks so that we can efficiently binary search them.
  std::sort(allocation_stack_->Begin(), allocation_stack_->End());
  std::sort(live_stack_->Begin(), live_stack_->End());
  // Perform the verification.
  VerifyObjectVisitor visitor(this);
  GetLiveBitmap()->Visit(visitor);
  // We don't want to verify the objects in the allocation stack since they themselves may be
  // pointing to dead objects if they are not reachable.
  if (visitor.Failed()) {
    DumpSpaces();
    return false;
  }
  return true;
}

class VerifyReferenceCardVisitor {
 public:
  VerifyReferenceCardVisitor(Heap* heap, bool* failed)
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_,
                            Locks::heap_bitmap_lock_)
      : heap_(heap),
        failed_(failed) {
  }

  // TODO: Fix lock analysis to not use NO_THREAD_SAFETY_ANALYSIS, requires support for
  // annotalysis on visitors.
  void operator ()(const mirror::Object* obj, const mirror::Object* ref, const MemberOffset& offset,
                   bool is_static) const NO_THREAD_SAFETY_ANALYSIS {
    // Filter out class references since changing an object's class does not mark the card as dirty.
    // Also handles large objects, since the only reference they hold is a class reference.
    if (ref != NULL && !ref->IsClass()) {
      CardTable* card_table = heap_->GetCardTable();
      // If the object is not dirty and it is referencing something in the live stack other than
      // class, then it must be on a dirty card.
      if (!card_table->AddrIsInCardTable(obj)) {
        LOG(ERROR) << "Object " << obj << " is not in the address range of the card table";
        *failed_ = true;
      } else if (!card_table->IsDirty(obj)) {
        // Card should be either kCardDirty if it got re-dirtied after we aged it, or
        // kCardDirty - 1 if it didnt get touched since we aged it.
        ObjectStack* live_stack = heap_->live_stack_.get();
        if (std::binary_search(live_stack->Begin(), live_stack->End(), ref)) {
          if (std::binary_search(live_stack->Begin(), live_stack->End(), obj)) {
            LOG(ERROR) << "Object " << obj << " found in live stack";
          }
          if (heap_->GetLiveBitmap()->Test(obj)) {
            LOG(ERROR) << "Object " << obj << " found in live bitmap";
          }
          LOG(ERROR) << "Object " << obj << " " << PrettyTypeOf(obj)
                    << " references " << ref << " " << PrettyTypeOf(ref) << " in live stack";

          // Print which field of the object is dead.
          if (!obj->IsObjectArray()) {
            const mirror::Class* klass = is_static ? obj->AsClass() : obj->GetClass();
            CHECK(klass != NULL);
            const mirror::ObjectArray<mirror::Field>* fields = is_static ? klass->GetSFields()
                                                                         : klass->GetIFields();
            CHECK(fields != NULL);
            for (int32_t i = 0; i < fields->GetLength(); ++i) {
              const mirror::Field* cur = fields->Get(i);
              if (cur->GetOffset().Int32Value() == offset.Int32Value()) {
                LOG(ERROR) << (is_static ? "Static " : "") << "field in the live stack is "
                          << PrettyField(cur);
                break;
              }
            }
          } else {
            const mirror::ObjectArray<mirror::Object>* object_array =
                obj->AsObjectArray<mirror::Object>();
            for (int32_t i = 0; i < object_array->GetLength(); ++i) {
              if (object_array->Get(i) == ref) {
                LOG(ERROR) << (is_static ? "Static " : "") << "obj[" << i << "] = ref";
              }
            }
          }

          *failed_ = true;
        }
      }
    }
  }

 private:
  Heap* heap_;
  bool* failed_;
};

class VerifyLiveStackReferences {
 public:
  VerifyLiveStackReferences(Heap* heap)
      : heap_(heap),
        failed_(false) {

  }

  void operator ()(const mirror::Object* obj) const
      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
    VerifyReferenceCardVisitor visitor(heap_, const_cast<bool*>(&failed_));
    MarkSweep::VisitObjectReferences(obj, visitor);
  }

  bool Failed() const {
    return failed_;
  }

 private:
  Heap* heap_;
  bool failed_;
};

bool Heap::VerifyMissingCardMarks() {
  Locks::mutator_lock_->AssertExclusiveHeld(Thread::Current());

  // We need to sort the live stack since we binary search it.
  std::sort(live_stack_->Begin(), live_stack_->End());
  VerifyLiveStackReferences visitor(this);
  GetLiveBitmap()->Visit(visitor);

  // We can verify objects in the live stack since none of these should reference dead objects.
  for (mirror::Object** it = live_stack_->Begin(); it != live_stack_->End(); ++it) {
    visitor(*it);
  }

  if (visitor.Failed()) {
    DumpSpaces();
    return false;
  }
  return true;
}

void Heap::SwapStacks() {
  allocation_stack_.swap(live_stack_);

  // Sort the live stack so that we can quickly binary search it later.
  if (VERIFY_OBJECT_ENABLED) {
    std::sort(live_stack_->Begin(), live_stack_->End());
  }
}

void Heap::ProcessCards(TimingLogger& timings) {
  // Clear image space cards and keep track of cards we cleared in the mod-union table.
  for (Spaces::iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    ContinuousSpace* space = *it;
    if (space->IsImageSpace()) {
      mod_union_table_->ClearCards(*it);
      timings.AddSplit("ModUnionClearCards");
    } else if (space->GetGcRetentionPolicy() == kGcRetentionPolicyFullCollect) {
      zygote_mod_union_table_->ClearCards(space);
      timings.AddSplit("ZygoteModUnionClearCards");
    } else {
      // No mod union table for the AllocSpace. Age the cards so that the GC knows that these cards
      // were dirty before the GC started.
      card_table_->ModifyCardsAtomic(space->Begin(), space->End(), AgeCardVisitor(), VoidFunctor());
      timings.AddSplit("AllocSpaceClearCards");
    }
  }
}

void Heap::PreGcVerification(GarbageCollector* gc) {
  ThreadList* thread_list = Runtime::Current()->GetThreadList();
  Thread* self = Thread::Current();

  if (verify_pre_gc_heap_) {
    thread_list->SuspendAll();
    {
      ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
      if (!VerifyHeapReferences()) {
        LOG(FATAL) << "Pre " << gc->GetName() << " heap verification failed";
      }
    }
    thread_list->ResumeAll();
  }

  // Check that all objects which reference things in the live stack are on dirty cards.
  if (verify_missing_card_marks_) {
    thread_list->SuspendAll();
    {
      ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
      SwapStacks();
      // Sort the live stack so that we can quickly binary search it later.
      if (!VerifyMissingCardMarks()) {
        LOG(FATAL) << "Pre " << gc->GetName() << " missing card mark verification failed";
      }
      SwapStacks();
    }
    thread_list->ResumeAll();
  }

  if (verify_mod_union_table_) {
    thread_list->SuspendAll();
    ReaderMutexLock reader_lock(self, *Locks::heap_bitmap_lock_);
    zygote_mod_union_table_->Update();
    zygote_mod_union_table_->Verify();
    mod_union_table_->Update();
    mod_union_table_->Verify();
    thread_list->ResumeAll();
  }
}

void Heap::PreSweepingGcVerification(GarbageCollector* gc) {
  ThreadList* thread_list = Runtime::Current()->GetThreadList();
  Thread* self = Thread::Current();

  // Called before sweeping occurs since we want to make sure we are not going so reclaim any
  // reachable objects.
  if (verify_post_gc_heap_) {
    thread_list->SuspendAll();
    WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
    // Swapping bound bitmaps does nothing.
    live_bitmap_.swap(mark_bitmap_);
    if (!VerifyHeapReferences()) {
      LOG(FATAL) << "Post " << gc->GetName() << "Gc verification failed";
    }
    live_bitmap_.swap(mark_bitmap_);
    thread_list->ResumeAll();
  }
}

void Heap::PostGcVerification(GarbageCollector* gc) {
  Thread* self = Thread::Current();

  if (verify_system_weaks_) {
    ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
    MarkSweep* mark_sweep = down_cast<MarkSweep*>(gc);
    mark_sweep->VerifySystemWeaks();
  }
}

GcType Heap::WaitForConcurrentGcToComplete(Thread* self) {
  GcType last_gc_type = kGcTypeNone;
  if (concurrent_gc_) {
    bool do_wait;
    uint64_t wait_start = NanoTime();
    {
      // Check if GC is running holding gc_complete_lock_.
      MutexLock mu(self, *gc_complete_lock_);
      do_wait = is_gc_running_;
    }
    if (do_wait) {
      uint64_t wait_time;
      // We must wait, change thread state then sleep on gc_complete_cond_;
      ScopedThreadStateChange tsc(Thread::Current(), kWaitingForGcToComplete);
      {
        MutexLock mu(self, *gc_complete_lock_);
        while (is_gc_running_) {
          gc_complete_cond_->Wait(self);
        }
        last_gc_type = last_gc_type_;
        wait_time = NanoTime() - wait_start;;
        total_wait_time_ += wait_time;
      }
      if (wait_time > kLongGcPauseThreshold) {
        LOG(INFO) << "WaitForConcurrentGcToComplete blocked for " << PrettyDuration(wait_time);
      }
    }
  }
  return last_gc_type;
}

void Heap::DumpForSigQuit(std::ostream& os) {
  os << "Heap: " << GetPercentFree() << "% free, " << PrettySize(GetUsedMemorySize()) << "/"
     << PrettySize(GetTotalMemory()) << "; " << GetObjectsAllocated() << " objects\n";
  DumpGcPerformanceInfo();
}

size_t Heap::GetPercentFree() {
  return static_cast<size_t>(100.0f * static_cast<float>(GetFreeMemory()) / GetTotalMemory());
}

void Heap::SetIdealFootprint(size_t max_allowed_footprint) {
  if (max_allowed_footprint > GetMaxMemory()) {
    VLOG(gc) << "Clamp target GC heap from " << PrettySize(max_allowed_footprint) << " to "
             << PrettySize(GetMaxMemory());
    max_allowed_footprint = GetMaxMemory();
  }
  max_allowed_footprint_ = max_allowed_footprint;
}

void Heap::GrowForUtilization(uint64_t gc_duration) {
  // We know what our utilization is at this moment.
  // This doesn't actually resize any memory. It just lets the heap grow more when necessary.
  const size_t bytes_allocated = GetBytesAllocated();
  last_gc_size_ = bytes_allocated;
  last_gc_time_ = NanoTime();

  size_t target_size = bytes_allocated / GetTargetHeapUtilization();
  if (target_size > bytes_allocated + max_free_) {
    target_size = bytes_allocated + max_free_;
  } else if (target_size < bytes_allocated + min_free_) {
    target_size = bytes_allocated + min_free_;
  }

  SetIdealFootprint(target_size);

  // Calculate when to perform the next ConcurrentGC if we have enough free memory.
  if (concurrent_gc_ && GetFreeMemory() >= concurrent_min_free_) {
    // Calculate the estimated GC duration.
    double gc_duration_seconds = NsToMs(gc_duration) / 1000.0;
    // Estimate how many remaining bytes we will have when we need to start the next GC.
    size_t remaining_bytes = allocation_rate_ * gc_duration_seconds;
    if (remaining_bytes < max_allowed_footprint_) {
      // Start a concurrent GC when we get close to the estimated remaining bytes. When the
      // allocation rate is very high, remaining_bytes could tell us that we should start a GC
      // right away.
      concurrent_start_bytes_ = std::max(max_allowed_footprint_ - remaining_bytes, bytes_allocated);
    } else {
      // The estimated rate is so high that we should request another GC straight away.
      concurrent_start_bytes_ = bytes_allocated;
    }
    DCHECK_LE(concurrent_start_bytes_, max_allowed_footprint_);
    DCHECK_LE(max_allowed_footprint_, growth_limit_);
  }
}

void Heap::ClearGrowthLimit() {
  growth_limit_ = capacity_;
  alloc_space_->ClearGrowthLimit();
}

void Heap::SetReferenceOffsets(MemberOffset reference_referent_offset,
                                MemberOffset reference_queue_offset,
                                MemberOffset reference_queueNext_offset,
                                MemberOffset reference_pendingNext_offset,
                                MemberOffset finalizer_reference_zombie_offset) {
  reference_referent_offset_ = reference_referent_offset;
  reference_queue_offset_ = reference_queue_offset;
  reference_queueNext_offset_ = reference_queueNext_offset;
  reference_pendingNext_offset_ = reference_pendingNext_offset;
  finalizer_reference_zombie_offset_ = finalizer_reference_zombie_offset;
  CHECK_NE(reference_referent_offset_.Uint32Value(), 0U);
  CHECK_NE(reference_queue_offset_.Uint32Value(), 0U);
  CHECK_NE(reference_queueNext_offset_.Uint32Value(), 0U);
  CHECK_NE(reference_pendingNext_offset_.Uint32Value(), 0U);
  CHECK_NE(finalizer_reference_zombie_offset_.Uint32Value(), 0U);
}

mirror::Object* Heap::GetReferenceReferent(mirror::Object* reference) {
  DCHECK(reference != NULL);
  DCHECK_NE(reference_referent_offset_.Uint32Value(), 0U);
  return reference->GetFieldObject<mirror::Object*>(reference_referent_offset_, true);
}

void Heap::ClearReferenceReferent(mirror::Object* reference) {
  DCHECK(reference != NULL);
  DCHECK_NE(reference_referent_offset_.Uint32Value(), 0U);
  reference->SetFieldObject(reference_referent_offset_, NULL, true);
}

// Returns true if the reference object has not yet been enqueued.
bool Heap::IsEnqueuable(const mirror::Object* ref) {
  DCHECK(ref != NULL);
  const mirror::Object* queue =
      ref->GetFieldObject<mirror::Object*>(reference_queue_offset_, false);
  const mirror::Object* queue_next =
      ref->GetFieldObject<mirror::Object*>(reference_queueNext_offset_, false);
  return (queue != NULL) && (queue_next == NULL);
}

void Heap::EnqueueReference(mirror::Object* ref, mirror::Object** cleared_reference_list) {
  DCHECK(ref != NULL);
  CHECK(ref->GetFieldObject<mirror::Object*>(reference_queue_offset_, false) != NULL);
  CHECK(ref->GetFieldObject<mirror::Object*>(reference_queueNext_offset_, false) == NULL);
  EnqueuePendingReference(ref, cleared_reference_list);
}

void Heap::EnqueuePendingReference(mirror::Object* ref, mirror::Object** list) {
  DCHECK(ref != NULL);
  DCHECK(list != NULL);

  // TODO: Remove this lock, use atomic stacks for storing references.
  MutexLock mu(Thread::Current(), *reference_queue_lock_);
  if (*list == NULL) {
    ref->SetFieldObject(reference_pendingNext_offset_, ref, false);
    *list = ref;
  } else {
    mirror::Object* head =
        (*list)->GetFieldObject<mirror::Object*>(reference_pendingNext_offset_, false);
    ref->SetFieldObject(reference_pendingNext_offset_, head, false);
    (*list)->SetFieldObject(reference_pendingNext_offset_, ref, false);
  }
}

mirror::Object* Heap::DequeuePendingReference(mirror::Object** list) {
  DCHECK(list != NULL);
  DCHECK(*list != NULL);
  mirror::Object* head = (*list)->GetFieldObject<mirror::Object*>(reference_pendingNext_offset_,
                                                                  false);
  mirror::Object* ref;

  // Note: the following code is thread-safe because it is only called from ProcessReferences which
  // is single threaded.
  if (*list == head) {
    ref = *list;
    *list = NULL;
  } else {
    mirror::Object* next = head->GetFieldObject<mirror::Object*>(reference_pendingNext_offset_,
                                                                 false);
    (*list)->SetFieldObject(reference_pendingNext_offset_, next, false);
    ref = head;
  }
  ref->SetFieldObject(reference_pendingNext_offset_, NULL, false);
  return ref;
}

void Heap::AddFinalizerReference(Thread* self, mirror::Object* object) {
  ScopedObjectAccess soa(self);
  JValue result;
  JValue float_result;
  ArgArray arg_array(NULL, 0);
  arg_array.Append(reinterpret_cast<uint32_t>(object));
  soa.DecodeMethod(WellKnownClasses::java_lang_ref_FinalizerReference_add)->Invoke(self,
      arg_array.GetArray(), arg_array.GetNumBytes(), &result, &float_result);
}

size_t Heap::GetBytesAllocated() const {
  return num_bytes_allocated_;
}

size_t Heap::GetObjectsAllocated() const {
  size_t total = 0;
  // TODO: C++0x
  for (Spaces::const_iterator it = spaces_.begin(); it != spaces_.end(); ++it) {
    Space* space = *it;
    if (space->IsAllocSpace()) {
      total += space->AsAllocSpace()->GetNumObjectsAllocated();
    }
  }
  return total;
}

size_t Heap::GetConcurrentStartSize() const {
  return concurrent_start_size_;
}

size_t Heap::GetConcurrentMinFree() const {
  return concurrent_min_free_;
}

void Heap::EnqueueClearedReferences(mirror::Object** cleared) {
  DCHECK(cleared != NULL);
  if (*cleared != NULL) {
    // When a runtime isn't started there are no reference queues to care about so ignore.
    if (LIKELY(Runtime::Current()->IsStarted())) {
      ScopedObjectAccess soa(Thread::Current());
      JValue result;
      JValue float_result;
      ArgArray arg_array(NULL, 0);
      arg_array.Append(reinterpret_cast<uint32_t>(*cleared));
      soa.DecodeMethod(WellKnownClasses::java_lang_ref_ReferenceQueue_add)->Invoke(soa.Self(),
          arg_array.GetArray(), arg_array.GetNumBytes(), &result, &float_result);
    }
    *cleared = NULL;
  }
}

void Heap::RequestConcurrentGC(Thread* self) {
  // Make sure that we can do a concurrent GC.
  Runtime* runtime = Runtime::Current();
  DCHECK(concurrent_gc_);
  if (runtime == NULL || !runtime->IsFinishedStarting() ||
      !runtime->IsConcurrentGcEnabled()) {
    return;
  }
  {
    MutexLock mu(self, *Locks::runtime_shutdown_lock_);
    if (runtime->IsShuttingDown()) {
      return;
    }
  }
  if (self->IsHandlingStackOverflow()) {
    return;
  }

  JNIEnv* env = self->GetJniEnv();
  DCHECK(WellKnownClasses::java_lang_Daemons != NULL);
  DCHECK(WellKnownClasses::java_lang_Daemons_requestGC != NULL);
  env->CallStaticVoidMethod(WellKnownClasses::java_lang_Daemons,
                            WellKnownClasses::java_lang_Daemons_requestGC);
  CHECK(!env->ExceptionCheck());
}

void Heap::ConcurrentGC(Thread* self) {
  {
    MutexLock mu(self, *Locks::runtime_shutdown_lock_);
    if (Runtime::Current()->IsShuttingDown()) {
      return;
    }
  }

  // Wait for any GCs currently running to finish.
  if (WaitForConcurrentGcToComplete(self) == kGcTypeNone) {
    if (alloc_space_->Size() > min_alloc_space_size_for_sticky_gc_) {
      CollectGarbageInternal(kGcTypeSticky, kGcCauseBackground, false);
    } else {
      CollectGarbageInternal(kGcTypePartial, kGcCauseBackground, false);
    }
  }
}

void Heap::RequestHeapTrim() {
  // GC completed and now we must decide whether to request a heap trim (advising pages back to the
  // kernel) or not. Issuing a request will also cause trimming of the libc heap. As a trim scans
  // a space it will hold its lock and can become a cause of jank.
  // Note, the large object space self trims and the Zygote space was trimmed and unchanging since
  // forking.

  // We don't have a good measure of how worthwhile a trim might be. We can't use the live bitmap
  // because that only marks object heads, so a large array looks like lots of empty space. We
  // don't just call dlmalloc all the time, because the cost of an _attempted_ trim is proportional
  // to utilization (which is probably inversely proportional to how much benefit we can expect).
  // We could try mincore(2) but that's only a measure of how many pages we haven't given away,
  // not how much use we're making of those pages.
  uint64_t ms_time = MilliTime();
  float utilization =
      static_cast<float>(alloc_space_->GetNumBytesAllocated()) / alloc_space_->Size();
  if ((utilization > 0.75f) || ((ms_time - last_trim_time_) < 2 * 1000)) {
    // Don't bother trimming the alloc space if it's more than 75% utilized, or if a
    // heap trim occurred in the last two seconds.
    return;
  }

  Thread* self = Thread::Current();
  {
    MutexLock mu(self, *Locks::runtime_shutdown_lock_);
    Runtime* runtime = Runtime::Current();
    if (runtime == NULL || !runtime->IsFinishedStarting() || runtime->IsShuttingDown()) {
      // Heap trimming isn't supported without a Java runtime or Daemons (such as at dex2oat time)
      // Also: we do not wish to start a heap trim if the runtime is shutting down (a racy check
      // as we don't hold the lock while requesting the trim).
      return;
    }
  }

  SchedPolicy policy;
  get_sched_policy(self->GetTid(), &policy);
  if (policy == SP_FOREGROUND || policy == SP_AUDIO_APP) {
    // Don't trim the heap if we are a foreground or audio app.
    return;
  }

  last_trim_time_ = ms_time;
  JNIEnv* env = self->GetJniEnv();
  DCHECK(WellKnownClasses::java_lang_Daemons != NULL);
  DCHECK(WellKnownClasses::java_lang_Daemons_requestHeapTrim != NULL);
  env->CallStaticVoidMethod(WellKnownClasses::java_lang_Daemons,
                            WellKnownClasses::java_lang_Daemons_requestHeapTrim);
  CHECK(!env->ExceptionCheck());
}

size_t Heap::Trim() {
  // Handle a requested heap trim on a thread outside of the main GC thread.
  return alloc_space_->Trim();
}

}  // namespace art