1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "mark_sweep.h"
18
19#include <atomic>
20#include <functional>
21#include <numeric>
22#include <climits>
23#include <vector>
24
25#include "base/bounded_fifo.h"
26#include "base/enums.h"
27#include "base/logging.h"
28#include "base/macros.h"
29#include "base/mutex-inl.h"
30#include "base/systrace.h"
31#include "base/time_utils.h"
32#include "base/timing_logger.h"
33#include "gc/accounting/card_table-inl.h"
34#include "gc/accounting/heap_bitmap-inl.h"
35#include "gc/accounting/mod_union_table.h"
36#include "gc/accounting/space_bitmap-inl.h"
37#include "gc/heap.h"
38#include "gc/reference_processor.h"
39#include "gc/space/large_object_space.h"
40#include "gc/space/space-inl.h"
41#include "mark_sweep-inl.h"
42#include "mirror/object-inl.h"
43#include "runtime.h"
44#include "scoped_thread_state_change-inl.h"
45#include "thread-inl.h"
46#include "thread_list.h"
47
48namespace art {
49namespace gc {
50namespace collector {
51
52// Performance options.
53static constexpr bool kUseRecursiveMark = false;
54static constexpr bool kUseMarkStackPrefetch = true;
55static constexpr size_t kSweepArrayChunkFreeSize = 1024;
56static constexpr bool kPreCleanCards = true;
57
58// Parallelism options.
59static constexpr bool kParallelCardScan = true;
60static constexpr bool kParallelRecursiveMark = true;
61// Don't attempt to parallelize mark stack processing unless the mark stack is at least n
62// elements. This is temporary until we reduce the overhead caused by allocating tasks, etc.. Not
63// having this can add overhead in ProcessReferences since we may end up doing many calls of
64// ProcessMarkStack with very small mark stacks.
65static constexpr size_t kMinimumParallelMarkStackSize = 128;
66static constexpr bool kParallelProcessMarkStack = true;
67
68// Profiling and information flags.
69static constexpr bool kProfileLargeObjects = false;
70static constexpr bool kMeasureOverhead = false;
71static constexpr bool kCountTasks = false;
72static constexpr bool kCountMarkedObjects = false;
73
74// Turn off kCheckLocks when profiling the GC since it slows the GC down by up to 40%.
75static constexpr bool kCheckLocks = kDebugLocking;
76static constexpr bool kVerifyRootsMarked = kIsDebugBuild;
77
78// If true, revoke the rosalloc thread-local buffers at the
79// checkpoint, as opposed to during the pause.
80static constexpr bool kRevokeRosAllocThreadLocalBuffersAtCheckpoint = true;
81
82void MarkSweep::BindBitmaps() {
83  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
84  WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
85  // Mark all of the spaces we never collect as immune.
86  for (const auto& space : GetHeap()->GetContinuousSpaces()) {
87    if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyNeverCollect) {
88      immune_spaces_.AddSpace(space);
89    }
90  }
91}
92
93MarkSweep::MarkSweep(Heap* heap, bool is_concurrent, const std::string& name_prefix)
94    : GarbageCollector(heap,
95                       name_prefix +
96                       (is_concurrent ? "concurrent mark sweep": "mark sweep")),
97      current_space_bitmap_(nullptr),
98      mark_bitmap_(nullptr),
99      mark_stack_(nullptr),
100      gc_barrier_(new Barrier(0)),
101      mark_stack_lock_("mark sweep mark stack lock", kMarkSweepMarkStackLock),
102      is_concurrent_(is_concurrent),
103      live_stack_freeze_size_(0) {
104  std::string error_msg;
105  MemMap* mem_map = MemMap::MapAnonymous(
106      "mark sweep sweep array free buffer", nullptr,
107      RoundUp(kSweepArrayChunkFreeSize * sizeof(mirror::Object*), kPageSize),
108      PROT_READ | PROT_WRITE, false, false, &error_msg);
109  CHECK(mem_map != nullptr) << "Couldn't allocate sweep array free buffer: " << error_msg;
110  sweep_array_free_buffer_mem_map_.reset(mem_map);
111}
112
113void MarkSweep::InitializePhase() {
114  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
115  mark_stack_ = heap_->GetMarkStack();
116  DCHECK(mark_stack_ != nullptr);
117  immune_spaces_.Reset();
118  no_reference_class_count_.StoreRelaxed(0);
119  normal_count_.StoreRelaxed(0);
120  class_count_.StoreRelaxed(0);
121  object_array_count_.StoreRelaxed(0);
122  other_count_.StoreRelaxed(0);
123  reference_count_.StoreRelaxed(0);
124  large_object_test_.StoreRelaxed(0);
125  large_object_mark_.StoreRelaxed(0);
126  overhead_time_ .StoreRelaxed(0);
127  work_chunks_created_.StoreRelaxed(0);
128  work_chunks_deleted_.StoreRelaxed(0);
129  mark_null_count_.StoreRelaxed(0);
130  mark_immune_count_.StoreRelaxed(0);
131  mark_fastpath_count_.StoreRelaxed(0);
132  mark_slowpath_count_.StoreRelaxed(0);
133  {
134    // TODO: I don't think we should need heap bitmap lock to Get the mark bitmap.
135    ReaderMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_);
136    mark_bitmap_ = heap_->GetMarkBitmap();
137  }
138  if (!GetCurrentIteration()->GetClearSoftReferences()) {
139    // Always clear soft references if a non-sticky collection.
140    GetCurrentIteration()->SetClearSoftReferences(GetGcType() != collector::kGcTypeSticky);
141  }
142}
143
144void MarkSweep::RunPhases() {
145  Thread* self = Thread::Current();
146  InitializePhase();
147  Locks::mutator_lock_->AssertNotHeld(self);
148  if (IsConcurrent()) {
149    GetHeap()->PreGcVerification(this);
150    {
151      ReaderMutexLock mu(self, *Locks::mutator_lock_);
152      MarkingPhase();
153    }
154    ScopedPause pause(this);
155    GetHeap()->PrePauseRosAllocVerification(this);
156    PausePhase();
157    RevokeAllThreadLocalBuffers();
158  } else {
159    ScopedPause pause(this);
160    GetHeap()->PreGcVerificationPaused(this);
161    MarkingPhase();
162    GetHeap()->PrePauseRosAllocVerification(this);
163    PausePhase();
164    RevokeAllThreadLocalBuffers();
165  }
166  {
167    // Sweeping always done concurrently, even for non concurrent mark sweep.
168    ReaderMutexLock mu(self, *Locks::mutator_lock_);
169    ReclaimPhase();
170  }
171  GetHeap()->PostGcVerification(this);
172  FinishPhase();
173}
174
175void MarkSweep::ProcessReferences(Thread* self) {
176  WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
177  GetHeap()->GetReferenceProcessor()->ProcessReferences(
178      true,
179      GetTimings(),
180      GetCurrentIteration()->GetClearSoftReferences(),
181      this);
182}
183
184void MarkSweep::PausePhase() {
185  TimingLogger::ScopedTiming t("(Paused)PausePhase", GetTimings());
186  Thread* self = Thread::Current();
187  Locks::mutator_lock_->AssertExclusiveHeld(self);
188  if (IsConcurrent()) {
189    // Handle the dirty objects if we are a concurrent GC.
190    WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
191    // Re-mark root set.
192    ReMarkRoots();
193    // Scan dirty objects, this is only required if we are not doing concurrent GC.
194    RecursiveMarkDirtyObjects(true, accounting::CardTable::kCardDirty);
195  }
196  {
197    TimingLogger::ScopedTiming t2("SwapStacks", GetTimings());
198    WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
199    heap_->SwapStacks();
200    live_stack_freeze_size_ = heap_->GetLiveStack()->Size();
201    // Need to revoke all the thread local allocation stacks since we just swapped the allocation
202    // stacks and don't want anybody to allocate into the live stack.
203    RevokeAllThreadLocalAllocationStacks(self);
204  }
205  heap_->PreSweepingGcVerification(this);
206  // Disallow new system weaks to prevent a race which occurs when someone adds a new system
207  // weak before we sweep them. Since this new system weak may not be marked, the GC may
208  // incorrectly sweep it. This also fixes a race where interning may attempt to return a strong
209  // reference to a string that is about to be swept.
210  Runtime::Current()->DisallowNewSystemWeaks();
211  // Enable the reference processing slow path, needs to be done with mutators paused since there
212  // is no lock in the GetReferent fast path.
213  GetHeap()->GetReferenceProcessor()->EnableSlowPath();
214}
215
216void MarkSweep::PreCleanCards() {
217  // Don't do this for non concurrent GCs since they don't have any dirty cards.
218  if (kPreCleanCards && IsConcurrent()) {
219    TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
220    Thread* self = Thread::Current();
221    CHECK(!Locks::mutator_lock_->IsExclusiveHeld(self));
222    // Process dirty cards and add dirty cards to mod union tables, also ages cards.
223    heap_->ProcessCards(GetTimings(), false, true, false);
224    // The checkpoint root marking is required to avoid a race condition which occurs if the
225    // following happens during a reference write:
226    // 1. mutator dirties the card (write barrier)
227    // 2. GC ages the card (the above ProcessCards call)
228    // 3. GC scans the object (the RecursiveMarkDirtyObjects call below)
229    // 4. mutator writes the value (corresponding to the write barrier in 1.)
230    // This causes the GC to age the card but not necessarily mark the reference which the mutator
231    // wrote into the object stored in the card.
232    // Having the checkpoint fixes this issue since it ensures that the card mark and the
233    // reference write are visible to the GC before the card is scanned (this is due to locks being
234    // acquired / released in the checkpoint code).
235    // The other roots are also marked to help reduce the pause.
236    MarkRootsCheckpoint(self, false);
237    MarkNonThreadRoots();
238    MarkConcurrentRoots(
239        static_cast<VisitRootFlags>(kVisitRootFlagClearRootLog | kVisitRootFlagNewRoots));
240    // Process the newly aged cards.
241    RecursiveMarkDirtyObjects(false, accounting::CardTable::kCardDirty - 1);
242    // TODO: Empty allocation stack to reduce the number of objects we need to test / mark as live
243    // in the next GC.
244  }
245}
246
247void MarkSweep::RevokeAllThreadLocalAllocationStacks(Thread* self) {
248  if (kUseThreadLocalAllocationStack) {
249    TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
250    Locks::mutator_lock_->AssertExclusiveHeld(self);
251    heap_->RevokeAllThreadLocalAllocationStacks(self);
252  }
253}
254
255void MarkSweep::MarkingPhase() {
256  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
257  Thread* self = Thread::Current();
258  BindBitmaps();
259  FindDefaultSpaceBitmap();
260  // Process dirty cards and add dirty cards to mod union tables.
261  // If the GC type is non sticky, then we just clear the cards instead of ageing them.
262  heap_->ProcessCards(GetTimings(), false, true, GetGcType() != kGcTypeSticky);
263  WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
264  MarkRoots(self);
265  MarkReachableObjects();
266  // Pre-clean dirtied cards to reduce pauses.
267  PreCleanCards();
268}
269
270class MarkSweep::ScanObjectVisitor {
271 public:
272  explicit ScanObjectVisitor(MarkSweep* const mark_sweep) ALWAYS_INLINE
273      : mark_sweep_(mark_sweep) {}
274
275  void operator()(ObjPtr<mirror::Object> obj) const
276      ALWAYS_INLINE
277      REQUIRES(Locks::heap_bitmap_lock_)
278      REQUIRES_SHARED(Locks::mutator_lock_) {
279    if (kCheckLocks) {
280      Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
281      Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
282    }
283    mark_sweep_->ScanObject(obj.Ptr());
284  }
285
286 private:
287  MarkSweep* const mark_sweep_;
288};
289
290void MarkSweep::UpdateAndMarkModUnion() {
291  for (const auto& space : immune_spaces_.GetSpaces()) {
292    const char* name = space->IsZygoteSpace()
293        ? "UpdateAndMarkZygoteModUnionTable"
294        : "UpdateAndMarkImageModUnionTable";
295    DCHECK(space->IsZygoteSpace() || space->IsImageSpace()) << *space;
296    TimingLogger::ScopedTiming t(name, GetTimings());
297    accounting::ModUnionTable* mod_union_table = heap_->FindModUnionTableFromSpace(space);
298    if (mod_union_table != nullptr) {
299      mod_union_table->UpdateAndMarkReferences(this);
300    } else {
301      // No mod-union table, scan all the live bits. This can only occur for app images.
302      space->GetLiveBitmap()->VisitMarkedRange(reinterpret_cast<uintptr_t>(space->Begin()),
303                                               reinterpret_cast<uintptr_t>(space->End()),
304                                               ScanObjectVisitor(this));
305    }
306  }
307}
308
309void MarkSweep::MarkReachableObjects() {
310  UpdateAndMarkModUnion();
311  // Recursively mark all the non-image bits set in the mark bitmap.
312  RecursiveMark();
313}
314
315void MarkSweep::ReclaimPhase() {
316  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
317  Thread* const self = Thread::Current();
318  // Process the references concurrently.
319  ProcessReferences(self);
320  SweepSystemWeaks(self);
321  Runtime* const runtime = Runtime::Current();
322  runtime->AllowNewSystemWeaks();
323  // Clean up class loaders after system weaks are swept since that is how we know if class
324  // unloading occurred.
325  runtime->GetClassLinker()->CleanupClassLoaders();
326  {
327    WriterMutexLock mu(self, *Locks::heap_bitmap_lock_);
328    GetHeap()->RecordFreeRevoke();
329    // Reclaim unmarked objects.
330    Sweep(false);
331    // Swap the live and mark bitmaps for each space which we modified space. This is an
332    // optimization that enables us to not clear live bits inside of the sweep. Only swaps unbound
333    // bitmaps.
334    SwapBitmaps();
335    // Unbind the live and mark bitmaps.
336    GetHeap()->UnBindBitmaps();
337  }
338}
339
340void MarkSweep::FindDefaultSpaceBitmap() {
341  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
342  for (const auto& space : GetHeap()->GetContinuousSpaces()) {
343    accounting::ContinuousSpaceBitmap* bitmap = space->GetMarkBitmap();
344    // We want to have the main space instead of non moving if possible.
345    if (bitmap != nullptr &&
346        space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) {
347      current_space_bitmap_ = bitmap;
348      // If we are not the non moving space exit the loop early since this will be good enough.
349      if (space != heap_->GetNonMovingSpace()) {
350        break;
351      }
352    }
353  }
354  CHECK(current_space_bitmap_ != nullptr) << "Could not find a default mark bitmap\n"
355      << heap_->DumpSpaces();
356}
357
358void MarkSweep::ExpandMarkStack() {
359  ResizeMarkStack(mark_stack_->Capacity() * 2);
360}
361
362void MarkSweep::ResizeMarkStack(size_t new_size) {
363  // Rare case, no need to have Thread::Current be a parameter.
364  if (UNLIKELY(mark_stack_->Size() < mark_stack_->Capacity())) {
365    // Someone else acquired the lock and expanded the mark stack before us.
366    return;
367  }
368  std::vector<StackReference<mirror::Object>> temp(mark_stack_->Begin(), mark_stack_->End());
369  CHECK_LE(mark_stack_->Size(), new_size);
370  mark_stack_->Resize(new_size);
371  for (auto& obj : temp) {
372    mark_stack_->PushBack(obj.AsMirrorPtr());
373  }
374}
375
376mirror::Object* MarkSweep::MarkObject(mirror::Object* obj) {
377  MarkObject(obj, nullptr, MemberOffset(0));
378  return obj;
379}
380
381inline void MarkSweep::MarkObjectNonNullParallel(mirror::Object* obj) {
382  DCHECK(obj != nullptr);
383  if (MarkObjectParallel(obj)) {
384    MutexLock mu(Thread::Current(), mark_stack_lock_);
385    if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) {
386      ExpandMarkStack();
387    }
388    // The object must be pushed on to the mark stack.
389    mark_stack_->PushBack(obj);
390  }
391}
392
393bool MarkSweep::IsNullOrMarkedHeapReference(mirror::HeapReference<mirror::Object>* ref,
394                                            bool do_atomic_update ATTRIBUTE_UNUSED) {
395  mirror::Object* obj = ref->AsMirrorPtr();
396  if (obj == nullptr) {
397    return true;
398  }
399  return IsMarked(obj);
400}
401
402class MarkSweep::MarkObjectSlowPath {
403 public:
404  explicit MarkObjectSlowPath(MarkSweep* mark_sweep,
405                              mirror::Object* holder = nullptr,
406                              MemberOffset offset = MemberOffset(0))
407      : mark_sweep_(mark_sweep),
408        holder_(holder),
409        offset_(offset) {}
410
411  void operator()(const mirror::Object* obj) const NO_THREAD_SAFETY_ANALYSIS {
412    if (kProfileLargeObjects) {
413      // TODO: Differentiate between marking and testing somehow.
414      ++mark_sweep_->large_object_test_;
415      ++mark_sweep_->large_object_mark_;
416    }
417    space::LargeObjectSpace* large_object_space = mark_sweep_->GetHeap()->GetLargeObjectsSpace();
418    if (UNLIKELY(obj == nullptr || !IsAligned<kPageSize>(obj) ||
419                 (kIsDebugBuild && large_object_space != nullptr &&
420                     !large_object_space->Contains(obj)))) {
421      // Lowest priority logging first:
422      PrintFileToLog("/proc/self/maps", LogSeverity::FATAL_WITHOUT_ABORT);
423      MemMap::DumpMaps(LOG_STREAM(FATAL_WITHOUT_ABORT), true);
424      // Buffer the output in the string stream since it is more important than the stack traces
425      // and we want it to have log priority. The stack traces are printed from Runtime::Abort
426      // which is called from LOG(FATAL) but before the abort message.
427      std::ostringstream oss;
428      oss << "Tried to mark " << obj << " not contained by any spaces" << std::endl;
429      if (holder_ != nullptr) {
430        size_t holder_size = holder_->SizeOf();
431        ArtField* field = holder_->FindFieldByOffset(offset_);
432        oss << "Field info: "
433            << " holder=" << holder_
434            << " holder is "
435            << (mark_sweep_->GetHeap()->IsLiveObjectLocked(holder_)
436                ? "alive" : "dead")
437            << " holder_size=" << holder_size
438            << " holder_type=" << holder_->PrettyTypeOf()
439            << " offset=" << offset_.Uint32Value()
440            << " field=" << (field != nullptr ? field->GetName() : "nullptr")
441            << " field_type="
442            << (field != nullptr ? field->GetTypeDescriptor() : "")
443            << " first_ref_field_offset="
444            << (holder_->IsClass()
445                ? holder_->AsClass()->GetFirstReferenceStaticFieldOffset(
446                    kRuntimePointerSize)
447                : holder_->GetClass()->GetFirstReferenceInstanceFieldOffset())
448            << " num_of_ref_fields="
449            << (holder_->IsClass()
450                ? holder_->AsClass()->NumReferenceStaticFields()
451                : holder_->GetClass()->NumReferenceInstanceFields())
452            << std::endl;
453        // Print the memory content of the holder.
454        for (size_t i = 0; i < holder_size / sizeof(uint32_t); ++i) {
455          uint32_t* p = reinterpret_cast<uint32_t*>(holder_);
456          oss << &p[i] << ": " << "holder+" << (i * sizeof(uint32_t)) << " = " << std::hex << p[i]
457              << std::endl;
458        }
459      }
460      oss << "Attempting see if it's a bad thread root" << std::endl;
461      mark_sweep_->VerifySuspendedThreadRoots(oss);
462      LOG(FATAL) << oss.str();
463    }
464  }
465
466 private:
467  MarkSweep* const mark_sweep_;
468  mirror::Object* const holder_;
469  MemberOffset offset_;
470};
471
472inline void MarkSweep::MarkObjectNonNull(mirror::Object* obj,
473                                         mirror::Object* holder,
474                                         MemberOffset offset) {
475  DCHECK(obj != nullptr);
476  if (kUseBakerReadBarrier) {
477    // Verify all the objects have the correct state installed.
478    obj->AssertReadBarrierState();
479  }
480  if (immune_spaces_.IsInImmuneRegion(obj)) {
481    if (kCountMarkedObjects) {
482      ++mark_immune_count_;
483    }
484    DCHECK(mark_bitmap_->Test(obj));
485  } else if (LIKELY(current_space_bitmap_->HasAddress(obj))) {
486    if (kCountMarkedObjects) {
487      ++mark_fastpath_count_;
488    }
489    if (UNLIKELY(!current_space_bitmap_->Set(obj))) {
490      PushOnMarkStack(obj);  // This object was not previously marked.
491    }
492  } else {
493    if (kCountMarkedObjects) {
494      ++mark_slowpath_count_;
495    }
496    MarkObjectSlowPath visitor(this, holder, offset);
497    // TODO: We already know that the object is not in the current_space_bitmap_ but MarkBitmap::Set
498    // will check again.
499    if (!mark_bitmap_->Set(obj, visitor)) {
500      PushOnMarkStack(obj);  // Was not already marked, push.
501    }
502  }
503}
504
505inline void MarkSweep::PushOnMarkStack(mirror::Object* obj) {
506  if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) {
507    // Lock is not needed but is here anyways to please annotalysis.
508    MutexLock mu(Thread::Current(), mark_stack_lock_);
509    ExpandMarkStack();
510  }
511  // The object must be pushed on to the mark stack.
512  mark_stack_->PushBack(obj);
513}
514
515inline bool MarkSweep::MarkObjectParallel(mirror::Object* obj) {
516  DCHECK(obj != nullptr);
517  if (kUseBakerReadBarrier) {
518    // Verify all the objects have the correct state installed.
519    obj->AssertReadBarrierState();
520  }
521  if (immune_spaces_.IsInImmuneRegion(obj)) {
522    DCHECK(IsMarked(obj) != nullptr);
523    return false;
524  }
525  // Try to take advantage of locality of references within a space, failing this find the space
526  // the hard way.
527  accounting::ContinuousSpaceBitmap* object_bitmap = current_space_bitmap_;
528  if (LIKELY(object_bitmap->HasAddress(obj))) {
529    return !object_bitmap->AtomicTestAndSet(obj);
530  }
531  MarkObjectSlowPath visitor(this);
532  return !mark_bitmap_->AtomicTestAndSet(obj, visitor);
533}
534
535void MarkSweep::MarkHeapReference(mirror::HeapReference<mirror::Object>* ref,
536                                  bool do_atomic_update ATTRIBUTE_UNUSED) {
537  MarkObject(ref->AsMirrorPtr(), nullptr, MemberOffset(0));
538}
539
540// Used to mark objects when processing the mark stack. If an object is null, it is not marked.
541inline void MarkSweep::MarkObject(mirror::Object* obj,
542                                  mirror::Object* holder,
543                                  MemberOffset offset) {
544  if (obj != nullptr) {
545    MarkObjectNonNull(obj, holder, offset);
546  } else if (kCountMarkedObjects) {
547    ++mark_null_count_;
548  }
549}
550
551class MarkSweep::VerifyRootMarkedVisitor : public SingleRootVisitor {
552 public:
553  explicit VerifyRootMarkedVisitor(MarkSweep* collector) : collector_(collector) { }
554
555  void VisitRoot(mirror::Object* root, const RootInfo& info) OVERRIDE
556      REQUIRES_SHARED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
557    CHECK(collector_->IsMarked(root) != nullptr) << info.ToString();
558  }
559
560 private:
561  MarkSweep* const collector_;
562};
563
564void MarkSweep::VisitRoots(mirror::Object*** roots,
565                           size_t count,
566                           const RootInfo& info ATTRIBUTE_UNUSED) {
567  for (size_t i = 0; i < count; ++i) {
568    MarkObjectNonNull(*roots[i]);
569  }
570}
571
572void MarkSweep::VisitRoots(mirror::CompressedReference<mirror::Object>** roots,
573                           size_t count,
574                           const RootInfo& info ATTRIBUTE_UNUSED) {
575  for (size_t i = 0; i < count; ++i) {
576    MarkObjectNonNull(roots[i]->AsMirrorPtr());
577  }
578}
579
580class MarkSweep::VerifyRootVisitor : public SingleRootVisitor {
581 public:
582  explicit VerifyRootVisitor(std::ostream& os) : os_(os) {}
583
584  void VisitRoot(mirror::Object* root, const RootInfo& info) OVERRIDE
585      REQUIRES_SHARED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
586    // See if the root is on any space bitmap.
587    auto* heap = Runtime::Current()->GetHeap();
588    if (heap->GetLiveBitmap()->GetContinuousSpaceBitmap(root) == nullptr) {
589      space::LargeObjectSpace* large_object_space = heap->GetLargeObjectsSpace();
590      if (large_object_space != nullptr && !large_object_space->Contains(root)) {
591        os_ << "Found invalid root: " << root << " " << info << std::endl;
592      }
593    }
594  }
595
596 private:
597  std::ostream& os_;
598};
599
600void MarkSweep::VerifySuspendedThreadRoots(std::ostream& os) {
601  VerifyRootVisitor visitor(os);
602  Runtime::Current()->GetThreadList()->VisitRootsForSuspendedThreads(&visitor);
603}
604
605void MarkSweep::MarkRoots(Thread* self) {
606  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
607  if (Locks::mutator_lock_->IsExclusiveHeld(self)) {
608    // If we exclusively hold the mutator lock, all threads must be suspended.
609    Runtime::Current()->VisitRoots(this);
610    RevokeAllThreadLocalAllocationStacks(self);
611  } else {
612    MarkRootsCheckpoint(self, kRevokeRosAllocThreadLocalBuffersAtCheckpoint);
613    // At this point the live stack should no longer have any mutators which push into it.
614    MarkNonThreadRoots();
615    MarkConcurrentRoots(
616        static_cast<VisitRootFlags>(kVisitRootFlagAllRoots | kVisitRootFlagStartLoggingNewRoots));
617  }
618}
619
620void MarkSweep::MarkNonThreadRoots() {
621  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
622  Runtime::Current()->VisitNonThreadRoots(this);
623}
624
625void MarkSweep::MarkConcurrentRoots(VisitRootFlags flags) {
626  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
627  // Visit all runtime roots and clear dirty flags.
628  Runtime::Current()->VisitConcurrentRoots(this, flags);
629}
630
631class MarkSweep::DelayReferenceReferentVisitor {
632 public:
633  explicit DelayReferenceReferentVisitor(MarkSweep* collector) : collector_(collector) {}
634
635  void operator()(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) const
636      REQUIRES(Locks::heap_bitmap_lock_)
637      REQUIRES_SHARED(Locks::mutator_lock_) {
638    collector_->DelayReferenceReferent(klass, ref);
639  }
640
641 private:
642  MarkSweep* const collector_;
643};
644
645template <bool kUseFinger = false>
646class MarkSweep::MarkStackTask : public Task {
647 public:
648  MarkStackTask(ThreadPool* thread_pool,
649                MarkSweep* mark_sweep,
650                size_t mark_stack_size,
651                StackReference<mirror::Object>* mark_stack)
652      : mark_sweep_(mark_sweep),
653        thread_pool_(thread_pool),
654        mark_stack_pos_(mark_stack_size) {
655    // We may have to copy part of an existing mark stack when another mark stack overflows.
656    if (mark_stack_size != 0) {
657      DCHECK(mark_stack != nullptr);
658      // TODO: Check performance?
659      std::copy(mark_stack, mark_stack + mark_stack_size, mark_stack_);
660    }
661    if (kCountTasks) {
662      ++mark_sweep_->work_chunks_created_;
663    }
664  }
665
666  static const size_t kMaxSize = 1 * KB;
667
668 protected:
669  class MarkObjectParallelVisitor {
670   public:
671    ALWAYS_INLINE MarkObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task,
672                                            MarkSweep* mark_sweep)
673        : chunk_task_(chunk_task), mark_sweep_(mark_sweep) {}
674
675    ALWAYS_INLINE void operator()(mirror::Object* obj,
676                    MemberOffset offset,
677                    bool is_static ATTRIBUTE_UNUSED) const
678        REQUIRES_SHARED(Locks::mutator_lock_) {
679      Mark(obj->GetFieldObject<mirror::Object>(offset));
680    }
681
682    void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
683        REQUIRES_SHARED(Locks::mutator_lock_) {
684      if (!root->IsNull()) {
685        VisitRoot(root);
686      }
687    }
688
689    void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
690        REQUIRES_SHARED(Locks::mutator_lock_) {
691      if (kCheckLocks) {
692        Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
693        Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
694      }
695      Mark(root->AsMirrorPtr());
696    }
697
698   private:
699    ALWAYS_INLINE void Mark(mirror::Object* ref) const REQUIRES_SHARED(Locks::mutator_lock_) {
700      if (ref != nullptr && mark_sweep_->MarkObjectParallel(ref)) {
701        if (kUseFinger) {
702          std::atomic_thread_fence(std::memory_order_seq_cst);
703          if (reinterpret_cast<uintptr_t>(ref) >=
704              static_cast<uintptr_t>(mark_sweep_->atomic_finger_.LoadRelaxed())) {
705            return;
706          }
707        }
708        chunk_task_->MarkStackPush(ref);
709      }
710    }
711
712    MarkStackTask<kUseFinger>* const chunk_task_;
713    MarkSweep* const mark_sweep_;
714  };
715
716  class ScanObjectParallelVisitor {
717   public:
718    ALWAYS_INLINE explicit ScanObjectParallelVisitor(MarkStackTask<kUseFinger>* chunk_task)
719        : chunk_task_(chunk_task) {}
720
721    // No thread safety analysis since multiple threads will use this visitor.
722    void operator()(mirror::Object* obj) const
723        REQUIRES(Locks::heap_bitmap_lock_)
724        REQUIRES_SHARED(Locks::mutator_lock_) {
725      MarkSweep* const mark_sweep = chunk_task_->mark_sweep_;
726      MarkObjectParallelVisitor mark_visitor(chunk_task_, mark_sweep);
727      DelayReferenceReferentVisitor ref_visitor(mark_sweep);
728      mark_sweep->ScanObjectVisit(obj, mark_visitor, ref_visitor);
729    }
730
731   private:
732    MarkStackTask<kUseFinger>* const chunk_task_;
733  };
734
735  virtual ~MarkStackTask() {
736    // Make sure that we have cleared our mark stack.
737    DCHECK_EQ(mark_stack_pos_, 0U);
738    if (kCountTasks) {
739      ++mark_sweep_->work_chunks_deleted_;
740    }
741  }
742
743  MarkSweep* const mark_sweep_;
744  ThreadPool* const thread_pool_;
745  // Thread local mark stack for this task.
746  StackReference<mirror::Object> mark_stack_[kMaxSize];
747  // Mark stack position.
748  size_t mark_stack_pos_;
749
750  ALWAYS_INLINE void MarkStackPush(mirror::Object* obj)
751      REQUIRES_SHARED(Locks::mutator_lock_) {
752    if (UNLIKELY(mark_stack_pos_ == kMaxSize)) {
753      // Mark stack overflow, give 1/2 the stack to the thread pool as a new work task.
754      mark_stack_pos_ /= 2;
755      auto* task = new MarkStackTask(thread_pool_,
756                                     mark_sweep_,
757                                     kMaxSize - mark_stack_pos_,
758                                     mark_stack_ + mark_stack_pos_);
759      thread_pool_->AddTask(Thread::Current(), task);
760    }
761    DCHECK(obj != nullptr);
762    DCHECK_LT(mark_stack_pos_, kMaxSize);
763    mark_stack_[mark_stack_pos_++].Assign(obj);
764  }
765
766  virtual void Finalize() {
767    delete this;
768  }
769
770  // Scans all of the objects
771  virtual void Run(Thread* self ATTRIBUTE_UNUSED)
772      REQUIRES(Locks::heap_bitmap_lock_)
773      REQUIRES_SHARED(Locks::mutator_lock_) {
774    ScanObjectParallelVisitor visitor(this);
775    // TODO: Tune this.
776    static const size_t kFifoSize = 4;
777    BoundedFifoPowerOfTwo<mirror::Object*, kFifoSize> prefetch_fifo;
778    for (;;) {
779      mirror::Object* obj = nullptr;
780      if (kUseMarkStackPrefetch) {
781        while (mark_stack_pos_ != 0 && prefetch_fifo.size() < kFifoSize) {
782          mirror::Object* const mark_stack_obj = mark_stack_[--mark_stack_pos_].AsMirrorPtr();
783          DCHECK(mark_stack_obj != nullptr);
784          __builtin_prefetch(mark_stack_obj);
785          prefetch_fifo.push_back(mark_stack_obj);
786        }
787        if (UNLIKELY(prefetch_fifo.empty())) {
788          break;
789        }
790        obj = prefetch_fifo.front();
791        prefetch_fifo.pop_front();
792      } else {
793        if (UNLIKELY(mark_stack_pos_ == 0)) {
794          break;
795        }
796        obj = mark_stack_[--mark_stack_pos_].AsMirrorPtr();
797      }
798      DCHECK(obj != nullptr);
799      visitor(obj);
800    }
801  }
802};
803
804class MarkSweep::CardScanTask : public MarkStackTask<false> {
805 public:
806  CardScanTask(ThreadPool* thread_pool,
807               MarkSweep* mark_sweep,
808               accounting::ContinuousSpaceBitmap* bitmap,
809               uint8_t* begin,
810               uint8_t* end,
811               uint8_t minimum_age,
812               size_t mark_stack_size,
813               StackReference<mirror::Object>* mark_stack_obj,
814               bool clear_card)
815      : MarkStackTask<false>(thread_pool, mark_sweep, mark_stack_size, mark_stack_obj),
816        bitmap_(bitmap),
817        begin_(begin),
818        end_(end),
819        minimum_age_(minimum_age),
820        clear_card_(clear_card) {}
821
822 protected:
823  accounting::ContinuousSpaceBitmap* const bitmap_;
824  uint8_t* const begin_;
825  uint8_t* const end_;
826  const uint8_t minimum_age_;
827  const bool clear_card_;
828
829  virtual void Finalize() {
830    delete this;
831  }
832
833  virtual void Run(Thread* self) NO_THREAD_SAFETY_ANALYSIS {
834    ScanObjectParallelVisitor visitor(this);
835    accounting::CardTable* card_table = mark_sweep_->GetHeap()->GetCardTable();
836    size_t cards_scanned = clear_card_
837        ? card_table->Scan<true>(bitmap_, begin_, end_, visitor, minimum_age_)
838        : card_table->Scan<false>(bitmap_, begin_, end_, visitor, minimum_age_);
839    VLOG(heap) << "Parallel scanning cards " << reinterpret_cast<void*>(begin_) << " - "
840        << reinterpret_cast<void*>(end_) << " = " << cards_scanned;
841    // Finish by emptying our local mark stack.
842    MarkStackTask::Run(self);
843  }
844};
845
846size_t MarkSweep::GetThreadCount(bool paused) const {
847  // Use less threads if we are in a background state (non jank perceptible) since we want to leave
848  // more CPU time for the foreground apps.
849  if (heap_->GetThreadPool() == nullptr || !Runtime::Current()->InJankPerceptibleProcessState()) {
850    return 1;
851  }
852  return (paused ? heap_->GetParallelGCThreadCount() : heap_->GetConcGCThreadCount()) + 1;
853}
854
855void MarkSweep::ScanGrayObjects(bool paused, uint8_t minimum_age) {
856  accounting::CardTable* card_table = GetHeap()->GetCardTable();
857  ThreadPool* thread_pool = GetHeap()->GetThreadPool();
858  size_t thread_count = GetThreadCount(paused);
859  // The parallel version with only one thread is faster for card scanning, TODO: fix.
860  if (kParallelCardScan && thread_count > 1) {
861    Thread* self = Thread::Current();
862    // Can't have a different split for each space since multiple spaces can have their cards being
863    // scanned at the same time.
864    TimingLogger::ScopedTiming t(paused ? "(Paused)ScanGrayObjects" : __FUNCTION__,
865        GetTimings());
866    // Try to take some of the mark stack since we can pass this off to the worker tasks.
867    StackReference<mirror::Object>* mark_stack_begin = mark_stack_->Begin();
868    StackReference<mirror::Object>* mark_stack_end = mark_stack_->End();
869    const size_t mark_stack_size = mark_stack_end - mark_stack_begin;
870    // Estimated number of work tasks we will create.
871    const size_t mark_stack_tasks = GetHeap()->GetContinuousSpaces().size() * thread_count;
872    DCHECK_NE(mark_stack_tasks, 0U);
873    const size_t mark_stack_delta = std::min(CardScanTask::kMaxSize / 2,
874                                             mark_stack_size / mark_stack_tasks + 1);
875    for (const auto& space : GetHeap()->GetContinuousSpaces()) {
876      if (space->GetMarkBitmap() == nullptr) {
877        continue;
878      }
879      uint8_t* card_begin = space->Begin();
880      uint8_t* card_end = space->End();
881      // Align up the end address. For example, the image space's end
882      // may not be card-size-aligned.
883      card_end = AlignUp(card_end, accounting::CardTable::kCardSize);
884      DCHECK_ALIGNED(card_begin, accounting::CardTable::kCardSize);
885      DCHECK_ALIGNED(card_end, accounting::CardTable::kCardSize);
886      // Calculate how many bytes of heap we will scan,
887      const size_t address_range = card_end - card_begin;
888      // Calculate how much address range each task gets.
889      const size_t card_delta = RoundUp(address_range / thread_count + 1,
890                                        accounting::CardTable::kCardSize);
891      // If paused and the space is neither zygote nor image space, we could clear the dirty
892      // cards to avoid accumulating them to increase card scanning load in the following GC
893      // cycles. We need to keep dirty cards of image space and zygote space in order to track
894      // references to the other spaces.
895      bool clear_card = paused && !space->IsZygoteSpace() && !space->IsImageSpace();
896      // Create the worker tasks for this space.
897      while (card_begin != card_end) {
898        // Add a range of cards.
899        size_t addr_remaining = card_end - card_begin;
900        size_t card_increment = std::min(card_delta, addr_remaining);
901        // Take from the back of the mark stack.
902        size_t mark_stack_remaining = mark_stack_end - mark_stack_begin;
903        size_t mark_stack_increment = std::min(mark_stack_delta, mark_stack_remaining);
904        mark_stack_end -= mark_stack_increment;
905        mark_stack_->PopBackCount(static_cast<int32_t>(mark_stack_increment));
906        DCHECK_EQ(mark_stack_end, mark_stack_->End());
907        // Add the new task to the thread pool.
908        auto* task = new CardScanTask(thread_pool,
909                                      this,
910                                      space->GetMarkBitmap(),
911                                      card_begin,
912                                      card_begin + card_increment,
913                                      minimum_age,
914                                      mark_stack_increment,
915                                      mark_stack_end,
916                                      clear_card);
917        thread_pool->AddTask(self, task);
918        card_begin += card_increment;
919      }
920    }
921
922    // Note: the card scan below may dirty new cards (and scan them)
923    // as a side effect when a Reference object is encountered and
924    // queued during the marking. See b/11465268.
925    thread_pool->SetMaxActiveWorkers(thread_count - 1);
926    thread_pool->StartWorkers(self);
927    thread_pool->Wait(self, true, true);
928    thread_pool->StopWorkers(self);
929  } else {
930    for (const auto& space : GetHeap()->GetContinuousSpaces()) {
931      if (space->GetMarkBitmap() != nullptr) {
932        // Image spaces are handled properly since live == marked for them.
933        const char* name = nullptr;
934        switch (space->GetGcRetentionPolicy()) {
935        case space::kGcRetentionPolicyNeverCollect:
936          name = paused ? "(Paused)ScanGrayImageSpaceObjects" : "ScanGrayImageSpaceObjects";
937          break;
938        case space::kGcRetentionPolicyFullCollect:
939          name = paused ? "(Paused)ScanGrayZygoteSpaceObjects" : "ScanGrayZygoteSpaceObjects";
940          break;
941        case space::kGcRetentionPolicyAlwaysCollect:
942          name = paused ? "(Paused)ScanGrayAllocSpaceObjects" : "ScanGrayAllocSpaceObjects";
943          break;
944        default:
945          LOG(FATAL) << "Unreachable";
946          UNREACHABLE();
947        }
948        TimingLogger::ScopedTiming t(name, GetTimings());
949        ScanObjectVisitor visitor(this);
950        bool clear_card = paused && !space->IsZygoteSpace() && !space->IsImageSpace();
951        if (clear_card) {
952          card_table->Scan<true>(space->GetMarkBitmap(),
953                                 space->Begin(),
954                                 space->End(),
955                                 visitor,
956                                 minimum_age);
957        } else {
958          card_table->Scan<false>(space->GetMarkBitmap(),
959                                  space->Begin(),
960                                  space->End(),
961                                  visitor,
962                                  minimum_age);
963        }
964      }
965    }
966  }
967}
968
969class MarkSweep::RecursiveMarkTask : public MarkStackTask<false> {
970 public:
971  RecursiveMarkTask(ThreadPool* thread_pool,
972                    MarkSweep* mark_sweep,
973                    accounting::ContinuousSpaceBitmap* bitmap,
974                    uintptr_t begin,
975                    uintptr_t end)
976      : MarkStackTask<false>(thread_pool, mark_sweep, 0, nullptr),
977        bitmap_(bitmap),
978        begin_(begin),
979        end_(end) {}
980
981 protected:
982  accounting::ContinuousSpaceBitmap* const bitmap_;
983  const uintptr_t begin_;
984  const uintptr_t end_;
985
986  virtual void Finalize() {
987    delete this;
988  }
989
990  // Scans all of the objects
991  virtual void Run(Thread* self) NO_THREAD_SAFETY_ANALYSIS {
992    ScanObjectParallelVisitor visitor(this);
993    bitmap_->VisitMarkedRange(begin_, end_, visitor);
994    // Finish by emptying our local mark stack.
995    MarkStackTask::Run(self);
996  }
997};
998
999// Populates the mark stack based on the set of marked objects and
1000// recursively marks until the mark stack is emptied.
1001void MarkSweep::RecursiveMark() {
1002  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1003  // RecursiveMark will build the lists of known instances of the Reference classes. See
1004  // DelayReferenceReferent for details.
1005  if (kUseRecursiveMark) {
1006    const bool partial = GetGcType() == kGcTypePartial;
1007    ScanObjectVisitor scan_visitor(this);
1008    auto* self = Thread::Current();
1009    ThreadPool* thread_pool = heap_->GetThreadPool();
1010    size_t thread_count = GetThreadCount(false);
1011    const bool parallel = kParallelRecursiveMark && thread_count > 1;
1012    mark_stack_->Reset();
1013    for (const auto& space : GetHeap()->GetContinuousSpaces()) {
1014      if ((space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) ||
1015          (!partial && space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect)) {
1016        current_space_bitmap_ = space->GetMarkBitmap();
1017        if (current_space_bitmap_ == nullptr) {
1018          continue;
1019        }
1020        if (parallel) {
1021          // We will use the mark stack the future.
1022          // CHECK(mark_stack_->IsEmpty());
1023          // This function does not handle heap end increasing, so we must use the space end.
1024          uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
1025          uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
1026          atomic_finger_.StoreRelaxed(AtomicInteger::MaxValue());
1027
1028          // Create a few worker tasks.
1029          const size_t n = thread_count * 2;
1030          while (begin != end) {
1031            uintptr_t start = begin;
1032            uintptr_t delta = (end - begin) / n;
1033            delta = RoundUp(delta, KB);
1034            if (delta < 16 * KB) delta = end - begin;
1035            begin += delta;
1036            auto* task = new RecursiveMarkTask(thread_pool,
1037                                               this,
1038                                               current_space_bitmap_,
1039                                               start,
1040                                               begin);
1041            thread_pool->AddTask(self, task);
1042          }
1043          thread_pool->SetMaxActiveWorkers(thread_count - 1);
1044          thread_pool->StartWorkers(self);
1045          thread_pool->Wait(self, true, true);
1046          thread_pool->StopWorkers(self);
1047        } else {
1048          // This function does not handle heap end increasing, so we must use the space end.
1049          uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
1050          uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
1051          current_space_bitmap_->VisitMarkedRange(begin, end, scan_visitor);
1052        }
1053      }
1054    }
1055  }
1056  ProcessMarkStack(false);
1057}
1058
1059void MarkSweep::RecursiveMarkDirtyObjects(bool paused, uint8_t minimum_age) {
1060  ScanGrayObjects(paused, minimum_age);
1061  ProcessMarkStack(paused);
1062}
1063
1064void MarkSweep::ReMarkRoots() {
1065  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1066  Locks::mutator_lock_->AssertExclusiveHeld(Thread::Current());
1067  Runtime::Current()->VisitRoots(this, static_cast<VisitRootFlags>(
1068      kVisitRootFlagNewRoots | kVisitRootFlagStopLoggingNewRoots | kVisitRootFlagClearRootLog));
1069  if (kVerifyRootsMarked) {
1070    TimingLogger::ScopedTiming t2("(Paused)VerifyRoots", GetTimings());
1071    VerifyRootMarkedVisitor visitor(this);
1072    Runtime::Current()->VisitRoots(&visitor);
1073  }
1074}
1075
1076void MarkSweep::SweepSystemWeaks(Thread* self) {
1077  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1078  ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_);
1079  Runtime::Current()->SweepSystemWeaks(this);
1080}
1081
1082class MarkSweep::VerifySystemWeakVisitor : public IsMarkedVisitor {
1083 public:
1084  explicit VerifySystemWeakVisitor(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) {}
1085
1086  virtual mirror::Object* IsMarked(mirror::Object* obj)
1087      OVERRIDE
1088      REQUIRES_SHARED(Locks::mutator_lock_, Locks::heap_bitmap_lock_) {
1089    mark_sweep_->VerifyIsLive(obj);
1090    return obj;
1091  }
1092
1093  MarkSweep* const mark_sweep_;
1094};
1095
1096void MarkSweep::VerifyIsLive(const mirror::Object* obj) {
1097  if (!heap_->GetLiveBitmap()->Test(obj)) {
1098    // TODO: Consider live stack? Has this code bitrotted?
1099    CHECK(!heap_->allocation_stack_->Contains(obj))
1100        << "Found dead object " << obj << "\n" << heap_->DumpSpaces();
1101  }
1102}
1103
1104void MarkSweep::VerifySystemWeaks() {
1105  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1106  // Verify system weaks, uses a special object visitor which returns the input object.
1107  VerifySystemWeakVisitor visitor(this);
1108  Runtime::Current()->SweepSystemWeaks(&visitor);
1109}
1110
1111class MarkSweep::CheckpointMarkThreadRoots : public Closure, public RootVisitor {
1112 public:
1113  CheckpointMarkThreadRoots(MarkSweep* mark_sweep,
1114                            bool revoke_ros_alloc_thread_local_buffers_at_checkpoint)
1115      : mark_sweep_(mark_sweep),
1116        revoke_ros_alloc_thread_local_buffers_at_checkpoint_(
1117            revoke_ros_alloc_thread_local_buffers_at_checkpoint) {
1118  }
1119
1120  void VisitRoots(mirror::Object*** roots, size_t count, const RootInfo& info ATTRIBUTE_UNUSED)
1121      OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_)
1122      REQUIRES(Locks::heap_bitmap_lock_) {
1123    for (size_t i = 0; i < count; ++i) {
1124      mark_sweep_->MarkObjectNonNullParallel(*roots[i]);
1125    }
1126  }
1127
1128  void VisitRoots(mirror::CompressedReference<mirror::Object>** roots,
1129                  size_t count,
1130                  const RootInfo& info ATTRIBUTE_UNUSED)
1131      OVERRIDE REQUIRES_SHARED(Locks::mutator_lock_)
1132      REQUIRES(Locks::heap_bitmap_lock_) {
1133    for (size_t i = 0; i < count; ++i) {
1134      mark_sweep_->MarkObjectNonNullParallel(roots[i]->AsMirrorPtr());
1135    }
1136  }
1137
1138  virtual void Run(Thread* thread) OVERRIDE NO_THREAD_SAFETY_ANALYSIS {
1139    ScopedTrace trace("Marking thread roots");
1140    // Note: self is not necessarily equal to thread since thread may be suspended.
1141    Thread* const self = Thread::Current();
1142    CHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc)
1143        << thread->GetState() << " thread " << thread << " self " << self;
1144    thread->VisitRoots(this);
1145    if (revoke_ros_alloc_thread_local_buffers_at_checkpoint_) {
1146      ScopedTrace trace2("RevokeRosAllocThreadLocalBuffers");
1147      mark_sweep_->GetHeap()->RevokeRosAllocThreadLocalBuffers(thread);
1148    }
1149    // If thread is a running mutator, then act on behalf of the garbage collector.
1150    // See the code in ThreadList::RunCheckpoint.
1151    mark_sweep_->GetBarrier().Pass(self);
1152  }
1153
1154 private:
1155  MarkSweep* const mark_sweep_;
1156  const bool revoke_ros_alloc_thread_local_buffers_at_checkpoint_;
1157};
1158
1159void MarkSweep::MarkRootsCheckpoint(Thread* self,
1160                                    bool revoke_ros_alloc_thread_local_buffers_at_checkpoint) {
1161  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1162  CheckpointMarkThreadRoots check_point(this, revoke_ros_alloc_thread_local_buffers_at_checkpoint);
1163  ThreadList* thread_list = Runtime::Current()->GetThreadList();
1164  // Request the check point is run on all threads returning a count of the threads that must
1165  // run through the barrier including self.
1166  size_t barrier_count = thread_list->RunCheckpoint(&check_point);
1167  // Release locks then wait for all mutator threads to pass the barrier.
1168  // If there are no threads to wait which implys that all the checkpoint functions are finished,
1169  // then no need to release locks.
1170  if (barrier_count == 0) {
1171    return;
1172  }
1173  Locks::heap_bitmap_lock_->ExclusiveUnlock(self);
1174  Locks::mutator_lock_->SharedUnlock(self);
1175  {
1176    ScopedThreadStateChange tsc(self, kWaitingForCheckPointsToRun);
1177    gc_barrier_->Increment(self, barrier_count);
1178  }
1179  Locks::mutator_lock_->SharedLock(self);
1180  Locks::heap_bitmap_lock_->ExclusiveLock(self);
1181}
1182
1183void MarkSweep::SweepArray(accounting::ObjectStack* allocations, bool swap_bitmaps) {
1184  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1185  Thread* self = Thread::Current();
1186  mirror::Object** chunk_free_buffer = reinterpret_cast<mirror::Object**>(
1187      sweep_array_free_buffer_mem_map_->BaseBegin());
1188  size_t chunk_free_pos = 0;
1189  ObjectBytePair freed;
1190  ObjectBytePair freed_los;
1191  // How many objects are left in the array, modified after each space is swept.
1192  StackReference<mirror::Object>* objects = allocations->Begin();
1193  size_t count = allocations->Size();
1194  // Change the order to ensure that the non-moving space last swept as an optimization.
1195  std::vector<space::ContinuousSpace*> sweep_spaces;
1196  space::ContinuousSpace* non_moving_space = nullptr;
1197  for (space::ContinuousSpace* space : heap_->GetContinuousSpaces()) {
1198    if (space->IsAllocSpace() &&
1199        !immune_spaces_.ContainsSpace(space) &&
1200        space->GetLiveBitmap() != nullptr) {
1201      if (space == heap_->GetNonMovingSpace()) {
1202        non_moving_space = space;
1203      } else {
1204        sweep_spaces.push_back(space);
1205      }
1206    }
1207  }
1208  // Unlikely to sweep a significant amount of non_movable objects, so we do these after the after
1209  // the other alloc spaces as an optimization.
1210  if (non_moving_space != nullptr) {
1211    sweep_spaces.push_back(non_moving_space);
1212  }
1213  // Start by sweeping the continuous spaces.
1214  for (space::ContinuousSpace* space : sweep_spaces) {
1215    space::AllocSpace* alloc_space = space->AsAllocSpace();
1216    accounting::ContinuousSpaceBitmap* live_bitmap = space->GetLiveBitmap();
1217    accounting::ContinuousSpaceBitmap* mark_bitmap = space->GetMarkBitmap();
1218    if (swap_bitmaps) {
1219      std::swap(live_bitmap, mark_bitmap);
1220    }
1221    StackReference<mirror::Object>* out = objects;
1222    for (size_t i = 0; i < count; ++i) {
1223      mirror::Object* const obj = objects[i].AsMirrorPtr();
1224      if (kUseThreadLocalAllocationStack && obj == nullptr) {
1225        continue;
1226      }
1227      if (space->HasAddress(obj)) {
1228        // This object is in the space, remove it from the array and add it to the sweep buffer
1229        // if needed.
1230        if (!mark_bitmap->Test(obj)) {
1231          if (chunk_free_pos >= kSweepArrayChunkFreeSize) {
1232            TimingLogger::ScopedTiming t2("FreeList", GetTimings());
1233            freed.objects += chunk_free_pos;
1234            freed.bytes += alloc_space->FreeList(self, chunk_free_pos, chunk_free_buffer);
1235            chunk_free_pos = 0;
1236          }
1237          chunk_free_buffer[chunk_free_pos++] = obj;
1238        }
1239      } else {
1240        (out++)->Assign(obj);
1241      }
1242    }
1243    if (chunk_free_pos > 0) {
1244      TimingLogger::ScopedTiming t2("FreeList", GetTimings());
1245      freed.objects += chunk_free_pos;
1246      freed.bytes += alloc_space->FreeList(self, chunk_free_pos, chunk_free_buffer);
1247      chunk_free_pos = 0;
1248    }
1249    // All of the references which space contained are no longer in the allocation stack, update
1250    // the count.
1251    count = out - objects;
1252  }
1253  // Handle the large object space.
1254  space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
1255  if (large_object_space != nullptr) {
1256    accounting::LargeObjectBitmap* large_live_objects = large_object_space->GetLiveBitmap();
1257    accounting::LargeObjectBitmap* large_mark_objects = large_object_space->GetMarkBitmap();
1258    if (swap_bitmaps) {
1259      std::swap(large_live_objects, large_mark_objects);
1260    }
1261    for (size_t i = 0; i < count; ++i) {
1262      mirror::Object* const obj = objects[i].AsMirrorPtr();
1263      // Handle large objects.
1264      if (kUseThreadLocalAllocationStack && obj == nullptr) {
1265        continue;
1266      }
1267      if (!large_mark_objects->Test(obj)) {
1268        ++freed_los.objects;
1269        freed_los.bytes += large_object_space->Free(self, obj);
1270      }
1271    }
1272  }
1273  {
1274    TimingLogger::ScopedTiming t2("RecordFree", GetTimings());
1275    RecordFree(freed);
1276    RecordFreeLOS(freed_los);
1277    t2.NewTiming("ResetStack");
1278    allocations->Reset();
1279  }
1280  sweep_array_free_buffer_mem_map_->MadviseDontNeedAndZero();
1281}
1282
1283void MarkSweep::Sweep(bool swap_bitmaps) {
1284  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1285  // Ensure that nobody inserted items in the live stack after we swapped the stacks.
1286  CHECK_GE(live_stack_freeze_size_, GetHeap()->GetLiveStack()->Size());
1287  {
1288    TimingLogger::ScopedTiming t2("MarkAllocStackAsLive", GetTimings());
1289    // Mark everything allocated since the last as GC live so that we can sweep concurrently,
1290    // knowing that new allocations won't be marked as live.
1291    accounting::ObjectStack* live_stack = heap_->GetLiveStack();
1292    heap_->MarkAllocStackAsLive(live_stack);
1293    live_stack->Reset();
1294    DCHECK(mark_stack_->IsEmpty());
1295  }
1296  for (const auto& space : GetHeap()->GetContinuousSpaces()) {
1297    if (space->IsContinuousMemMapAllocSpace()) {
1298      space::ContinuousMemMapAllocSpace* alloc_space = space->AsContinuousMemMapAllocSpace();
1299      TimingLogger::ScopedTiming split(
1300          alloc_space->IsZygoteSpace() ? "SweepZygoteSpace" : "SweepMallocSpace",
1301          GetTimings());
1302      RecordFree(alloc_space->Sweep(swap_bitmaps));
1303    }
1304  }
1305  SweepLargeObjects(swap_bitmaps);
1306}
1307
1308void MarkSweep::SweepLargeObjects(bool swap_bitmaps) {
1309  space::LargeObjectSpace* los = heap_->GetLargeObjectsSpace();
1310  if (los != nullptr) {
1311    TimingLogger::ScopedTiming split(__FUNCTION__, GetTimings());
1312    RecordFreeLOS(los->Sweep(swap_bitmaps));
1313  }
1314}
1315
1316// Process the "referent" field lin a java.lang.ref.Reference.  If the referent has not yet been
1317// marked, put it on the appropriate list in the heap for later processing.
1318void MarkSweep::DelayReferenceReferent(ObjPtr<mirror::Class> klass, ObjPtr<mirror::Reference> ref) {
1319  heap_->GetReferenceProcessor()->DelayReferenceReferent(klass, ref, this);
1320}
1321
1322class MarkVisitor {
1323 public:
1324  ALWAYS_INLINE explicit MarkVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {}
1325
1326  ALWAYS_INLINE void operator()(mirror::Object* obj,
1327                                MemberOffset offset,
1328                                bool is_static ATTRIBUTE_UNUSED) const
1329      REQUIRES(Locks::heap_bitmap_lock_)
1330      REQUIRES_SHARED(Locks::mutator_lock_) {
1331    if (kCheckLocks) {
1332      Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
1333      Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
1334    }
1335    mark_sweep_->MarkObject(obj->GetFieldObject<mirror::Object>(offset), obj, offset);
1336  }
1337
1338  void VisitRootIfNonNull(mirror::CompressedReference<mirror::Object>* root) const
1339      REQUIRES(Locks::heap_bitmap_lock_)
1340      REQUIRES_SHARED(Locks::mutator_lock_) {
1341    if (!root->IsNull()) {
1342      VisitRoot(root);
1343    }
1344  }
1345
1346  void VisitRoot(mirror::CompressedReference<mirror::Object>* root) const
1347      REQUIRES(Locks::heap_bitmap_lock_)
1348      REQUIRES_SHARED(Locks::mutator_lock_) {
1349    if (kCheckLocks) {
1350      Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
1351      Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
1352    }
1353    mark_sweep_->MarkObject(root->AsMirrorPtr());
1354  }
1355
1356 private:
1357  MarkSweep* const mark_sweep_;
1358};
1359
1360// Scans an object reference.  Determines the type of the reference
1361// and dispatches to a specialized scanning routine.
1362void MarkSweep::ScanObject(mirror::Object* obj) {
1363  MarkVisitor mark_visitor(this);
1364  DelayReferenceReferentVisitor ref_visitor(this);
1365  ScanObjectVisit(obj, mark_visitor, ref_visitor);
1366}
1367
1368void MarkSweep::ProcessMarkStackParallel(size_t thread_count) {
1369  Thread* self = Thread::Current();
1370  ThreadPool* thread_pool = GetHeap()->GetThreadPool();
1371  const size_t chunk_size = std::min(mark_stack_->Size() / thread_count + 1,
1372                                     static_cast<size_t>(MarkStackTask<false>::kMaxSize));
1373  CHECK_GT(chunk_size, 0U);
1374  // Split the current mark stack up into work tasks.
1375  for (auto* it = mark_stack_->Begin(), *end = mark_stack_->End(); it < end; ) {
1376    const size_t delta = std::min(static_cast<size_t>(end - it), chunk_size);
1377    thread_pool->AddTask(self, new MarkStackTask<false>(thread_pool, this, delta, it));
1378    it += delta;
1379  }
1380  thread_pool->SetMaxActiveWorkers(thread_count - 1);
1381  thread_pool->StartWorkers(self);
1382  thread_pool->Wait(self, true, true);
1383  thread_pool->StopWorkers(self);
1384  mark_stack_->Reset();
1385  CHECK_EQ(work_chunks_created_.LoadSequentiallyConsistent(),
1386           work_chunks_deleted_.LoadSequentiallyConsistent())
1387      << " some of the work chunks were leaked";
1388}
1389
1390// Scan anything that's on the mark stack.
1391void MarkSweep::ProcessMarkStack(bool paused) {
1392  TimingLogger::ScopedTiming t(paused ? "(Paused)ProcessMarkStack" : __FUNCTION__, GetTimings());
1393  size_t thread_count = GetThreadCount(paused);
1394  if (kParallelProcessMarkStack && thread_count > 1 &&
1395      mark_stack_->Size() >= kMinimumParallelMarkStackSize) {
1396    ProcessMarkStackParallel(thread_count);
1397  } else {
1398    // TODO: Tune this.
1399    static const size_t kFifoSize = 4;
1400    BoundedFifoPowerOfTwo<mirror::Object*, kFifoSize> prefetch_fifo;
1401    for (;;) {
1402      mirror::Object* obj = nullptr;
1403      if (kUseMarkStackPrefetch) {
1404        while (!mark_stack_->IsEmpty() && prefetch_fifo.size() < kFifoSize) {
1405          mirror::Object* mark_stack_obj = mark_stack_->PopBack();
1406          DCHECK(mark_stack_obj != nullptr);
1407          __builtin_prefetch(mark_stack_obj);
1408          prefetch_fifo.push_back(mark_stack_obj);
1409        }
1410        if (prefetch_fifo.empty()) {
1411          break;
1412        }
1413        obj = prefetch_fifo.front();
1414        prefetch_fifo.pop_front();
1415      } else {
1416        if (mark_stack_->IsEmpty()) {
1417          break;
1418        }
1419        obj = mark_stack_->PopBack();
1420      }
1421      DCHECK(obj != nullptr);
1422      ScanObject(obj);
1423    }
1424  }
1425}
1426
1427inline mirror::Object* MarkSweep::IsMarked(mirror::Object* object) {
1428  if (immune_spaces_.IsInImmuneRegion(object)) {
1429    return object;
1430  }
1431  if (current_space_bitmap_->HasAddress(object)) {
1432    return current_space_bitmap_->Test(object) ? object : nullptr;
1433  }
1434  return mark_bitmap_->Test(object) ? object : nullptr;
1435}
1436
1437void MarkSweep::FinishPhase() {
1438  TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1439  if (kCountScannedTypes) {
1440    VLOG(gc)
1441        << "MarkSweep scanned"
1442        << " no reference objects=" << no_reference_class_count_.LoadRelaxed()
1443        << " normal objects=" << normal_count_.LoadRelaxed()
1444        << " classes=" << class_count_.LoadRelaxed()
1445        << " object arrays=" << object_array_count_.LoadRelaxed()
1446        << " references=" << reference_count_.LoadRelaxed()
1447        << " other=" << other_count_.LoadRelaxed();
1448  }
1449  if (kCountTasks) {
1450    VLOG(gc) << "Total number of work chunks allocated: " << work_chunks_created_.LoadRelaxed();
1451  }
1452  if (kMeasureOverhead) {
1453    VLOG(gc) << "Overhead time " << PrettyDuration(overhead_time_.LoadRelaxed());
1454  }
1455  if (kProfileLargeObjects) {
1456    VLOG(gc) << "Large objects tested " << large_object_test_.LoadRelaxed()
1457        << " marked " << large_object_mark_.LoadRelaxed();
1458  }
1459  if (kCountMarkedObjects) {
1460    VLOG(gc) << "Marked: null=" << mark_null_count_.LoadRelaxed()
1461        << " immune=" <<  mark_immune_count_.LoadRelaxed()
1462        << " fastpath=" << mark_fastpath_count_.LoadRelaxed()
1463        << " slowpath=" << mark_slowpath_count_.LoadRelaxed();
1464  }
1465  CHECK(mark_stack_->IsEmpty());  // Ensure that the mark stack is empty.
1466  mark_stack_->Reset();
1467  Thread* const self = Thread::Current();
1468  ReaderMutexLock mu(self, *Locks::mutator_lock_);
1469  WriterMutexLock mu2(self, *Locks::heap_bitmap_lock_);
1470  heap_->ClearMarkedObjects();
1471}
1472
1473void MarkSweep::RevokeAllThreadLocalBuffers() {
1474  if (kRevokeRosAllocThreadLocalBuffersAtCheckpoint && IsConcurrent()) {
1475    // If concurrent, rosalloc thread-local buffers are revoked at the
1476    // thread checkpoint. Bump pointer space thread-local buffers must
1477    // not be in use.
1478    GetHeap()->AssertAllBumpPointerSpaceThreadLocalBuffersAreRevoked();
1479  } else {
1480    TimingLogger::ScopedTiming t(__FUNCTION__, GetTimings());
1481    GetHeap()->RevokeAllThreadLocalBuffers();
1482  }
1483}
1484
1485}  // namespace collector
1486}  // namespace gc
1487}  // namespace art
1488