mark_sweep.cc revision 7934ac288acfb2552bb0b06ec1f61e5820d924a4
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 <functional> 20#include <numeric> 21#include <climits> 22#include <vector> 23 24#include "base/logging.h" 25#include "base/macros.h" 26#include "base/mutex-inl.h" 27#include "base/timing_logger.h" 28#include "gc/accounting/card_table-inl.h" 29#include "gc/accounting/heap_bitmap.h" 30#include "gc/accounting/space_bitmap-inl.h" 31#include "gc/heap.h" 32#include "gc/space/image_space.h" 33#include "gc/space/large_object_space.h" 34#include "gc/space/space-inl.h" 35#include "indirect_reference_table.h" 36#include "intern_table.h" 37#include "jni_internal.h" 38#include "monitor.h" 39#include "mark_sweep-inl.h" 40#include "mirror/class-inl.h" 41#include "mirror/class_loader.h" 42#include "mirror/dex_cache.h" 43#include "mirror/field.h" 44#include "mirror/field-inl.h" 45#include "mirror/object-inl.h" 46#include "mirror/object_array.h" 47#include "mirror/object_array-inl.h" 48#include "runtime.h" 49#include "thread-inl.h" 50#include "thread_list.h" 51#include "verifier/method_verifier.h" 52 53using ::art::mirror::Class; 54using ::art::mirror::Field; 55using ::art::mirror::Object; 56using ::art::mirror::ObjectArray; 57 58namespace art { 59namespace gc { 60namespace collector { 61 62// Performance options. 63static const bool kParallelMarkStack = true; 64static const bool kDisableFinger = true; // TODO: Fix, bit rotten. 65static const bool kUseMarkStackPrefetch = true; 66 67// Profiling and information flags. 68static const bool kCountClassesMarked = false; 69static const bool kProfileLargeObjects = false; 70static const bool kMeasureOverhead = false; 71static const bool kCountTasks = false; 72static const bool kCountJavaLangRefs = false; 73 74class SetFingerVisitor { 75 public: 76 explicit SetFingerVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {} 77 78 void operator()(void* finger) const { 79 mark_sweep_->SetFinger(reinterpret_cast<Object*>(finger)); 80 } 81 82 private: 83 MarkSweep* const mark_sweep_; 84}; 85 86void MarkSweep::ImmuneSpace(space::ContinuousSpace* space) { 87 // Bind live to mark bitmap if necessary. 88 if (space->GetLiveBitmap() != space->GetMarkBitmap()) { 89 BindLiveToMarkBitmap(space); 90 } 91 92 // Add the space to the immune region. 93 if (immune_begin_ == NULL) { 94 DCHECK(immune_end_ == NULL); 95 SetImmuneRange(reinterpret_cast<Object*>(space->Begin()), 96 reinterpret_cast<Object*>(space->End())); 97 } else { 98 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 99 const space::ContinuousSpace* prev_space = NULL; 100 // Find out if the previous space is immune. 101 // TODO: C++0x 102 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 103 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 104 if (*it == space) { 105 break; 106 } 107 prev_space = *it; 108 } 109 110 // If previous space was immune, then extend the immune region. Relies on continuous spaces 111 // being sorted by Heap::AddContinuousSpace. 112 if (prev_space != NULL && 113 immune_begin_ <= reinterpret_cast<Object*>(prev_space->Begin()) && 114 immune_end_ >= reinterpret_cast<Object*>(prev_space->End())) { 115 immune_begin_ = std::min(reinterpret_cast<Object*>(space->Begin()), immune_begin_); 116 immune_end_ = std::max(reinterpret_cast<Object*>(space->End()), immune_end_); 117 } 118 } 119} 120 121void MarkSweep::BindBitmaps() { 122 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 123 WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_); 124 125 // Mark all of the spaces we never collect as immune. 126 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 127 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 128 space::ContinuousSpace* space = *it; 129 if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyNeverCollect) { 130 ImmuneSpace(space); 131 } 132 } 133} 134 135MarkSweep::MarkSweep(Heap* heap, bool is_concurrent, const std::string& name_prefix) 136 : GarbageCollector(heap, 137 name_prefix + (name_prefix.empty() ? "" : " ") + 138 (is_concurrent ? "concurrent mark sweep": "mark sweep")), 139 current_mark_bitmap_(NULL), 140 java_lang_Class_(NULL), 141 mark_stack_(NULL), 142 finger_(NULL), 143 immune_begin_(NULL), 144 immune_end_(NULL), 145 soft_reference_list_(NULL), 146 weak_reference_list_(NULL), 147 finalizer_reference_list_(NULL), 148 phantom_reference_list_(NULL), 149 cleared_reference_list_(NULL), 150 gc_barrier_(new Barrier(0)), 151 large_object_lock_("mark sweep large object lock", kMarkSweepLargeObjectLock), 152 mark_stack_expand_lock_("mark sweep mark stack expand lock"), 153 is_concurrent_(is_concurrent), 154 clear_soft_references_(false) { 155} 156 157void MarkSweep::InitializePhase() { 158 timings_.Reset(); 159 timings_.StartSplit("InitializePhase"); 160 mark_stack_ = GetHeap()->mark_stack_.get(); 161 DCHECK(mark_stack_ != NULL); 162 finger_ = NULL; 163 SetImmuneRange(NULL, NULL); 164 soft_reference_list_ = NULL; 165 weak_reference_list_ = NULL; 166 finalizer_reference_list_ = NULL; 167 phantom_reference_list_ = NULL; 168 cleared_reference_list_ = NULL; 169 freed_bytes_ = 0; 170 freed_objects_ = 0; 171 class_count_ = 0; 172 array_count_ = 0; 173 other_count_ = 0; 174 large_object_test_ = 0; 175 large_object_mark_ = 0; 176 classes_marked_ = 0; 177 overhead_time_ = 0; 178 work_chunks_created_ = 0; 179 work_chunks_deleted_ = 0; 180 reference_count_ = 0; 181 java_lang_Class_ = Class::GetJavaLangClass(); 182 CHECK(java_lang_Class_ != NULL); 183 FindDefaultMarkBitmap(); 184 // Do any pre GC verification. 185 heap_->PreGcVerification(this); 186} 187 188void MarkSweep::ProcessReferences(Thread* self) { 189 timings_.NewSplit("ProcessReferences"); 190 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 191 ProcessReferences(&soft_reference_list_, clear_soft_references_, &weak_reference_list_, 192 &finalizer_reference_list_, &phantom_reference_list_); 193} 194 195bool MarkSweep::HandleDirtyObjectsPhase() { 196 Thread* self = Thread::Current(); 197 accounting::ObjectStack* allocation_stack = GetHeap()->allocation_stack_.get(); 198 Locks::mutator_lock_->AssertExclusiveHeld(self); 199 200 { 201 timings_.NewSplit("ReMarkRoots"); 202 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 203 204 // Re-mark root set. 205 ReMarkRoots(); 206 207 // Scan dirty objects, this is only required if we are not doing concurrent GC. 208 RecursiveMarkDirtyObjects(accounting::CardTable::kCardDirty); 209 } 210 211 ProcessReferences(self); 212 213 // Only need to do this if we have the card mark verification on, and only during concurrent GC. 214 if (GetHeap()->verify_missing_card_marks_) { 215 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 216 // This second sweep makes sure that we don't have any objects in the live stack which point to 217 // freed objects. These cause problems since their references may be previously freed objects. 218 SweepArray(allocation_stack, false); 219 } else { 220 timings_.NewSplit("UnMarkAllocStack"); 221 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 222 // The allocation stack contains things allocated since the start of the GC. These may have been 223 // marked during this GC meaning they won't be eligible for reclaiming in the next sticky GC. 224 // Remove these objects from the mark bitmaps so that they will be eligible for sticky 225 // collection. 226 heap_->UnMarkAllocStack(GetHeap()->alloc_space_->GetMarkBitmap(), 227 GetHeap()->large_object_space_->GetMarkObjects(), 228 allocation_stack); 229 } 230 return true; 231} 232 233bool MarkSweep::IsConcurrent() const { 234 return is_concurrent_; 235} 236 237void MarkSweep::MarkingPhase() { 238 Heap* heap = GetHeap(); 239 Thread* self = Thread::Current(); 240 241 timings_.NewSplit("BindBitmaps"); 242 BindBitmaps(); 243 FindDefaultMarkBitmap(); 244 // Process dirty cards and add dirty cards to mod union tables. 245 heap->ProcessCards(timings_); 246 247 // Need to do this before the checkpoint since we don't want any threads to add references to 248 // the live stack during the recursive mark. 249 timings_.NewSplit("SwapStacks"); 250 heap->SwapStacks(); 251 252 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 253 if (Locks::mutator_lock_->IsExclusiveHeld(self)) { 254 // If we exclusively hold the mutator lock, all threads must be suspended. 255 timings_.NewSplit("MarkRoots"); 256 MarkRoots(); 257 } else { 258 timings_.NewSplit("MarkRootsCheckpoint"); 259 MarkRootsCheckpoint(self); 260 timings_.NewSplit("MarkNonThreadRoots"); 261 MarkNonThreadRoots(); 262 } 263 timings_.NewSplit("MarkConcurrentRoots"); 264 MarkConcurrentRoots(); 265 266 heap->UpdateAndMarkModUnion(this, timings_, GetGcType()); 267 MarkReachableObjects(); 268} 269 270void MarkSweep::MarkReachableObjects() { 271 // Mark everything allocated since the last as GC live so that we can sweep concurrently, 272 // knowing that new allocations won't be marked as live. 273 timings_.NewSplit("MarkStackAsLive"); 274 accounting::ObjectStack* live_stack = heap_->GetLiveStack(); 275 heap_->MarkAllocStack(heap_->alloc_space_->GetLiveBitmap(), 276 heap_->large_object_space_->GetLiveObjects(), 277 live_stack); 278 live_stack->Reset(); 279 // Recursively mark all the non-image bits set in the mark bitmap. 280 RecursiveMark(); 281 DisableFinger(); 282} 283 284void MarkSweep::ReclaimPhase() { 285 Thread* self = Thread::Current(); 286 287 if (!IsConcurrent()) { 288 ProcessReferences(self); 289 } 290 291 // Before freeing anything, lets verify the heap. 292 if (kIsDebugBuild) { 293 ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_); 294 VerifyImageRoots(); 295 } 296 heap_->PreSweepingGcVerification(this); 297 298 { 299 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 300 301 // Reclaim unmarked objects. 302 Sweep(false); 303 304 // Swap the live and mark bitmaps for each space which we modified space. This is an 305 // optimization that enables us to not clear live bits inside of the sweep. Only swaps unbound 306 // bitmaps. 307 timings_.NewSplit("SwapBitmaps"); 308 SwapBitmaps(); 309 310 // Unbind the live and mark bitmaps. 311 UnBindBitmaps(); 312 } 313} 314 315void MarkSweep::SetImmuneRange(Object* begin, Object* end) { 316 immune_begin_ = begin; 317 immune_end_ = end; 318} 319 320void MarkSweep::FindDefaultMarkBitmap() { 321 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 322 // TODO: C++0x 323 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 324 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 325 space::ContinuousSpace* space = *it; 326 if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) { 327 current_mark_bitmap_ = (*it)->GetMarkBitmap(); 328 CHECK(current_mark_bitmap_ != NULL); 329 return; 330 } 331 } 332 GetHeap()->DumpSpaces(); 333 LOG(FATAL) << "Could not find a default mark bitmap"; 334} 335 336void MarkSweep::ExpandMarkStack() { 337 // Rare case, no need to have Thread::Current be a parameter. 338 MutexLock mu(Thread::Current(), mark_stack_expand_lock_); 339 if (UNLIKELY(mark_stack_->Size() < mark_stack_->Capacity())) { 340 // Someone else acquired the lock and expanded the mark stack before us. 341 return; 342 } 343 std::vector<Object*> temp; 344 temp.insert(temp.begin(), mark_stack_->Begin(), mark_stack_->End()); 345 mark_stack_->Resize(mark_stack_->Capacity() * 2); 346 for (size_t i = 0; i < temp.size(); ++i) { 347 mark_stack_->PushBack(temp[i]); 348 } 349} 350 351inline void MarkSweep::MarkObjectNonNullParallel(const Object* obj, bool check_finger) { 352 DCHECK(obj != NULL); 353 if (MarkObjectParallel(obj)) { 354 if (kDisableFinger || (check_finger && obj < finger_)) { 355 while (UNLIKELY(!mark_stack_->AtomicPushBack(const_cast<Object*>(obj)))) { 356 // Only reason a push can fail is that the mark stack is full. 357 ExpandMarkStack(); 358 } 359 } 360 } 361} 362 363inline void MarkSweep::MarkObjectNonNull(const Object* obj, bool check_finger) { 364 DCHECK(obj != NULL); 365 366 if (obj >= immune_begin_ && obj < immune_end_) { 367 DCHECK(IsMarked(obj)); 368 return; 369 } 370 371 // Try to take advantage of locality of references within a space, failing this find the space 372 // the hard way. 373 accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_; 374 if (UNLIKELY(!object_bitmap->HasAddress(obj))) { 375 accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj); 376 if (LIKELY(new_bitmap != NULL)) { 377 object_bitmap = new_bitmap; 378 } else { 379 MarkLargeObject(obj); 380 return; 381 } 382 } 383 384 // This object was not previously marked. 385 if (!object_bitmap->Test(obj)) { 386 object_bitmap->Set(obj); 387 if (kDisableFinger || (check_finger && obj < finger_)) { 388 // Do we need to expand the mark stack? 389 if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) { 390 ExpandMarkStack(); 391 } 392 // The object must be pushed on to the mark stack. 393 mark_stack_->PushBack(const_cast<Object*>(obj)); 394 } 395 } 396} 397 398// Rare case, probably not worth inlining since it will increase instruction cache miss rate. 399bool MarkSweep::MarkLargeObject(const Object* obj) { 400 // TODO: support >1 discontinuous space. 401 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 402 accounting::SpaceSetMap* large_objects = large_object_space->GetMarkObjects(); 403 if (kProfileLargeObjects) { 404 ++large_object_test_; 405 } 406 if (UNLIKELY(!large_objects->Test(obj))) { 407 if (!large_object_space->Contains(obj)) { 408 LOG(ERROR) << "Tried to mark " << obj << " not contained by any spaces"; 409 LOG(ERROR) << "Attempting see if it's a bad root"; 410 VerifyRoots(); 411 LOG(FATAL) << "Can't mark bad root"; 412 } 413 if (kProfileLargeObjects) { 414 ++large_object_mark_; 415 } 416 large_objects->Set(obj); 417 // Don't need to check finger since large objects never have any object references. 418 return true; 419 } 420 return false; 421} 422 423inline bool MarkSweep::MarkObjectParallel(const Object* obj) { 424 DCHECK(obj != NULL); 425 426 if (obj >= immune_begin_ && obj < immune_end_) { 427 DCHECK(IsMarked(obj)); 428 return false; 429 } 430 431 // Try to take advantage of locality of references within a space, failing this find the space 432 // the hard way. 433 accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_; 434 if (UNLIKELY(!object_bitmap->HasAddress(obj))) { 435 accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj); 436 if (new_bitmap != NULL) { 437 object_bitmap = new_bitmap; 438 } else { 439 // TODO: Remove the Thread::Current here? 440 // TODO: Convert this to some kind of atomic marking? 441 MutexLock mu(Thread::Current(), large_object_lock_); 442 return MarkLargeObject(obj); 443 } 444 } 445 446 // Return true if the object was not previously marked. 447 return !object_bitmap->AtomicTestAndSet(obj); 448} 449 450// Used to mark objects when recursing. Recursion is done by moving 451// the finger across the bitmaps in address order and marking child 452// objects. Any newly-marked objects whose addresses are lower than 453// the finger won't be visited by the bitmap scan, so those objects 454// need to be added to the mark stack. 455void MarkSweep::MarkObject(const Object* obj) { 456 if (obj != NULL) { 457 MarkObjectNonNull(obj, true); 458 } 459} 460 461void MarkSweep::MarkRoot(const Object* obj) { 462 if (obj != NULL) { 463 MarkObjectNonNull(obj, false); 464 } 465} 466 467void MarkSweep::MarkRootParallelCallback(const Object* root, void* arg) { 468 DCHECK(root != NULL); 469 DCHECK(arg != NULL); 470 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 471 mark_sweep->MarkObjectNonNullParallel(root, false); 472} 473 474void MarkSweep::MarkObjectCallback(const Object* root, void* arg) { 475 DCHECK(root != NULL); 476 DCHECK(arg != NULL); 477 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 478 mark_sweep->MarkObjectNonNull(root, false); 479} 480 481void MarkSweep::ReMarkObjectVisitor(const Object* root, void* arg) { 482 DCHECK(root != NULL); 483 DCHECK(arg != NULL); 484 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 485 mark_sweep->MarkObjectNonNull(root, true); 486} 487 488void MarkSweep::VerifyRootCallback(const Object* root, void* arg, size_t vreg, 489 const StackVisitor* visitor) { 490 reinterpret_cast<MarkSweep*>(arg)->VerifyRoot(root, vreg, visitor); 491} 492 493void MarkSweep::VerifyRoot(const Object* root, size_t vreg, const StackVisitor* visitor) { 494 // See if the root is on any space bitmap. 495 if (GetHeap()->GetLiveBitmap()->GetContinuousSpaceBitmap(root) == NULL) { 496 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 497 if (!large_object_space->Contains(root)) { 498 LOG(ERROR) << "Found invalid root: " << root; 499 if (visitor != NULL) { 500 LOG(ERROR) << visitor->DescribeLocation() << " in VReg: " << vreg; 501 } 502 } 503 } 504} 505 506void MarkSweep::VerifyRoots() { 507 Runtime::Current()->GetThreadList()->VerifyRoots(VerifyRootCallback, this); 508} 509 510// Marks all objects in the root set. 511void MarkSweep::MarkRoots() { 512 Runtime::Current()->VisitNonConcurrentRoots(MarkObjectCallback, this); 513} 514 515void MarkSweep::MarkNonThreadRoots() { 516 Runtime::Current()->VisitNonThreadRoots(MarkObjectCallback, this); 517} 518 519void MarkSweep::MarkConcurrentRoots() { 520 // Visit all runtime roots and clear dirty flags. 521 Runtime::Current()->VisitConcurrentRoots(MarkObjectCallback, this, false, true); 522} 523 524class CheckObjectVisitor { 525 public: 526 explicit CheckObjectVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {} 527 528 void operator()(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) const 529 NO_THREAD_SAFETY_ANALYSIS { 530 if (kDebugLocking) { 531 Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current()); 532 } 533 mark_sweep_->CheckReference(obj, ref, offset, is_static); 534 } 535 536 private: 537 MarkSweep* const mark_sweep_; 538}; 539 540void MarkSweep::CheckObject(const Object* obj) { 541 DCHECK(obj != NULL); 542 CheckObjectVisitor visitor(this); 543 VisitObjectReferences(obj, visitor); 544} 545 546void MarkSweep::VerifyImageRootVisitor(Object* root, void* arg) { 547 DCHECK(root != NULL); 548 DCHECK(arg != NULL); 549 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 550 DCHECK(mark_sweep->heap_->GetMarkBitmap()->Test(root)); 551 mark_sweep->CheckObject(root); 552} 553 554void MarkSweep::BindLiveToMarkBitmap(space::ContinuousSpace* space) { 555 CHECK(space->IsDlMallocSpace()); 556 space::DlMallocSpace* alloc_space = space->AsDlMallocSpace(); 557 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 558 accounting::SpaceBitmap* mark_bitmap = alloc_space->mark_bitmap_.release(); 559 GetHeap()->GetMarkBitmap()->ReplaceBitmap(mark_bitmap, live_bitmap); 560 alloc_space->temp_bitmap_.reset(mark_bitmap); 561 alloc_space->mark_bitmap_.reset(live_bitmap); 562} 563 564class ScanObjectVisitor { 565 public: 566 explicit ScanObjectVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {} 567 568 // TODO: Fixme when anotatalysis works with visitors. 569 void operator()(const Object* obj) const NO_THREAD_SAFETY_ANALYSIS { 570 if (kDebugLocking) { 571 Locks::mutator_lock_->AssertSharedHeld(Thread::Current()); 572 Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current()); 573 } 574 mark_sweep_->ScanObject(obj); 575 } 576 577 private: 578 MarkSweep* const mark_sweep_; 579}; 580 581void MarkSweep::ScanGrayObjects(byte minimum_age) { 582 accounting::CardTable* card_table = GetHeap()->GetCardTable(); 583 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 584 ScanObjectVisitor visitor(this); 585 SetFingerVisitor finger_visitor(this); 586 // TODO: C++0x 587 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 588 for (It it = spaces.begin(), space_end = spaces.end(); it != space_end; ++it) { 589 space::ContinuousSpace* space = *it; 590 switch (space->GetGcRetentionPolicy()) { 591 case space::kGcRetentionPolicyNeverCollect: 592 timings_.NewSplit("ScanGrayImageSpaceObjects"); 593 break; 594 case space::kGcRetentionPolicyFullCollect: 595 timings_.NewSplit("ScanGrayZygoteSpaceObjects"); 596 break; 597 case space::kGcRetentionPolicyAlwaysCollect: 598 timings_.NewSplit("ScanGrayAllocSpaceObjects"); 599 break; 600 } 601 byte* begin = space->Begin(); 602 byte* end = space->End(); 603 // Image spaces are handled properly since live == marked for them. 604 accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap(); 605 card_table->Scan(mark_bitmap, begin, end, visitor, finger_visitor, minimum_age); 606 } 607} 608 609class CheckBitmapVisitor { 610 public: 611 explicit CheckBitmapVisitor(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) {} 612 613 void operator()(const Object* obj) const NO_THREAD_SAFETY_ANALYSIS { 614 if (kDebugLocking) { 615 Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current()); 616 } 617 DCHECK(obj != NULL); 618 mark_sweep_->CheckObject(obj); 619 } 620 621 private: 622 MarkSweep* mark_sweep_; 623}; 624 625void MarkSweep::VerifyImageRoots() { 626 // Verify roots ensures that all the references inside the image space point 627 // objects which are either in the image space or marked objects in the alloc 628 // space 629 CheckBitmapVisitor visitor(this); 630 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 631 // TODO: C++0x 632 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 633 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 634 if ((*it)->IsImageSpace()) { 635 space::ImageSpace* space = (*it)->AsImageSpace(); 636 uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin()); 637 uintptr_t end = reinterpret_cast<uintptr_t>(space->End()); 638 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 639 DCHECK(live_bitmap != NULL); 640 live_bitmap->VisitMarkedRange(begin, end, visitor, VoidFunctor()); 641 } 642 } 643} 644 645// Populates the mark stack based on the set of marked objects and 646// recursively marks until the mark stack is emptied. 647void MarkSweep::RecursiveMark() { 648 timings_.NewSplit("RecursiveMark"); 649 // RecursiveMark will build the lists of known instances of the Reference classes. 650 // See DelayReferenceReferent for details. 651 CHECK(soft_reference_list_ == NULL); 652 CHECK(weak_reference_list_ == NULL); 653 CHECK(finalizer_reference_list_ == NULL); 654 CHECK(phantom_reference_list_ == NULL); 655 CHECK(cleared_reference_list_ == NULL); 656 657 const bool partial = GetGcType() == kGcTypePartial; 658 SetFingerVisitor set_finger_visitor(this); 659 ScanObjectVisitor scan_visitor(this); 660 if (!kDisableFinger) { 661 finger_ = NULL; 662 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 663 // TODO: C++0x 664 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 665 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 666 space::ContinuousSpace* space = *it; 667 if ((space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) || 668 (!partial && space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect)) { 669 current_mark_bitmap_ = space->GetMarkBitmap(); 670 if (current_mark_bitmap_ == NULL) { 671 GetHeap()->DumpSpaces(); 672 LOG(FATAL) << "invalid bitmap"; 673 } 674 // This function does not handle heap end increasing, so we must use the space end. 675 uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin()); 676 uintptr_t end = reinterpret_cast<uintptr_t>(space->End()); 677 current_mark_bitmap_->VisitMarkedRange(begin, end, scan_visitor, set_finger_visitor); 678 } 679 } 680 } 681 DisableFinger(); 682 timings_.NewSplit("ProcessMarkStack"); 683 ProcessMarkStack(); 684} 685 686bool MarkSweep::IsMarkedCallback(const Object* object, void* arg) { 687 return 688 reinterpret_cast<MarkSweep*>(arg)->IsMarked(object) || 689 !reinterpret_cast<MarkSweep*>(arg)->GetHeap()->GetLiveBitmap()->Test(object); 690} 691 692void MarkSweep::RecursiveMarkDirtyObjects(byte minimum_age) { 693 ScanGrayObjects(minimum_age); 694 timings_.NewSplit("ProcessMarkStack"); 695 ProcessMarkStack(); 696} 697 698void MarkSweep::ReMarkRoots() { 699 Runtime::Current()->VisitRoots(ReMarkObjectVisitor, this, true, true); 700} 701 702void MarkSweep::SweepJniWeakGlobals(IsMarkedTester is_marked, void* arg) { 703 JavaVMExt* vm = Runtime::Current()->GetJavaVM(); 704 MutexLock mu(Thread::Current(), vm->weak_globals_lock); 705 IndirectReferenceTable* table = &vm->weak_globals; 706 typedef IndirectReferenceTable::iterator It; // TODO: C++0x auto 707 for (It it = table->begin(), end = table->end(); it != end; ++it) { 708 const Object** entry = *it; 709 if (!is_marked(*entry, arg)) { 710 *entry = kClearedJniWeakGlobal; 711 } 712 } 713} 714 715struct ArrayMarkedCheck { 716 accounting::ObjectStack* live_stack; 717 MarkSweep* mark_sweep; 718}; 719 720// Either marked or not live. 721bool MarkSweep::IsMarkedArrayCallback(const Object* object, void* arg) { 722 ArrayMarkedCheck* array_check = reinterpret_cast<ArrayMarkedCheck*>(arg); 723 if (array_check->mark_sweep->IsMarked(object)) { 724 return true; 725 } 726 accounting::ObjectStack* live_stack = array_check->live_stack; 727 return std::find(live_stack->Begin(), live_stack->End(), object) == live_stack->End(); 728} 729 730void MarkSweep::SweepSystemWeaksArray(accounting::ObjectStack* allocations) { 731 Runtime* runtime = Runtime::Current(); 732 // The callbacks check 733 // !is_marked where is_marked is the callback but we want 734 // !IsMarked && IsLive 735 // So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive). 736 // Or for swapped (IsLive || !IsMarked). 737 738 ArrayMarkedCheck visitor; 739 visitor.live_stack = allocations; 740 visitor.mark_sweep = this; 741 runtime->GetInternTable()->SweepInternTableWeaks(IsMarkedArrayCallback, &visitor); 742 runtime->GetMonitorList()->SweepMonitorList(IsMarkedArrayCallback, &visitor); 743 SweepJniWeakGlobals(IsMarkedArrayCallback, &visitor); 744} 745 746void MarkSweep::SweepSystemWeaks() { 747 Runtime* runtime = Runtime::Current(); 748 // The callbacks check 749 // !is_marked where is_marked is the callback but we want 750 // !IsMarked && IsLive 751 // So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive). 752 // Or for swapped (IsLive || !IsMarked). 753 runtime->GetInternTable()->SweepInternTableWeaks(IsMarkedCallback, this); 754 runtime->GetMonitorList()->SweepMonitorList(IsMarkedCallback, this); 755 SweepJniWeakGlobals(IsMarkedCallback, this); 756} 757 758bool MarkSweep::VerifyIsLiveCallback(const Object* obj, void* arg) { 759 reinterpret_cast<MarkSweep*>(arg)->VerifyIsLive(obj); 760 // We don't actually want to sweep the object, so lets return "marked" 761 return true; 762} 763 764void MarkSweep::VerifyIsLive(const Object* obj) { 765 Heap* heap = GetHeap(); 766 if (!heap->GetLiveBitmap()->Test(obj)) { 767 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 768 if (!large_object_space->GetLiveObjects()->Test(obj)) { 769 if (std::find(heap->allocation_stack_->Begin(), heap->allocation_stack_->End(), obj) == 770 heap->allocation_stack_->End()) { 771 // Object not found! 772 heap->DumpSpaces(); 773 LOG(FATAL) << "Found dead object " << obj; 774 } 775 } 776 } 777} 778 779void MarkSweep::VerifySystemWeaks() { 780 Runtime* runtime = Runtime::Current(); 781 // Verify system weaks, uses a special IsMarked callback which always returns true. 782 runtime->GetInternTable()->SweepInternTableWeaks(VerifyIsLiveCallback, this); 783 runtime->GetMonitorList()->SweepMonitorList(VerifyIsLiveCallback, this); 784 785 JavaVMExt* vm = runtime->GetJavaVM(); 786 MutexLock mu(Thread::Current(), vm->weak_globals_lock); 787 IndirectReferenceTable* table = &vm->weak_globals; 788 typedef IndirectReferenceTable::iterator It; // TODO: C++0x auto 789 for (It it = table->begin(), end = table->end(); it != end; ++it) { 790 const Object** entry = *it; 791 VerifyIsLive(*entry); 792 } 793} 794 795struct SweepCallbackContext { 796 MarkSweep* mark_sweep; 797 space::AllocSpace* space; 798 Thread* self; 799}; 800 801class CheckpointMarkThreadRoots : public Closure { 802 public: 803 explicit CheckpointMarkThreadRoots(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) {} 804 805 virtual void Run(Thread* thread) NO_THREAD_SAFETY_ANALYSIS { 806 // Note: self is not necessarily equal to thread since thread may be suspended. 807 Thread* self = Thread::Current(); 808 CHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc) 809 << thread->GetState() << " thread " << thread << " self " << self; 810 thread->VisitRoots(MarkSweep::MarkRootParallelCallback, mark_sweep_); 811 mark_sweep_->GetBarrier().Pass(self); 812 } 813 814 private: 815 MarkSweep* mark_sweep_; 816}; 817 818void MarkSweep::MarkRootsCheckpoint(Thread* self) { 819 CheckpointMarkThreadRoots check_point(this); 820 ThreadList* thread_list = Runtime::Current()->GetThreadList(); 821 // Request the check point is run on all threads returning a count of the threads that must 822 // run through the barrier including self. 823 size_t barrier_count = thread_list->RunCheckpoint(&check_point); 824 // Release locks then wait for all mutator threads to pass the barrier. 825 // TODO: optimize to not release locks when there are no threads to wait for. 826 Locks::heap_bitmap_lock_->ExclusiveUnlock(self); 827 Locks::mutator_lock_->SharedUnlock(self); 828 ThreadState old_state = self->SetState(kWaitingForCheckPointsToRun); 829 CHECK_EQ(old_state, kWaitingPerformingGc); 830 gc_barrier_->Increment(self, barrier_count); 831 self->SetState(kWaitingPerformingGc); 832 Locks::mutator_lock_->SharedLock(self); 833 Locks::heap_bitmap_lock_->ExclusiveLock(self); 834} 835 836void MarkSweep::SweepCallback(size_t num_ptrs, Object** ptrs, void* arg) { 837 SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg); 838 MarkSweep* mark_sweep = context->mark_sweep; 839 Heap* heap = mark_sweep->GetHeap(); 840 space::AllocSpace* space = context->space; 841 Thread* self = context->self; 842 Locks::heap_bitmap_lock_->AssertExclusiveHeld(self); 843 // Use a bulk free, that merges consecutive objects before freeing or free per object? 844 // Documentation suggests better free performance with merging, but this may be at the expensive 845 // of allocation. 846 size_t freed_objects = num_ptrs; 847 // AllocSpace::FreeList clears the value in ptrs, so perform after clearing the live bit 848 size_t freed_bytes = space->FreeList(self, num_ptrs, ptrs); 849 heap->RecordFree(freed_objects, freed_bytes); 850 mark_sweep->freed_objects_.fetch_add(freed_objects); 851 mark_sweep->freed_bytes_.fetch_add(freed_bytes); 852} 853 854void MarkSweep::ZygoteSweepCallback(size_t num_ptrs, Object** ptrs, void* arg) { 855 SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg); 856 Locks::heap_bitmap_lock_->AssertExclusiveHeld(context->self); 857 Heap* heap = context->mark_sweep->GetHeap(); 858 // We don't free any actual memory to avoid dirtying the shared zygote pages. 859 for (size_t i = 0; i < num_ptrs; ++i) { 860 Object* obj = static_cast<Object*>(ptrs[i]); 861 heap->GetLiveBitmap()->Clear(obj); 862 heap->GetCardTable()->MarkCard(obj); 863 } 864} 865 866void MarkSweep::SweepArray(accounting::ObjectStack* allocations, bool swap_bitmaps) { 867 size_t freed_bytes = 0; 868 space::DlMallocSpace* space = heap_->GetAllocSpace(); 869 870 // If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark 871 // bitmap, resulting in occasional frees of Weaks which are still in use. 872 timings_.NewSplit("SweepSystemWeaks"); 873 SweepSystemWeaksArray(allocations); 874 875 timings_.NewSplit("Process allocation stack"); 876 // Newly allocated objects MUST be in the alloc space and those are the only objects which we are 877 // going to free. 878 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 879 accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap(); 880 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 881 accounting::SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects(); 882 accounting::SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects(); 883 if (swap_bitmaps) { 884 std::swap(live_bitmap, mark_bitmap); 885 std::swap(large_live_objects, large_mark_objects); 886 } 887 888 size_t freed_large_objects = 0; 889 size_t count = allocations->Size(); 890 Object** objects = const_cast<Object**>(allocations->Begin()); 891 Object** out = objects; 892 893 // Empty the allocation stack. 894 Thread* self = Thread::Current(); 895 for (size_t i = 0; i < count; ++i) { 896 Object* obj = objects[i]; 897 // There should only be objects in the AllocSpace/LargeObjectSpace in the allocation stack. 898 if (LIKELY(mark_bitmap->HasAddress(obj))) { 899 if (!mark_bitmap->Test(obj)) { 900 // Don't bother un-marking since we clear the mark bitmap anyways. 901 *(out++) = obj; 902 } 903 } else if (!large_mark_objects->Test(obj)) { 904 ++freed_large_objects; 905 freed_bytes += large_object_space->Free(self, obj); 906 } 907 } 908 CHECK_EQ(count, allocations->Size()); 909 timings_.NewSplit("FreeList"); 910 911 size_t freed_objects = out - objects; 912 freed_bytes += space->FreeList(self, freed_objects, objects); 913 VLOG(heap) << "Freed " << freed_objects << "/" << count 914 << " objects with size " << PrettySize(freed_bytes); 915 heap_->RecordFree(freed_objects + freed_large_objects, freed_bytes); 916 freed_objects_.fetch_add(freed_objects); 917 freed_bytes_.fetch_add(freed_bytes); 918 919 timings_.NewSplit("ResetStack"); 920 allocations->Reset(); 921} 922 923void MarkSweep::Sweep(bool swap_bitmaps) { 924 DCHECK(mark_stack_->IsEmpty()); 925 926 // If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark 927 // bitmap, resulting in occasional frees of Weaks which are still in use. 928 timings_.NewSplit("SweepSystemWeaks"); 929 SweepSystemWeaks(); 930 931 const bool partial = (GetGcType() == kGcTypePartial); 932 SweepCallbackContext scc; 933 scc.mark_sweep = this; 934 scc.self = Thread::Current(); 935 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 936 // TODO: C++0x 937 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 938 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 939 space::ContinuousSpace* space = *it; 940 // We always sweep always collect spaces. 941 bool sweep_space = (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect); 942 if (!partial && !sweep_space) { 943 // We sweep full collect spaces when the GC isn't a partial GC (ie its full). 944 sweep_space = (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect); 945 } 946 if (sweep_space) { 947 uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin()); 948 uintptr_t end = reinterpret_cast<uintptr_t>(space->End()); 949 scc.space = space->AsDlMallocSpace(); 950 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 951 accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap(); 952 if (swap_bitmaps) { 953 std::swap(live_bitmap, mark_bitmap); 954 } 955 if (!space->IsZygoteSpace()) { 956 timings_.NewSplit("SweepAllocSpace"); 957 // Bitmaps are pre-swapped for optimization which enables sweeping with the heap unlocked. 958 accounting::SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end, 959 &SweepCallback, reinterpret_cast<void*>(&scc)); 960 } else { 961 timings_.NewSplit("SweepZygote"); 962 // Zygote sweep takes care of dirtying cards and clearing live bits, does not free actual 963 // memory. 964 accounting::SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end, 965 &ZygoteSweepCallback, reinterpret_cast<void*>(&scc)); 966 } 967 } 968 } 969 970 timings_.NewSplit("SweepLargeObjects"); 971 SweepLargeObjects(swap_bitmaps); 972} 973 974void MarkSweep::SweepLargeObjects(bool swap_bitmaps) { 975 // Sweep large objects 976 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 977 accounting::SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects(); 978 accounting::SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects(); 979 if (swap_bitmaps) { 980 std::swap(large_live_objects, large_mark_objects); 981 } 982 accounting::SpaceSetMap::Objects& live_objects = large_live_objects->GetObjects(); 983 // O(n*log(n)) but hopefully there are not too many large objects. 984 size_t freed_objects = 0; 985 size_t freed_bytes = 0; 986 Thread* self = Thread::Current(); 987 // TODO: C++0x 988 typedef accounting::SpaceSetMap::Objects::iterator It; 989 for (It it = live_objects.begin(), end = live_objects.end(); it != end; ++it) { 990 if (!large_mark_objects->Test(*it)) { 991 freed_bytes += large_object_space->Free(self, const_cast<Object*>(*it)); 992 ++freed_objects; 993 } 994 } 995 freed_objects_.fetch_add(freed_objects); 996 freed_bytes_.fetch_add(freed_bytes); 997 GetHeap()->RecordFree(freed_objects, freed_bytes); 998} 999 1000void MarkSweep::CheckReference(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) { 1001 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 1002 // TODO: C++0x 1003 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 1004 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 1005 space::ContinuousSpace* space = *it; 1006 if (space->IsDlMallocSpace() && space->Contains(ref)) { 1007 DCHECK(IsMarked(obj)); 1008 1009 bool is_marked = IsMarked(ref); 1010 if (!is_marked) { 1011 LOG(INFO) << *space; 1012 LOG(WARNING) << (is_static ? "Static ref'" : "Instance ref'") << PrettyTypeOf(ref) 1013 << "' (" << reinterpret_cast<const void*>(ref) << ") in '" << PrettyTypeOf(obj) 1014 << "' (" << reinterpret_cast<const void*>(obj) << ") at offset " 1015 << reinterpret_cast<void*>(offset.Int32Value()) << " wasn't marked"; 1016 1017 const Class* klass = is_static ? obj->AsClass() : obj->GetClass(); 1018 DCHECK(klass != NULL); 1019 const ObjectArray<Field>* fields = is_static ? klass->GetSFields() : klass->GetIFields(); 1020 DCHECK(fields != NULL); 1021 bool found = false; 1022 for (int32_t i = 0; i < fields->GetLength(); ++i) { 1023 const Field* cur = fields->Get(i); 1024 if (cur->GetOffset().Int32Value() == offset.Int32Value()) { 1025 LOG(WARNING) << "Field referencing the alloc space was " << PrettyField(cur); 1026 found = true; 1027 break; 1028 } 1029 } 1030 if (!found) { 1031 LOG(WARNING) << "Could not find field in object alloc space with offset " << offset.Int32Value(); 1032 } 1033 1034 bool obj_marked = heap_->GetCardTable()->IsDirty(obj); 1035 if (!obj_marked) { 1036 LOG(WARNING) << "Object '" << PrettyTypeOf(obj) << "' " 1037 << "(" << reinterpret_cast<const void*>(obj) << ") contains references to " 1038 << "the alloc space, but wasn't card marked"; 1039 } 1040 } 1041 } 1042 break; 1043 } 1044} 1045 1046// Process the "referent" field in a java.lang.ref.Reference. If the 1047// referent has not yet been marked, put it on the appropriate list in 1048// the gcHeap for later processing. 1049void MarkSweep::DelayReferenceReferent(Object* obj) { 1050 DCHECK(obj != NULL); 1051 Class* klass = obj->GetClass(); 1052 DCHECK(klass != NULL); 1053 DCHECK(klass->IsReferenceClass()); 1054 Object* pending = obj->GetFieldObject<Object*>(heap_->GetReferencePendingNextOffset(), false); 1055 Object* referent = heap_->GetReferenceReferent(obj); 1056 if (kCountJavaLangRefs) { 1057 ++reference_count_; 1058 } 1059 if (pending == NULL && referent != NULL && !IsMarked(referent)) { 1060 Object** list = NULL; 1061 if (klass->IsSoftReferenceClass()) { 1062 list = &soft_reference_list_; 1063 } else if (klass->IsWeakReferenceClass()) { 1064 list = &weak_reference_list_; 1065 } else if (klass->IsFinalizerReferenceClass()) { 1066 list = &finalizer_reference_list_; 1067 } else if (klass->IsPhantomReferenceClass()) { 1068 list = &phantom_reference_list_; 1069 } 1070 DCHECK(list != NULL) << PrettyClass(klass) << " " << std::hex << klass->GetAccessFlags(); 1071 // TODO: One lock per list? 1072 heap_->EnqueuePendingReference(obj, list); 1073 } 1074} 1075 1076void MarkSweep::ScanRoot(const Object* obj) { 1077 ScanObject(obj); 1078} 1079 1080class MarkObjectVisitor { 1081 public: 1082 explicit MarkObjectVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {} 1083 1084 // TODO: Fixme when anotatalysis works with visitors. 1085 void operator()(const Object* /* obj */, const Object* ref, const MemberOffset& /* offset */, 1086 bool /* is_static */) const 1087 NO_THREAD_SAFETY_ANALYSIS { 1088 if (kDebugLocking) { 1089 Locks::mutator_lock_->AssertSharedHeld(Thread::Current()); 1090 Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current()); 1091 } 1092 mark_sweep_->MarkObject(ref); 1093 } 1094 1095 private: 1096 MarkSweep* const mark_sweep_; 1097}; 1098 1099// Scans an object reference. Determines the type of the reference 1100// and dispatches to a specialized scanning routine. 1101void MarkSweep::ScanObject(const Object* obj) { 1102 MarkObjectVisitor visitor(this); 1103 ScanObjectVisit(obj, visitor); 1104} 1105 1106class MarkStackChunk : public Task { 1107 public: 1108 MarkStackChunk(ThreadPool* thread_pool, MarkSweep* mark_sweep, Object** begin, Object** end) 1109 : mark_sweep_(mark_sweep), 1110 thread_pool_(thread_pool), 1111 index_(0), 1112 length_(0), 1113 output_(NULL) { 1114 length_ = end - begin; 1115 if (begin != end) { 1116 // Cost not significant since we only do this for the initial set of mark stack chunks. 1117 memcpy(data_, begin, length_ * sizeof(*begin)); 1118 } 1119 if (kCountTasks) { 1120 ++mark_sweep_->work_chunks_created_; 1121 } 1122 } 1123 1124 ~MarkStackChunk() { 1125 DCHECK(output_ == NULL || output_->length_ == 0); 1126 DCHECK_GE(index_, length_); 1127 delete output_; 1128 if (kCountTasks) { 1129 ++mark_sweep_->work_chunks_deleted_; 1130 } 1131 } 1132 1133 MarkSweep* const mark_sweep_; 1134 ThreadPool* const thread_pool_; 1135 static const size_t max_size = 1 * KB; 1136 // Index of which object we are scanning. Only needs to be atomic if we are doing work stealing. 1137 size_t index_; 1138 // Input / output mark stack. We add newly marked references to data_ until length reaches 1139 // max_size. This is an optimization so that less tasks are created. 1140 // TODO: Investigate using a bounded buffer FIFO. 1141 Object* data_[max_size]; 1142 // How many elements in data_ we need to scan. 1143 size_t length_; 1144 // Output block, newly marked references get added to the ouput block so that another thread can 1145 // scan them. 1146 MarkStackChunk* output_; 1147 1148 class MarkObjectParallelVisitor { 1149 public: 1150 explicit MarkObjectParallelVisitor(MarkStackChunk* chunk_task) : chunk_task_(chunk_task) {} 1151 1152 void operator()(const Object* /* obj */, const Object* ref, 1153 const MemberOffset& /* offset */, bool /* is_static */) const { 1154 if (ref != NULL && chunk_task_->mark_sweep_->MarkObjectParallel(ref)) { 1155 chunk_task_->MarkStackPush(ref); 1156 } 1157 } 1158 1159 private: 1160 MarkStackChunk* const chunk_task_; 1161 }; 1162 1163 // Push an object into the block. 1164 // Don't need to use atomic ++ since we only one thread is writing to an output block at any 1165 // given time. 1166 void Push(Object* obj) { 1167 CHECK(obj != NULL); 1168 data_[length_++] = obj; 1169 } 1170 1171 void MarkStackPush(const Object* obj) { 1172 if (static_cast<size_t>(length_) < max_size) { 1173 Push(const_cast<Object*>(obj)); 1174 } else { 1175 // Internal (thread-local) buffer is full, push to a new buffer instead. 1176 if (UNLIKELY(output_ == NULL)) { 1177 AllocateOutputChunk(); 1178 } else if (UNLIKELY(static_cast<size_t>(output_->length_) == max_size)) { 1179 // Output block is full, queue it up for processing and obtain a new block. 1180 EnqueueOutput(); 1181 AllocateOutputChunk(); 1182 } 1183 output_->Push(const_cast<Object*>(obj)); 1184 } 1185 } 1186 1187 void ScanObject(Object* obj) { 1188 mark_sweep_->ScanObjectVisit(obj, MarkObjectParallelVisitor(this)); 1189 } 1190 1191 void EnqueueOutput() { 1192 if (output_ != NULL) { 1193 uint64_t start = 0; 1194 if (kMeasureOverhead) { 1195 start = NanoTime(); 1196 } 1197 thread_pool_->AddTask(Thread::Current(), output_); 1198 output_ = NULL; 1199 if (kMeasureOverhead) { 1200 mark_sweep_->overhead_time_.fetch_add(NanoTime() - start); 1201 } 1202 } 1203 } 1204 1205 void AllocateOutputChunk() { 1206 uint64_t start = 0; 1207 if (kMeasureOverhead) { 1208 start = NanoTime(); 1209 } 1210 output_ = new MarkStackChunk(thread_pool_, mark_sweep_, NULL, NULL); 1211 if (kMeasureOverhead) { 1212 mark_sweep_->overhead_time_.fetch_add(NanoTime() - start); 1213 } 1214 } 1215 1216 void Finalize() { 1217 EnqueueOutput(); 1218 delete this; 1219 } 1220 1221 // Scans all of the objects 1222 virtual void Run(Thread* self) { 1223 size_t index; 1224 while ((index = index_++) < length_) { 1225 if (kUseMarkStackPrefetch) { 1226 static const size_t prefetch_look_ahead = 1; 1227 __builtin_prefetch(data_[std::min(index + prefetch_look_ahead, length_ - 1)]); 1228 } 1229 Object* obj = data_[index]; 1230 DCHECK(obj != NULL); 1231 ScanObject(obj); 1232 } 1233 } 1234}; 1235 1236void MarkSweep::ProcessMarkStackParallel() { 1237 CHECK(kDisableFinger) << "parallel mark stack processing cannot work when finger is enabled"; 1238 Thread* self = Thread::Current(); 1239 ThreadPool* thread_pool = GetHeap()->GetThreadPool(); 1240 // Split the current mark stack up into work tasks. 1241 const size_t num_threads = thread_pool->GetThreadCount(); 1242 const size_t stack_size = mark_stack_->Size(); 1243 const size_t chunk_size = 1244 std::min((stack_size + num_threads - 1) / num_threads, 1245 static_cast<size_t>(MarkStackChunk::max_size)); 1246 size_t index = 0; 1247 for (size_t i = 0; i < num_threads || index < stack_size; ++i) { 1248 Object** begin = &mark_stack_->Begin()[std::min(stack_size, index)]; 1249 Object** end = &mark_stack_->Begin()[std::min(stack_size, index + chunk_size)]; 1250 index += chunk_size; 1251 thread_pool->AddTask(self, new MarkStackChunk(thread_pool, this, begin, end)); 1252 } 1253 thread_pool->StartWorkers(self); 1254 thread_pool->Wait(self, true, true); 1255 mark_stack_->Reset(); 1256 // LOG(INFO) << "Idle wait time " << PrettyDuration(thread_pool->GetWaitTime()); 1257 CHECK_EQ(work_chunks_created_, work_chunks_deleted_) << " some of the work chunks were leaked"; 1258} 1259 1260// Scan anything that's on the mark stack. 1261void MarkSweep::ProcessMarkStack() { 1262 ThreadPool* thread_pool = GetHeap()->GetThreadPool(); 1263 if (kParallelMarkStack && thread_pool != NULL && thread_pool->GetThreadCount() > 0) { 1264 ProcessMarkStackParallel(); 1265 return; 1266 } 1267 1268 if (kUseMarkStackPrefetch) { 1269 const size_t fifo_size = 4; 1270 const size_t fifo_mask = fifo_size - 1; 1271 const Object* fifo[fifo_size]; 1272 for (size_t i = 0; i < fifo_size; ++i) { 1273 fifo[i] = NULL; 1274 } 1275 size_t fifo_pos = 0; 1276 size_t fifo_count = 0; 1277 for (;;) { 1278 const Object* obj = fifo[fifo_pos & fifo_mask]; 1279 if (obj != NULL) { 1280 ScanObject(obj); 1281 fifo[fifo_pos & fifo_mask] = NULL; 1282 --fifo_count; 1283 } 1284 1285 if (!mark_stack_->IsEmpty()) { 1286 const Object* obj = mark_stack_->PopBack(); 1287 DCHECK(obj != NULL); 1288 fifo[fifo_pos & fifo_mask] = obj; 1289 __builtin_prefetch(obj); 1290 fifo_count++; 1291 } 1292 fifo_pos++; 1293 1294 if (!fifo_count) { 1295 CHECK(mark_stack_->IsEmpty()) << mark_stack_->Size(); 1296 break; 1297 } 1298 } 1299 } else { 1300 while (!mark_stack_->IsEmpty()) { 1301 const Object* obj = mark_stack_->PopBack(); 1302 DCHECK(obj != NULL); 1303 ScanObject(obj); 1304 } 1305 } 1306} 1307 1308// Walks the reference list marking any references subject to the 1309// reference clearing policy. References with a black referent are 1310// removed from the list. References with white referents biased 1311// toward saving are blackened and also removed from the list. 1312void MarkSweep::PreserveSomeSoftReferences(Object** list) { 1313 DCHECK(list != NULL); 1314 Object* clear = NULL; 1315 size_t counter = 0; 1316 1317 DCHECK(mark_stack_->IsEmpty()); 1318 1319 while (*list != NULL) { 1320 Object* ref = heap_->DequeuePendingReference(list); 1321 Object* referent = heap_->GetReferenceReferent(ref); 1322 if (referent == NULL) { 1323 // Referent was cleared by the user during marking. 1324 continue; 1325 } 1326 bool is_marked = IsMarked(referent); 1327 if (!is_marked && ((++counter) & 1)) { 1328 // Referent is white and biased toward saving, mark it. 1329 MarkObject(referent); 1330 is_marked = true; 1331 } 1332 if (!is_marked) { 1333 // Referent is white, queue it for clearing. 1334 heap_->EnqueuePendingReference(ref, &clear); 1335 } 1336 } 1337 *list = clear; 1338 // Restart the mark with the newly black references added to the 1339 // root set. 1340 ProcessMarkStack(); 1341} 1342 1343inline bool MarkSweep::IsMarked(const Object* object) const 1344 SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) { 1345 if (object >= immune_begin_ && object < immune_end_) { 1346 return true; 1347 } 1348 DCHECK(current_mark_bitmap_ != NULL); 1349 if (current_mark_bitmap_->HasAddress(object)) { 1350 return current_mark_bitmap_->Test(object); 1351 } 1352 return heap_->GetMarkBitmap()->Test(object); 1353} 1354 1355 1356// Unlink the reference list clearing references objects with white 1357// referents. Cleared references registered to a reference queue are 1358// scheduled for appending by the heap worker thread. 1359void MarkSweep::ClearWhiteReferences(Object** list) { 1360 DCHECK(list != NULL); 1361 while (*list != NULL) { 1362 Object* ref = heap_->DequeuePendingReference(list); 1363 Object* referent = heap_->GetReferenceReferent(ref); 1364 if (referent != NULL && !IsMarked(referent)) { 1365 // Referent is white, clear it. 1366 heap_->ClearReferenceReferent(ref); 1367 if (heap_->IsEnqueuable(ref)) { 1368 heap_->EnqueueReference(ref, &cleared_reference_list_); 1369 } 1370 } 1371 } 1372 DCHECK(*list == NULL); 1373} 1374 1375// Enqueues finalizer references with white referents. White 1376// referents are blackened, moved to the zombie field, and the 1377// referent field is cleared. 1378void MarkSweep::EnqueueFinalizerReferences(Object** list) { 1379 DCHECK(list != NULL); 1380 MemberOffset zombie_offset = heap_->GetFinalizerReferenceZombieOffset(); 1381 bool has_enqueued = false; 1382 while (*list != NULL) { 1383 Object* ref = heap_->DequeuePendingReference(list); 1384 Object* referent = heap_->GetReferenceReferent(ref); 1385 if (referent != NULL && !IsMarked(referent)) { 1386 MarkObject(referent); 1387 // If the referent is non-null the reference must queuable. 1388 DCHECK(heap_->IsEnqueuable(ref)); 1389 ref->SetFieldObject(zombie_offset, referent, false); 1390 heap_->ClearReferenceReferent(ref); 1391 heap_->EnqueueReference(ref, &cleared_reference_list_); 1392 has_enqueued = true; 1393 } 1394 } 1395 if (has_enqueued) { 1396 ProcessMarkStack(); 1397 } 1398 DCHECK(*list == NULL); 1399} 1400 1401// Process reference class instances and schedule finalizations. 1402void MarkSweep::ProcessReferences(Object** soft_references, bool clear_soft, 1403 Object** weak_references, 1404 Object** finalizer_references, 1405 Object** phantom_references) { 1406 DCHECK(soft_references != NULL); 1407 DCHECK(weak_references != NULL); 1408 DCHECK(finalizer_references != NULL); 1409 DCHECK(phantom_references != NULL); 1410 1411 // Unless we are in the zygote or required to clear soft references 1412 // with white references, preserve some white referents. 1413 if (!clear_soft && !Runtime::Current()->IsZygote()) { 1414 PreserveSomeSoftReferences(soft_references); 1415 } 1416 1417 // Clear all remaining soft and weak references with white 1418 // referents. 1419 ClearWhiteReferences(soft_references); 1420 ClearWhiteReferences(weak_references); 1421 1422 // Preserve all white objects with finalize methods and schedule 1423 // them for finalization. 1424 EnqueueFinalizerReferences(finalizer_references); 1425 1426 // Clear all f-reachable soft and weak references with white 1427 // referents. 1428 ClearWhiteReferences(soft_references); 1429 ClearWhiteReferences(weak_references); 1430 1431 // Clear all phantom references with white referents. 1432 ClearWhiteReferences(phantom_references); 1433 1434 // At this point all reference lists should be empty. 1435 DCHECK(*soft_references == NULL); 1436 DCHECK(*weak_references == NULL); 1437 DCHECK(*finalizer_references == NULL); 1438 DCHECK(*phantom_references == NULL); 1439} 1440 1441void MarkSweep::UnBindBitmaps() { 1442 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 1443 // TODO: C++0x 1444 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 1445 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 1446 space::ContinuousSpace* space = *it; 1447 if (space->IsDlMallocSpace()) { 1448 space::DlMallocSpace* alloc_space = space->AsDlMallocSpace(); 1449 if (alloc_space->temp_bitmap_.get() != NULL) { 1450 // At this point, the temp_bitmap holds our old mark bitmap. 1451 accounting::SpaceBitmap* new_bitmap = alloc_space->temp_bitmap_.release(); 1452 GetHeap()->GetMarkBitmap()->ReplaceBitmap(alloc_space->mark_bitmap_.get(), new_bitmap); 1453 CHECK_EQ(alloc_space->mark_bitmap_.release(), alloc_space->live_bitmap_.get()); 1454 alloc_space->mark_bitmap_.reset(new_bitmap); 1455 DCHECK(alloc_space->temp_bitmap_.get() == NULL); 1456 } 1457 } 1458 } 1459} 1460 1461void MarkSweep::FinishPhase() { 1462 // Can't enqueue referneces if we hold the mutator lock. 1463 Object* cleared_references = GetClearedReferences(); 1464 Heap* heap = GetHeap(); 1465 heap->EnqueueClearedReferences(&cleared_references); 1466 1467 heap->PostGcVerification(this); 1468 1469 timings_.NewSplit("GrowForUtilization"); 1470 heap->GrowForUtilization(GetGcType(), GetDurationNs()); 1471 1472 timings_.NewSplit("RequestHeapTrim"); 1473 heap->RequestHeapTrim(); 1474 1475 // Update the cumulative statistics 1476 total_time_ns_ += GetDurationNs(); 1477 total_paused_time_ns_ += std::accumulate(GetPauseTimes().begin(), GetPauseTimes().end(), 0, 1478 std::plus<uint64_t>()); 1479 total_freed_objects_ += GetFreedObjects(); 1480 total_freed_bytes_ += GetFreedBytes(); 1481 1482 // Ensure that the mark stack is empty. 1483 CHECK(mark_stack_->IsEmpty()); 1484 1485 if (kCountScannedTypes) { 1486 VLOG(gc) << "MarkSweep scanned classes=" << class_count_ << " arrays=" << array_count_ 1487 << " other=" << other_count_; 1488 } 1489 1490 if (kCountTasks) { 1491 VLOG(gc) << "Total number of work chunks allocated: " << work_chunks_created_; 1492 } 1493 1494 if (kMeasureOverhead) { 1495 VLOG(gc) << "Overhead time " << PrettyDuration(overhead_time_); 1496 } 1497 1498 if (kProfileLargeObjects) { 1499 VLOG(gc) << "Large objects tested " << large_object_test_ << " marked " << large_object_mark_; 1500 } 1501 1502 if (kCountClassesMarked) { 1503 VLOG(gc) << "Classes marked " << classes_marked_; 1504 } 1505 1506 if (kCountJavaLangRefs) { 1507 VLOG(gc) << "References scanned " << reference_count_; 1508 } 1509 1510 // Update the cumulative loggers. 1511 cumulative_timings_.Start(); 1512 cumulative_timings_.AddNewLogger(timings_); 1513 cumulative_timings_.End(); 1514 1515 // Clear all of the spaces' mark bitmaps. 1516 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 1517 // TODO: C++0x 1518 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 1519 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 1520 space::ContinuousSpace* space = *it; 1521 if (space->GetGcRetentionPolicy() != space::kGcRetentionPolicyNeverCollect) { 1522 space->GetMarkBitmap()->Clear(); 1523 } 1524 } 1525 mark_stack_->Reset(); 1526 1527 // Reset the marked large objects. 1528 space::LargeObjectSpace* large_objects = GetHeap()->GetLargeObjectsSpace(); 1529 large_objects->GetMarkObjects()->Clear(); 1530} 1531 1532} // namespace collector 1533} // namespace gc 1534} // namespace art 1535