mark_sweep.cc revision 4b95e8fad803ad307fa09c11c08894544e07a731
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 namespace art::mirror; 54 55namespace art { 56namespace gc { 57namespace collector { 58 59// Performance options. 60static const bool kParallelMarkStack = true; 61static const bool kDisableFinger = true; // TODO: Fix, bit rotten. 62static const bool kUseMarkStackPrefetch = true; 63 64// Profiling and information flags. 65static const bool kCountClassesMarked = false; 66static const bool kProfileLargeObjects = false; 67static const bool kMeasureOverhead = false; 68static const bool kCountTasks = false; 69static const bool kCountJavaLangRefs = false; 70 71class SetFingerVisitor { 72 public: 73 SetFingerVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) { 74 } 75 76 void operator ()(void* finger) const { 77 mark_sweep_->SetFinger(reinterpret_cast<Object*>(finger)); 78 } 79 80 private: 81 MarkSweep* const mark_sweep_; 82}; 83 84void MarkSweep::ImmuneSpace(space::ContinuousSpace* space) { 85 // Bind live to mark bitmap if necessary. 86 if (space->GetLiveBitmap() != space->GetMarkBitmap()) { 87 BindLiveToMarkBitmap(space); 88 } 89 90 // Add the space to the immune region. 91 if (immune_begin_ == NULL) { 92 DCHECK(immune_end_ == NULL); 93 SetImmuneRange(reinterpret_cast<Object*>(space->Begin()), 94 reinterpret_cast<Object*>(space->End())); 95 } else { 96 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 97 const space::ContinuousSpace* prev_space = NULL; 98 // Find out if the previous space is immune. 99 // TODO: C++0x 100 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 101 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 102 if (*it == space) { 103 break; 104 } 105 prev_space = *it; 106 } 107 108 // If previous space was immune, then extend the immune region. Relies on continuous spaces 109 // being sorted by Heap::AddContinuousSpace. 110 if (prev_space != NULL && 111 immune_begin_ <= reinterpret_cast<Object*>(prev_space->Begin()) && 112 immune_end_ >= reinterpret_cast<Object*>(prev_space->End())) { 113 immune_begin_ = std::min(reinterpret_cast<Object*>(space->Begin()), immune_begin_); 114 immune_end_ = std::max(reinterpret_cast<Object*>(space->End()), immune_end_); 115 } 116 } 117} 118 119void MarkSweep::BindBitmaps() { 120 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 121 WriterMutexLock mu(Thread::Current(), *Locks::heap_bitmap_lock_); 122 123 // Mark all of the spaces we never collect as immune. 124 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 125 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 126 space::ContinuousSpace* space = *it; 127 if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyNeverCollect) { 128 ImmuneSpace(space); 129 } 130 } 131} 132 133MarkSweep::MarkSweep(Heap* heap, bool is_concurrent, const std::string& name_prefix) 134 : GarbageCollector(heap, 135 name_prefix + (name_prefix.empty() ? "" : " ") + 136 (is_concurrent ? "concurrent mark sweep": "mark sweep")), 137 current_mark_bitmap_(NULL), 138 java_lang_Class_(NULL), 139 mark_stack_(NULL), 140 finger_(NULL), 141 immune_begin_(NULL), 142 immune_end_(NULL), 143 soft_reference_list_(NULL), 144 weak_reference_list_(NULL), 145 finalizer_reference_list_(NULL), 146 phantom_reference_list_(NULL), 147 cleared_reference_list_(NULL), 148 gc_barrier_(new Barrier(0)), 149 large_object_lock_("mark sweep large object lock", kMarkSweepLargeObjectLock), 150 mark_stack_expand_lock_("mark sweep mark stack expand lock"), 151 is_concurrent_(is_concurrent), 152 clear_soft_references_(false) { 153} 154 155void MarkSweep::InitializePhase() { 156 timings_.Reset(); 157 timings_.StartSplit("InitializePhase"); 158 mark_stack_ = GetHeap()->mark_stack_.get(); 159 DCHECK(mark_stack_ != NULL); 160 finger_ = NULL; 161 SetImmuneRange(NULL, NULL); 162 soft_reference_list_ = NULL; 163 weak_reference_list_ = NULL; 164 finalizer_reference_list_ = NULL; 165 phantom_reference_list_ = NULL; 166 cleared_reference_list_ = NULL; 167 freed_bytes_ = 0; 168 freed_objects_ = 0; 169 class_count_ = 0; 170 array_count_ = 0; 171 other_count_ = 0; 172 large_object_test_ = 0; 173 large_object_mark_ = 0; 174 classes_marked_ = 0; 175 overhead_time_ = 0; 176 work_chunks_created_ = 0; 177 work_chunks_deleted_ = 0; 178 reference_count_ = 0; 179 java_lang_Class_ = Class::GetJavaLangClass(); 180 CHECK(java_lang_Class_ != NULL); 181 FindDefaultMarkBitmap(); 182 // Do any pre GC verification. 183 heap_->PreGcVerification(this); 184} 185 186void MarkSweep::ProcessReferences(Thread* self) { 187 timings_.NewSplit("ProcessReferences"); 188 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 189 ProcessReferences(&soft_reference_list_, clear_soft_references_, &weak_reference_list_, 190 &finalizer_reference_list_, &phantom_reference_list_); 191} 192 193bool MarkSweep::HandleDirtyObjectsPhase() { 194 Thread* self = Thread::Current(); 195 accounting::ObjectStack* allocation_stack = GetHeap()->allocation_stack_.get(); 196 Locks::mutator_lock_->AssertExclusiveHeld(self); 197 198 { 199 timings_.NewSplit("ReMarkRoots"); 200 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 201 202 // Re-mark root set. 203 ReMarkRoots(); 204 205 // Scan dirty objects, this is only required if we are not doing concurrent GC. 206 RecursiveMarkDirtyObjects(accounting::CardTable::kCardDirty); 207 } 208 209 ProcessReferences(self); 210 211 // Only need to do this if we have the card mark verification on, and only during concurrent GC. 212 if (GetHeap()->verify_missing_card_marks_) { 213 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 214 // This second sweep makes sure that we don't have any objects in the live stack which point to 215 // freed objects. These cause problems since their references may be previously freed objects. 216 SweepArray(allocation_stack, false); 217 } else { 218 timings_.NewSplit("UnMarkAllocStack"); 219 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 220 // The allocation stack contains things allocated since the start of the GC. These may have been 221 // marked during this GC meaning they won't be eligible for reclaiming in the next sticky GC. 222 // Remove these objects from the mark bitmaps so that they will be eligible for sticky 223 // collection. 224 heap_->UnMarkAllocStack(GetHeap()->alloc_space_->GetMarkBitmap(), 225 GetHeap()->large_object_space_->GetMarkObjects(), 226 allocation_stack); 227 } 228 return true; 229} 230 231bool MarkSweep::IsConcurrent() const { 232 return is_concurrent_; 233} 234 235void MarkSweep::MarkingPhase() { 236 Heap* heap = GetHeap(); 237 Thread* self = Thread::Current(); 238 239 timings_.NewSplit("BindBitmaps"); 240 BindBitmaps(); 241 FindDefaultMarkBitmap(); 242 // Process dirty cards and add dirty cards to mod union tables. 243 heap->ProcessCards(timings_); 244 245 // Need to do this before the checkpoint since we don't want any threads to add references to 246 // the live stack during the recursive mark. 247 timings_.NewSplit("SwapStacks"); 248 heap->SwapStacks(); 249 250 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 251 if (Locks::mutator_lock_->IsExclusiveHeld(self)) { 252 // If we exclusively hold the mutator lock, all threads must be suspended. 253 timings_.NewSplit("MarkRoots"); 254 MarkRoots(); 255 } else { 256 timings_.NewSplit("MarkRootsCheckpoint"); 257 MarkRootsCheckpoint(self); 258 timings_.NewSplit("MarkNonThreadRoots"); 259 MarkNonThreadRoots(); 260 } 261 timings_.NewSplit("MarkConcurrentRoots"); 262 MarkConcurrentRoots(); 263 264 heap->UpdateAndMarkModUnion(this, timings_, GetGcType()); 265 MarkReachableObjects(); 266} 267 268void MarkSweep::MarkReachableObjects() { 269 // Mark everything allocated since the last as GC live so that we can sweep concurrently, 270 // knowing that new allocations won't be marked as live. 271 timings_.NewSplit("MarkStackAsLive"); 272 accounting::ObjectStack* live_stack = heap_->GetLiveStack(); 273 heap_->MarkAllocStack(heap_->alloc_space_->GetLiveBitmap(), 274 heap_->large_object_space_->GetLiveObjects(), 275 live_stack); 276 live_stack->Reset(); 277 // Recursively mark all the non-image bits set in the mark bitmap. 278 RecursiveMark(); 279 DisableFinger(); 280} 281 282void MarkSweep::ReclaimPhase() { 283 Thread* self = Thread::Current(); 284 285 if (!IsConcurrent()) { 286 ProcessReferences(self); 287 } 288 289 // Before freeing anything, lets verify the heap. 290 if (kIsDebugBuild) { 291 ReaderMutexLock mu(self, *Locks::heap_bitmap_lock_); 292 VerifyImageRoots(); 293 } 294 heap_->PreSweepingGcVerification(this); 295 296 { 297 WriterMutexLock mu(self, *Locks::heap_bitmap_lock_); 298 299 // Reclaim unmarked objects. 300 Sweep(false); 301 302 // Swap the live and mark bitmaps for each space which we modified space. This is an 303 // optimization that enables us to not clear live bits inside of the sweep. Only swaps unbound 304 // bitmaps. 305 timings_.NewSplit("SwapBitmaps"); 306 SwapBitmaps(); 307 308 // Unbind the live and mark bitmaps. 309 UnBindBitmaps(); 310 } 311} 312 313void MarkSweep::SetImmuneRange(Object* begin, Object* end) { 314 immune_begin_ = begin; 315 immune_end_ = end; 316} 317 318void MarkSweep::FindDefaultMarkBitmap() { 319 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 320 // TODO: C++0x 321 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 322 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 323 space::ContinuousSpace* space = *it; 324 if (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) { 325 current_mark_bitmap_ = (*it)->GetMarkBitmap(); 326 CHECK(current_mark_bitmap_ != NULL); 327 return; 328 } 329 } 330 GetHeap()->DumpSpaces(); 331 LOG(FATAL) << "Could not find a default mark bitmap"; 332} 333 334void MarkSweep::ExpandMarkStack() { 335 // Rare case, no need to have Thread::Current be a parameter. 336 MutexLock mu(Thread::Current(), mark_stack_expand_lock_); 337 if (UNLIKELY(mark_stack_->Size() < mark_stack_->Capacity())) { 338 // Someone else acquired the lock and expanded the mark stack before us. 339 return; 340 } 341 std::vector<Object*> temp; 342 temp.insert(temp.begin(), mark_stack_->Begin(), mark_stack_->End()); 343 mark_stack_->Resize(mark_stack_->Capacity() * 2); 344 for (size_t i = 0; i < temp.size(); ++i) { 345 mark_stack_->PushBack(temp[i]); 346 } 347} 348 349inline void MarkSweep::MarkObjectNonNullParallel(const Object* obj, bool check_finger) { 350 DCHECK(obj != NULL); 351 if (MarkObjectParallel(obj)) { 352 if (kDisableFinger || (check_finger && obj < finger_)) { 353 while (UNLIKELY(!mark_stack_->AtomicPushBack(const_cast<Object*>(obj)))) { 354 // Only reason a push can fail is that the mark stack is full. 355 ExpandMarkStack(); 356 } 357 } 358 } 359} 360 361inline void MarkSweep::MarkObjectNonNull(const Object* obj, bool check_finger) { 362 DCHECK(obj != NULL); 363 364 if (obj >= immune_begin_ && obj < immune_end_) { 365 DCHECK(IsMarked(obj)); 366 return; 367 } 368 369 // Try to take advantage of locality of references within a space, failing this find the space 370 // the hard way. 371 accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_; 372 if (UNLIKELY(!object_bitmap->HasAddress(obj))) { 373 accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj); 374 if (LIKELY(new_bitmap != NULL)) { 375 object_bitmap = new_bitmap; 376 } else { 377 MarkLargeObject(obj); 378 return; 379 } 380 } 381 382 // This object was not previously marked. 383 if (!object_bitmap->Test(obj)) { 384 object_bitmap->Set(obj); 385 if (kDisableFinger || (check_finger && obj < finger_)) { 386 // Do we need to expand the mark stack? 387 if (UNLIKELY(mark_stack_->Size() >= mark_stack_->Capacity())) { 388 ExpandMarkStack(); 389 } 390 // The object must be pushed on to the mark stack. 391 mark_stack_->PushBack(const_cast<Object*>(obj)); 392 } 393 } 394} 395 396// Rare case, probably not worth inlining since it will increase instruction cache miss rate. 397bool MarkSweep::MarkLargeObject(const Object* obj) { 398 // TODO: support >1 discontinuous space. 399 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 400 accounting::SpaceSetMap* large_objects = large_object_space->GetMarkObjects(); 401 if (kProfileLargeObjects) { 402 ++large_object_test_; 403 } 404 if (UNLIKELY(!large_objects->Test(obj))) { 405 if (!large_object_space->Contains(obj)) { 406 LOG(ERROR) << "Tried to mark " << obj << " not contained by any spaces"; 407 LOG(ERROR) << "Attempting see if it's a bad root"; 408 VerifyRoots(); 409 LOG(FATAL) << "Can't mark bad root"; 410 } 411 if (kProfileLargeObjects) { 412 ++large_object_mark_; 413 } 414 large_objects->Set(obj); 415 // Don't need to check finger since large objects never have any object references. 416 return true; 417 } 418 return false; 419} 420 421inline bool MarkSweep::MarkObjectParallel(const Object* obj) { 422 DCHECK(obj != NULL); 423 424 if (obj >= immune_begin_ && obj < immune_end_) { 425 DCHECK(IsMarked(obj)); 426 return false; 427 } 428 429 // Try to take advantage of locality of references within a space, failing this find the space 430 // the hard way. 431 accounting::SpaceBitmap* object_bitmap = current_mark_bitmap_; 432 if (UNLIKELY(!object_bitmap->HasAddress(obj))) { 433 accounting::SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetContinuousSpaceBitmap(obj); 434 if (new_bitmap != NULL) { 435 object_bitmap = new_bitmap; 436 } else { 437 // TODO: Remove the Thread::Current here? 438 // TODO: Convert this to some kind of atomic marking? 439 MutexLock mu(Thread::Current(), large_object_lock_); 440 return MarkLargeObject(obj); 441 } 442 } 443 444 // Return true if the object was not previously marked. 445 return !object_bitmap->AtomicTestAndSet(obj); 446} 447 448// Used to mark objects when recursing. Recursion is done by moving 449// the finger across the bitmaps in address order and marking child 450// objects. Any newly-marked objects whose addresses are lower than 451// the finger won't be visited by the bitmap scan, so those objects 452// need to be added to the mark stack. 453void MarkSweep::MarkObject(const Object* obj) { 454 if (obj != NULL) { 455 MarkObjectNonNull(obj, true); 456 } 457} 458 459void MarkSweep::MarkRoot(const Object* obj) { 460 if (obj != NULL) { 461 MarkObjectNonNull(obj, false); 462 } 463} 464 465void MarkSweep::MarkRootParallelCallback(const Object* root, void* arg) { 466 DCHECK(root != NULL); 467 DCHECK(arg != NULL); 468 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 469 mark_sweep->MarkObjectNonNullParallel(root, false); 470} 471 472void MarkSweep::MarkObjectCallback(const Object* root, void* arg) { 473 DCHECK(root != NULL); 474 DCHECK(arg != NULL); 475 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 476 mark_sweep->MarkObjectNonNull(root, false); 477} 478 479void MarkSweep::ReMarkObjectVisitor(const Object* root, void* arg) { 480 DCHECK(root != NULL); 481 DCHECK(arg != NULL); 482 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 483 mark_sweep->MarkObjectNonNull(root, true); 484} 485 486void MarkSweep::VerifyRootCallback(const Object* root, void* arg, size_t vreg, 487 const StackVisitor* visitor) { 488 reinterpret_cast<MarkSweep*>(arg)->VerifyRoot(root, vreg, visitor); 489} 490 491void MarkSweep::VerifyRoot(const Object* root, size_t vreg, const StackVisitor* visitor) { 492 // See if the root is on any space bitmap. 493 if (GetHeap()->GetLiveBitmap()->GetContinuousSpaceBitmap(root) == NULL) { 494 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 495 if (!large_object_space->Contains(root)) { 496 LOG(ERROR) << "Found invalid root: " << root; 497 if (visitor != NULL) { 498 LOG(ERROR) << visitor->DescribeLocation() << " in VReg: " << vreg; 499 } 500 } 501 } 502} 503 504void MarkSweep::VerifyRoots() { 505 Runtime::Current()->GetThreadList()->VerifyRoots(VerifyRootCallback, this); 506} 507 508// Marks all objects in the root set. 509void MarkSweep::MarkRoots() { 510 Runtime::Current()->VisitNonConcurrentRoots(MarkObjectCallback, this); 511} 512 513void MarkSweep::MarkNonThreadRoots() { 514 Runtime::Current()->VisitNonThreadRoots(MarkObjectCallback, this); 515} 516 517void MarkSweep::MarkConcurrentRoots() { 518 // Visit all runtime roots and clear dirty flags. 519 Runtime::Current()->VisitConcurrentRoots(MarkObjectCallback, this, false, true); 520} 521 522class CheckObjectVisitor { 523 public: 524 CheckObjectVisitor(MarkSweep* const mark_sweep) 525 : mark_sweep_(mark_sweep) { 526 527 } 528 529 void operator ()(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) const 530 NO_THREAD_SAFETY_ANALYSIS { 531 if (kDebugLocking) { 532 Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current()); 533 } 534 mark_sweep_->CheckReference(obj, ref, offset, is_static); 535 } 536 537 private: 538 MarkSweep* const mark_sweep_; 539}; 540 541void MarkSweep::CheckObject(const Object* obj) { 542 DCHECK(obj != NULL); 543 CheckObjectVisitor visitor(this); 544 VisitObjectReferences(obj, visitor); 545} 546 547void MarkSweep::VerifyImageRootVisitor(Object* root, void* arg) { 548 DCHECK(root != NULL); 549 DCHECK(arg != NULL); 550 MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg); 551 DCHECK(mark_sweep->heap_->GetMarkBitmap()->Test(root)); 552 mark_sweep->CheckObject(root); 553} 554 555void MarkSweep::BindLiveToMarkBitmap(space::ContinuousSpace* space) { 556 CHECK(space->IsDlMallocSpace()); 557 space::DlMallocSpace* alloc_space = space->AsDlMallocSpace(); 558 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 559 accounting::SpaceBitmap* mark_bitmap = alloc_space->mark_bitmap_.release(); 560 GetHeap()->GetMarkBitmap()->ReplaceBitmap(mark_bitmap, live_bitmap); 561 alloc_space->temp_bitmap_.reset(mark_bitmap); 562 alloc_space->mark_bitmap_.reset(live_bitmap); 563} 564 565class ScanObjectVisitor { 566 public: 567 ScanObjectVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) { 568 } 569 570 // TODO: Fixme when anotatalysis works with visitors. 571 void operator ()(const Object* obj) const NO_THREAD_SAFETY_ANALYSIS { 572 if (kDebugLocking) { 573 Locks::mutator_lock_->AssertSharedHeld(Thread::Current()); 574 Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current()); 575 } 576 mark_sweep_->ScanObject(obj); 577 } 578 579 private: 580 MarkSweep* const mark_sweep_; 581}; 582 583void MarkSweep::ScanGrayObjects(byte minimum_age) { 584 accounting::CardTable* card_table = GetHeap()->GetCardTable(); 585 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 586 ScanObjectVisitor visitor(this); 587 SetFingerVisitor finger_visitor(this); 588 // TODO: C++0x 589 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 590 for (It it = spaces.begin(), space_end = spaces.end(); it != space_end; ++it) { 591 space::ContinuousSpace* space = *it; 592 switch (space->GetGcRetentionPolicy()) { 593 case space::kGcRetentionPolicyNeverCollect: 594 timings_.NewSplit("ScanGrayImageSpaceObjects"); 595 break; 596 case space::kGcRetentionPolicyFullCollect: 597 timings_.NewSplit("ScanGrayZygoteSpaceObjects"); 598 break; 599 case space::kGcRetentionPolicyAlwaysCollect: 600 timings_.NewSplit("ScanGrayAllocSpaceObjects"); 601 break; 602 } 603 byte* begin = space->Begin(); 604 byte* end = space->End(); 605 // Image spaces are handled properly since live == marked for them. 606 accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap(); 607 card_table->Scan(mark_bitmap, begin, end, visitor, finger_visitor, minimum_age); 608 } 609} 610 611class CheckBitmapVisitor { 612 public: 613 CheckBitmapVisitor(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) { 614 } 615 616 void operator ()(const Object* obj) const NO_THREAD_SAFETY_ANALYSIS { 617 if (kDebugLocking) { 618 Locks::heap_bitmap_lock_->AssertSharedHeld(Thread::Current()); 619 } 620 DCHECK(obj != NULL); 621 mark_sweep_->CheckObject(obj); 622 } 623 624 private: 625 MarkSweep* mark_sweep_; 626}; 627 628void MarkSweep::VerifyImageRoots() { 629 // Verify roots ensures that all the references inside the image space point 630 // objects which are either in the image space or marked objects in the alloc 631 // space 632 CheckBitmapVisitor visitor(this); 633 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 634 // TODO: C++0x 635 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 636 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 637 if ((*it)->IsImageSpace()) { 638 space::ImageSpace* space = (*it)->AsImageSpace(); 639 uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin()); 640 uintptr_t end = reinterpret_cast<uintptr_t>(space->End()); 641 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 642 DCHECK(live_bitmap != NULL); 643 live_bitmap->VisitMarkedRange(begin, end, visitor, VoidFunctor()); 644 } 645 } 646} 647 648// Populates the mark stack based on the set of marked objects and 649// recursively marks until the mark stack is emptied. 650void MarkSweep::RecursiveMark() { 651 timings_.NewSplit("RecursiveMark"); 652 // RecursiveMark will build the lists of known instances of the Reference classes. 653 // See DelayReferenceReferent for details. 654 CHECK(soft_reference_list_ == NULL); 655 CHECK(weak_reference_list_ == NULL); 656 CHECK(finalizer_reference_list_ == NULL); 657 CHECK(phantom_reference_list_ == NULL); 658 CHECK(cleared_reference_list_ == NULL); 659 660 const bool partial = GetGcType() == kGcTypePartial; 661 SetFingerVisitor set_finger_visitor(this); 662 ScanObjectVisitor scan_visitor(this); 663 if (!kDisableFinger) { 664 finger_ = NULL; 665 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 666 // TODO: C++0x 667 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 668 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 669 space::ContinuousSpace* space = *it; 670 if ((space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect) || 671 (!partial && space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect)) { 672 current_mark_bitmap_ = space->GetMarkBitmap(); 673 if (current_mark_bitmap_ == NULL) { 674 GetHeap()->DumpSpaces(); 675 LOG(FATAL) << "invalid bitmap"; 676 } 677 // This function does not handle heap end increasing, so we must use the space end. 678 uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin()); 679 uintptr_t end = reinterpret_cast<uintptr_t>(space->End()); 680 current_mark_bitmap_->VisitMarkedRange(begin, end, scan_visitor, set_finger_visitor); 681 } 682 } 683 } 684 DisableFinger(); 685 timings_.NewSplit("ProcessMarkStack"); 686 ProcessMarkStack(); 687} 688 689bool MarkSweep::IsMarkedCallback(const Object* object, void* arg) { 690 return 691 reinterpret_cast<MarkSweep*>(arg)->IsMarked(object) || 692 !reinterpret_cast<MarkSweep*>(arg)->GetHeap()->GetLiveBitmap()->Test(object); 693} 694 695void MarkSweep::RecursiveMarkDirtyObjects(byte minimum_age) { 696 ScanGrayObjects(minimum_age); 697 timings_.NewSplit("ProcessMarkStack"); 698 ProcessMarkStack(); 699} 700 701void MarkSweep::ReMarkRoots() { 702 Runtime::Current()->VisitRoots(ReMarkObjectVisitor, this, true, true); 703} 704 705void MarkSweep::SweepJniWeakGlobals(IsMarkedTester is_marked, void* arg) { 706 JavaVMExt* vm = Runtime::Current()->GetJavaVM(); 707 MutexLock mu(Thread::Current(), vm->weak_globals_lock); 708 IndirectReferenceTable* table = &vm->weak_globals; 709 typedef IndirectReferenceTable::iterator It; // TODO: C++0x auto 710 for (It it = table->begin(), end = table->end(); it != end; ++it) { 711 const Object** entry = *it; 712 if (!is_marked(*entry, arg)) { 713 *entry = kClearedJniWeakGlobal; 714 } 715 } 716} 717 718struct ArrayMarkedCheck { 719 accounting::ObjectStack* live_stack; 720 MarkSweep* mark_sweep; 721}; 722 723// Either marked or not live. 724bool MarkSweep::IsMarkedArrayCallback(const Object* object, void* arg) { 725 ArrayMarkedCheck* array_check = reinterpret_cast<ArrayMarkedCheck*>(arg); 726 if (array_check->mark_sweep->IsMarked(object)) { 727 return true; 728 } 729 accounting::ObjectStack* live_stack = array_check->live_stack; 730 return std::find(live_stack->Begin(), live_stack->End(), object) == live_stack->End(); 731} 732 733void MarkSweep::SweepSystemWeaksArray(accounting::ObjectStack* allocations) { 734 Runtime* runtime = Runtime::Current(); 735 // The callbacks check 736 // !is_marked where is_marked is the callback but we want 737 // !IsMarked && IsLive 738 // So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive). 739 // Or for swapped (IsLive || !IsMarked). 740 741 ArrayMarkedCheck visitor; 742 visitor.live_stack = allocations; 743 visitor.mark_sweep = this; 744 runtime->GetInternTable()->SweepInternTableWeaks(IsMarkedArrayCallback, &visitor); 745 runtime->GetMonitorList()->SweepMonitorList(IsMarkedArrayCallback, &visitor); 746 SweepJniWeakGlobals(IsMarkedArrayCallback, &visitor); 747} 748 749void MarkSweep::SweepSystemWeaks() { 750 Runtime* runtime = Runtime::Current(); 751 // The callbacks check 752 // !is_marked where is_marked is the callback but we want 753 // !IsMarked && IsLive 754 // So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive). 755 // Or for swapped (IsLive || !IsMarked). 756 runtime->GetInternTable()->SweepInternTableWeaks(IsMarkedCallback, this); 757 runtime->GetMonitorList()->SweepMonitorList(IsMarkedCallback, this); 758 SweepJniWeakGlobals(IsMarkedCallback, this); 759} 760 761bool MarkSweep::VerifyIsLiveCallback(const Object* obj, void* arg) { 762 reinterpret_cast<MarkSweep*>(arg)->VerifyIsLive(obj); 763 // We don't actually want to sweep the object, so lets return "marked" 764 return true; 765} 766 767void MarkSweep::VerifyIsLive(const Object* obj) { 768 Heap* heap = GetHeap(); 769 if (!heap->GetLiveBitmap()->Test(obj)) { 770 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 771 if (!large_object_space->GetLiveObjects()->Test(obj)) { 772 if (std::find(heap->allocation_stack_->Begin(), heap->allocation_stack_->End(), obj) == 773 heap->allocation_stack_->End()) { 774 // Object not found! 775 heap->DumpSpaces(); 776 LOG(FATAL) << "Found dead object " << obj; 777 } 778 } 779 } 780} 781 782void MarkSweep::VerifySystemWeaks() { 783 Runtime* runtime = Runtime::Current(); 784 // Verify system weaks, uses a special IsMarked callback which always returns true. 785 runtime->GetInternTable()->SweepInternTableWeaks(VerifyIsLiveCallback, this); 786 runtime->GetMonitorList()->SweepMonitorList(VerifyIsLiveCallback, this); 787 788 JavaVMExt* vm = runtime->GetJavaVM(); 789 MutexLock mu(Thread::Current(), vm->weak_globals_lock); 790 IndirectReferenceTable* table = &vm->weak_globals; 791 typedef IndirectReferenceTable::iterator It; // TODO: C++0x auto 792 for (It it = table->begin(), end = table->end(); it != end; ++it) { 793 const Object** entry = *it; 794 VerifyIsLive(*entry); 795 } 796} 797 798struct SweepCallbackContext { 799 MarkSweep* mark_sweep; 800 space::AllocSpace* space; 801 Thread* self; 802}; 803 804class CheckpointMarkThreadRoots : public Closure { 805 public: 806 CheckpointMarkThreadRoots(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) { 807 808 } 809 810 virtual void Run(Thread* thread) NO_THREAD_SAFETY_ANALYSIS { 811 // Note: self is not necessarily equal to thread since thread may be suspended. 812 Thread* self = Thread::Current(); 813 CHECK(thread == self || thread->IsSuspended() || thread->GetState() == kWaitingPerformingGc) 814 << thread->GetState() << " thread " << thread << " self " << self; 815 thread->VisitRoots(MarkSweep::MarkRootParallelCallback, mark_sweep_); 816 mark_sweep_->GetBarrier().Pass(self); 817 } 818 819 private: 820 MarkSweep* mark_sweep_; 821}; 822 823void MarkSweep::MarkRootsCheckpoint(Thread* self) { 824 CheckpointMarkThreadRoots check_point(this); 825 ThreadList* thread_list = Runtime::Current()->GetThreadList(); 826 // Request the check point is run on all threads returning a count of the threads that must 827 // run through the barrier including self. 828 size_t barrier_count = thread_list->RunCheckpoint(&check_point); 829 // Release locks then wait for all mutator threads to pass the barrier. 830 // TODO: optimize to not release locks when there are no threads to wait for. 831 Locks::heap_bitmap_lock_->ExclusiveUnlock(self); 832 Locks::mutator_lock_->SharedUnlock(self); 833 ThreadState old_state = self->SetState(kWaitingForCheckPointsToRun); 834 CHECK_EQ(old_state, kWaitingPerformingGc); 835 gc_barrier_->Increment(self, barrier_count); 836 self->SetState(kWaitingPerformingGc); 837 Locks::mutator_lock_->SharedLock(self); 838 Locks::heap_bitmap_lock_->ExclusiveLock(self); 839} 840 841void MarkSweep::SweepCallback(size_t num_ptrs, Object** ptrs, void* arg) { 842 SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg); 843 MarkSweep* mark_sweep = context->mark_sweep; 844 Heap* heap = mark_sweep->GetHeap(); 845 space::AllocSpace* space = context->space; 846 Thread* self = context->self; 847 Locks::heap_bitmap_lock_->AssertExclusiveHeld(self); 848 // Use a bulk free, that merges consecutive objects before freeing or free per object? 849 // Documentation suggests better free performance with merging, but this may be at the expensive 850 // of allocation. 851 size_t freed_objects = num_ptrs; 852 // AllocSpace::FreeList clears the value in ptrs, so perform after clearing the live bit 853 size_t freed_bytes = space->FreeList(self, num_ptrs, ptrs); 854 heap->RecordFree(freed_objects, freed_bytes); 855 mark_sweep->freed_objects_.fetch_add(freed_objects); 856 mark_sweep->freed_bytes_.fetch_add(freed_bytes); 857} 858 859void MarkSweep::ZygoteSweepCallback(size_t num_ptrs, Object** ptrs, void* arg) { 860 SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg); 861 Locks::heap_bitmap_lock_->AssertExclusiveHeld(context->self); 862 Heap* heap = context->mark_sweep->GetHeap(); 863 // We don't free any actual memory to avoid dirtying the shared zygote pages. 864 for (size_t i = 0; i < num_ptrs; ++i) { 865 Object* obj = static_cast<Object*>(ptrs[i]); 866 heap->GetLiveBitmap()->Clear(obj); 867 heap->GetCardTable()->MarkCard(obj); 868 } 869} 870 871void MarkSweep::SweepArray(accounting::ObjectStack* allocations, bool swap_bitmaps) { 872 size_t freed_bytes = 0; 873 space::DlMallocSpace* space = heap_->GetAllocSpace(); 874 875 // If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark 876 // bitmap, resulting in occasional frees of Weaks which are still in use. 877 timings_.NewSplit("SweepSystemWeaks"); 878 SweepSystemWeaksArray(allocations); 879 880 timings_.NewSplit("Process allocation stack"); 881 // Newly allocated objects MUST be in the alloc space and those are the only objects which we are 882 // going to free. 883 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 884 accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap(); 885 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 886 accounting::SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects(); 887 accounting::SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects(); 888 if (swap_bitmaps) { 889 std::swap(live_bitmap, mark_bitmap); 890 std::swap(large_live_objects, large_mark_objects); 891 } 892 893 size_t freed_large_objects = 0; 894 size_t count = allocations->Size(); 895 Object** objects = const_cast<Object**>(allocations->Begin()); 896 Object** out = objects; 897 898 // Empty the allocation stack. 899 Thread* self = Thread::Current(); 900 for (size_t i = 0;i < count;++i) { 901 Object* obj = objects[i]; 902 // There should only be objects in the AllocSpace/LargeObjectSpace in the allocation stack. 903 if (LIKELY(mark_bitmap->HasAddress(obj))) { 904 if (!mark_bitmap->Test(obj)) { 905 // Don't bother un-marking since we clear the mark bitmap anyways. 906 *(out++) = obj; 907 } 908 } else if (!large_mark_objects->Test(obj)) { 909 ++freed_large_objects; 910 freed_bytes += large_object_space->Free(self, obj); 911 } 912 } 913 CHECK_EQ(count, allocations->Size()); 914 timings_.NewSplit("FreeList"); 915 916 size_t freed_objects = out - objects; 917 freed_bytes += space->FreeList(self, freed_objects, objects); 918 VLOG(heap) << "Freed " << freed_objects << "/" << count 919 << " objects with size " << PrettySize(freed_bytes); 920 heap_->RecordFree(freed_objects + freed_large_objects, freed_bytes); 921 freed_objects_.fetch_add(freed_objects); 922 freed_bytes_.fetch_add(freed_bytes); 923 924 timings_.NewSplit("ResetStack"); 925 allocations->Reset(); 926} 927 928void MarkSweep::Sweep(bool swap_bitmaps) { 929 DCHECK(mark_stack_->IsEmpty()); 930 931 // If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark 932 // bitmap, resulting in occasional frees of Weaks which are still in use. 933 timings_.NewSplit("SweepSystemWeaks"); 934 SweepSystemWeaks(); 935 936 const bool partial = (GetGcType() == kGcTypePartial); 937 SweepCallbackContext scc; 938 scc.mark_sweep = this; 939 scc.self = Thread::Current(); 940 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 941 // TODO: C++0x 942 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 943 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 944 space::ContinuousSpace* space = *it; 945 // We always sweep always collect spaces. 946 bool sweep_space = (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyAlwaysCollect); 947 if (!partial && !sweep_space) { 948 // We sweep full collect spaces when the GC isn't a partial GC (ie its full). 949 sweep_space = (space->GetGcRetentionPolicy() == space::kGcRetentionPolicyFullCollect); 950 } 951 if (sweep_space) { 952 uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin()); 953 uintptr_t end = reinterpret_cast<uintptr_t>(space->End()); 954 scc.space = space->AsDlMallocSpace(); 955 accounting::SpaceBitmap* live_bitmap = space->GetLiveBitmap(); 956 accounting::SpaceBitmap* mark_bitmap = space->GetMarkBitmap(); 957 if (swap_bitmaps) { 958 std::swap(live_bitmap, mark_bitmap); 959 } 960 if (!space->IsZygoteSpace()) { 961 timings_.NewSplit("SweepAllocSpace"); 962 // Bitmaps are pre-swapped for optimization which enables sweeping with the heap unlocked. 963 accounting::SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end, 964 &SweepCallback, reinterpret_cast<void*>(&scc)); 965 } else { 966 timings_.NewSplit("SweepZygote"); 967 // Zygote sweep takes care of dirtying cards and clearing live bits, does not free actual 968 // memory. 969 accounting::SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end, 970 &ZygoteSweepCallback, reinterpret_cast<void*>(&scc)); 971 } 972 } 973 } 974 975 timings_.NewSplit("SweepLargeObjects"); 976 SweepLargeObjects(swap_bitmaps); 977} 978 979void MarkSweep::SweepLargeObjects(bool swap_bitmaps) { 980 // Sweep large objects 981 space::LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace(); 982 accounting::SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects(); 983 accounting::SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects(); 984 if (swap_bitmaps) { 985 std::swap(large_live_objects, large_mark_objects); 986 } 987 accounting::SpaceSetMap::Objects& live_objects = large_live_objects->GetObjects(); 988 // O(n*log(n)) but hopefully there are not too many large objects. 989 size_t freed_objects = 0; 990 size_t freed_bytes = 0; 991 Thread* self = Thread::Current(); 992 // TODO: C++0x 993 typedef accounting::SpaceSetMap::Objects::iterator It; 994 for (It it = live_objects.begin(), end = live_objects.end(); it != end; ++it) { 995 if (!large_mark_objects->Test(*it)) { 996 freed_bytes += large_object_space->Free(self, const_cast<Object*>(*it)); 997 ++freed_objects; 998 } 999 } 1000 freed_objects_.fetch_add(freed_objects); 1001 freed_bytes_.fetch_add(freed_bytes); 1002 GetHeap()->RecordFree(freed_objects, freed_bytes); 1003} 1004 1005void MarkSweep::CheckReference(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) { 1006 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 1007 // TODO: C++0x 1008 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 1009 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 1010 space::ContinuousSpace* space = *it; 1011 if (space->IsDlMallocSpace() && space->Contains(ref)) { 1012 DCHECK(IsMarked(obj)); 1013 1014 bool is_marked = IsMarked(ref); 1015 if (!is_marked) { 1016 LOG(INFO) << *space; 1017 LOG(WARNING) << (is_static ? "Static ref'" : "Instance ref'") << PrettyTypeOf(ref) 1018 << "' (" << reinterpret_cast<const void*>(ref) << ") in '" << PrettyTypeOf(obj) 1019 << "' (" << reinterpret_cast<const void*>(obj) << ") at offset " 1020 << reinterpret_cast<void*>(offset.Int32Value()) << " wasn't marked"; 1021 1022 const Class* klass = is_static ? obj->AsClass() : obj->GetClass(); 1023 DCHECK(klass != NULL); 1024 const ObjectArray<Field>* fields = is_static ? klass->GetSFields() : klass->GetIFields(); 1025 DCHECK(fields != NULL); 1026 bool found = false; 1027 for (int32_t i = 0; i < fields->GetLength(); ++i) { 1028 const Field* cur = fields->Get(i); 1029 if (cur->GetOffset().Int32Value() == offset.Int32Value()) { 1030 LOG(WARNING) << "Field referencing the alloc space was " << PrettyField(cur); 1031 found = true; 1032 break; 1033 } 1034 } 1035 if (!found) { 1036 LOG(WARNING) << "Could not find field in object alloc space with offset " << offset.Int32Value(); 1037 } 1038 1039 bool obj_marked = heap_->GetCardTable()->IsDirty(obj); 1040 if (!obj_marked) { 1041 LOG(WARNING) << "Object '" << PrettyTypeOf(obj) << "' " 1042 << "(" << reinterpret_cast<const void*>(obj) << ") contains references to " 1043 << "the alloc space, but wasn't card marked"; 1044 } 1045 } 1046 } 1047 break; 1048 } 1049} 1050 1051// Process the "referent" field in a java.lang.ref.Reference. If the 1052// referent has not yet been marked, put it on the appropriate list in 1053// the gcHeap for later processing. 1054void MarkSweep::DelayReferenceReferent(Object* obj) { 1055 DCHECK(obj != NULL); 1056 Class* klass = obj->GetClass(); 1057 DCHECK(klass != NULL); 1058 DCHECK(klass->IsReferenceClass()); 1059 Object* pending = obj->GetFieldObject<Object*>(heap_->GetReferencePendingNextOffset(), false); 1060 Object* referent = heap_->GetReferenceReferent(obj); 1061 if (kCountJavaLangRefs) { 1062 ++reference_count_; 1063 } 1064 if (pending == NULL && referent != NULL && !IsMarked(referent)) { 1065 Object** list = NULL; 1066 if (klass->IsSoftReferenceClass()) { 1067 list = &soft_reference_list_; 1068 } else if (klass->IsWeakReferenceClass()) { 1069 list = &weak_reference_list_; 1070 } else if (klass->IsFinalizerReferenceClass()) { 1071 list = &finalizer_reference_list_; 1072 } else if (klass->IsPhantomReferenceClass()) { 1073 list = &phantom_reference_list_; 1074 } 1075 DCHECK(list != NULL) << PrettyClass(klass) << " " << std::hex << klass->GetAccessFlags(); 1076 // TODO: One lock per list? 1077 heap_->EnqueuePendingReference(obj, list); 1078 } 1079} 1080 1081void MarkSweep::ScanRoot(const Object* obj) { 1082 ScanObject(obj); 1083} 1084 1085class MarkObjectVisitor { 1086 public: 1087 MarkObjectVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) { 1088 } 1089 1090 // TODO: Fixme when anotatalysis works with visitors. 1091 void operator ()(const Object* /* obj */, const Object* ref, const MemberOffset& /* offset */, 1092 bool /* is_static */) const 1093 NO_THREAD_SAFETY_ANALYSIS { 1094 if (kDebugLocking) { 1095 Locks::mutator_lock_->AssertSharedHeld(Thread::Current()); 1096 Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current()); 1097 } 1098 mark_sweep_->MarkObject(ref); 1099 } 1100 1101 private: 1102 MarkSweep* const mark_sweep_; 1103}; 1104 1105// Scans an object reference. Determines the type of the reference 1106// and dispatches to a specialized scanning routine. 1107void MarkSweep::ScanObject(const Object* obj) { 1108 MarkObjectVisitor visitor(this); 1109 ScanObjectVisit(obj, visitor); 1110} 1111 1112class MarkStackChunk : public Task { 1113 public: 1114 MarkStackChunk(ThreadPool* thread_pool, MarkSweep* mark_sweep, Object** begin, Object** end) 1115 : mark_sweep_(mark_sweep), 1116 thread_pool_(thread_pool), 1117 index_(0), 1118 length_(0), 1119 output_(NULL) { 1120 length_ = end - begin; 1121 if (begin != end) { 1122 // Cost not significant since we only do this for the initial set of mark stack chunks. 1123 memcpy(data_, begin, length_ * sizeof(*begin)); 1124 } 1125 if (kCountTasks) { 1126 ++mark_sweep_->work_chunks_created_; 1127 } 1128 } 1129 1130 ~MarkStackChunk() { 1131 DCHECK(output_ == NULL || output_->length_ == 0); 1132 DCHECK_GE(index_, length_); 1133 delete output_; 1134 if (kCountTasks) { 1135 ++mark_sweep_->work_chunks_deleted_; 1136 } 1137 } 1138 1139 MarkSweep* const mark_sweep_; 1140 ThreadPool* const thread_pool_; 1141 static const size_t max_size = 1 * KB; 1142 // Index of which object we are scanning. Only needs to be atomic if we are doing work stealing. 1143 size_t index_; 1144 // Input / output mark stack. We add newly marked references to data_ until length reaches 1145 // max_size. This is an optimization so that less tasks are created. 1146 // TODO: Investigate using a bounded buffer FIFO. 1147 Object* data_[max_size]; 1148 // How many elements in data_ we need to scan. 1149 size_t length_; 1150 // Output block, newly marked references get added to the ouput block so that another thread can 1151 // scan them. 1152 MarkStackChunk* output_; 1153 1154 class MarkObjectParallelVisitor { 1155 public: 1156 MarkObjectParallelVisitor(MarkStackChunk* chunk_task) : chunk_task_(chunk_task) { 1157 1158 } 1159 1160 void operator ()(const Object* /* obj */, const Object* ref, 1161 const MemberOffset& /* offset */, bool /* is_static */) const { 1162 if (ref != NULL && chunk_task_->mark_sweep_->MarkObjectParallel(ref)) { 1163 chunk_task_->MarkStackPush(ref); 1164 } 1165 } 1166 1167 private: 1168 MarkStackChunk* const chunk_task_; 1169 }; 1170 1171 // Push an object into the block. 1172 // Don't need to use atomic ++ since we only one thread is writing to an output block at any 1173 // given time. 1174 void Push(Object* obj) { 1175 CHECK(obj != NULL); 1176 data_[length_++] = obj; 1177 } 1178 1179 void MarkStackPush(const Object* obj) { 1180 if (static_cast<size_t>(length_) < max_size) { 1181 Push(const_cast<Object*>(obj)); 1182 } else { 1183 // Internal (thread-local) buffer is full, push to a new buffer instead. 1184 if (UNLIKELY(output_ == NULL)) { 1185 AllocateOutputChunk(); 1186 } else if (UNLIKELY(static_cast<size_t>(output_->length_) == max_size)) { 1187 // Output block is full, queue it up for processing and obtain a new block. 1188 EnqueueOutput(); 1189 AllocateOutputChunk(); 1190 } 1191 output_->Push(const_cast<Object*>(obj)); 1192 } 1193 } 1194 1195 void ScanObject(Object* obj) { 1196 mark_sweep_->ScanObjectVisit(obj, MarkObjectParallelVisitor(this)); 1197 } 1198 1199 void EnqueueOutput() { 1200 if (output_ != NULL) { 1201 uint64_t start = 0; 1202 if (kMeasureOverhead) { 1203 start = NanoTime(); 1204 } 1205 thread_pool_->AddTask(Thread::Current(), output_); 1206 output_ = NULL; 1207 if (kMeasureOverhead) { 1208 mark_sweep_->overhead_time_.fetch_add(NanoTime() - start); 1209 } 1210 } 1211 } 1212 1213 void AllocateOutputChunk() { 1214 uint64_t start = 0; 1215 if (kMeasureOverhead) { 1216 start = NanoTime(); 1217 } 1218 output_ = new MarkStackChunk(thread_pool_, mark_sweep_, NULL, NULL); 1219 if (kMeasureOverhead) { 1220 mark_sweep_->overhead_time_.fetch_add(NanoTime() - start); 1221 } 1222 } 1223 1224 void Finalize() { 1225 EnqueueOutput(); 1226 delete this; 1227 } 1228 1229 // Scans all of the objects 1230 virtual void Run(Thread* self) { 1231 size_t index; 1232 while ((index = index_++) < length_) { 1233 if (kUseMarkStackPrefetch) { 1234 static const size_t prefetch_look_ahead = 1; 1235 __builtin_prefetch(data_[std::min(index + prefetch_look_ahead, length_ - 1)]); 1236 } 1237 Object* obj = data_[index]; 1238 DCHECK(obj != NULL); 1239 ScanObject(obj); 1240 } 1241 } 1242}; 1243 1244void MarkSweep::ProcessMarkStackParallel() { 1245 CHECK(kDisableFinger) << "parallel mark stack processing cannot work when finger is enabled"; 1246 Thread* self = Thread::Current(); 1247 ThreadPool* thread_pool = GetHeap()->GetThreadPool(); 1248 // Split the current mark stack up into work tasks. 1249 const size_t num_threads = thread_pool->GetThreadCount(); 1250 const size_t stack_size = mark_stack_->Size(); 1251 const size_t chunk_size = 1252 std::min((stack_size + num_threads - 1) / num_threads, 1253 static_cast<size_t>(MarkStackChunk::max_size)); 1254 size_t index = 0; 1255 for (size_t i = 0; i < num_threads || index < stack_size; ++i) { 1256 Object** begin = &mark_stack_->Begin()[std::min(stack_size, index)]; 1257 Object** end = &mark_stack_->Begin()[std::min(stack_size, index + chunk_size)]; 1258 index += chunk_size; 1259 thread_pool->AddTask(self, new MarkStackChunk(thread_pool, this, begin, end)); 1260 } 1261 thread_pool->StartWorkers(self); 1262 thread_pool->Wait(self, true, true); 1263 mark_stack_->Reset(); 1264 //LOG(INFO) << "Idle wait time " << PrettyDuration(thread_pool->GetWaitTime()); 1265 CHECK_EQ(work_chunks_created_, work_chunks_deleted_) << " some of the work chunks were leaked"; 1266} 1267 1268// Scan anything that's on the mark stack. 1269void MarkSweep::ProcessMarkStack() { 1270 ThreadPool* thread_pool = GetHeap()->GetThreadPool(); 1271 if (kParallelMarkStack && thread_pool != NULL && thread_pool->GetThreadCount() > 0) { 1272 ProcessMarkStackParallel(); 1273 return; 1274 } 1275 1276 if (kUseMarkStackPrefetch) { 1277 const size_t fifo_size = 4; 1278 const size_t fifo_mask = fifo_size - 1; 1279 const Object* fifo[fifo_size]; 1280 for (size_t i = 0;i < fifo_size;++i) { 1281 fifo[i] = NULL; 1282 } 1283 size_t fifo_pos = 0; 1284 size_t fifo_count = 0; 1285 for (;;) { 1286 const Object* obj = fifo[fifo_pos & fifo_mask]; 1287 if (obj != NULL) { 1288 ScanObject(obj); 1289 fifo[fifo_pos & fifo_mask] = NULL; 1290 --fifo_count; 1291 } 1292 1293 if (!mark_stack_->IsEmpty()) { 1294 const Object* obj = mark_stack_->PopBack(); 1295 DCHECK(obj != NULL); 1296 fifo[fifo_pos & fifo_mask] = obj; 1297 __builtin_prefetch(obj); 1298 fifo_count++; 1299 } 1300 fifo_pos++; 1301 1302 if (!fifo_count) { 1303 CHECK(mark_stack_->IsEmpty()) << mark_stack_->Size(); 1304 break; 1305 } 1306 } 1307 } else { 1308 while (!mark_stack_->IsEmpty()) { 1309 const Object* obj = mark_stack_->PopBack(); 1310 DCHECK(obj != NULL); 1311 ScanObject(obj); 1312 } 1313 } 1314} 1315 1316// Walks the reference list marking any references subject to the 1317// reference clearing policy. References with a black referent are 1318// removed from the list. References with white referents biased 1319// toward saving are blackened and also removed from the list. 1320void MarkSweep::PreserveSomeSoftReferences(Object** list) { 1321 DCHECK(list != NULL); 1322 Object* clear = NULL; 1323 size_t counter = 0; 1324 1325 DCHECK(mark_stack_->IsEmpty()); 1326 1327 while (*list != NULL) { 1328 Object* ref = heap_->DequeuePendingReference(list); 1329 Object* referent = heap_->GetReferenceReferent(ref); 1330 if (referent == NULL) { 1331 // Referent was cleared by the user during marking. 1332 continue; 1333 } 1334 bool is_marked = IsMarked(referent); 1335 if (!is_marked && ((++counter) & 1)) { 1336 // Referent is white and biased toward saving, mark it. 1337 MarkObject(referent); 1338 is_marked = true; 1339 } 1340 if (!is_marked) { 1341 // Referent is white, queue it for clearing. 1342 heap_->EnqueuePendingReference(ref, &clear); 1343 } 1344 } 1345 *list = clear; 1346 // Restart the mark with the newly black references added to the 1347 // root set. 1348 ProcessMarkStack(); 1349} 1350 1351inline bool MarkSweep::IsMarked(const Object* object) const 1352 SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) { 1353 if (object >= immune_begin_ && object < immune_end_) { 1354 return true; 1355 } 1356 DCHECK(current_mark_bitmap_ != NULL); 1357 if (current_mark_bitmap_->HasAddress(object)) { 1358 return current_mark_bitmap_->Test(object); 1359 } 1360 return heap_->GetMarkBitmap()->Test(object); 1361} 1362 1363 1364// Unlink the reference list clearing references objects with white 1365// referents. Cleared references registered to a reference queue are 1366// scheduled for appending by the heap worker thread. 1367void MarkSweep::ClearWhiteReferences(Object** list) { 1368 DCHECK(list != NULL); 1369 while (*list != NULL) { 1370 Object* ref = heap_->DequeuePendingReference(list); 1371 Object* referent = heap_->GetReferenceReferent(ref); 1372 if (referent != NULL && !IsMarked(referent)) { 1373 // Referent is white, clear it. 1374 heap_->ClearReferenceReferent(ref); 1375 if (heap_->IsEnqueuable(ref)) { 1376 heap_->EnqueueReference(ref, &cleared_reference_list_); 1377 } 1378 } 1379 } 1380 DCHECK(*list == NULL); 1381} 1382 1383// Enqueues finalizer references with white referents. White 1384// referents are blackened, moved to the zombie field, and the 1385// referent field is cleared. 1386void MarkSweep::EnqueueFinalizerReferences(Object** list) { 1387 DCHECK(list != NULL); 1388 MemberOffset zombie_offset = heap_->GetFinalizerReferenceZombieOffset(); 1389 bool has_enqueued = false; 1390 while (*list != NULL) { 1391 Object* ref = heap_->DequeuePendingReference(list); 1392 Object* referent = heap_->GetReferenceReferent(ref); 1393 if (referent != NULL && !IsMarked(referent)) { 1394 MarkObject(referent); 1395 // If the referent is non-null the reference must queuable. 1396 DCHECK(heap_->IsEnqueuable(ref)); 1397 ref->SetFieldObject(zombie_offset, referent, false); 1398 heap_->ClearReferenceReferent(ref); 1399 heap_->EnqueueReference(ref, &cleared_reference_list_); 1400 has_enqueued = true; 1401 } 1402 } 1403 if (has_enqueued) { 1404 ProcessMarkStack(); 1405 } 1406 DCHECK(*list == NULL); 1407} 1408 1409// Process reference class instances and schedule finalizations. 1410void MarkSweep::ProcessReferences(Object** soft_references, bool clear_soft, 1411 Object** weak_references, 1412 Object** finalizer_references, 1413 Object** phantom_references) { 1414 DCHECK(soft_references != NULL); 1415 DCHECK(weak_references != NULL); 1416 DCHECK(finalizer_references != NULL); 1417 DCHECK(phantom_references != NULL); 1418 1419 // Unless we are in the zygote or required to clear soft references 1420 // with white references, preserve some white referents. 1421 if (!clear_soft && !Runtime::Current()->IsZygote()) { 1422 PreserveSomeSoftReferences(soft_references); 1423 } 1424 1425 // Clear all remaining soft and weak references with white 1426 // referents. 1427 ClearWhiteReferences(soft_references); 1428 ClearWhiteReferences(weak_references); 1429 1430 // Preserve all white objects with finalize methods and schedule 1431 // them for finalization. 1432 EnqueueFinalizerReferences(finalizer_references); 1433 1434 // Clear all f-reachable soft and weak references with white 1435 // referents. 1436 ClearWhiteReferences(soft_references); 1437 ClearWhiteReferences(weak_references); 1438 1439 // Clear all phantom references with white referents. 1440 ClearWhiteReferences(phantom_references); 1441 1442 // At this point all reference lists should be empty. 1443 DCHECK(*soft_references == NULL); 1444 DCHECK(*weak_references == NULL); 1445 DCHECK(*finalizer_references == NULL); 1446 DCHECK(*phantom_references == NULL); 1447} 1448 1449void MarkSweep::UnBindBitmaps() { 1450 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 1451 // TODO: C++0x 1452 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 1453 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 1454 space::ContinuousSpace* space = *it; 1455 if (space->IsDlMallocSpace()) { 1456 space::DlMallocSpace* alloc_space = space->AsDlMallocSpace(); 1457 if (alloc_space->temp_bitmap_.get() != NULL) { 1458 // At this point, the temp_bitmap holds our old mark bitmap. 1459 accounting::SpaceBitmap* new_bitmap = alloc_space->temp_bitmap_.release(); 1460 GetHeap()->GetMarkBitmap()->ReplaceBitmap(alloc_space->mark_bitmap_.get(), new_bitmap); 1461 CHECK_EQ(alloc_space->mark_bitmap_.release(), alloc_space->live_bitmap_.get()); 1462 alloc_space->mark_bitmap_.reset(new_bitmap); 1463 DCHECK(alloc_space->temp_bitmap_.get() == NULL); 1464 } 1465 } 1466 } 1467} 1468 1469void MarkSweep::FinishPhase() { 1470 // Can't enqueue referneces if we hold the mutator lock. 1471 Object* cleared_references = GetClearedReferences(); 1472 Heap* heap = GetHeap(); 1473 heap->EnqueueClearedReferences(&cleared_references); 1474 1475 heap->PostGcVerification(this); 1476 1477 timings_.NewSplit("GrowForUtilization"); 1478 heap->GrowForUtilization(GetGcType(), GetDurationNs()); 1479 1480 timings_.NewSplit("RequestHeapTrim"); 1481 heap->RequestHeapTrim(); 1482 1483 // Update the cumulative statistics 1484 total_time_ns_ += GetDurationNs(); 1485 total_paused_time_ns_ += std::accumulate(GetPauseTimes().begin(), GetPauseTimes().end(), 0, 1486 std::plus<uint64_t>()); 1487 total_freed_objects_ += GetFreedObjects(); 1488 total_freed_bytes_ += GetFreedBytes(); 1489 1490 // Ensure that the mark stack is empty. 1491 CHECK(mark_stack_->IsEmpty()); 1492 1493 if (kCountScannedTypes) { 1494 VLOG(gc) << "MarkSweep scanned classes=" << class_count_ << " arrays=" << array_count_ 1495 << " other=" << other_count_; 1496 } 1497 1498 if (kCountTasks) { 1499 VLOG(gc) << "Total number of work chunks allocated: " << work_chunks_created_; 1500 } 1501 1502 if (kMeasureOverhead) { 1503 VLOG(gc) << "Overhead time " << PrettyDuration(overhead_time_); 1504 } 1505 1506 if (kProfileLargeObjects) { 1507 VLOG(gc) << "Large objects tested " << large_object_test_ << " marked " << large_object_mark_; 1508 } 1509 1510 if (kCountClassesMarked) { 1511 VLOG(gc) << "Classes marked " << classes_marked_; 1512 } 1513 1514 if (kCountJavaLangRefs) { 1515 VLOG(gc) << "References scanned " << reference_count_; 1516 } 1517 1518 // Update the cumulative loggers. 1519 cumulative_timings_.Start(); 1520 cumulative_timings_.AddNewLogger(timings_); 1521 cumulative_timings_.End(); 1522 1523 // Clear all of the spaces' mark bitmaps. 1524 const std::vector<space::ContinuousSpace*>& spaces = GetHeap()->GetContinuousSpaces(); 1525 // TODO: C++0x 1526 typedef std::vector<space::ContinuousSpace*>::const_iterator It; 1527 for (It it = spaces.begin(), end = spaces.end(); it != end; ++it) { 1528 space::ContinuousSpace* space = *it; 1529 if (space->GetGcRetentionPolicy() != space::kGcRetentionPolicyNeverCollect) { 1530 space->GetMarkBitmap()->Clear(); 1531 } 1532 } 1533 mark_stack_->Reset(); 1534 1535 // Reset the marked large objects. 1536 space::LargeObjectSpace* large_objects = GetHeap()->GetLargeObjectsSpace(); 1537 large_objects->GetMarkObjects()->Clear(); 1538} 1539 1540} // namespace collector 1541} // namespace gc 1542} // namespace art 1543