blob: cdb73db51e6dd21eed7824fffedd5be056bc7fd1 [file] [log] [blame]
/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "mark_sweep.h"
#include <climits>
#include <vector>
#include "card_table.h"
#include "class_loader.h"
#include "dex_cache.h"
#include "heap.h"
#include "indirect_reference_table.h"
#include "intern_table.h"
#include "jni_internal.h"
#include "logging.h"
#include "macros.h"
#include "mark_stack.h"
#include "monitor.h"
#include "mutex.h"
#include "object.h"
#include "runtime.h"
#include "space.h"
#include "timing_logger.h"
#include "thread.h"
#define MARK_STACK_PREFETCH 1
namespace art {
class SetFingerVisitor {
public:
SetFingerVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {
}
void operator ()(void* finger) const {
mark_sweep_->SetFinger(reinterpret_cast<Object*>(finger));
}
private:
MarkSweep* const mark_sweep_;
};
MarkSweep::MarkSweep(MarkStack* mark_stack)
: current_mark_bitmap_(NULL),
mark_stack_(mark_stack),
heap_(NULL),
finger_(NULL),
immune_begin_(NULL),
immune_end_(NULL),
soft_reference_list_(NULL),
weak_reference_list_(NULL),
finalizer_reference_list_(NULL),
phantom_reference_list_(NULL),
cleared_reference_list_(NULL),
freed_bytes_(0), freed_objects_(0),
class_count_(0), array_count_(0), other_count_(0) {
DCHECK(mark_stack_ != NULL);
}
void MarkSweep::Init() {
heap_ = Runtime::Current()->GetHeap();
mark_stack_->Reset();
const Spaces& spaces = heap_->GetSpaces();
// TODO: C++0x auto
for (Spaces::const_iterator cur = spaces.begin(); cur != spaces.end(); ++cur) {
if (current_mark_bitmap_ == NULL || (*cur)->GetGcRetentionPolicy() == GCRP_ALWAYS_COLLECT) {
current_mark_bitmap_ = (*cur)->GetMarkBitmap();
break;
}
}
if (current_mark_bitmap_ == NULL) {
GetHeap()->DumpSpaces();
DCHECK(false) << "current_mark_bitmap_ == NULL";
}
// TODO: if concurrent, enable card marking in compiler
// TODO: check that the mark bitmap is entirely clear.
}
inline void MarkSweep::MarkObject0(const Object* obj, bool check_finger) {
DCHECK(obj != NULL);
if (obj >= immune_begin_ && obj < immune_end_) {
DCHECK(IsMarked(obj));
return;
}
// Try to take advantage of locality of references within a space, failing this find the space
// the hard way.
if (UNLIKELY(!current_mark_bitmap_->HasAddress(obj))) {
SpaceBitmap* new_bitmap = heap_->GetMarkBitmap()->GetSpaceBitmap(obj);
if (new_bitmap != NULL) {
current_mark_bitmap_ = new_bitmap;
} else {
LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
SpaceSetMap* large_objects = large_object_space->GetMarkObjects();
if (!large_objects->Test(obj)) {
CHECK(large_object_space->Contains(obj)) << "Attempting to mark object " << obj << " not in large object space";
large_objects->Set(obj);
// Don't need to check finger since large objects never have any object references.
}
// TODO: Improve clarity of control flow in this function?
return;
}
}
// This object was not previously marked.
if (!current_mark_bitmap_->Test(obj)) {
current_mark_bitmap_->Set(obj);
if (check_finger && obj < finger_) {
// The object must be pushed on to the mark stack.
mark_stack_->Push(obj);
}
}
}
// Used to mark objects when recursing. Recursion is done by moving
// the finger across the bitmaps in address order and marking child
// objects. Any newly-marked objects whose addresses are lower than
// the finger won't be visited by the bitmap scan, so those objects
// need to be added to the mark stack.
void MarkSweep::MarkObject(const Object* obj) {
if (obj != NULL) {
MarkObject0(obj, true);
}
}
void MarkSweep::MarkObjectVisitor(const Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->MarkObject0(root, false);
}
void MarkSweep::ReMarkObjectVisitor(const Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->MarkObject0(root, true);
}
// Marks all objects in the root set.
void MarkSweep::MarkRoots() {
Runtime::Current()->VisitRoots(MarkObjectVisitor, this);
}
class CheckObjectVisitor {
public:
CheckObjectVisitor(MarkSweep* const mark_sweep)
: mark_sweep_(mark_sweep) {
}
void operator ()(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) const
SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_,
Locks::mutator_lock_) {
mark_sweep_->CheckReference(obj, ref, offset, is_static);
}
private:
MarkSweep* const mark_sweep_;
};
void MarkSweep::CheckObject(const Object* obj) {
DCHECK(obj != NULL);
CheckObjectVisitor visitor(this);
VisitObjectReferences(obj, visitor);
}
void MarkSweep::VerifyImageRootVisitor(Object* root, void* arg) {
DCHECK(root != NULL);
DCHECK(arg != NULL);
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
DCHECK(mark_sweep->heap_->GetMarkBitmap()->Test(root));
mark_sweep->CheckObject(root);
}
void MarkSweep::CopyMarkBits(Space* space) {
SpaceBitmap* live_bitmap = space->GetLiveBitmap();
SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
mark_bitmap->CopyFrom(live_bitmap);
}
class ScanImageRootVisitor {
public:
ScanImageRootVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {
}
void operator ()(const Object* root) const
EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
DCHECK(root != NULL);
mark_sweep_->ScanObject(root);
}
private:
MarkSweep* const mark_sweep_;
};
// Marks all objects that are in images and have been touched by the mutator
void MarkSweep::ScanDirtyImageRoots() {
const Spaces& spaces = heap_->GetSpaces();
CardTable* card_table = heap_->GetCardTable();
ScanImageRootVisitor image_root_visitor(this);
// TODO: C++ 0x auto
for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
Space* space = *it;
if (space->IsImageSpace()) {
card_table->Scan(space->GetLiveBitmap(), space->Begin(), space->End(), image_root_visitor,
IdentityFunctor());
}
}
}
void MarkSweep::ScanGrayObjects(bool update_finger) {
const Spaces& spaces = heap_->GetSpaces();
CardTable* card_table = heap_->GetCardTable();
ScanImageRootVisitor image_root_visitor(this);
SetFingerVisitor finger_visitor(this);
// TODO: C++ 0x auto
for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
Space* space = *it;
byte* begin = space->Begin();
byte* end = space->End();
// Image spaces are handled properly since live == marked for them.
SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
if (update_finger) {
card_table->Scan(mark_bitmap, begin, end, image_root_visitor, finger_visitor);
} else {
card_table->Scan(mark_bitmap, begin, end, image_root_visitor, IdentityFunctor());
}
}
}
class CheckBitmapVisitor {
public:
CheckBitmapVisitor(MarkSweep* mark_sweep) : mark_sweep_(mark_sweep) {
}
void operator ()(const Object* obj) const
SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_,
Locks::mutator_lock_) {
DCHECK(obj != NULL);
mark_sweep_->CheckObject(obj);
}
private:
MarkSweep* mark_sweep_;
};
void MarkSweep::VerifyImageRoots() {
// Verify roots ensures that all the references inside the image space point
// objects which are either in the image space or marked objects in the alloc
// space
CheckBitmapVisitor visitor(this);
const Spaces& spaces = heap_->GetSpaces();
for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
const Space* space = *it;
if (space->IsImageSpace()) {
uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
SpaceBitmap* live_bitmap = space->GetLiveBitmap();
DCHECK(live_bitmap != NULL);
live_bitmap->VisitMarkedRange(begin, end, visitor, IdentityFunctor());
}
}
}
class ScanObjectVisitor {
public:
ScanObjectVisitor(MarkSweep* const mark_sweep) : mark_sweep_(mark_sweep) {
}
void operator ()(const Object* obj) const
EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
mark_sweep_->ScanObject(obj);
}
private:
MarkSweep* const mark_sweep_;
};
// Populates the mark stack based on the set of marked objects and
// recursively marks until the mark stack is emptied.
void MarkSweep::RecursiveMark(bool partial, TimingLogger& timings) {
// RecursiveMark will build the lists of known instances of the Reference classes.
// See DelayReferenceReferent for details.
CHECK(soft_reference_list_ == NULL);
CHECK(weak_reference_list_ == NULL);
CHECK(finalizer_reference_list_ == NULL);
CHECK(phantom_reference_list_ == NULL);
CHECK(cleared_reference_list_ == NULL);
const Spaces& spaces = heap_->GetSpaces();
SetFingerVisitor set_finger_visitor(this);
ScanObjectVisitor scan_visitor(this);
for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
Space* space = *it;
if (space->GetGcRetentionPolicy() == GCRP_ALWAYS_COLLECT ||
(!partial && space->GetGcRetentionPolicy() == GCRP_FULL_COLLECT)
) {
current_mark_bitmap_ = space->GetMarkBitmap();
if (current_mark_bitmap_ == NULL) {
GetHeap()->DumpSpaces();
LOG(FATAL) << "invalid bitmap";
}
// This function does not handle heap end increasing, so we must use the space end.
uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
current_mark_bitmap_->VisitMarkedRange(begin, end, scan_visitor, set_finger_visitor);
}
}
finger_ = reinterpret_cast<Object*>(~0);
timings.AddSplit("RecursiveMark");
// TODO: tune the frequency of emptying the mark stack
ProcessMarkStack();
timings.AddSplit("ProcessMarkStack");
}
void MarkSweep::RecursiveMarkCards(CardTable* card_table, const std::vector<byte*>& cards,
TimingLogger& timings) {
ScanImageRootVisitor image_root_visitor(this);
SetFingerVisitor finger_visitor(this);
for (size_t i = 0;i < cards.size();) {
Object* start_obj = reinterpret_cast<Object*>(card_table->AddrFromCard(cards[i]));
uintptr_t begin = reinterpret_cast<uintptr_t>(start_obj);
uintptr_t end = begin + GC_CARD_SIZE;
for (++i; reinterpret_cast<uintptr_t>(cards[i]) == end && i < cards.size(); ++i) {
end += GC_CARD_SIZE;
}
if (current_mark_bitmap_ == NULL || !current_mark_bitmap_->HasAddress(start_obj)) {
current_mark_bitmap_ = heap_->GetMarkBitmap()->GetSpaceBitmap(start_obj);
#ifndef NDEBUG
if (current_mark_bitmap_ == NULL) {
GetHeap()->DumpSpaces();
LOG(FATAL) << "Object " << reinterpret_cast<const void*>(start_obj);
}
#endif
}
current_mark_bitmap_->VisitMarkedRange(begin, end, image_root_visitor, finger_visitor);
}
timings.AddSplit("RecursiveMarkCards");
ProcessMarkStack();
timings.AddSplit("ProcessMarkStack");
}
bool MarkSweep::IsMarkedCallback(const Object* object, void* arg) {
return
reinterpret_cast<MarkSweep*>(arg)->IsMarked(object) ||
!reinterpret_cast<MarkSweep*>(arg)->GetHeap()->GetLiveBitmap()->Test(object);
}
bool MarkSweep::IsLiveCallback(const Object* object, void* arg) {
return
reinterpret_cast<MarkSweep*>(arg)->GetHeap()->GetLiveBitmap()->Test(object) ||
!reinterpret_cast<MarkSweep*>(arg)->IsMarked(object);
}
void MarkSweep::RecursiveMarkDirtyObjects(bool update_finger) {
ScanGrayObjects(update_finger);
ProcessMarkStack();
}
void MarkSweep::ReMarkRoots() {
Runtime::Current()->VisitRoots(ReMarkObjectVisitor, this);
}
void MarkSweep::SweepJniWeakGlobals(bool swap_bitmaps) {
HeapBitmap* live_bitmap = GetHeap()->GetLiveBitmap();
HeapBitmap* mark_bitmap = GetHeap()->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
}
JavaVMExt* vm = Runtime::Current()->GetJavaVM();
MutexLock mu(vm->weak_globals_lock);
IndirectReferenceTable* table = &vm->weak_globals;
typedef IndirectReferenceTable::iterator It; // TODO: C++0x auto
for (It it = table->begin(), end = table->end(); it != end; ++it) {
const Object** entry = *it;
if (live_bitmap->Test(*entry) && !mark_bitmap->Test(*entry)) {
*entry = kClearedJniWeakGlobal;
}
}
}
void MarkSweep::SweepSystemWeaks(bool swap_bitmaps) {
Runtime* runtime = Runtime::Current();
// The callbacks check
// !is_marked where is_marked is the callback but we want
// !IsMarked && IsLive
// So compute !(!IsMarked && IsLive) which is equal to (IsMarked || !IsLive).
// Or for swapped (IsLive || !IsMarked).
runtime->GetInternTable()->SweepInternTableWeaks(swap_bitmaps ? IsLiveCallback : IsMarkedCallback,
this);
runtime->GetMonitorList()->SweepMonitorList(swap_bitmaps ? IsLiveCallback : IsMarkedCallback,
this);
SweepJniWeakGlobals(swap_bitmaps);
}
bool MarkSweep::VerifyIsLiveCallback(const Object* obj, void* arg) {
reinterpret_cast<MarkSweep*>(arg)->VerifyIsLive(obj);
// We don't actually want to sweep the object, so lets return "marked"
return true;
}
void MarkSweep::VerifyIsLive(const Object* obj) {
Heap* heap = GetHeap();
if (!heap->GetLiveBitmap()->Test(obj)) {
if (std::find(heap->allocation_stack_->Begin(), heap->allocation_stack_->End(), obj) ==
heap->allocation_stack_->End()) {
// Object not found!
heap->DumpSpaces();
LOG(FATAL) << "Found dead object " << obj;
}
}
}
void MarkSweep::VerifySystemWeaks() {
Runtime* runtime = Runtime::Current();
// Verify system weaks, uses a special IsMarked callback which always returns true.
runtime->GetInternTable()->SweepInternTableWeaks(VerifyIsLiveCallback, this);
runtime->GetMonitorList()->SweepMonitorList(VerifyIsLiveCallback, this);
JavaVMExt* vm = runtime->GetJavaVM();
MutexLock mu(vm->weak_globals_lock);
IndirectReferenceTable* table = &vm->weak_globals;
typedef IndirectReferenceTable::iterator It; // TODO: C++0x auto
for (It it = table->begin(), end = table->end(); it != end; ++it) {
const Object** entry = *it;
VerifyIsLive(*entry);
}
}
struct SweepCallbackContext {
MarkSweep* mark_sweep;
AllocSpace* space;
};
void MarkSweep::SweepCallback(size_t num_ptrs, Object** ptrs, void* arg) {
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
size_t freed_objects = num_ptrs;
size_t freed_bytes = 0;
SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg);
MarkSweep* mark_sweep = context->mark_sweep;
Heap* heap = mark_sweep->GetHeap();
AllocSpace* space = context->space;
// Use a bulk free, that merges consecutive objects before freeing or free per object?
// Documentation suggests better free performance with merging, but this may be at the expensive
// of allocation.
// TODO: investigate performance
static const bool kUseFreeList = true;
if (kUseFreeList) {
for (size_t i = 0; i < num_ptrs; ++i) {
Object* obj = static_cast<Object*>(ptrs[i]);
freed_bytes += space->AllocationSize(obj);
}
// AllocSpace::FreeList clears the value in ptrs, so perform after clearing the live bit
space->FreeList(num_ptrs, ptrs);
} else {
for (size_t i = 0; i < num_ptrs; ++i) {
Object* obj = static_cast<Object*>(ptrs[i]);
freed_bytes += space->AllocationSize(obj);
space->Free(obj);
}
}
heap->RecordFree(freed_objects, freed_bytes);
mark_sweep->freed_objects_ += freed_objects;
mark_sweep->freed_bytes_ += freed_bytes;
}
void MarkSweep::ZygoteSweepCallback(size_t num_ptrs, Object** ptrs, void* arg) {
Locks::heap_bitmap_lock_->AssertExclusiveHeld(Thread::Current());
SweepCallbackContext* context = static_cast<SweepCallbackContext*>(arg);
Heap* heap = context->mark_sweep->GetHeap();
// We don't free any actual memory to avoid dirtying the shared zygote pages.
for (size_t i = 0; i < num_ptrs; ++i) {
Object* obj = static_cast<Object*>(ptrs[i]);
heap->GetLiveBitmap()->Clear(obj);
heap->GetCardTable()->MarkCard(obj);
}
}
void MarkSweep::SweepArray(TimingLogger& logger, MarkStack* allocations, bool swap_bitmaps) {
size_t freed_bytes = 0;
AllocSpace* space = heap_->GetAllocSpace();
// If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark
// bitmap, resulting in occasional frees of Weaks which are still in use.
// TODO: Fix when sweeping weaks works properly with mutators unpaused + allocation list.
// SweepSystemWeaks(swap_bitmaps);
// Newly allocated objects MUST be in the alloc space and those are the only objects which we are
// going to free.
SpaceBitmap* live_bitmap = space->GetLiveBitmap();
SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects();
SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
std::swap(large_live_objects, large_mark_objects);
}
size_t freed_large_objects = 0;
size_t count = allocations->Size();
Object** objects = allocations->Begin();
Object** out = objects;
// Empty the allocation stack.
for (size_t i = 0;i < count;++i) {
Object* obj = objects[i];
// There should only be objects in the AllocSpace/LargeObjectSpace in the allocation stack.
if (LIKELY(mark_bitmap->HasAddress(obj))) {
if (!mark_bitmap->Test(obj)) {
// Don't bother un-marking since we clear the mark bitmap anyways.
*(out++) = obj;
size_t size = space->AllocationSize(obj);
freed_bytes += size;
}
} else if (!large_mark_objects->Test(obj)) {
++freed_large_objects;
size_t size = large_object_space->AllocationSize(obj);
freed_bytes_ += size;
large_object_space->Free(obj);
}
}
logger.AddSplit("Process allocation stack");
size_t freed_objects = out - objects;
VLOG(heap) << "Freed " << freed_objects << "/" << count
<< " objects with size " << PrettySize(freed_bytes);
space->FreeList(freed_objects, objects);
heap_->RecordFree(freed_objects + freed_large_objects, freed_bytes);
freed_objects_ += freed_objects;
freed_bytes_ += freed_bytes;
logger.AddSplit("FreeList");
allocations->Reset();
logger.AddSplit("Reset stack");
}
void MarkSweep::Sweep(bool partial, bool swap_bitmaps) {
DCHECK(mark_stack_->IsEmpty());
// If we don't swap bitmaps then newly allocated Weaks go into the live bitmap but not mark
// bitmap, resulting in occasional frees of Weaks which are still in use.
// SweepSystemWeaks(swap_bitmaps);
const Spaces& spaces = heap_->GetSpaces();
SweepCallbackContext scc;
scc.mark_sweep = this;
// TODO: C++0x auto
for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
Space* space = *it;
if (
space->GetGcRetentionPolicy() == GCRP_ALWAYS_COLLECT ||
(!partial && space->GetGcRetentionPolicy() == GCRP_FULL_COLLECT)
) {
uintptr_t begin = reinterpret_cast<uintptr_t>(space->Begin());
uintptr_t end = reinterpret_cast<uintptr_t>(space->End());
scc.space = space->AsAllocSpace();
SpaceBitmap* live_bitmap = space->GetLiveBitmap();
SpaceBitmap* mark_bitmap = space->GetMarkBitmap();
if (swap_bitmaps) {
std::swap(live_bitmap, mark_bitmap);
}
if (space->GetGcRetentionPolicy() == GCRP_ALWAYS_COLLECT) {
// Bitmaps are pre-swapped for optimization which enables sweeping with the heap unlocked.
SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end,
&SweepCallback, reinterpret_cast<void*>(&scc));
} else {
// Zygote sweep takes care of dirtying cards and clearing live bits, does not free actual memory.
SpaceBitmap::SweepWalk(*live_bitmap, *mark_bitmap, begin, end,
&ZygoteSweepCallback, reinterpret_cast<void*>(&scc));
}
}
}
}
void MarkSweep::SweepLargeObjects(bool swap_bitmaps) {
// Sweep large objects
LargeObjectSpace* large_object_space = GetHeap()->GetLargeObjectsSpace();
MutexLock mu(large_object_space->GetLock());
SpaceSetMap* large_live_objects = large_object_space->GetLiveObjects();
SpaceSetMap* large_mark_objects = large_object_space->GetMarkObjects();
if (swap_bitmaps) {
std::swap(large_live_objects, large_mark_objects);
}
SpaceSetMap::Objects& live_objects = large_live_objects->GetObjects();
// O(n*log(n)) but hopefully there are not too many large objects.
size_t freed_objects = 0;
// TODO: C++0x
for (SpaceSetMap::Objects::iterator it = live_objects.begin(); it != live_objects.end(); ++it) {
if (!large_mark_objects->Test(*it)) {
freed_bytes_ += large_object_space->AllocationSize(*it);
large_object_space->Free(const_cast<Object*>(*it));
++freed_objects;
}
}
freed_objects_ += freed_objects;
// Large objects don't count towards bytes_allocated.
GetHeap()->RecordFree(freed_objects, 0);
}
// Scans instance fields.
inline void MarkSweep::ScanInstanceFields(const Object* obj) {
DCHECK(obj != NULL);
Class* klass = obj->GetClass();
DCHECK(klass != NULL);
ScanFields(obj, klass->GetReferenceInstanceOffsets(), false);
}
// Scans static storage on a Class.
inline void MarkSweep::ScanStaticFields(const Class* klass) {
DCHECK(klass != NULL);
ScanFields(klass, klass->GetReferenceStaticOffsets(), true);
}
inline void MarkSweep::ScanFields(const Object* obj, uint32_t ref_offsets, bool is_static) {
if (ref_offsets != CLASS_WALK_SUPER) {
// Found a reference offset bitmap. Mark the specified offsets.
while (ref_offsets != 0) {
const size_t right_shift = CLZ(ref_offsets);
MemberOffset byte_offset = CLASS_OFFSET_FROM_CLZ(right_shift);
const Object* ref = obj->GetFieldObject<const Object*>(byte_offset, false);
MarkObject(ref);
ref_offsets ^= CLASS_HIGH_BIT >> right_shift;
}
} else {
// There is no reference offset bitmap. In the non-static case,
// walk up the class inheritance hierarchy and find reference
// offsets the hard way. In the static case, just consider this
// class.
for (const Class* klass = is_static ? obj->AsClass() : obj->GetClass();
klass != NULL;
klass = is_static ? NULL : klass->GetSuperClass()) {
size_t num_reference_fields = (is_static
? klass->NumReferenceStaticFields()
: klass->NumReferenceInstanceFields());
for (size_t i = 0; i < num_reference_fields; ++i) {
Field* field = (is_static
? klass->GetStaticField(i)
: klass->GetInstanceField(i));
MemberOffset field_offset = field->GetOffset();
const Object* ref = obj->GetFieldObject<const Object*>(field_offset, false);
MarkObject(ref);
}
}
}
}
void MarkSweep::CheckReference(const Object* obj, const Object* ref, MemberOffset offset, bool is_static) {
const Spaces& spaces = heap_->GetSpaces();
// TODO: C++0x auto
for (Spaces::const_iterator cur = spaces.begin(); cur != spaces.end(); ++cur) {
if ((*cur)->IsAllocSpace() && (*cur)->Contains(ref)) {
DCHECK(IsMarked(obj));
bool is_marked = IsMarked(ref);
if (!is_marked) {
LOG(INFO) << **cur;
LOG(WARNING) << (is_static ? "Static ref'" : "Instance ref'") << PrettyTypeOf(ref)
<< "' (" << reinterpret_cast<const void*>(ref) << ") in '" << PrettyTypeOf(obj)
<< "' (" << reinterpret_cast<const void*>(obj) << ") at offset "
<< reinterpret_cast<void*>(offset.Int32Value()) << " wasn't marked";
const Class* klass = is_static ? obj->AsClass() : obj->GetClass();
DCHECK(klass != NULL);
const ObjectArray<Field>* fields = is_static ? klass->GetSFields() : klass->GetIFields();
DCHECK(fields != NULL);
bool found = false;
for (int32_t i = 0; i < fields->GetLength(); ++i) {
const Field* cur = fields->Get(i);
if (cur->GetOffset().Int32Value() == offset.Int32Value()) {
LOG(WARNING) << "Field referencing the alloc space was " << PrettyField(cur);
found = true;
break;
}
}
if (!found) {
LOG(WARNING) << "Could not find field in object alloc space with offset " << offset.Int32Value();
}
bool obj_marked = heap_->GetCardTable()->IsDirty(obj);
if (!obj_marked) {
LOG(WARNING) << "Object '" << PrettyTypeOf(obj) << "' "
<< "(" << reinterpret_cast<const void*>(obj) << ") contains references to "
<< "the alloc space, but wasn't card marked";
}
}
}
break;
}
}
// Scans the header, static field references, and interface pointers
// of a class object.
inline void MarkSweep::ScanClass(const Object* obj) {
#ifndef NDEBUG
++class_count_;
#endif
ScanInstanceFields(obj);
ScanStaticFields(obj->AsClass());
}
// Scans the header of all array objects. If the array object is
// specialized to a reference type, scans the array data as well.
inline void MarkSweep::ScanArray(const Object* obj) {
#ifndef NDEBUG
++array_count_;
#endif
MarkObject(obj->GetClass());
if (obj->IsObjectArray()) {
const ObjectArray<Object>* array = obj->AsObjectArray<Object>();
for (int32_t i = 0; i < array->GetLength(); ++i) {
const Object* element = array->GetWithoutChecks(i);
MarkObject(element);
}
}
}
// Process the "referent" field in a java.lang.ref.Reference. If the
// referent has not yet been marked, put it on the appropriate list in
// the gcHeap for later processing.
void MarkSweep::DelayReferenceReferent(Object* obj) {
DCHECK(obj != NULL);
Class* klass = obj->GetClass();
DCHECK(klass != NULL);
DCHECK(klass->IsReferenceClass());
Object* pending = obj->GetFieldObject<Object*>(heap_->GetReferencePendingNextOffset(), false);
Object* referent = heap_->GetReferenceReferent(obj);
if (pending == NULL && referent != NULL && !IsMarked(referent)) {
Object** list = NULL;
if (klass->IsSoftReferenceClass()) {
list = &soft_reference_list_;
} else if (klass->IsWeakReferenceClass()) {
list = &weak_reference_list_;
} else if (klass->IsFinalizerReferenceClass()) {
list = &finalizer_reference_list_;
} else if (klass->IsPhantomReferenceClass()) {
list = &phantom_reference_list_;
}
DCHECK(list != NULL) << PrettyClass(klass) << " " << std::hex << klass->GetAccessFlags();
heap_->EnqueuePendingReference(obj, list);
}
}
// Scans the header and field references of a data object. If the
// scanned object is a reference subclass, it is scheduled for later
// processing.
inline void MarkSweep::ScanOther(const Object* obj) {
#ifndef NDEBUG
++other_count_;
#endif
ScanInstanceFields(obj);
if (obj->GetClass()->IsReferenceClass()) {
DelayReferenceReferent(const_cast<Object*>(obj));
}
}
void MarkSweep::ScanRoot(const Object* obj) {
ScanObject(obj);
}
// Scans an object reference. Determines the type of the reference
// and dispatches to a specialized scanning routine.
void MarkSweep::ScanObject(const Object* obj) {
DCHECK(obj != NULL);
DCHECK(obj->GetClass() != NULL);
#ifndef NDEBUG
if (!IsMarked(obj)) {
heap_->DumpSpaces();
LOG(FATAL) << "Scanning unmarked object " << reinterpret_cast<const void*>(obj);
}
#endif
if (obj->IsClass()) {
ScanClass(obj);
} else if (obj->IsArrayInstance()) {
ScanArray(obj);
} else {
ScanOther(obj);
}
}
// Scan anything that's on the mark stack.
void MarkSweep::ProcessMarkStack() {
#if MARK_STACK_PREFETCH
const size_t fifo_size = 4;
const size_t fifo_mask = fifo_size - 1;
const Object* fifo[fifo_size];
for (size_t i = 0;i < fifo_size;++i) {
fifo[i] = NULL;
}
size_t fifo_pos = 0;
size_t fifo_count = 0;
for (;;) {
const Object* obj = fifo[fifo_pos & fifo_mask];
if (obj != NULL) {
ScanObject(obj);
fifo[fifo_pos & fifo_mask] = NULL;
--fifo_count;
}
if (!mark_stack_->IsEmpty()) {
const Object* obj = mark_stack_->Pop();
DCHECK(obj != NULL);
fifo[fifo_pos & fifo_mask] = obj;
__builtin_prefetch(obj);
fifo_count++;
}
fifo_pos++;
if (!fifo_count) {
CHECK(mark_stack_->IsEmpty()) << mark_stack_->Size();
break;
}
}
#else
while (!mark_stack_->IsEmpty()) {
const Object* obj = mark_stack_->Pop();
DCHECK(obj != NULL);
ScanObject(obj);
}
#endif
}
// Walks the reference list marking any references subject to the
// reference clearing policy. References with a black referent are
// removed from the list. References with white referents biased
// toward saving are blackened and also removed from the list.
void MarkSweep::PreserveSomeSoftReferences(Object** list) {
DCHECK(list != NULL);
Object* clear = NULL;
size_t counter = 0;
DCHECK(mark_stack_->IsEmpty());
while (*list != NULL) {
Object* ref = heap_->DequeuePendingReference(list);
Object* referent = heap_->GetReferenceReferent(ref);
if (referent == NULL) {
// Referent was cleared by the user during marking.
continue;
}
bool is_marked = IsMarked(referent);
if (!is_marked && ((++counter) & 1)) {
// Referent is white and biased toward saving, mark it.
MarkObject(referent);
is_marked = true;
}
if (!is_marked) {
// Referent is white, queue it for clearing.
heap_->EnqueuePendingReference(ref, &clear);
}
}
*list = clear;
// Restart the mark with the newly black references added to the
// root set.
ProcessMarkStack();
}
// Unlink the reference list clearing references objects with white
// referents. Cleared references registered to a reference queue are
// scheduled for appending by the heap worker thread.
void MarkSweep::ClearWhiteReferences(Object** list) {
DCHECK(list != NULL);
while (*list != NULL) {
Object* ref = heap_->DequeuePendingReference(list);
Object* referent = heap_->GetReferenceReferent(ref);
if (referent != NULL && !IsMarked(referent)) {
// Referent is white, clear it.
heap_->ClearReferenceReferent(ref);
if (heap_->IsEnqueuable(ref)) {
heap_->EnqueueReference(ref, &cleared_reference_list_);
}
}
}
DCHECK(*list == NULL);
}
// Enqueues finalizer references with white referents. White
// referents are blackened, moved to the zombie field, and the
// referent field is cleared.
void MarkSweep::EnqueueFinalizerReferences(Object** list) {
DCHECK(list != NULL);
MemberOffset zombie_offset = heap_->GetFinalizerReferenceZombieOffset();
bool has_enqueued = false;
while (*list != NULL) {
Object* ref = heap_->DequeuePendingReference(list);
Object* referent = heap_->GetReferenceReferent(ref);
if (referent != NULL && !IsMarked(referent)) {
MarkObject(referent);
// If the referent is non-null the reference must queuable.
DCHECK(heap_->IsEnqueuable(ref));
ref->SetFieldObject(zombie_offset, referent, false);
heap_->ClearReferenceReferent(ref);
heap_->EnqueueReference(ref, &cleared_reference_list_);
has_enqueued = true;
}
}
if (has_enqueued) {
ProcessMarkStack();
}
DCHECK(*list == NULL);
}
// Process reference class instances and schedule finalizations.
void MarkSweep::ProcessReferences(Object** soft_references, bool clear_soft,
Object** weak_references,
Object** finalizer_references,
Object** phantom_references) {
DCHECK(soft_references != NULL);
DCHECK(weak_references != NULL);
DCHECK(finalizer_references != NULL);
DCHECK(phantom_references != NULL);
// Unless we are in the zygote or required to clear soft references
// with white references, preserve some white referents.
if (!clear_soft && !Runtime::Current()->IsZygote()) {
PreserveSomeSoftReferences(soft_references);
}
// Clear all remaining soft and weak references with white
// referents.
ClearWhiteReferences(soft_references);
ClearWhiteReferences(weak_references);
// Preserve all white objects with finalize methods and schedule
// them for finalization.
EnqueueFinalizerReferences(finalizer_references);
// Clear all f-reachable soft and weak references with white
// referents.
ClearWhiteReferences(soft_references);
ClearWhiteReferences(weak_references);
// Clear all phantom references with white referents.
ClearWhiteReferences(phantom_references);
// At this point all reference lists should be empty.
DCHECK(*soft_references == NULL);
DCHECK(*weak_references == NULL);
DCHECK(*finalizer_references == NULL);
DCHECK(*phantom_references == NULL);
}
MarkSweep::~MarkSweep() {
#ifndef NDEBUG
VLOG(heap) << "MarkSweep scanned classes=" << class_count_ << " arrays=" << array_count_ << " other=" << other_count_;
#endif
// Ensure that the mark stack is empty.
CHECK(mark_stack_->IsEmpty());
// Clear all of the alloc spaces' mark bitmaps.
const Spaces& spaces = heap_->GetSpaces();
// TODO: C++0x auto
for (Spaces::const_iterator it = spaces.begin(); it != spaces.end(); ++it) {
if ((*it)->GetGcRetentionPolicy() != GCRP_NEVER_COLLECT) {
(*it)->GetMarkBitmap()->Clear();
}
}
mark_stack_->Reset();
// Reset the marked large objects.
LargeObjectSpace* large_objects = GetHeap()->GetLargeObjectsSpace();
MutexLock mu(large_objects->GetLock());
large_objects->GetMarkObjects()->Clear();
}
} // namespace art