blob: 71983fef4e446e9e87e4019ff58f4aed2af369e8 [file] [log] [blame]
// Copyright 2011 Google Inc. All Rights Reserved.
#include "mark_sweep.h"
#include <climits>
#include <vector>
#include "class_loader.h"
#include "dex_cache.h"
#include "heap.h"
#include "indirect_reference_table.h"
#include "intern_table.h"
#include "logging.h"
#include "macros.h"
#include "mark_stack.h"
#include "monitor.h"
#include "object.h"
#include "runtime.h"
#include "space.h"
#include "timing_logger.h"
#include "thread.h"
namespace art {
bool MarkSweep::Init() {
mark_stack_ = MarkStack::Create();
if (mark_stack_ == NULL) {
return false;
}
mark_bitmap_ = Heap::GetMarkBits();
live_bitmap_ = Heap::GetLiveBits();
// TODO: if concurrent, clear the card table.
// TODO: if concurrent, enable card marking in compiler
// TODO: check that the mark bitmap is entirely clear.
return true;
}
inline void MarkSweep::MarkObject0(const Object* obj, bool check_finger) {
DCHECK(obj != NULL);
if (obj < condemned_) {
DCHECK(IsMarked(obj));
return;
}
bool is_marked = mark_bitmap_->Test(obj);
// This object was not previously marked.
if (!is_marked) {
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.
inline 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, true);
}
// Marks all objects in the root set.
void MarkSweep::MarkRoots() {
Runtime::Current()->VisitRoots(MarkObjectVisitor, this);
}
void MarkSweep::ScanBitmapCallback(Object* obj, void* finger, void* arg) {
MarkSweep* mark_sweep = reinterpret_cast<MarkSweep*>(arg);
mark_sweep->finger_ = reinterpret_cast<Object*>(finger);
mark_sweep->ScanObject(obj);
}
// Populates the mark stack based on the set of marked objects and
// recursively marks until the mark stack is emptied.
void MarkSweep::RecursiveMark() {
// 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);
TimingLogger timings("MarkSweep::RecursiveMark");
void* arg = reinterpret_cast<void*>(this);
const std::vector<Space*>& spaces = Heap::GetSpaces();
for (size_t i = 0; i < spaces.size(); ++i) {
if (!spaces[i]->IsImageSpace()) {
uintptr_t base = reinterpret_cast<uintptr_t>(spaces[i]->GetBase());
mark_bitmap_->ScanWalk(base, &MarkSweep::ScanBitmapCallback, arg);
}
timings.AddSplit(StringPrintf("ScanWalk space #%i (%s)", i, spaces[i]->GetName().c_str()));
}
finger_ = reinterpret_cast<Object*>(~0);
ProcessMarkStack();
timings.AddSplit("ProcessMarkStack");
timings.Dump();
}
void MarkSweep::ReMarkRoots() {
UNIMPLEMENTED(FATAL);
}
void MarkSweep::SweepJniWeakGlobals() {
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 (!IsMarked(*entry)) {
*entry = kClearedJniWeakGlobal;
}
}
}
void MarkSweep::SweepSystemWeaks() {
Runtime::Current()->GetInternTable()->SweepInternTableWeaks(IsMarked, this);
Runtime::Current()->GetMonitorList()->SweepMonitorList(IsMarked, this);
SweepJniWeakGlobals();
}
void MarkSweep::SweepCallback(size_t num_ptrs, void** ptrs, void* arg) {
// TODO: lock heap if concurrent
size_t freed_objects = num_ptrs;
size_t freed_bytes = 0;
Space* space = static_cast<Space*>(arg);
for (size_t i = 0; i < num_ptrs; ++i) {
Object* obj = static_cast<Object*>(ptrs[i]);
freed_bytes += space->AllocationSize(obj);
Heap::GetLiveBits()->Clear(obj);
space->Free(obj);
}
Heap::RecordFreeLocked(freed_objects, freed_bytes);
// TODO: unlock heap if concurrent
}
void MarkSweep::Sweep() {
SweepSystemWeaks();
const std::vector<Space*>& spaces = Heap::GetSpaces();
for (size_t i = 0; i < spaces.size(); ++i) {
if (!spaces[i]->IsImageSpace()) {
uintptr_t base = reinterpret_cast<uintptr_t>(spaces[i]->GetBase());
uintptr_t limit = reinterpret_cast<uintptr_t>(spaces[i]->GetLimit());
void* arg = static_cast<void*>(spaces[i]);
HeapBitmap::SweepWalk(*live_bitmap_, *mark_bitmap_, base, limit,
&MarkSweep::SweepCallback, arg);
}
}
}
// 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) {
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);
}
}
}
}
// Scans the header, static field references, and interface pointers
// of a class object.
inline void MarkSweep::ScanClass(const Object* obj) {
DCHECK(obj != NULL);
DCHECK(obj->IsClass());
const Class* klass = obj->AsClass();
MarkObject(klass->GetClass());
ScanInstanceFields(obj);
MarkObject(klass->GetDescriptor());
MarkObject(klass->GetDexCache());
MarkObject(klass->GetVerifyErrorClass());
if (klass->IsArrayClass()) {
MarkObject(klass->GetComponentType());
}
if (klass->IsLoaded()) {
MarkObject(klass->GetSuperClass());
}
MarkObject(klass->GetClassLoader());
if (klass->IsLoaded()) {
MarkObject(klass->GetInterfaces());
MarkObject(klass->GetDirectMethods());
MarkObject(klass->GetVirtualMethods());
MarkObject(klass->GetIFields());
MarkObject(klass->GetSFields());
}
ScanStaticFields(klass);
}
// 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) {
DCHECK(obj != NULL);
DCHECK(obj->GetClass() != NULL);
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->Get(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) {
DCHECK(obj != NULL);
Class* klass = obj->GetClass();
DCHECK(klass != NULL);
MarkObject(klass);
ScanInstanceFields(obj);
if (klass->IsReferenceClass()) {
DelayReferenceReferent(const_cast<Object*>(obj));
}
}
// Scans an object reference. Determines the type of the reference
// and dispatches to a specialized scanning routine.
inline void MarkSweep::ScanObject(const Object* obj) {
DCHECK(obj != NULL);
DCHECK(obj->GetClass() != NULL);
DCHECK(IsMarked(obj));
if (obj->IsClass()) {
ScanClass(obj);
} else if (obj->IsArrayInstance()) {
ScanArray(obj);
} else {
ScanOther(obj);
}
}
// Scan anything that's on the mark stack. We can't use the bitmaps
// anymore, so use a finger that points past the end of them.
void MarkSweep::ProcessMarkStack() {
while (!mark_stack_->IsEmpty()) {
const Object* obj = mark_stack_->Pop();
ScanObject(obj);
}
}
void MarkSweep::ScanDirtyObjects() {
ProcessMarkStack();
}
// 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;
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) {
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() {
delete mark_stack_;
mark_bitmap_->Clear();
}
} // namespace art