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* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <memory>
#include "base/locks.h"
#include "base/mem_map.h"
#include "runtime_globals.h"
namespace art {
namespace mirror {
class Object;
} // namespace mirror
namespace gc {
namespace space {
class ContinuousSpace;
} // namespace space
class Heap;
namespace accounting {
template<size_t kAlignment> class SpaceBitmap;
// Maintain a card table from the the write barrier. All writes of
// non-null values to heap addresses should go through an entry in
// WriteBarrier, and from there to here.
class CardTable {
static constexpr size_t kCardShift = 10;
static constexpr size_t kCardSize = 1 << kCardShift;
static constexpr uint8_t kCardClean = 0x0;
static constexpr uint8_t kCardDirty = 0x70;
static constexpr uint8_t kCardAged = kCardDirty - 1;
static CardTable* Create(const uint8_t* heap_begin, size_t heap_capacity);
// Set the card associated with the given address to `kCardDirty`.
ALWAYS_INLINE void MarkCard(const void *addr) {
*CardFromAddr(addr) = kCardDirty;
// Is the object on a dirty card?
bool IsDirty(const mirror::Object* obj) const {
return GetCard(obj) == kCardDirty;
// Is the object on a clean card?
bool IsClean(const mirror::Object* obj) const {
return GetCard(obj) == kCardClean;
// Return the state of the card at an address.
uint8_t GetCard(const mirror::Object* obj) const {
return *CardFromAddr(obj);
// Visit and clear cards within memory range, only visits dirty cards.
template <typename Visitor>
void VisitClear(const void* start, const void* end, const Visitor& visitor) {
uint8_t* card_start = CardFromAddr(start);
uint8_t* card_end = CardFromAddr(end);
for (uint8_t* it = card_start; it != card_end; ++it) {
if (*it == kCardDirty) {
*it = kCardClean;
// Returns a value that when added to a heap address >> `kCardShift` will address the appropriate
// card table byte. For convenience this value is cached in every Thread.
uint8_t* GetBiasedBegin() const {
return biased_begin_;
* Modify cards in the range from scan_begin (inclusive) to scan_end (exclusive). Each card
* value v is replaced by visitor(v). Visitor() should not have side-effects.
* Whenever a card value is changed, modified(card_address, old_value, new_value) is invoked.
* For opportunistic performance reasons, this assumes that visitor(kCardClean) is kCardClean!
template <typename Visitor, typename ModifiedVisitor>
void ModifyCardsAtomic(uint8_t* scan_begin,
uint8_t* scan_end,
const Visitor& visitor,
const ModifiedVisitor& modified);
// For every dirty at least minumum age between begin and end invoke the visitor with the
// specified argument. Returns how many cards the visitor was run on.
template <bool kClearCard, typename Visitor>
size_t Scan(SpaceBitmap<kObjectAlignment>* bitmap,
uint8_t* scan_begin,
uint8_t* scan_end,
const Visitor& visitor,
const uint8_t minimum_age = kCardDirty)
// Assertion used to check the given address is covered by the card table
void CheckAddrIsInCardTable(const uint8_t* addr) const;
// Resets all of the bytes in the card table to clean.
void ClearCardTable();
// Clear a range of cards that covers start to end, start and end must be aligned to kCardSize.
void ClearCardRange(uint8_t* start, uint8_t* end);
// Returns the first address in the heap which maps to this card.
void* AddrFromCard(const uint8_t *card_addr) const ALWAYS_INLINE;
// Returns the address of the relevant byte in the card table, given an address on the heap.
uint8_t* CardFromAddr(const void *addr) const ALWAYS_INLINE;
bool AddrIsInCardTable(const void* addr) const;
CardTable(MemMap&& mem_map, uint8_t* biased_begin, size_t offset);
// Returns true iff the card table address is within the bounds of the card table.
bool IsValidCard(const uint8_t* card_addr) const ALWAYS_INLINE;
void CheckCardValid(uint8_t* card) const ALWAYS_INLINE;
// Verifies that all gray objects are on a dirty card.
void VerifyCardTable();
// Mmapped pages for the card table
MemMap mem_map_;
// Value used to compute card table addresses from object addresses, see GetBiasedBegin
uint8_t* const biased_begin_;
// Card table doesn't begin at the beginning of the mem_map_, instead it is displaced by offset
// to allow the byte value of `biased_begin_` to equal `kCardDirty`.
const size_t offset_;
} // namespace accounting
class AgeCardVisitor {
uint8_t operator()(uint8_t card) const {
return (card == accounting::CardTable::kCardDirty) ? card - 1 : 0;
} // namespace gc
} // namespace art