card_table.h revision 2c26501d24d929abe096ecce44f91410290b33c0 
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#ifndef ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_H_
18#define ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_H_
19
20#include <memory>
21
22#include "base/mutex.h"
23#include "globals.h"
24#include "mem_map.h"
25
26namespace art {
27
28namespace mirror {
29  class Object;
30}  // namespace mirror
31
32namespace gc {
33
34namespace space {
35  class ContinuousSpace;
36}  // namespace space
37
38class Heap;
39
40namespace accounting {
41
42template<size_t kAlignment> class SpaceBitmap;
43
44// Maintain a card table from the the write barrier. All writes of
45// non-NULL values to heap addresses should go through an entry in
46// WriteBarrier, and from there to here.
47class CardTable {
48 public:
49  static constexpr size_t kCardShift = 7;
50  static constexpr size_t kCardSize = 1 << kCardShift;
51  static constexpr uint8_t kCardClean = 0x0;
52  static constexpr uint8_t kCardDirty = 0x70;
53
54  static CardTable* Create(const byte* heap_begin, size_t heap_capacity);
55
56  // Set the card associated with the given address to GC_CARD_DIRTY.
57  void MarkCard(const void *addr) {
58    byte* card_addr = CardFromAddr(addr);
59    *card_addr = kCardDirty;
60  }
61
62  // Is the object on a dirty card?
63  bool IsDirty(const mirror::Object* obj) const {
64    return GetCard(obj) == kCardDirty;
65  }
66
67  // Return the state of the card at an address.
68  byte GetCard(const mirror::Object* obj) const {
69    return *CardFromAddr(obj);
70  }
71
72  // Visit and clear cards within memory range, only visits dirty cards.
73  template <typename Visitor>
74  void VisitClear(const void* start, const void* end, const Visitor& visitor) {
75    byte* card_start = CardFromAddr(start);
76    byte* card_end = CardFromAddr(end);
77    for (byte* it = card_start; it != card_end; ++it) {
78      if (*it == kCardDirty) {
79        *it = kCardClean;
80        visitor(it);
81      }
82    }
83  }
84
85  // Returns a value that when added to a heap address >> GC_CARD_SHIFT will address the appropriate
86  // card table byte. For convenience this value is cached in every Thread
87  byte* GetBiasedBegin() const {
88    return biased_begin_;
89  }
90
91  /*
92   * Visitor is expected to take in a card and return the new value. When a value is modified, the
93   * modify visitor is called.
94   * visitor: The visitor which modifies the cards. Returns the new value for a card given an old
95   * value.
96   * modified: Whenever the visitor modifies a card, this visitor is called on the card. Enables
97   * us to know which cards got cleared.
98   */
99  template <typename Visitor, typename ModifiedVisitor>
100  void ModifyCardsAtomic(byte* scan_begin, byte* scan_end, const Visitor& visitor,
101                         const ModifiedVisitor& modified);
102
103  // For every dirty at least minumum age between begin and end invoke the visitor with the
104  // specified argument. Returns how many cards the visitor was run on.
105  template <typename Visitor>
106  size_t Scan(SpaceBitmap<kObjectAlignment>* bitmap, byte* scan_begin, byte* scan_end,
107              const Visitor& visitor,
108              const byte minimum_age = kCardDirty) const
109      EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
110      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
111
112  // Assertion used to check the given address is covered by the card table
113  void CheckAddrIsInCardTable(const byte* addr) const;
114
115  // Resets all of the bytes in the card table to clean.
116  void ClearCardTable();
117
118  // Resets all of the bytes in the card table which do not map to the image space.
119  void ClearSpaceCards(space::ContinuousSpace* space);
120
121  // Returns the first address in the heap which maps to this card.
122  void* AddrFromCard(const byte *card_addr) const ALWAYS_INLINE;
123
124  // Returns the address of the relevant byte in the card table, given an address on the heap.
125  byte* CardFromAddr(const void *addr) const ALWAYS_INLINE;
126
127  bool AddrIsInCardTable(const void* addr) const;
128
129 private:
130  CardTable(MemMap* begin, byte* biased_begin, size_t offset);
131
132  // Returns true iff the card table address is within the bounds of the card table.
133  bool IsValidCard(const byte* card_addr) const {
134    byte* begin = mem_map_->Begin() + offset_;
135    byte* end = mem_map_->End();
136    return card_addr >= begin && card_addr < end;
137  }
138
139  void CheckCardValid(byte* card) const ALWAYS_INLINE;
140
141  // Verifies that all gray objects are on a dirty card.
142  void VerifyCardTable();
143
144  // Mmapped pages for the card table
145  std::unique_ptr<MemMap> mem_map_;
146  // Value used to compute card table addresses from object addresses, see GetBiasedBegin
147  byte* const biased_begin_;
148  // Card table doesn't begin at the beginning of the mem_map_, instead it is displaced by offset
149  // to allow the byte value of biased_begin_ to equal GC_CARD_DIRTY
150  const size_t offset_;
151};
152
153}  // namespace accounting
154}  // namespace gc
155}  // namespace art
156
157#endif  // ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_H_
158