card_table.h revision 507dfdd147c97bfbadebfd63584d094b6a4e7b47 
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 "base/mutex.h"
21#include "globals.h"
22#include "mem_map.h"
23#include "UniquePtrCompat.h"
24
25namespace art {
26
27namespace mirror {
28  class Object;
29}  // namespace mirror
30
31namespace gc {
32
33namespace space {
34  class ContinuousSpace;
35}  // namespace space
36
37class Heap;
38
39namespace accounting {
40
41template<size_t kAlignment> class SpaceBitmap;
42
43// Maintain a card table from the the write barrier. All writes of
44// non-NULL values to heap addresses should go through an entry in
45// WriteBarrier, and from there to here.
46class CardTable {
47 public:
48  static const size_t kCardShift = 7;
49  static const size_t kCardSize = (1 << kCardShift);
50  static const uint8_t kCardClean = 0x0;
51  static const uint8_t kCardDirty = 0x70;
52
53  static CardTable* Create(const byte* heap_begin, size_t heap_capacity);
54
55  // Set the card associated with the given address to GC_CARD_DIRTY.
56  void MarkCard(const void *addr) {
57    byte* card_addr = CardFromAddr(addr);
58    *card_addr = kCardDirty;
59  }
60
61  // Is the object on a dirty card?
62  bool IsDirty(const mirror::Object* obj) const {
63    return GetCard(obj) == kCardDirty;
64  }
65
66  // Return the state of the card at an address.
67  byte GetCard(const mirror::Object* obj) const {
68    return *CardFromAddr(obj);
69  }
70
71  // Visit and clear cards within memory range, only visits dirty cards.
72  template <typename Visitor>
73  void VisitClear(const void* start, const void* end, const Visitor& visitor) {
74    byte* card_start = CardFromAddr(start);
75    byte* card_end = CardFromAddr(end);
76    for (byte* it = card_start; it != card_end; ++it) {
77      if (*it == kCardDirty) {
78        *it = kCardClean;
79        visitor(it);
80      }
81    }
82  }
83
84  // Returns a value that when added to a heap address >> GC_CARD_SHIFT will address the appropriate
85  // card table byte. For convenience this value is cached in every Thread
86  byte* GetBiasedBegin() const {
87    return biased_begin_;
88  }
89
90  /*
91   * Visitor is expected to take in a card and return the new value. When a value is modified, the
92   * modify visitor is called.
93   * visitor: The visitor which modifies the cards. Returns the new value for a card given an old
94   * value.
95   * modified: Whenever the visitor modifies a card, this visitor is called on the card. Enables
96   * us to know which cards got cleared.
97   */
98  template <typename Visitor, typename ModifiedVisitor>
99  void ModifyCardsAtomic(byte* scan_begin, byte* scan_end, const Visitor& visitor,
100                         const ModifiedVisitor& modified);
101
102  // For every dirty at least minumum age between begin and end invoke the visitor with the
103  // specified argument. Returns how many cards the visitor was run on.
104  template <typename Visitor>
105  size_t Scan(SpaceBitmap<kObjectAlignment>* bitmap, byte* scan_begin, byte* scan_end,
106              const Visitor& visitor,
107              const byte minimum_age = kCardDirty) const
108      EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_)
109      SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
110
111  // Assertion used to check the given address is covered by the card table
112  void CheckAddrIsInCardTable(const byte* addr) const;
113
114  // Resets all of the bytes in the card table to clean.
115  void ClearCardTable();
116
117  // Resets all of the bytes in the card table which do not map to the image space.
118  void ClearSpaceCards(space::ContinuousSpace* space);
119
120  // Returns the first address in the heap which maps to this card.
121  void* AddrFromCard(const byte *card_addr) const ALWAYS_INLINE;
122
123  // Returns the address of the relevant byte in the card table, given an address on the heap.
124  byte* CardFromAddr(const void *addr) const ALWAYS_INLINE;
125
126  bool AddrIsInCardTable(const void* addr) const;
127
128 private:
129  CardTable(MemMap* begin, byte* biased_begin, size_t offset);
130
131  // Returns true iff the card table address is within the bounds of the card table.
132  bool IsValidCard(const byte* card_addr) const {
133    byte* begin = mem_map_->Begin() + offset_;
134    byte* end = mem_map_->End();
135    return card_addr >= begin && card_addr < end;
136  }
137
138  void CheckCardValid(byte* card) const ALWAYS_INLINE;
139
140  // Verifies that all gray objects are on a dirty card.
141  void VerifyCardTable();
142
143  // Mmapped pages for the card table
144  UniquePtr<MemMap> mem_map_;
145  // Value used to compute card table addresses from object addresses, see GetBiasedBegin
146  byte* const biased_begin_;
147  // Card table doesn't begin at the beginning of the mem_map_, instead it is displaced by offset
148  // to allow the byte value of biased_begin_ to equal GC_CARD_DIRTY
149  const size_t offset_;
150};
151
152}  // namespace accounting
153}  // namespace gc
154}  // namespace art
155
156#endif  // ART_RUNTIME_GC_ACCOUNTING_CARD_TABLE_H_
157