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 
26 namespace art {
27 
28 namespace mirror {
29   class Object;
30 }  // namespace mirror
31 
32 namespace gc {
33 
34 namespace space {
35   class ContinuousSpace;
36 }  // namespace space
37 
38 class Heap;
39 
40 namespace accounting {
41 
42 template<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.
47 class 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.
MarkCard(const void * addr)57   ALWAYS_INLINE void MarkCard(const void *addr) {
58     *CardFromAddr(addr) = kCardDirty;
59   }
60 
61   // Is the object on a dirty card?
IsDirty(const mirror::Object * obj)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.
GetCard(const mirror::Object * obj)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>
VisitClear(const void * start,const void * end,const Visitor & 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
GetBiasedBegin()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.
IsValidCard(const byte * card_addr)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   std::unique_ptr<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