1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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13 * accompanied this code).
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24
25 #ifndef SHARE_GC_G1_G1BLOCKOFFSETTABLE_HPP
26 #define SHARE_GC_G1_G1BLOCKOFFSETTABLE_HPP
27
28 #include "gc/g1/g1RegionToSpaceMapper.hpp"
29 #include "gc/shared/blockOffsetTable.hpp"
30 #include "memory/memRegion.hpp"
31 #include "memory/virtualspace.hpp"
32 #include "utilities/globalDefinitions.hpp"
33
34 // Forward declarations
35 class G1BlockOffsetTable;
36 class G1ContiguousSpace;
37
38 // This implementation of "G1BlockOffsetTable" divides the covered region
39 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
40 // for each such subregion indicates how far back one must go to find the
41 // start of the chunk that includes the first word of the subregion.
42 //
43 // Each G1BlockOffsetTablePart is owned by a G1ContiguousSpace.
44
45 class G1BlockOffsetTable: public CHeapObj<mtGC> {
46 friend class G1BlockOffsetTablePart;
47 friend class VMStructs;
48
49 private:
50 // The reserved region covered by the table.
51 MemRegion _reserved;
52
53 // Array for keeping offsets for retrieving object start fast given an
54 // address.
55 volatile u_char* _offset_array; // byte array keeping backwards offsets
56
57 void check_offset(size_t offset, const char* msg) const {
58 assert(offset <= BOTConstants::N_words,
59 "%s - offset: " SIZE_FORMAT ", N_words: %u",
60 msg, offset, BOTConstants::N_words);
61 }
62
63 // Bounds checking accessors:
64 // For performance these have to devolve to array accesses in product builds.
65 inline u_char offset_array(size_t index) const;
66
67 inline void set_offset_array(size_t index, u_char offset);
68
69 inline void set_offset_array_raw(size_t index, u_char offset);
70
71 inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
72
73 inline void set_offset_array(size_t left, size_t right, u_char offset);
74
75 bool is_card_boundary(HeapWord* p) const;
76
77 void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;
78
79 public:
80
81 // Return the number of slots needed for an offset array
82 // that covers mem_region_words words.
83 static size_t compute_size(size_t mem_region_words) {
84 size_t number_of_slots = (mem_region_words / BOTConstants::N_words);
85 return ReservedSpace::allocation_align_size_up(number_of_slots);
86 }
87
88 // Returns how many bytes of the heap a single byte of the BOT corresponds to.
89 static size_t heap_map_factor() {
90 return BOTConstants::N_bytes;
91 }
92
93 // Initialize the Block Offset Table to cover the memory region passed
94 // in the heap parameter.
95 G1BlockOffsetTable(MemRegion heap, G1RegionToSpaceMapper* storage);
96
97 // Return the appropriate index into "_offset_array" for "p".
98 inline size_t index_for(const void* p) const;
99 inline size_t index_for_raw(const void* p) const;
100
101 // Return the address indicating the start of the region corresponding to
102 // "index" in "_offset_array".
103 inline HeapWord* address_for_index(size_t index) const;
104 // Variant of address_for_index that does not check the index for validity.
105 inline HeapWord* address_for_index_raw(size_t index) const {
106 return _reserved.start() + (index << BOTConstants::LogN_words);
107 }
108 };
109
110 class G1BlockOffsetTablePart {
111 friend class G1BlockOffsetTable;
112 friend class VMStructs;
113 private:
114 // allocation boundary at which offset array must be updated
115 HeapWord* _next_offset_threshold;
116 size_t _next_offset_index; // index corresponding to that boundary
117
118 // Indicates if an object can span into this G1BlockOffsetTablePart.
119 debug_only(bool _object_can_span;)
120
121 // This is the global BlockOffsetTable.
122 G1BlockOffsetTable* _bot;
123
124 // The space that owns this subregion.
125 G1ContiguousSpace* _space;
126
127 // Sets the entries
128 // corresponding to the cards starting at "start" and ending at "end"
129 // to point back to the card before "start": the interval [start, end)
130 // is right-open.
131 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
132 // Same as above, except that the args here are a card _index_ interval
133 // that is closed: [start_index, end_index]
134 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
135
136 // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
137 // memory first.
138 void zero_bottom_entry_raw();
139 // Variant of initialize_threshold that does not check for availability of the
140 // memory first.
141 HeapWord* initialize_threshold_raw();
142
143 inline size_t block_size(const HeapWord* p) const;
144
145 // Returns the address of a block whose start is at most "addr".
146 // If "has_max_index" is true, "assumes "max_index" is the last valid one
147 // in the array.
148 inline HeapWord* block_at_or_preceding(const void* addr,
149 bool has_max_index,
150 size_t max_index) const;
151
152 // "q" is a block boundary that is <= "addr"; "n" is the address of the
153 // next block (or the end of the space.) Return the address of the
154 // beginning of the block that contains "addr". Does so without side
155 // effects (see, e.g., spec of block_start.)
156 inline HeapWord* forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
157 const void* addr) const;
158
159 // "q" is a block boundary that is <= "addr"; return the address of the
160 // beginning of the block that contains "addr". May have side effects
161 // on "this", by updating imprecise entries.
162 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
163 const void* addr);
164
165 // "q" is a block boundary that is <= "addr"; "n" is the address of the
166 // next block (or the end of the space.) Return the address of the
167 // beginning of the block that contains "addr". May have side effects
168 // on "this", by updating imprecise entries.
169 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
170 HeapWord* n,
171 const void* addr);
172
173 // Requires that "*threshold_" be the first array entry boundary at or
174 // above "blk_start", and that "*index_" be the corresponding array
175 // index. If the block starts at or crosses "*threshold_", records
176 // "blk_start" as the appropriate block start for the array index
177 // starting at "*threshold_", and for any other indices crossed by the
178 // block. Updates "*threshold_" and "*index_" to correspond to the first
179 // index after the block end.
180 void alloc_block_work(HeapWord** threshold_, size_t* index_,
181 HeapWord* blk_start, HeapWord* blk_end);
182
183 void check_all_cards(size_t left_card, size_t right_card) const;
184
185 public:
186 // The elements of the array are initialized to zero.
187 G1BlockOffsetTablePart(G1BlockOffsetTable* array, G1ContiguousSpace* gsp);
188
189 void verify() const;
190
191 // Returns the address of the start of the block containing "addr", or
192 // else "null" if it is covered by no block. (May have side effects,
193 // namely updating of shared array entries that "point" too far
194 // backwards. This can occur, for example, when lab allocation is used
195 // in a space covered by the table.)
196 inline HeapWord* block_start(const void* addr);
197 // Same as above, but does not have any of the possible side effects
198 // discussed above.
199 inline HeapWord* block_start_const(const void* addr) const;
200
201 // Initialize the threshold to reflect the first boundary after the
202 // bottom of the covered region.
203 HeapWord* initialize_threshold();
204
205 void reset_bot() {
206 zero_bottom_entry_raw();
207 initialize_threshold_raw();
208 }
209
210 // Return the next threshold, the point at which the table should be
211 // updated.
212 HeapWord* threshold() const { return _next_offset_threshold; }
213
214 // These must be guaranteed to work properly (i.e., do nothing)
215 // when "blk_start" ("blk" for second version) is "NULL". In this
216 // implementation, that's true because NULL is represented as 0, and thus
217 // never exceeds the "_next_offset_threshold".
218 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
219 if (blk_end > _next_offset_threshold) {
220 alloc_block_work(&_next_offset_threshold, &_next_offset_index, blk_start, blk_end);
221 }
222 }
223 void alloc_block(HeapWord* blk, size_t size) {
224 alloc_block(blk, blk+size);
225 }
226
227 void set_for_starts_humongous(HeapWord* obj_top, size_t fill_size);
228 void set_object_can_span(bool can_span) NOT_DEBUG_RETURN;
229
230 void print_on(outputStream* out) PRODUCT_RETURN;
231 };
232
233 #endif // SHARE_GC_G1_G1BLOCKOFFSETTABLE_HPP