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