1 /*
2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_OBJECTSTARTARRAY_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_OBJECTSTARTARRAY_HPP
27
28 #include "gc_implementation/parallelScavenge/psVirtualspace.hpp"
29 #include "memory/allocation.hpp"
30 #include "memory/memRegion.hpp"
31 #include "oops/oop.hpp"
32
33 //
34 // This class can be used to locate the beginning of an object in the
35 // covered region.
36 //
37
38 class ObjectStartArray : public CHeapObj {
39 friend class VerifyObjectStartArrayClosure;
40
41 private:
42 PSVirtualSpace _virtual_space;
43 MemRegion _reserved_region;
44 MemRegion _covered_region;
45 MemRegion _blocks_region;
46 jbyte* _raw_base;
47 jbyte* _offset_base;
48
49 public:
50
51 enum BlockValueConstants {
52 clean_block = -1
53 };
54
55 enum BlockSizeConstants {
56 block_shift = 9,
57 block_size = 1 << block_shift,
58 block_size_in_words = block_size / sizeof(HeapWord)
59 };
60
61 protected:
62
63 // Mapping from address to object start array entry
64 jbyte* block_for_addr(void* p) const {
65 assert(_covered_region.contains(p),
66 "out of bounds access to object start array");
67 jbyte* result = &_offset_base[uintptr_t(p) >> block_shift];
68 assert(_blocks_region.contains(result),
69 "out of bounds result in byte_for");
70 return result;
71 }
72
73 // Mapping from object start array entry to address of first word
74 HeapWord* addr_for_block(jbyte* p) {
75 assert(_blocks_region.contains(p),
76 "out of bounds access to object start array");
77 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
78 HeapWord* result = (HeapWord*) (delta << block_shift);
79 assert(_covered_region.contains(result),
80 "out of bounds accessor from card marking array");
81 return result;
82 }
83
84 // Mapping that includes the derived offset.
85 // If the block is clean, returns the last address in the covered region.
86 // If the block is < index 0, returns the start of the covered region.
87 HeapWord* offset_addr_for_block (jbyte* p) const {
88 // We have to do this before the assert
89 if (p < _raw_base) {
90 return _covered_region.start();
91 }
92
93 assert(_blocks_region.contains(p),
94 "out of bounds access to object start array");
95
96 if (*p == clean_block) {
97 return _covered_region.end();
98 }
99
100 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
101 HeapWord* result = (HeapWord*) (delta << block_shift);
102 result += *p;
103
104 assert(_covered_region.contains(result),
105 "out of bounds accessor from card marking array");
106
107 return result;
108 }
109
110 public:
111
112 // This method is in lieu of a constructor, so that this class can be
113 // embedded inline in other classes.
114 void initialize(MemRegion reserved_region);
115
116 void set_covered_region(MemRegion mr);
117
118 void reset();
119
120 MemRegion covered_region() { return _covered_region; }
121
122 void allocate_block(HeapWord* p) {
123 assert(_covered_region.contains(p), "Must be in covered region");
124 jbyte* block = block_for_addr(p);
125 HeapWord* block_base = addr_for_block(block);
126 size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*));
127 assert(offset < 128, "Sanity");
128 // When doing MT offsets, we can't assert this.
129 //assert(offset > *block, "Found backwards allocation");
130 *block = (jbyte)offset;
131
132 // tty->print_cr("[%p]", p);
133 }
134
135 // Optimized for finding the first object that crosses into
136 // a given block. The blocks contain the offset of the last
137 // object in that block. Scroll backwards by one, and the first
138 // object hit should be at the beginning of the block
139 HeapWord* object_start(HeapWord* addr) const {
140 assert(_covered_region.contains(addr), "Must be in covered region");
141 jbyte* block = block_for_addr(addr);
142 HeapWord* scroll_forward = offset_addr_for_block(block--);
143 while (scroll_forward > addr) {
144 scroll_forward = offset_addr_for_block(block--);
145 }
146
147 HeapWord* next = scroll_forward;
148 while (next <= addr) {
149 scroll_forward = next;
150 next += oop(next)->size();
151 }
152 assert(scroll_forward <= addr, "wrong order for current and arg");
153 assert(addr <= next, "wrong order for arg and next");
154 return scroll_forward;
155 }
156
157 bool is_block_allocated(HeapWord* addr) {
158 assert(_covered_region.contains(addr), "Must be in covered region");
159 jbyte* block = block_for_addr(addr);
160 if (*block == clean_block)
161 return false;
162
163 return true;
164 }
165
166 // Return true if an object starts in the range of heap addresses.
167 // If an object starts at an address corresponding to
168 // "start", the method will return true.
169 bool object_starts_in_range(HeapWord* start_addr, HeapWord* end_addr) const;
170 };
171
172 #endif // SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_OBJECTSTARTARRAY_HPP