1 /*
2 * Copyright (c) 2001, 2005, 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 //
26 // This class can be used to locate the beginning of an object in the
27 // covered region.
28 //
29
30 class ObjectStartArray : public CHeapObj {
31 friend class VerifyObjectStartArrayClosure;
32
33 private:
34 PSVirtualSpace _virtual_space;
35 MemRegion _reserved_region;
36 MemRegion _covered_region;
37 MemRegion _blocks_region;
38 jbyte* _raw_base;
39 jbyte* _offset_base;
40
41 public:
42
43 enum BlockValueConstants {
44 clean_block = -1
45 };
46
47 enum BlockSizeConstants {
48 block_shift = 9,
49 block_size = 1 << block_shift,
50 block_size_in_words = block_size / sizeof(HeapWord)
51 };
52
53 protected:
54
55 // Mapping from address to object start array entry
56 jbyte* block_for_addr(void* p) const {
57 assert(_covered_region.contains(p),
58 "out of bounds access to object start array");
59 jbyte* result = &_offset_base[uintptr_t(p) >> block_shift];
60 assert(_blocks_region.contains(result),
61 "out of bounds result in byte_for");
62 return result;
63 }
64
65 // Mapping from object start array entry to address of first word
66 HeapWord* addr_for_block(jbyte* p) {
67 assert(_blocks_region.contains(p),
68 "out of bounds access to object start array");
69 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
70 HeapWord* result = (HeapWord*) (delta << block_shift);
71 assert(_covered_region.contains(result),
72 "out of bounds accessor from card marking array");
73 return result;
74 }
75
76 // Mapping that includes the derived offset.
77 // If the block is clean, returns the last address in the covered region.
78 // If the block is < index 0, returns the start of the covered region.
79 HeapWord* offset_addr_for_block (jbyte* p) const {
80 // We have to do this before the assert
81 if (p < _raw_base) {
82 return _covered_region.start();
83 }
84
85 assert(_blocks_region.contains(p),
86 "out of bounds access to object start array");
87
88 if (*p == clean_block) {
89 return _covered_region.end();
90 }
91
92 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte));
93 HeapWord* result = (HeapWord*) (delta << block_shift);
94 result += *p;
95
96 assert(_covered_region.contains(result),
97 "out of bounds accessor from card marking array");
98
99 return result;
100 }
101
102 public:
103
104 // This method is in lieu of a constructor, so that this class can be
105 // embedded inline in other classes.
106 void initialize(MemRegion reserved_region);
107
108 void set_covered_region(MemRegion mr);
109
110 void reset();
111
112 MemRegion covered_region() { return _covered_region; }
113
114 void allocate_block(HeapWord* p) {
115 assert(_covered_region.contains(p), "Must be in covered region");
116 jbyte* block = block_for_addr(p);
117 HeapWord* block_base = addr_for_block(block);
118 size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*));
119 assert(offset < 128, "Sanity");
120 // When doing MT offsets, we can't assert this.
121 //assert(offset > *block, "Found backwards allocation");
122 *block = (jbyte)offset;
123
124 // tty->print_cr("[%p]", p);
125 }
126
127 // Optimized for finding the first object that crosses into
128 // a given block. The blocks contain the offset of the last
129 // object in that block. Scroll backwards by one, and the first
130 // object hit should be at the beginning of the block
131 HeapWord* object_start(HeapWord* addr) const {
132 assert(_covered_region.contains(addr), "Must be in covered region");
133 jbyte* block = block_for_addr(addr);
134 HeapWord* scroll_forward = offset_addr_for_block(block--);
135 while (scroll_forward > addr) {
136 scroll_forward = offset_addr_for_block(block--);
137 }
138
139 HeapWord* next = scroll_forward;
140 while (next <= addr) {
141 scroll_forward = next;
142 next += oop(next)->size();
143 }
144 assert(scroll_forward <= addr, "wrong order for current and arg");
145 assert(addr <= next, "wrong order for arg and next");
146 return scroll_forward;
147 }
148
149 bool is_block_allocated(HeapWord* addr) {
150 assert(_covered_region.contains(addr), "Must be in covered region");
151 jbyte* block = block_for_addr(addr);
152 if (*block == clean_block)
153 return false;
154
155 return true;
156 }
157
158 // Return true if an object starts in the range of heap addresses.
159 // If an object starts at an address corresponding to
160 // "start", the method will return true.
161 bool object_starts_in_range(HeapWord* start_addr, HeapWord* end_addr) const;
162 };