1 /*
2 * Copyright (c) 2013, 2015, Red Hat, Inc. and/or its affiliates.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #ifndef SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP
25 #define SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP
26
27 #include "oops/oop.hpp"
28 #include "utilities/globalDefinitions.hpp"
29
30 class BrooksPointer {
31
32 public:
33
34 /*
35 * Notes:
36 *
37 * a. It is important to have byte_offset and word_offset return constant
38 * expressions, because that will allow to constant-fold forwarding ptr
39 * accesses. This is not a problem in JIT compilers that would generate
40 * the code once, but it is problematic in GC hotpath code.
41 *
42 * b. With filler object mechanics, we may need to allocate more space for
43 * the forwarding ptr to meet alignment requirements for objects. This
44 * means *_offset and *_size calls are NOT interchangeable. The accesses
45 * to forwarding ptrs should always be via *_offset. Storage size
46 * calculations should always be via *_size.
47 */
48
49 /* Offset from the object start, in HeapWords. */
50 static inline int word_offset() {
51 return -1; // exactly one HeapWord
52 }
53
54 /* Offset from the object start, in bytes. */
55 static inline int byte_offset() {
56 return -HeapWordSize; // exactly one HeapWord
57 }
58
59 /* Allocated size, in HeapWords. */
60 static inline uint word_size() {
61 return (uint) MinObjAlignment;
62 }
63
64 /* Allocated size, in bytes */
65 static inline uint byte_size() {
66 return (uint) MinObjAlignmentInBytes;
67 }
68
88 static inline oop try_update_forwardee(oop obj, oop update);
89
90 /* Sets raw value for forwardee slot.
91 * THIS IS DANGEROUS: USERS HAVE TO INITIALIZE/SET FORWARDEE BACK AFTER THEY ARE DONE.
92 */
93 static inline void set_raw(oop obj, HeapWord* update);
94
95 /* Returns the raw value from forwardee slot.
96 */
97 static inline HeapWord* get_raw(oop obj);
98
99 /* Returns the raw value from forwardee slot without any checks.
100 * Used for quick verification.
101 */
102 static inline HeapWord* get_raw_unchecked(oop obj);
103
104 private:
105 static inline HeapWord** brooks_ptr_addr(oop obj);
106 };
107
108 #endif // SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP
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1 /*
2 * Copyright (c) 2013, 2018, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHBROOKSPOINTER_HPP
25 #define SHARE_VM_GC_SHENANDOAH_SHENANDOAHBROOKSPOINTER_HPP
26
27 #include "oops/oop.hpp"
28 #include "utilities/globalDefinitions.hpp"
29
30 class ShenandoahBrooksPointer {
31 /*
32 * Notes:
33 *
34 * a. It is important to have byte_offset and word_offset return constant
35 * expressions, because that will allow to constant-fold forwarding ptr
36 * accesses. This is not a problem in JIT compilers that would generate
37 * the code once, but it is problematic in GC hotpath code.
38 *
39 * b. With filler object mechanics, we may need to allocate more space for
40 * the forwarding ptr to meet alignment requirements for objects. This
41 * means *_offset and *_size calls are NOT interchangeable. The accesses
42 * to forwarding ptrs should always be via *_offset. Storage size
43 * calculations should always be via *_size.
44 */
45
46 public:
47 /* Offset from the object start, in HeapWords. */
48 static inline int word_offset() {
49 return -1; // exactly one HeapWord
50 }
51
52 /* Offset from the object start, in bytes. */
53 static inline int byte_offset() {
54 return -HeapWordSize; // exactly one HeapWord
55 }
56
57 /* Allocated size, in HeapWords. */
58 static inline uint word_size() {
59 return (uint) MinObjAlignment;
60 }
61
62 /* Allocated size, in bytes */
63 static inline uint byte_size() {
64 return (uint) MinObjAlignmentInBytes;
65 }
66
86 static inline oop try_update_forwardee(oop obj, oop update);
87
88 /* Sets raw value for forwardee slot.
89 * THIS IS DANGEROUS: USERS HAVE TO INITIALIZE/SET FORWARDEE BACK AFTER THEY ARE DONE.
90 */
91 static inline void set_raw(oop obj, HeapWord* update);
92
93 /* Returns the raw value from forwardee slot.
94 */
95 static inline HeapWord* get_raw(oop obj);
96
97 /* Returns the raw value from forwardee slot without any checks.
98 * Used for quick verification.
99 */
100 static inline HeapWord* get_raw_unchecked(oop obj);
101
102 private:
103 static inline HeapWord** brooks_ptr_addr(oop obj);
104 };
105
106 #endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHBROOKSPOINTER_HPP
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