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_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
25 #define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
26
27 #include "oops/oop.hpp"
28 #include "utilities/globalDefinitions.hpp"
29
30 class ShenandoahForwarding {
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
67 /* Assert basic stuff once at startup. */
68 static void initial_checks() {
69 guarantee (MinObjAlignment > 0, "sanity, word_size is correct");
70 guarantee (MinObjAlignmentInBytes > 0, "sanity, byte_size is correct");
71 }
72
73 /* Initializes forwarding pointer (to self).
74 */
75 static inline void initialize(oop obj);
76
77 /* Gets forwardee from the given object.
78 */
79 static inline oop get_forwardee(oop obj);
80
81 /* Tries to atomically update forwardee in $holder object to $update.
82 * Assumes $holder points at itself.
83 * Asserts $holder is in from-space.
84 * Asserts $update is in to-space.
85 */
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_forwardee_raw(oop obj, HeapWord* update);
92
93 /* Returns the raw value from forwardee slot.
94 */
95 static inline HeapWord* get_forwardee_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_forwardee_raw_unchecked(oop obj);
101
102 private:
103 static inline HeapWord** forward_ptr_addr(oop obj);
104 };
105
106 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
|
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_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
25 #define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
26
27 #include "oops/oop.hpp"
28 #include "utilities/globalDefinitions.hpp"
29
30 class ShenandoahForwarding {
31 public:
32 /* Gets forwardee from the given object.
33 */
34 static inline oop get_forwardee(oop obj);
35
36 /* Returns the raw value from forwardee slot.
37 */
38 static inline HeapWord* get_forwardee_raw(oop obj);
39
40 /* Returns the raw value from forwardee slot without any checks.
41 * Used for quick verification.
42 */
43 static inline HeapWord* get_forwardee_raw_unchecked(oop obj);
44
45 /**
46 * Returns true if the object is forwarded, false otherwise.
47 */
48 static inline bool is_forwarded(oop obj);
49
50 /* Tries to atomically update forwardee in $holder object to $update.
51 * Assumes $holder points at itself.
52 * Asserts $holder is in from-space.
53 * Asserts $update is in to-space.
54 */
55 static inline oop try_update_forwardee(oop obj, oop update);
56
57 };
58
59 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_HPP
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