1 /*
2 * Copyright (c) 2015, 2019, Red Hat, Inc. 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_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP
26 #define SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP
27
28 #include "gc/shenandoah/shenandoahForwarding.hpp"
29
30 #include "gc/shenandoah/shenandoahAsserts.hpp"
31 #include "oops/klass.hpp"
32 #include "oops/markWord.hpp"
33 #include "runtime/javaThread.hpp"
34
35 inline oop ShenandoahForwarding::get_forwardee_raw(oop obj) {
36 shenandoah_assert_in_heap_bounds(nullptr, obj);
37 return get_forwardee_raw_unchecked(obj);
38 }
39
40 static HeapWord* to_forwardee(markWord mark) {
41 return reinterpret_cast<HeapWord*>(mark.value() & ~(markWord::lock_mask_in_place | markWord::self_fwd_mask_in_place));
42 }
43
44 inline bool ShenandoahForwarding::has_forwardee(markWord m) {
45 // Lock bits == marked_value (0b11): the upper bits encode a forwardee
46 // pointer. Matches normal-forwarded (0b011) and forward-expanded (0b111);
47 // excludes self-forwarded (0b100, 0b101, 0b110).
48 return (m.value() & markWord::lock_mask_in_place) == markWord::marked_value;
49 }
50
51 inline oop ShenandoahForwarding::get_forwardee_raw_unchecked(oop obj) {
52 // JVMTI and JFR code use mark words for marking objects for their needs.
53 // On this path, we can encounter the "marked" object, but with null
54 // fwdptr. That object is still not forwarded, and we need to return
55 // the object itself.
56 markWord mark = obj->mark();
57 if (has_forwardee(mark)) {
58 HeapWord* fwdptr = to_forwardee(mark);
59 if (fwdptr != nullptr) {
60 return cast_to_oop(fwdptr);
61 }
62 }
63 // Self-forwarded (evacuation failure): the object stays put; the
64 // self-fwd bit is set alongside normal lock bits.
65 return obj;
66 }
67
68 inline oop ShenandoahForwarding::get_forwardee_mutator(oop obj) {
69 // Same as above, but mutator thread cannot ever see null forwardee.
70 shenandoah_assert_correct(nullptr, obj);
71 assert(Thread::current()->is_Java_thread(), "Must be a mutator thread");
72
73 markWord mark = obj->mark();
74 if (has_forwardee(mark)) {
75 HeapWord* fwdptr = to_forwardee(mark);
76 assert(fwdptr != nullptr, "Forwarding pointer is never null here");
77 return cast_to_oop(fwdptr);
78 }
79 // Self-forwarded or not forwarded: return the object itself.
80 return obj;
81 }
82
83 inline oop ShenandoahForwarding::get_forwardee(oop obj) {
84 shenandoah_assert_correct(nullptr, obj);
85 return get_forwardee_raw_unchecked(obj);
86 }
87
88 inline bool ShenandoahForwarding::is_forwarded(markWord m) {
89 return (m.value() & (markWord::lock_mask_in_place | markWord::self_fwd_mask_in_place)) > markWord::monitor_value;
90 }
91
92 inline bool ShenandoahForwarding::is_forwarded(oop obj) {
93 return obj->mark().is_forwarded();
94 }
95
96 inline bool ShenandoahForwarding::is_self_forwarded(oop obj) {
97 return obj->mark().is_self_forwarded();
98 }
99
100 inline oop ShenandoahForwarding::try_update_forwardee(oop obj, oop update) {
101 markWord old_mark = obj->mark();
102 if (has_forwardee(old_mark)) {
103 return cast_to_oop(to_forwardee(old_mark));
104 }
105 if (old_mark.is_self_forwarded()) {
106 // Another thread lost the evacuation race; the object stays put.
107 return obj;
108 }
109
110 markWord new_mark = markWord::encode_pointer_as_mark(update);
111 if (UseCompactObjectHeaders && old_mark.is_hashed_not_expanded()) {
112 new_mark = markWord(new_mark.value() | FWDED_HASH_TRANSITION);
113 }
114 markWord prev_mark = obj->cas_set_mark(new_mark, old_mark, memory_order_conservative);
115 if (prev_mark == old_mark) {
116 return update;
117 }
118 // Concurrent writers on a cset object's mark can only be other evacuation
119 // threads installing forwarding (real or self). Mutators cannot reach the
120 // mark of a not-yet-forwarded cset object: LRB + stack watermark barriers
121 // redirect all reference uses before a Java-level operation can touch it.
122 // So the only possible failure modes are a regular forwardee (marked) or
123 // a self-forward (possibly with mutator lock/hash mods layered on top
124 // after the self-forward became visible).
125 if (has_forwardee(prev_mark)) {
126 return cast_to_oop(to_forwardee(prev_mark));
127 }
128 assert(prev_mark.is_self_forwarded(),
129 "concurrent writers on cset objects must install forwarding: prev=" INTPTR_FORMAT,
130 prev_mark.value());
131 return obj;
132 }
133
134 inline oop ShenandoahForwarding::try_forward_to_self(oop obj, markWord old_mark) {
135 assert(!old_mark.is_forwarded(),
136 "caller must pass a non-forwarded mark: old=" INTPTR_FORMAT, old_mark.value());
137 markWord new_mark = old_mark.set_self_forwarded();
138 markWord prev_mark = obj->cas_set_mark(new_mark, old_mark, memory_order_conservative);
139 if (prev_mark == old_mark) {
140 // We installed the self-forward.
141 return nullptr;
142 }
143 // Same invariant as in try_update_forwardee: the only races on a
144 // cset object's mark come from other evac threads installing forwarding.
145 if (has_forwardee(prev_mark)) {
146 return cast_to_oop(to_forwardee(prev_mark));
147 }
148 assert(prev_mark.is_self_forwarded(),
149 "concurrent writers on cset objects must install forwarding: prev=" INTPTR_FORMAT,
150 prev_mark.value());
151 return obj;
152 }
153
154 inline Klass* ShenandoahForwarding::klass(oop obj) {
155 if (UseCompactObjectHeaders) {
156 markWord mark = obj->mark();
157 if (has_forwardee(mark)) {
158 oop fwd = cast_to_oop(to_forwardee(mark));
159 mark = fwd->mark();
160 }
161 return mark.klass();
162 } else {
163 return obj->klass();
164 }
165 }
166
167 inline size_t ShenandoahForwarding::size(oop obj) {
168 markWord mark = obj->mark();
169 if (has_forwardee(mark)) {
170 oop fwd = cast_to_oop(to_forwardee(mark));
171 markWord fwd_mark = fwd->mark();
172 Klass* klass = UseCompactObjectHeaders ? fwd_mark.klass() : fwd->klass();
173 size_t size = fwd->base_size_given_klass(fwd_mark, klass);
174 if (UseCompactObjectHeaders) {
175 if ((mark.value() & FWDED_HASH_TRANSITION) != FWDED_HASH_TRANSITION) {
176 if (fwd_mark.is_expanded() && klass->expand_for_hash(fwd, fwd_mark)) {
177 size = align_object_size(size + 1);
178 }
179 }
180 }
181 return size;
182 } else {
183 Klass* klass = UseCompactObjectHeaders ? mark.klass() : obj->klass();
184 return obj->size_given_mark_and_klass(mark, klass);
185 }
186 }
187
188 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHFORWARDING_INLINE_HPP