1 /*
2 * Copyright (c) 2005, 2025, 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_OOPS_KLASS_INLINE_HPP
26 #define SHARE_OOPS_KLASS_INLINE_HPP
27
28 #include "oops/klass.hpp"
29
30 #include "classfile/classLoaderData.inline.hpp"
31 #include "oops/klassVtable.hpp"
32 #include "oops/markWord.hpp"
33 #include "utilities/rotate_bits.hpp"
34
35 // This loads and keeps the klass's loader alive.
36 inline oop Klass::klass_holder() const {
37 return class_loader_data()->holder();
38 }
39
40 inline void Klass::keep_alive() const {
41 // Resolving the holder (a WeakHandle) will keep the klass alive until the next safepoint.
42 // Making the klass's CLD handle oops (e.g. the java_mirror), safe to store in the object
43 // graph and its roots (e.g. Handles).
44 static_cast<void>(klass_holder());
45 }
46
47 inline bool Klass::is_non_strong_hidden() const {
48 return is_hidden() && class_loader_data()->has_class_mirror_holder();
49 }
50
51 // Iff the class loader (or mirror for non-strong hidden classes) is alive the
52 // Klass is considered alive. This is safe to call before the CLD is marked as
53 // unloading, and hence during concurrent class unloading.
54 // This returns false if the Klass is unloaded, or about to be unloaded because the holder of
55 // the CLD is no longer strongly reachable.
56 // The return value of this function may change from true to false after a safepoint. So the caller
57 // of this function must ensure that a safepoint doesn't happen while interpreting the return value.
58 inline bool Klass::is_loader_alive() const {
59 return class_loader_data()->is_alive();
60 }
61
62 inline markWord Klass::make_prototype_header(const Klass* kls, markWord prototype) {
63 if (UseCompactObjectHeaders) {
64 // With compact object headers, the narrow Klass ID is part of the mark word.
65 // We therefore seed the mark word with the narrow Klass ID.
66 precond(CompressedKlassPointers::is_encodable(kls));
67 const narrowKlass nk = CompressedKlassPointers::encode(const_cast<Klass*>(kls));
68 prototype = prototype.set_narrow_klass(nk);
69 }
70 return prototype;
71 }
72
73 inline void Klass::set_prototype_header(markWord header) {
74 _prototype_header = header;
75 }
76
77 inline bool Klass::is_loader_present_and_alive() const {
78 ClassLoaderData* cld = class_loader_data();
79 return (cld != nullptr) ? cld->is_alive() : false;
80 }
81
82 inline markWord Klass::prototype_header() const {
83 // You only need prototypes for allocating objects. If the class is not instantiable, it won't live in
84 // class space and have no narrow Klass ID. But in that case we should not need the prototype.
85 assert(!UseCompactObjectHeaders || _prototype_header.narrow_klass() > 0, "Klass " PTR_FORMAT ": invalid prototype (" PTR_FORMAT ")",
86 p2i(this), _prototype_header.value());
87 return _prototype_header;
88 }
89
90 inline void Klass::set_prototype_header_klass(narrowKlass klass) {
91 // Merge narrowKlass in existing prototype header.
92 _prototype_header = _prototype_header.set_narrow_klass(klass);
93 }
94
95 // Loading the java_mirror does not keep its holder alive. See Klass::keep_alive().
96 inline oop Klass::java_mirror() const {
97 return _java_mirror.resolve();
98 }
99
100 inline oop Klass::java_mirror_no_keepalive() const {
101 return _java_mirror.peek();
102 }
103
104 inline klassVtable Klass::vtable() const {
105 return klassVtable(const_cast<Klass*>(this), start_of_vtable(), vtable_length() / vtableEntry::size());
106 }
107
108 inline oop Klass::class_loader() const {
109 return class_loader_data()->class_loader();
110 }
111
112 inline vtableEntry* Klass::start_of_vtable() const {
113 return (vtableEntry*) ((address)this + in_bytes(vtable_start_offset()));
114 }
115
116 inline ByteSize Klass::vtable_start_offset() {
117 return in_ByteSize(InstanceKlass::header_size() * wordSize);
118 }
119
120 // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
121 inline bool Klass::is_subtype_of(Klass* k) const {
122 assert(secondary_supers() != nullptr, "must be");
123 const juint off = k->super_check_offset();
124 const juint secondary_offset = in_bytes(secondary_super_cache_offset());
125 if (off == secondary_offset) {
126 return search_secondary_supers(k);
127 } else {
128 Klass* sup = *(Klass**)( (address)this + off );
129 return (sup == k);
130 }
131 }
132
133 // Hashed search for secondary super k.
134 inline bool Klass::lookup_secondary_supers_table(Klass* k) const {
135 uintx bitmap = _secondary_supers_bitmap;
136
137 constexpr int highest_bit_number = SECONDARY_SUPERS_TABLE_SIZE - 1;
138 uint8_t slot = k->_hash_slot;
139 uintx shifted_bitmap = bitmap << (highest_bit_number - slot);
140
141 precond((int)population_count(bitmap) <= secondary_supers()->length());
142
143 // First check the bitmap to see if super_klass might be present. If
144 // the bit is zero, we are certain that super_klass is not one of
145 // the secondary supers.
146 if (((shifted_bitmap >> highest_bit_number) & 1) == 0) {
147 return false;
148 }
149
150 // Calculate the initial hash probe
151 int index = population_count(shifted_bitmap) - 1;
152 if (secondary_supers()->at(index) == k) {
153 // Yes! It worked the first time.
154 return true;
155 }
156
157 // Is there another entry to check? Consult the bitmap. If Bit 1,
158 // the next bit to test, is zero, we are certain that super_klass is
159 // not one of the secondary supers.
160 bitmap = rotate_right(bitmap, slot);
161 if ((bitmap & 2) == 0) {
162 return false;
163 }
164
165 // Continue probing the hash table
166 return fallback_search_secondary_supers(k, index, bitmap);
167 }
168
169 inline bool Klass::search_secondary_supers(Klass *k) const {
170 // This is necessary because I am never in my own secondary_super list.
171 if (this == k)
172 return true;
173
174 bool result = lookup_secondary_supers_table(k);
175
176 #ifndef PRODUCT
177 if (VerifySecondarySupers) {
178 bool linear_result = linear_search_secondary_supers(k);
179 if (linear_result != result) {
180 on_secondary_supers_verification_failure((Klass*)this, k, linear_result, result, "mismatch");
181 }
182 }
183 #endif // PRODUCT
184
185 return result;
186 }
187
188 #endif // SHARE_OOPS_KLASS_INLINE_HPP