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 // Note that only those Klass that can be instantiated have a narrow Klass ID.
67 // For those who don't, we leave the klass bits empty and assert if someone
68 // tries to use those.
69 const narrowKlass nk = CompressedKlassPointers::is_encodable(kls) ?
70 CompressedKlassPointers::encode(const_cast<Klass*>(kls)) : 0;
71 prototype = prototype.set_narrow_klass(nk);
72 }
73 return prototype;
74 }
75
76 inline void Klass::set_prototype_header(markWord header) {
77 _prototype_header = header;
78 }
79
80 inline bool Klass::is_loader_present_and_alive() const {
81 ClassLoaderData* cld = class_loader_data();
82 return (cld != nullptr) ? cld->is_alive() : false;
83 }
84
85 inline markWord Klass::prototype_header() const {
86 // You only need prototypes for allocating objects. If the class is not instantiable, it won't live in
87 // class space and have no narrow Klass ID. But in that case we should not need the prototype.
88 assert(!UseCompactObjectHeaders || _prototype_header.narrow_klass() > 0, "Klass " PTR_FORMAT ": invalid prototype (" PTR_FORMAT ")",
89 p2i(this), _prototype_header.value());
90 return _prototype_header;
91 }
92
93 inline void Klass::set_prototype_header_klass(narrowKlass klass) {
94 // Merge narrowKlass in existing prototype header.
95 _prototype_header = _prototype_header.set_narrow_klass(klass);
96 }
97
98 // Loading the java_mirror does not keep its holder alive. See Klass::keep_alive().
99 inline oop Klass::java_mirror() const {
100 return _java_mirror.resolve();
101 }
102
103 inline oop Klass::java_mirror_no_keepalive() const {
104 return _java_mirror.peek();
105 }
106
107 inline klassVtable Klass::vtable() const {
108 return klassVtable(const_cast<Klass*>(this), start_of_vtable(), vtable_length() / vtableEntry::size());
109 }
110
111 inline oop Klass::class_loader() const {
112 return class_loader_data()->class_loader();
113 }
114
115 inline vtableEntry* Klass::start_of_vtable() const {
116 return (vtableEntry*) ((address)this + in_bytes(vtable_start_offset()));
117 }
118
119 inline ByteSize Klass::vtable_start_offset() {
120 return in_ByteSize(InstanceKlass::header_size() * wordSize);
121 }
122
123 // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
124 inline bool Klass::is_subtype_of(Klass* k) const {
125 assert(secondary_supers() != nullptr, "must be");
126 const juint off = k->super_check_offset();
127 const juint secondary_offset = in_bytes(secondary_super_cache_offset());
128 if (off == secondary_offset) {
129 return search_secondary_supers(k);
130 } else {
131 Klass* sup = *(Klass**)( (address)this + off );
132 return (sup == k);
133 }
134 }
135
136 // Hashed search for secondary super k.
137 inline bool Klass::lookup_secondary_supers_table(Klass* k) const {
138 uintx bitmap = _secondary_supers_bitmap;
139
140 constexpr int highest_bit_number = SECONDARY_SUPERS_TABLE_SIZE - 1;
141 uint8_t slot = k->_hash_slot;
142 uintx shifted_bitmap = bitmap << (highest_bit_number - slot);
143
144 precond((int)population_count(bitmap) <= secondary_supers()->length());
145
146 // First check the bitmap to see if super_klass might be present. If
147 // the bit is zero, we are certain that super_klass is not one of
148 // the secondary supers.
149 if (((shifted_bitmap >> highest_bit_number) & 1) == 0) {
150 return false;
151 }
152
153 // Calculate the initial hash probe
154 int index = population_count(shifted_bitmap) - 1;
155 if (secondary_supers()->at(index) == k) {
156 // Yes! It worked the first time.
157 return true;
158 }
159
160 // Is there another entry to check? Consult the bitmap. If Bit 1,
161 // the next bit to test, is zero, we are certain that super_klass is
162 // not one of the secondary supers.
163 bitmap = rotate_right(bitmap, slot);
164 if ((bitmap & 2) == 0) {
165 return false;
166 }
167
168 // Continue probing the hash table
169 return fallback_search_secondary_supers(k, index, bitmap);
170 }
171
172 inline bool Klass::search_secondary_supers(Klass *k) const {
173 // This is necessary because I am never in my own secondary_super list.
174 if (this == k)
175 return true;
176
177 bool result = lookup_secondary_supers_table(k);
178
179 #ifndef PRODUCT
180 if (VerifySecondarySupers) {
181 bool linear_result = linear_search_secondary_supers(k);
182 if (linear_result != result) {
183 on_secondary_supers_verification_failure((Klass*)this, k, linear_result, result, "mismatch");
184 }
185 }
186 #endif // PRODUCT
187
188 return result;
189 }
190
191 // Returns true if this Klass needs to be addressable via narrow Klass ID.
192 inline bool Klass::needs_narrow_id() const {
193 // Classes that are never instantiated need no narrow Klass Id, since the
194 // only point of having a narrow id is to put it into an object header. Keeping
195 // never instantiated classes out of class space lessens the class space pressure.
196 // For more details, see JDK-8338526.
197 // Note: don't call this function before access flags are initialized.
198 return UseClassMetaspaceForAllClasses || (!is_abstract() && !is_interface());
199 }
200 #endif // SHARE_OOPS_KLASS_INLINE_HPP