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 // May no longer be required (was used to avoid a bootstrapping problem...
94 inline markWord Klass::default_prototype_header(Klass* k) {
95 return (k == nullptr) ? markWord::prototype() : k->prototype_header();
96 }
97
98 inline void Klass::set_prototype_header_klass(narrowKlass klass) {
99 // Merge narrowKlass in existing prototype header.
100 _prototype_header = _prototype_header.set_narrow_klass(klass);
101 }
102
103 // Loading the java_mirror does not keep its holder alive. See Klass::keep_alive().
104 inline oop Klass::java_mirror() const {
105 return _java_mirror.resolve();
106 }
107
108 inline oop Klass::java_mirror_no_keepalive() const {
109 return _java_mirror.peek();
110 }
111
112 inline klassVtable Klass::vtable() const {
113 return klassVtable(const_cast<Klass*>(this), start_of_vtable(), vtable_length() / vtableEntry::size());
114 }
115
116 inline oop Klass::class_loader() const {
117 return class_loader_data()->class_loader();
118 }
119
120 inline vtableEntry* Klass::start_of_vtable() const {
121 return (vtableEntry*) ((address)this + in_bytes(vtable_start_offset()));
122 }
123
124 inline ByteSize Klass::vtable_start_offset() {
125 return in_ByteSize(InstanceKlass::header_size() * wordSize);
126 }
127
128 // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
129 inline bool Klass::is_subtype_of(Klass* k) const {
130 assert(secondary_supers() != nullptr, "must be");
131 const juint off = k->super_check_offset();
132 const juint secondary_offset = in_bytes(secondary_super_cache_offset());
133 if (off == secondary_offset) {
134 return search_secondary_supers(k);
135 } else {
136 Klass* sup = *(Klass**)( (address)this + off );
137 return (sup == k);
138 }
139 }
140
141 // Hashed search for secondary super k.
142 inline bool Klass::lookup_secondary_supers_table(Klass* k) const {
143 uintx bitmap = _secondary_supers_bitmap;
144
145 constexpr int highest_bit_number = SECONDARY_SUPERS_TABLE_SIZE - 1;
146 uint8_t slot = k->_hash_slot;
147 uintx shifted_bitmap = bitmap << (highest_bit_number - slot);
148
149 precond((int)population_count(bitmap) <= secondary_supers()->length());
150
151 // First check the bitmap to see if super_klass might be present. If
152 // the bit is zero, we are certain that super_klass is not one of
153 // the secondary supers.
154 if (((shifted_bitmap >> highest_bit_number) & 1) == 0) {
155 return false;
156 }
157
158 // Calculate the initial hash probe
159 int index = population_count(shifted_bitmap) - 1;
160 if (secondary_supers()->at(index) == k) {
161 // Yes! It worked the first time.
162 return true;
163 }
164
165 // Is there another entry to check? Consult the bitmap. If Bit 1,
166 // the next bit to test, is zero, we are certain that super_klass is
167 // not one of the secondary supers.
168 bitmap = rotate_right(bitmap, slot);
169 if ((bitmap & 2) == 0) {
170 return false;
171 }
172
173 // Continue probing the hash table
174 return fallback_search_secondary_supers(k, index, bitmap);
175 }
176
177 inline bool Klass::search_secondary_supers(Klass *k) const {
178 // This is necessary because I am never in my own secondary_super list.
179 if (this == k)
180 return true;
181
182 bool result = lookup_secondary_supers_table(k);
183
184 #ifndef PRODUCT
185 if (VerifySecondarySupers) {
186 bool linear_result = linear_search_secondary_supers(k);
187 if (linear_result != result) {
188 on_secondary_supers_verification_failure((Klass*)this, k, linear_result, result, "mismatch");
189 }
190 }
191 #endif // PRODUCT
192
193 return result;
194 }
195
196 // Returns true if this Klass needs to be addressable via narrow Klass ID.
197 inline bool Klass::needs_narrow_id() const {
198 // Classes that are never instantiated need no narrow Klass Id, since the
199 // only point of having a narrow id is to put it into an object header. Keeping
200 // never instantiated classes out of class space lessens the class space pressure.
201 // For more details, see JDK-8338526.
202 // Note: don't call this function before access flags are initialized.
203 return !is_abstract() && !is_interface();
204 }
205 #endif // SHARE_OOPS_KLASS_INLINE_HPP