1 /*
2 * Copyright (c) 2005, 2024, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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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
99 // Loading the java_mirror does not keep its holder alive. See Klass::keep_alive().
100 inline oop Klass::java_mirror() const {
101 return _java_mirror.resolve();
102 }
103
104 inline oop Klass::java_mirror_no_keepalive() const {
105 return _java_mirror.peek();
106 }
107
108 inline klassVtable Klass::vtable() const {
109 return klassVtable(const_cast<Klass*>(this), start_of_vtable(), vtable_length() / vtableEntry::size());
110 }
111
112 inline oop Klass::class_loader() const {
113 return class_loader_data()->class_loader();
114 }
115
116 inline vtableEntry* Klass::start_of_vtable() const {
117 return (vtableEntry*) ((address)this + in_bytes(vtable_start_offset()));
118 }
119
120 inline ByteSize Klass::vtable_start_offset() {
121 return in_ByteSize(InstanceKlass::header_size() * wordSize);
122 }
123
124 // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
125 inline bool Klass::is_subtype_of(Klass* k) const {
126 assert(secondary_supers() != nullptr, "must be");
127 const juint off = k->super_check_offset();
128 const juint secondary_offset = in_bytes(secondary_super_cache_offset());
129 if (off == secondary_offset) {
130 return search_secondary_supers(k);
131 } else {
132 Klass* sup = *(Klass**)( (address)this + off );
133 return (sup == k);
134 }
135 }
136
137 // Hashed search for secondary super k.
138 inline bool Klass::lookup_secondary_supers_table(Klass* k) const {
139 uintx bitmap = _secondary_supers_bitmap;
140
141 constexpr int highest_bit_number = SECONDARY_SUPERS_TABLE_SIZE - 1;
142 uint8_t slot = k->_hash_slot;
143 uintx shifted_bitmap = bitmap << (highest_bit_number - slot);
144
145 precond((int)population_count(bitmap) <= secondary_supers()->length());
146
147 // First check the bitmap to see if super_klass might be present. If
148 // the bit is zero, we are certain that super_klass is not one of
149 // the secondary supers.
150 if (((shifted_bitmap >> highest_bit_number) & 1) == 0) {
151 return false;
152 }
153
154 // Calculate the initial hash probe
155 int index = population_count(shifted_bitmap) - 1;
156 if (secondary_supers()->at(index) == k) {
157 // Yes! It worked the first time.
158 return true;
159 }
160
161 // Is there another entry to check? Consult the bitmap. If Bit 1,
162 // the next bit to test, is zero, we are certain that super_klass is
163 // not one of the secondary supers.
164 bitmap = rotate_right(bitmap, slot);
165 if ((bitmap & 2) == 0) {
166 return false;
167 }
168
169 // Continue probing the hash table
170 return fallback_search_secondary_supers(k, index, bitmap);
171 }
172
173 inline bool Klass::search_secondary_supers(Klass *k) const {
174 // This is necessary because I am never in my own secondary_super list.
175 if (this == k)
176 return true;
177
178 bool result = lookup_secondary_supers_table(k);
179
180 #ifndef PRODUCT
181 if (VerifySecondarySupers) {
182 bool linear_result = linear_search_secondary_supers(k);
183 if (linear_result != result) {
184 on_secondary_supers_verification_failure((Klass*)this, k, linear_result, result, "mismatch");
185 }
186 }
187 #endif // PRODUCT
188
189 return result;
190 }
191
192 // Returns true if this Klass needs to be addressable via narrow Klass ID.
193 inline bool Klass::needs_narrow_id() const {
194 // Classes that are never instantiated need no narrow Klass Id, since the
195 // only point of having a narrow id is to put it into an object header. Keeping
196 // never instantiated classes out of class space lessens the class space pressure.
197 // For more details, see JDK-8338526.
198 // Note: don't call this function before access flags are initialized.
199 return !is_abstract() && !is_interface();
200 }
201 #endif // SHARE_OOPS_KLASS_INLINE_HPP