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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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 bool Klass::is_loader_present_and_alive() const {
63 ClassLoaderData* cld = class_loader_data();
64 return (cld != nullptr) ? cld->is_alive() : false;
65 }
66
67 inline markWord Klass::prototype_header() const {
68 assert(UseCompactObjectHeaders, "only use with compact object headers");
69 #ifdef _LP64
70 // You only need prototypes for allocating objects. If the class is not instantiable, it won't live in
71 // class space and have no narrow Klass ID. But in that case we should not need the prototype.
72 assert(_prototype_header.narrow_klass() > 0, "Klass " PTR_FORMAT ": invalid prototype (" PTR_FORMAT ")",
73 p2i(this), _prototype_header.value());
74 #endif
75 return _prototype_header;
76 }
77
78 // This is only used when dumping the archive. In other cases,
79 // the _prototype_header is already initialized to the right thing.
80 inline void Klass::set_prototype_header(markWord header) {
81 assert(UseCompactObjectHeaders, "only with compact headers");
82 _prototype_header = header;
83 }
84
85 // Loading the java_mirror does not keep its holder alive. See Klass::keep_alive().
86 inline oop Klass::java_mirror() const {
87 return _java_mirror.resolve();
88 }
89
90 inline oop Klass::java_mirror_no_keepalive() const {
91 return _java_mirror.peek();
92 }
93
94 inline klassVtable Klass::vtable() const {
95 return klassVtable(const_cast<Klass*>(this), start_of_vtable(), vtable_length() / vtableEntry::size());
96 }
97
98 inline oop Klass::class_loader() const {
99 return class_loader_data()->class_loader();
100 }
101
102 inline vtableEntry* Klass::start_of_vtable() const {
103 return (vtableEntry*) ((address)this + in_bytes(vtable_start_offset()));
104 }
105
106 inline ByteSize Klass::vtable_start_offset() {
107 return in_ByteSize(InstanceKlass::header_size() * wordSize);
108 }
109
110 // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
111 inline bool Klass::is_subtype_of(Klass* k) const {
112 assert(secondary_supers() != nullptr, "must be");
113 const juint off = k->super_check_offset();
114 const juint secondary_offset = in_bytes(secondary_super_cache_offset());
115 if (off == secondary_offset) {
116 return search_secondary_supers(k);
117 } else {
118 Klass* sup = *(Klass**)( (address)this + off );
119 return (sup == k);
120 }
121 }
122
123 // Hashed search for secondary super k.
124 inline bool Klass::lookup_secondary_supers_table(Klass* k) const {
125 uintx bitmap = _secondary_supers_bitmap;
126
127 constexpr int highest_bit_number = SECONDARY_SUPERS_TABLE_SIZE - 1;
128 uint8_t slot = k->_hash_slot;
129 uintx shifted_bitmap = bitmap << (highest_bit_number - slot);
130
131 precond((int)population_count(bitmap) <= secondary_supers()->length());
132
133 // First check the bitmap to see if super_klass might be present. If
134 // the bit is zero, we are certain that super_klass is not one of
135 // the secondary supers.
136 if (((shifted_bitmap >> highest_bit_number) & 1) == 0) {
137 return false;
138 }
139
140 // Calculate the initial hash probe
141 int index = population_count(shifted_bitmap) - 1;
142 if (secondary_supers()->at(index) == k) {
143 // Yes! It worked the first time.
144 return true;
145 }
146
147 // Is there another entry to check? Consult the bitmap. If Bit 1,
148 // the next bit to test, is zero, we are certain that super_klass is
149 // not one of the secondary supers.
150 bitmap = rotate_right(bitmap, slot);
151 if ((bitmap & 2) == 0) {
152 return false;
153 }
154
155 // Continue probing the hash table
156 return fallback_search_secondary_supers(k, index, bitmap);
157 }
158
159 inline bool Klass::search_secondary_supers(Klass *k) const {
160 // This is necessary because I am never in my own secondary_super list.
161 if (this == k)
162 return true;
163
164 bool result = lookup_secondary_supers_table(k);
165
166 #ifndef PRODUCT
167 if (VerifySecondarySupers) {
168 bool linear_result = linear_search_secondary_supers(k);
169 if (linear_result != result) {
170 on_secondary_supers_verification_failure((Klass*)this, k, linear_result, result, "mismatch");
171 }
172 }
173 #endif // PRODUCT
174
175 return result;
176 }
177
178 // Returns true if this Klass needs to be addressable via narrow Klass ID.
179 inline bool Klass::needs_narrow_id() const {
180 // Classes that are never instantiated need no narrow Klass Id, since the
181 // only point of having a narrow id is to put it into an object header. Keeping
182 // never instantiated classes out of class space lessens the class space pressure.
183 // For more details, see JDK-8338526.
184 // Note: don't call this function before access flags are initialized.
185 return !is_abstract() && !is_interface();
186 }
187 #endif // SHARE_OOPS_KLASS_INLINE_HPP