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