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