1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
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  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  *
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 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
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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