1 /*
   2  * Copyright (c) 1997, 2024, 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 #include "precompiled.hpp"
  26 #include "cds/archiveHeapLoader.hpp"
  27 #include "cds/cdsConfig.hpp"
  28 #include "cds/heapShared.hpp"
  29 #include "classfile/classLoader.hpp"
  30 #include "classfile/classLoaderData.inline.hpp"
  31 #include "classfile/classLoaderDataGraph.inline.hpp"
  32 #include "classfile/javaClasses.inline.hpp"
  33 #include "classfile/moduleEntry.hpp"
  34 #include "classfile/systemDictionary.hpp"
  35 #include "classfile/systemDictionaryShared.hpp"
  36 #include "classfile/vmClasses.hpp"
  37 #include "classfile/vmSymbols.hpp"
  38 #include "gc/shared/collectedHeap.inline.hpp"
  39 #include "jvm_io.h"
  40 #include "logging/log.hpp"
  41 #include "memory/metadataFactory.hpp"
  42 #include "memory/metaspaceClosure.hpp"
  43 #include "memory/oopFactory.hpp"
  44 #include "memory/resourceArea.hpp"
  45 #include "memory/universe.hpp"
  46 #include "oops/compressedOops.inline.hpp"
  47 #include "oops/instanceKlass.hpp"
  48 #include "oops/klass.inline.hpp"
  49 #include "oops/objArrayKlass.hpp"
  50 #include "oops/oop.inline.hpp"
  51 #include "oops/oopHandle.inline.hpp"
  52 #include "prims/jvmtiExport.hpp"
  53 #include "runtime/atomic.hpp"
  54 #include "runtime/handles.inline.hpp"
  55 #include "runtime/perfData.hpp"
  56 #include "utilities/macros.hpp"
  57 #include "utilities/powerOfTwo.hpp"
  58 #include "utilities/rotate_bits.hpp"
  59 #include "utilities/stack.inline.hpp"
  60 
  61 void Klass::set_java_mirror(Handle m) {
  62   assert(!m.is_null(), "New mirror should never be null.");
  63   assert(_java_mirror.is_empty(), "should only be used to initialize mirror");
  64   _java_mirror = class_loader_data()->add_handle(m);
  65 }
  66 
  67 bool Klass::is_cloneable() const {
  68   return _misc_flags.is_cloneable_fast() ||
  69          is_subtype_of(vmClasses::Cloneable_klass());
  70 }
  71 
  72 void Klass::set_is_cloneable() {
  73   if (name() == vmSymbols::java_lang_invoke_MemberName()) {
  74     assert(is_final(), "no subclasses allowed");
  75     // MemberName cloning should not be intrinsified and always happen in JVM_Clone.
  76   } else if (is_instance_klass() && InstanceKlass::cast(this)->reference_type() != REF_NONE) {
  77     // Reference cloning should not be intrinsified and always happen in JVM_Clone.
  78   } else {
  79     _misc_flags.set_is_cloneable_fast(true);
  80   }
  81 }
  82 
  83 uint8_t Klass::compute_hash_slot(Symbol* n) {
  84   uint hash_code;
  85   // Special cases for the two superclasses of all Array instances.
  86   // Code elsewhere assumes, for all instances of ArrayKlass, that
  87   // these two interfaces will be in this order.
  88 
  89   // We ensure there are some empty slots in the hash table between
  90   // these two very common interfaces because if they were adjacent
  91   // (e.g. Slots 0 and 1), then any other class which hashed to 0 or 1
  92   // would result in a probe length of 3.
  93   if (n == vmSymbols::java_lang_Cloneable()) {
  94     hash_code = 0;
  95   } else if (n == vmSymbols::java_io_Serializable()) {
  96     hash_code = SECONDARY_SUPERS_TABLE_SIZE / 2;
  97   } else {
  98     auto s = (const jbyte*) n->bytes();
  99     hash_code = java_lang_String::hash_code(s, n->utf8_length());
 100     // We use String::hash_code here (rather than e.g.
 101     // Symbol::identity_hash()) in order to have a hash code that
 102     // does not change from run to run. We want that because the
 103     // hash value for a secondary superclass appears in generated
 104     // code as a constant.
 105 
 106     // This constant is magic: see Knuth, "Fibonacci Hashing".
 107     constexpr uint multiplier
 108       = 2654435769; // (uint)(((u8)1 << 32) / ((1 + sqrt(5)) / 2 ))
 109     constexpr uint hash_shift = sizeof(hash_code) * 8 - 6;
 110     // The leading bits of the least significant half of the product.
 111     hash_code = (hash_code * multiplier) >> hash_shift;
 112 
 113     if (StressSecondarySupers) {
 114       // Generate many hash collisions in order to stress-test the
 115       // linear search fallback.
 116       hash_code = hash_code % 3;
 117       hash_code = hash_code * (SECONDARY_SUPERS_TABLE_SIZE / 3);
 118     }
 119   }
 120 
 121   return (hash_code & SECONDARY_SUPERS_TABLE_MASK);
 122 }
 123 
 124 void Klass::set_name(Symbol* n) {
 125   _name = n;
 126 
 127   if (_name != nullptr) {
 128     _name->increment_refcount();
 129   }
 130 
 131   {
 132     elapsedTimer selftime;
 133     selftime.start();
 134 
 135     _hash_slot = compute_hash_slot(n);
 136     assert(_hash_slot < SECONDARY_SUPERS_TABLE_SIZE, "required");
 137 
 138     selftime.stop();
 139     if (UsePerfData) {
 140       ClassLoader::perf_secondary_hash_time()->inc(selftime.ticks());
 141     }
 142   }
 143 
 144   if (CDSConfig::is_dumping_archive() && is_instance_klass()) {
 145     SystemDictionaryShared::init_dumptime_info(InstanceKlass::cast(this));
 146   }
 147 }
 148 
 149 bool Klass::is_subclass_of(const Klass* k) const {
 150   // Run up the super chain and check
 151   if (this == k) return true;
 152 
 153   Klass* t = const_cast<Klass*>(this)->super();
 154 
 155   while (t != nullptr) {
 156     if (t == k) return true;
 157     t = t->super();
 158   }
 159   return false;
 160 }
 161 
 162 void Klass::release_C_heap_structures(bool release_constant_pool) {
 163   if (_name != nullptr) _name->decrement_refcount();
 164 }
 165 
 166 bool Klass::linear_search_secondary_supers(const Klass* k) const {
 167   // Scan the array-of-objects for a match
 168   // FIXME: We could do something smarter here, maybe a vectorized
 169   // comparison or a binary search, but is that worth any added
 170   // complexity?
 171   int cnt = secondary_supers()->length();
 172   for (int i = 0; i < cnt; i++) {
 173     if (secondary_supers()->at(i) == k) {
 174       return true;
 175     }
 176   }
 177   return false;
 178 }
 179 
 180 // Given a secondary superklass k, an initial array index, and an
 181 // occupancy bitmap rotated such that Bit 1 is the next bit to test,
 182 // search for k.
 183 bool Klass::fallback_search_secondary_supers(const Klass* k, int index, uintx rotated_bitmap) const {
 184   // Once the occupancy bitmap is almost full, it's faster to use a
 185   // linear search.
 186   if (secondary_supers()->length() > SECONDARY_SUPERS_TABLE_SIZE - 2) {
 187     return linear_search_secondary_supers(k);
 188   }
 189 
 190   // This is conventional linear probing, but instead of terminating
 191   // when a null entry is found in the table, we maintain a bitmap
 192   // in which a 0 indicates missing entries.
 193 
 194   precond((int)population_count(rotated_bitmap) == secondary_supers()->length());
 195 
 196   // The check for secondary_supers()->length() <= SECONDARY_SUPERS_TABLE_SIZE - 2
 197   // at the start of this function guarantees there are 0s in the
 198   // bitmap, so this loop eventually terminates.
 199   while ((rotated_bitmap & 2) != 0) {
 200     if (++index == secondary_supers()->length()) {
 201       index = 0;
 202     }
 203     if (secondary_supers()->at(index) == k) {
 204       return true;
 205     }
 206     rotated_bitmap = rotate_right(rotated_bitmap, 1);
 207   }
 208   return false;
 209 }
 210 
 211 // Return self, except for abstract classes with exactly 1
 212 // implementor.  Then return the 1 concrete implementation.
 213 Klass *Klass::up_cast_abstract() {
 214   Klass *r = this;
 215   while( r->is_abstract() ) {   // Receiver is abstract?
 216     Klass *s = r->subklass();   // Check for exactly 1 subklass
 217     if (s == nullptr || s->next_sibling() != nullptr) // Oops; wrong count; give up
 218       return this;              // Return 'this' as a no-progress flag
 219     r = s;                    // Loop till find concrete class
 220   }
 221   return r;                   // Return the 1 concrete class
 222 }
 223 
 224 // Find LCA in class hierarchy
 225 Klass *Klass::LCA( Klass *k2 ) {
 226   Klass *k1 = this;
 227   while( 1 ) {
 228     if( k1->is_subtype_of(k2) ) return k2;
 229     if( k2->is_subtype_of(k1) ) return k1;
 230     k1 = k1->super();
 231     k2 = k2->super();
 232   }
 233 }
 234 
 235 
 236 void Klass::check_valid_for_instantiation(bool throwError, TRAPS) {
 237   ResourceMark rm(THREAD);
 238   THROW_MSG(throwError ? vmSymbols::java_lang_InstantiationError()
 239             : vmSymbols::java_lang_InstantiationException(), external_name());
 240 }
 241 
 242 
 243 void Klass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS) {
 244   ResourceMark rm(THREAD);
 245   assert(s != nullptr, "Throw NPE!");
 246   THROW_MSG(vmSymbols::java_lang_ArrayStoreException(),
 247             err_msg("arraycopy: source type %s is not an array", s->klass()->external_name()));
 248 }
 249 
 250 
 251 void Klass::initialize(TRAPS) {
 252   ShouldNotReachHere();
 253 }
 254 
 255 Klass* Klass::find_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const {
 256 #ifdef ASSERT
 257   tty->print_cr("Error: find_field called on a klass oop."
 258                 " Likely error: reflection method does not correctly"
 259                 " wrap return value in a mirror object.");
 260 #endif
 261   ShouldNotReachHere();
 262   return nullptr;
 263 }
 264 
 265 Method* Klass::uncached_lookup_method(const Symbol* name, const Symbol* signature,
 266                                       OverpassLookupMode overpass_mode,
 267                                       PrivateLookupMode private_mode) const {
 268 #ifdef ASSERT
 269   tty->print_cr("Error: uncached_lookup_method called on a klass oop."
 270                 " Likely error: reflection method does not correctly"
 271                 " wrap return value in a mirror object.");
 272 #endif
 273   ShouldNotReachHere();
 274   return nullptr;
 275 }
 276 
 277 Klass::Klass() : _kind(UnknownKlassKind) {
 278   assert(CDSConfig::is_dumping_static_archive() || CDSConfig::is_using_archive(), "only for cds");
 279 }
 280 
 281 // "Normal" instantiation is preceded by a MetaspaceObj allocation
 282 // which zeros out memory - calloc equivalent.
 283 // The constructor is also used from CppVtableCloner,
 284 // which doesn't zero out the memory before calling the constructor.
 285 Klass::Klass(KlassKind kind) : _kind(kind),
 286                                _prototype_header(markWord::prototype()),
 287                                _shared_class_path_index(-1) {
 288   CDS_ONLY(_shared_class_flags = 0;)
 289   CDS_JAVA_HEAP_ONLY(_archived_mirror_index = -1;)
 290   _primary_supers[0] = this;
 291   set_super_check_offset(in_bytes(primary_supers_offset()));
 292 }
 293 
 294 jint Klass::array_layout_helper(BasicType etype) {
 295   assert(etype >= T_BOOLEAN && etype <= T_OBJECT, "valid etype");
 296   // Note that T_ARRAY is not allowed here.
 297   int  hsize = arrayOopDesc::base_offset_in_bytes(etype);
 298   int  esize = type2aelembytes(etype);
 299   bool isobj = (etype == T_OBJECT);
 300   int  tag   =  isobj ? _lh_array_tag_obj_value : _lh_array_tag_type_value;
 301   int lh = array_layout_helper(tag, false, hsize, etype, exact_log2(esize));
 302 
 303   assert(lh < (int)_lh_neutral_value, "must look like an array layout");
 304   assert(layout_helper_is_array(lh), "correct kind");
 305   assert(layout_helper_is_objArray(lh) == isobj, "correct kind");
 306   assert(layout_helper_is_typeArray(lh) == !isobj, "correct kind");
 307   assert(layout_helper_header_size(lh) == hsize, "correct decode");
 308   assert(layout_helper_element_type(lh) == etype, "correct decode");
 309   assert(1 << layout_helper_log2_element_size(lh) == esize, "correct decode");
 310 
 311   return lh;
 312 }
 313 
 314 bool Klass::can_be_primary_super_slow() const {
 315   if (super() == nullptr)
 316     return true;
 317   else if (super()->super_depth() >= primary_super_limit()-1)
 318     return false;
 319   else
 320     return true;
 321 }
 322 
 323 void Klass::set_secondary_supers(Array<Klass*>* secondaries, uintx bitmap) {
 324 #ifdef ASSERT
 325   if (secondaries != nullptr) {
 326     uintx real_bitmap = compute_secondary_supers_bitmap(secondaries);
 327     assert(bitmap == real_bitmap, "must be");
 328     assert(secondaries->length() >= (int)population_count(bitmap), "must be");
 329   }
 330 #endif
 331   _secondary_supers_bitmap = bitmap;
 332   _secondary_supers = secondaries;
 333 
 334   if (secondaries != nullptr) {
 335     LogMessage(class, load) msg;
 336     NonInterleavingLogStream log {LogLevel::Debug, msg};
 337     if (log.is_enabled()) {
 338       ResourceMark rm;
 339       log.print_cr("set_secondary_supers: hash_slot: %d; klass: %s", hash_slot(), external_name());
 340       print_secondary_supers_on(&log);
 341     }
 342   }
 343 }
 344 
 345 // Hashed secondary superclasses
 346 //
 347 // We use a compressed 64-entry hash table with linear probing. We
 348 // start by creating a hash table in the usual way, followed by a pass
 349 // that removes all the null entries. To indicate which entries would
 350 // have been null we use a bitmap that contains a 1 in each position
 351 // where an entry is present, 0 otherwise. This bitmap also serves as
 352 // a kind of Bloom filter, which in many cases allows us quickly to
 353 // eliminate the possibility that something is a member of a set of
 354 // secondaries.
 355 uintx Klass::hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite) {
 356   const int length = secondaries->length();
 357 
 358   if (length == 0) {
 359     return SECONDARY_SUPERS_BITMAP_EMPTY;
 360   }
 361 
 362   if (length == 1) {
 363     int hash_slot = secondaries->at(0)->hash_slot();
 364     return uintx(1) << hash_slot;
 365   }
 366 
 367   // Invariant: _secondary_supers.length >= population_count(_secondary_supers_bitmap)
 368 
 369   // Don't attempt to hash a table that's completely full, because in
 370   // the case of an absent interface linear probing would not
 371   // terminate.
 372   if (length >= SECONDARY_SUPERS_TABLE_SIZE) {
 373     return SECONDARY_SUPERS_BITMAP_FULL;
 374   }
 375 
 376   {
 377     PerfTraceTime ptt(ClassLoader::perf_secondary_hash_time());
 378 
 379     ResourceMark rm;
 380     uintx bitmap = SECONDARY_SUPERS_BITMAP_EMPTY;
 381     auto hashed_secondaries = new GrowableArray<Klass*>(SECONDARY_SUPERS_TABLE_SIZE,
 382                                                         SECONDARY_SUPERS_TABLE_SIZE, nullptr);
 383 
 384     for (int j = 0; j < length; j++) {
 385       Klass* k = secondaries->at(j);
 386       hash_insert(k, hashed_secondaries, bitmap);
 387     }
 388 
 389     // Pack the hashed secondaries array by copying it into the
 390     // secondaries array, sans nulls, if modification is allowed.
 391     // Otherwise, validate the order.
 392     int i = 0;
 393     for (int slot = 0; slot < SECONDARY_SUPERS_TABLE_SIZE; slot++) {
 394       bool has_element = ((bitmap >> slot) & 1) != 0;
 395       assert(has_element == (hashed_secondaries->at(slot) != nullptr), "");
 396       if (has_element) {
 397         Klass* k = hashed_secondaries->at(slot);
 398         if (rewrite) {
 399           secondaries->at_put(i, k);
 400         } else if (secondaries->at(i) != k) {
 401           assert(false, "broken secondary supers hash table");
 402           return SECONDARY_SUPERS_BITMAP_FULL;
 403         }
 404         i++;
 405       }
 406     }
 407     assert(i == secondaries->length(), "mismatch");
 408     postcond((int)population_count(bitmap) == secondaries->length());
 409 
 410     return bitmap;
 411   }
 412 }
 413 
 414 void Klass::hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap) {
 415   assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 416 
 417   int dist = 0;
 418   for (int slot = klass->hash_slot(); true; slot = (slot + 1) & SECONDARY_SUPERS_TABLE_MASK) {
 419     Klass* existing = secondaries->at(slot);
 420     assert(((bitmap >> slot) & 1) == (existing != nullptr), "mismatch");
 421     if (existing == nullptr) { // no conflict
 422       secondaries->at_put(slot, klass);
 423       bitmap |= uintx(1) << slot;
 424       assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 425       return;
 426     } else {
 427       // Use Robin Hood hashing to minimize the worst case search.
 428       // Also, every permutation of the insertion sequence produces
 429       // the same final Robin Hood hash table, provided that a
 430       // consistent tie breaker is used.
 431       int existing_dist = (slot - existing->hash_slot()) & SECONDARY_SUPERS_TABLE_MASK;
 432       if (existing_dist < dist
 433           // This tie breaker ensures that the hash order is maintained.
 434           || ((existing_dist == dist)
 435               && (uintptr_t(existing) < uintptr_t(klass)))) {
 436         Klass* tmp = secondaries->at(slot);
 437         secondaries->at_put(slot, klass);
 438         klass = tmp;
 439         dist = existing_dist;
 440       }
 441       ++dist;
 442     }
 443   }
 444 }
 445 
 446 Array<Klass*>* Klass::pack_secondary_supers(ClassLoaderData* loader_data,
 447                                             GrowableArray<Klass*>* primaries,
 448                                             GrowableArray<Klass*>* secondaries,
 449                                             uintx& bitmap, TRAPS) {
 450   int new_length = primaries->length() + secondaries->length();
 451   Array<Klass*>* secondary_supers = MetadataFactory::new_array<Klass*>(loader_data, new_length, CHECK_NULL);
 452 
 453   // Combine the two arrays into a metadata object to pack the array.
 454   // The primaries are added in the reverse order, then the secondaries.
 455   int fill_p = primaries->length();
 456   for (int j = 0; j < fill_p; j++) {
 457     secondary_supers->at_put(j, primaries->pop());  // add primaries in reverse order.
 458   }
 459   for( int j = 0; j < secondaries->length(); j++ ) {
 460     secondary_supers->at_put(j+fill_p, secondaries->at(j));  // add secondaries on the end.
 461   }
 462 #ifdef ASSERT
 463   // We must not copy any null placeholders left over from bootstrap.
 464   for (int j = 0; j < secondary_supers->length(); j++) {
 465     assert(secondary_supers->at(j) != nullptr, "correct bootstrapping order");
 466   }
 467 #endif
 468 
 469   bitmap = hash_secondary_supers(secondary_supers, /*rewrite=*/true); // rewrites freshly allocated array
 470   return secondary_supers;
 471 }
 472 
 473 uintx Klass::compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers) {
 474   return hash_secondary_supers(secondary_supers, /*rewrite=*/false); // no rewrites allowed
 475 }
 476 
 477 uint8_t Klass::compute_home_slot(Klass* k, uintx bitmap) {
 478   uint8_t hash = k->hash_slot();
 479   if (hash > 0) {
 480     return population_count(bitmap << (SECONDARY_SUPERS_TABLE_SIZE - hash));
 481   }
 482   return 0;
 483 }
 484 
 485 
 486 void Klass::initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS) {
 487   if (k == nullptr) {
 488     set_super(nullptr);
 489     _primary_supers[0] = this;
 490     assert(super_depth() == 0, "Object must already be initialized properly");
 491   } else if (k != super() || k == vmClasses::Object_klass()) {
 492     assert(super() == nullptr || super() == vmClasses::Object_klass(),
 493            "initialize this only once to a non-trivial value");
 494     set_super(k);
 495     Klass* sup = k;
 496     int sup_depth = sup->super_depth();
 497     juint my_depth  = MIN2(sup_depth + 1, (int)primary_super_limit());
 498     if (!can_be_primary_super_slow())
 499       my_depth = primary_super_limit();
 500     for (juint i = 0; i < my_depth; i++) {
 501       _primary_supers[i] = sup->_primary_supers[i];
 502     }
 503     Klass* *super_check_cell;
 504     if (my_depth < primary_super_limit()) {
 505       _primary_supers[my_depth] = this;
 506       super_check_cell = &_primary_supers[my_depth];
 507     } else {
 508       // Overflow of the primary_supers array forces me to be secondary.
 509       super_check_cell = &_secondary_super_cache;
 510     }
 511     set_super_check_offset(u4((address)super_check_cell - (address) this));
 512 
 513 #ifdef ASSERT
 514     {
 515       juint j = super_depth();
 516       assert(j == my_depth, "computed accessor gets right answer");
 517       Klass* t = this;
 518       while (!t->can_be_primary_super()) {
 519         t = t->super();
 520         j = t->super_depth();
 521       }
 522       for (juint j1 = j+1; j1 < primary_super_limit(); j1++) {
 523         assert(primary_super_of_depth(j1) == nullptr, "super list padding");
 524       }
 525       while (t != nullptr) {
 526         assert(primary_super_of_depth(j) == t, "super list initialization");
 527         t = t->super();
 528         --j;
 529       }
 530       assert(j == (juint)-1, "correct depth count");
 531     }
 532 #endif
 533   }
 534 
 535   if (secondary_supers() == nullptr) {
 536 
 537     // Now compute the list of secondary supertypes.
 538     // Secondaries can occasionally be on the super chain,
 539     // if the inline "_primary_supers" array overflows.
 540     int extras = 0;
 541     Klass* p;
 542     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 543       ++extras;
 544     }
 545 
 546     ResourceMark rm(THREAD);  // need to reclaim GrowableArrays allocated below
 547 
 548     // Compute the "real" non-extra secondaries.
 549     GrowableArray<Klass*>* secondaries = compute_secondary_supers(extras, transitive_interfaces);
 550     if (secondaries == nullptr) {
 551       // secondary_supers set by compute_secondary_supers
 552       return;
 553     }
 554 
 555     GrowableArray<Klass*>* primaries = new GrowableArray<Klass*>(extras);
 556 
 557     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 558       int i;                    // Scan for overflow primaries being duplicates of 2nd'arys
 559 
 560       // This happens frequently for very deeply nested arrays: the
 561       // primary superclass chain overflows into the secondary.  The
 562       // secondary list contains the element_klass's secondaries with
 563       // an extra array dimension added.  If the element_klass's
 564       // secondary list already contains some primary overflows, they
 565       // (with the extra level of array-ness) will collide with the
 566       // normal primary superclass overflows.
 567       for( i = 0; i < secondaries->length(); i++ ) {
 568         if( secondaries->at(i) == p )
 569           break;
 570       }
 571       if( i < secondaries->length() )
 572         continue;               // It's a dup, don't put it in
 573       primaries->push(p);
 574     }
 575     // Combine the two arrays into a metadata object to pack the array.
 576     uintx bitmap = 0;
 577     Array<Klass*>* s2 = pack_secondary_supers(class_loader_data(), primaries, secondaries, bitmap, CHECK);
 578     set_secondary_supers(s2, bitmap);
 579   }
 580 }
 581 
 582 GrowableArray<Klass*>* Klass::compute_secondary_supers(int num_extra_slots,
 583                                                        Array<InstanceKlass*>* transitive_interfaces) {
 584   assert(num_extra_slots == 0, "override for complex klasses");
 585   assert(transitive_interfaces == nullptr, "sanity");
 586   set_secondary_supers(Universe::the_empty_klass_array(), Universe::the_empty_klass_bitmap());
 587   return nullptr;
 588 }
 589 
 590 
 591 // superklass links
 592 InstanceKlass* Klass::superklass() const {
 593   assert(super() == nullptr || super()->is_instance_klass(), "must be instance klass");
 594   return _super == nullptr ? nullptr : InstanceKlass::cast(_super);
 595 }
 596 
 597 // subklass links.  Used by the compiler (and vtable initialization)
 598 // May be cleaned concurrently, so must use the Compile_lock.
 599 // The log parameter is for clean_weak_klass_links to report unlinked classes.
 600 Klass* Klass::subklass(bool log) const {
 601   // Need load_acquire on the _subklass, because it races with inserts that
 602   // publishes freshly initialized data.
 603   for (Klass* chain = Atomic::load_acquire(&_subklass);
 604        chain != nullptr;
 605        // Do not need load_acquire on _next_sibling, because inserts never
 606        // create _next_sibling edges to dead data.
 607        chain = Atomic::load(&chain->_next_sibling))
 608   {
 609     if (chain->is_loader_alive()) {
 610       return chain;
 611     } else if (log) {
 612       if (log_is_enabled(Trace, class, unload)) {
 613         ResourceMark rm;
 614         log_trace(class, unload)("unlinking class (subclass): %s", chain->external_name());
 615       }
 616     }
 617   }
 618   return nullptr;
 619 }
 620 
 621 Klass* Klass::next_sibling(bool log) const {
 622   // Do not need load_acquire on _next_sibling, because inserts never
 623   // create _next_sibling edges to dead data.
 624   for (Klass* chain = Atomic::load(&_next_sibling);
 625        chain != nullptr;
 626        chain = Atomic::load(&chain->_next_sibling)) {
 627     // Only return alive klass, there may be stale klass
 628     // in this chain if cleaned concurrently.
 629     if (chain->is_loader_alive()) {
 630       return chain;
 631     } else if (log) {
 632       if (log_is_enabled(Trace, class, unload)) {
 633         ResourceMark rm;
 634         log_trace(class, unload)("unlinking class (sibling): %s", chain->external_name());
 635       }
 636     }
 637   }
 638   return nullptr;
 639 }
 640 
 641 void Klass::set_subklass(Klass* s) {
 642   assert(s != this, "sanity check");
 643   Atomic::release_store(&_subklass, s);
 644 }
 645 
 646 void Klass::set_next_sibling(Klass* s) {
 647   assert(s != this, "sanity check");
 648   // Does not need release semantics. If used by cleanup, it will link to
 649   // already safely published data, and if used by inserts, will be published
 650   // safely using cmpxchg.
 651   Atomic::store(&_next_sibling, s);
 652 }
 653 
 654 void Klass::append_to_sibling_list() {
 655   if (Universe::is_fully_initialized()) {
 656     assert_locked_or_safepoint(Compile_lock);
 657   }
 658   debug_only(verify();)
 659   // add ourselves to superklass' subklass list
 660   InstanceKlass* super = superklass();
 661   if (super == nullptr) return;     // special case: class Object
 662   assert((!super->is_interface()    // interfaces cannot be supers
 663           && (super->superklass() == nullptr || !is_interface())),
 664          "an interface can only be a subklass of Object");
 665 
 666   // Make sure there is no stale subklass head
 667   super->clean_subklass();
 668 
 669   for (;;) {
 670     Klass* prev_first_subklass = Atomic::load_acquire(&_super->_subklass);
 671     if (prev_first_subklass != nullptr) {
 672       // set our sibling to be the superklass' previous first subklass
 673       assert(prev_first_subklass->is_loader_alive(), "May not attach not alive klasses");
 674       set_next_sibling(prev_first_subklass);
 675     }
 676     // Note that the prev_first_subklass is always alive, meaning no sibling_next links
 677     // are ever created to not alive klasses. This is an important invariant of the lock-free
 678     // cleaning protocol, that allows us to safely unlink dead klasses from the sibling list.
 679     if (Atomic::cmpxchg(&super->_subklass, prev_first_subklass, this) == prev_first_subklass) {
 680       return;
 681     }
 682   }
 683   debug_only(verify();)
 684 }
 685 
 686 void Klass::clean_subklass() {
 687   for (;;) {
 688     // Need load_acquire, due to contending with concurrent inserts
 689     Klass* subklass = Atomic::load_acquire(&_subklass);
 690     if (subklass == nullptr || subklass->is_loader_alive()) {
 691       return;
 692     }
 693     // Try to fix _subklass until it points at something not dead.
 694     Atomic::cmpxchg(&_subklass, subklass, subklass->next_sibling());
 695   }
 696 }
 697 
 698 void Klass::clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses) {
 699   if (!ClassUnloading || !unloading_occurred) {
 700     return;
 701   }
 702 
 703   Klass* root = vmClasses::Object_klass();
 704   Stack<Klass*, mtGC> stack;
 705 
 706   stack.push(root);
 707   while (!stack.is_empty()) {
 708     Klass* current = stack.pop();
 709 
 710     assert(current->is_loader_alive(), "just checking, this should be live");
 711 
 712     // Find and set the first alive subklass
 713     Klass* sub = current->subklass(true);
 714     current->clean_subklass();
 715     if (sub != nullptr) {
 716       stack.push(sub);
 717     }
 718 
 719     // Find and set the first alive sibling
 720     Klass* sibling = current->next_sibling(true);
 721     current->set_next_sibling(sibling);
 722     if (sibling != nullptr) {
 723       stack.push(sibling);
 724     }
 725 
 726     // Clean the implementors list and method data.
 727     if (clean_alive_klasses && current->is_instance_klass()) {
 728       InstanceKlass* ik = InstanceKlass::cast(current);
 729       ik->clean_weak_instanceklass_links();
 730 
 731       // JVMTI RedefineClasses creates previous versions that are not in
 732       // the class hierarchy, so process them here.
 733       while ((ik = ik->previous_versions()) != nullptr) {
 734         ik->clean_weak_instanceklass_links();
 735       }
 736     }
 737   }
 738 }
 739 
 740 void Klass::metaspace_pointers_do(MetaspaceClosure* it) {
 741   if (log_is_enabled(Trace, cds)) {
 742     ResourceMark rm;
 743     log_trace(cds)("Iter(Klass): %p (%s)", this, external_name());
 744   }
 745 
 746   it->push(&_name);
 747   it->push(&_secondary_supers);
 748   for (int i = 0; i < _primary_super_limit; i++) {
 749     it->push(&_primary_supers[i]);
 750   }
 751   it->push(&_super);
 752   if (!CDSConfig::is_dumping_archive()) {
 753     // If dumping archive, these may point to excluded classes. There's no need
 754     // to follow these pointers anyway, as they will be set to null in
 755     // remove_unshareable_info().
 756     it->push((Klass**)&_subklass);
 757     it->push((Klass**)&_next_sibling);
 758     it->push(&_next_link);
 759   }
 760 
 761   vtableEntry* vt = start_of_vtable();
 762   for (int i=0; i<vtable_length(); i++) {
 763     it->push(vt[i].method_addr());
 764   }
 765 }
 766 
 767 #if INCLUDE_CDS
 768 void Klass::remove_unshareable_info() {
 769   assert(CDSConfig::is_dumping_archive(),
 770           "only called during CDS dump time");
 771   JFR_ONLY(REMOVE_ID(this);)
 772   if (log_is_enabled(Trace, cds, unshareable)) {
 773     ResourceMark rm;
 774     log_trace(cds, unshareable)("remove: %s", external_name());
 775   }
 776 
 777   // _secondary_super_cache may be updated by an is_subtype_of() call
 778   // while ArchiveBuilder is copying metaspace objects. Let's reset it to
 779   // null and let it be repopulated at runtime.
 780   set_secondary_super_cache(nullptr);
 781 
 782   set_subklass(nullptr);
 783   set_next_sibling(nullptr);
 784   set_next_link(nullptr);
 785 
 786   // Null out class_loader_data because we don't share that yet.
 787   set_class_loader_data(nullptr);
 788   set_is_shared();
 789 
 790   // FIXME: validation in Klass::hash_secondary_supers() may fail for shared klasses.
 791   // Even though the bitmaps always match, the canonical order of elements in the table
 792   // is not guaranteed to stay the same (see tie breaker during Robin Hood hashing in Klass::hash_insert).
 793   //assert(compute_secondary_supers_bitmap(secondary_supers()) == _secondary_supers_bitmap, "broken table");
 794 }
 795 
 796 void Klass::remove_java_mirror() {
 797   assert(CDSConfig::is_dumping_archive(), "sanity");
 798   if (log_is_enabled(Trace, cds, unshareable)) {
 799     ResourceMark rm;
 800     log_trace(cds, unshareable)("remove java_mirror: %s", external_name());
 801   }
 802   // Just null out the mirror.  The class_loader_data() no longer exists.
 803   clear_java_mirror_handle();
 804 }
 805 
 806 void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS) {
 807   assert(is_klass(), "ensure C++ vtable is restored");
 808   assert(is_shared(), "must be set");
 809   assert(secondary_supers()->length() >= (int)population_count(_secondary_supers_bitmap), "must be");
 810   JFR_ONLY(RESTORE_ID(this);)
 811   if (log_is_enabled(Trace, cds, unshareable)) {
 812     ResourceMark rm(THREAD);
 813     oop class_loader = loader_data->class_loader();
 814     log_trace(cds, unshareable)("restore: %s with class loader: %s", external_name(),
 815       class_loader != nullptr ? class_loader->klass()->external_name() : "boot");
 816   }
 817 
 818   // If an exception happened during CDS restore, some of these fields may already be
 819   // set.  We leave the class on the CLD list, even if incomplete so that we don't
 820   // modify the CLD list outside a safepoint.
 821   if (class_loader_data() == nullptr) {
 822     set_class_loader_data(loader_data);
 823 
 824     // Add to class loader list first before creating the mirror
 825     // (same order as class file parsing)
 826     loader_data->add_class(this);
 827   }
 828 
 829   Handle loader(THREAD, loader_data->class_loader());
 830   ModuleEntry* module_entry = nullptr;
 831   Klass* k = this;
 832   if (k->is_objArray_klass()) {
 833     k = ObjArrayKlass::cast(k)->bottom_klass();
 834   }
 835   // Obtain klass' module.
 836   if (k->is_instance_klass()) {
 837     InstanceKlass* ik = (InstanceKlass*) k;
 838     module_entry = ik->module();
 839   } else {
 840     module_entry = ModuleEntryTable::javabase_moduleEntry();
 841   }
 842   // Obtain java.lang.Module, if available
 843   Handle module_handle(THREAD, ((module_entry != nullptr) ? module_entry->module() : (oop)nullptr));
 844 
 845   if (this->has_archived_mirror_index()) {
 846     ResourceMark rm(THREAD);
 847     log_debug(cds, mirror)("%s has raw archived mirror", external_name());
 848     if (ArchiveHeapLoader::is_in_use()) {
 849       bool present = java_lang_Class::restore_archived_mirror(this, loader, module_handle,
 850                                                               protection_domain,
 851                                                               CHECK);
 852       if (present) {
 853         return;
 854       }
 855     }
 856 
 857     // No archived mirror data
 858     log_debug(cds, mirror)("No archived mirror data for %s", external_name());
 859     clear_java_mirror_handle();
 860     this->clear_archived_mirror_index();
 861   }
 862 
 863   // Only recreate it if not present.  A previous attempt to restore may have
 864   // gotten an OOM later but keep the mirror if it was created.
 865   if (java_mirror() == nullptr) {
 866     ResourceMark rm(THREAD);
 867     log_trace(cds, mirror)("Recreate mirror for %s", external_name());
 868     java_lang_Class::create_mirror(this, loader, module_handle, protection_domain, Handle(), CHECK);
 869   }
 870 }
 871 #endif // INCLUDE_CDS
 872 
 873 #if INCLUDE_CDS_JAVA_HEAP
 874 oop Klass::archived_java_mirror() {
 875   assert(has_archived_mirror_index(), "must have archived mirror");
 876   return HeapShared::get_root(_archived_mirror_index);
 877 }
 878 
 879 void Klass::clear_archived_mirror_index() {
 880   if (_archived_mirror_index >= 0) {
 881     HeapShared::clear_root(_archived_mirror_index);
 882   }
 883   _archived_mirror_index = -1;
 884 }
 885 
 886 // No GC barrier
 887 void Klass::set_archived_java_mirror(int mirror_index) {
 888   assert(CDSConfig::is_dumping_heap(), "sanity");
 889   _archived_mirror_index = mirror_index;
 890 }
 891 #endif // INCLUDE_CDS_JAVA_HEAP
 892 
 893 void Klass::check_array_allocation_length(int length, int max_length, TRAPS) {
 894   if (length > max_length) {
 895     if (!THREAD->is_in_internal_oome_mark()) {
 896       report_java_out_of_memory("Requested array size exceeds VM limit");
 897       JvmtiExport::post_array_size_exhausted();
 898       THROW_OOP(Universe::out_of_memory_error_array_size());
 899     } else {
 900       THROW_OOP(Universe::out_of_memory_error_java_heap_without_backtrace());
 901     }
 902   } else if (length < 0) {
 903     THROW_MSG(vmSymbols::java_lang_NegativeArraySizeException(), err_msg("%d", length));
 904   }
 905 }
 906 
 907 // Replace the last '+' char with '/'.
 908 static char* convert_hidden_name_to_java(Symbol* name) {
 909   size_t name_len = name->utf8_length();
 910   char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 911   name->as_klass_external_name(result, (int)name_len + 1);
 912   for (int index = (int)name_len; index > 0; index--) {
 913     if (result[index] == '+') {
 914       result[index] = JVM_SIGNATURE_SLASH;
 915       break;
 916     }
 917   }
 918   return result;
 919 }
 920 
 921 // In product mode, this function doesn't have virtual function calls so
 922 // there might be some performance advantage to handling InstanceKlass here.
 923 const char* Klass::external_name() const {
 924   if (is_instance_klass()) {
 925     const InstanceKlass* ik = static_cast<const InstanceKlass*>(this);
 926     if (ik->is_hidden()) {
 927       char* result = convert_hidden_name_to_java(name());
 928       return result;
 929     }
 930   } else if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 931     char* result = convert_hidden_name_to_java(name());
 932     return result;
 933   }
 934   if (name() == nullptr)  return "<unknown>";
 935   return name()->as_klass_external_name();
 936 }
 937 
 938 const char* Klass::signature_name() const {
 939   if (name() == nullptr)  return "<unknown>";
 940   if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 941     size_t name_len = name()->utf8_length();
 942     char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 943     name()->as_C_string(result, (int)name_len + 1);
 944     for (int index = (int)name_len; index > 0; index--) {
 945       if (result[index] == '+') {
 946         result[index] = JVM_SIGNATURE_DOT;
 947         break;
 948       }
 949     }
 950     return result;
 951   }
 952   return name()->as_C_string();
 953 }
 954 
 955 const char* Klass::external_kind() const {
 956   if (is_interface()) return "interface";
 957   if (is_abstract()) return "abstract class";
 958   return "class";
 959 }
 960 
 961 // Unless overridden, jvmti_class_status has no flags set.
 962 jint Klass::jvmti_class_status() const {
 963   return 0;
 964 }
 965 
 966 
 967 // Printing
 968 
 969 void Klass::print_on(outputStream* st) const {
 970   ResourceMark rm;
 971   // print title
 972   st->print("%s", internal_name());
 973   print_address_on(st);
 974   st->cr();
 975 }
 976 
 977 #define BULLET  " - "
 978 
 979 // Caller needs ResourceMark
 980 void Klass::oop_print_on(oop obj, outputStream* st) {
 981   // print title
 982   st->print_cr("%s ", internal_name());
 983   obj->print_address_on(st);
 984 
 985   if (WizardMode) {
 986      // print header
 987      obj->mark().print_on(st);
 988      st->cr();
 989      st->print(BULLET"prototype_header: " INTPTR_FORMAT, _prototype_header.value());
 990      st->cr();
 991   }
 992 
 993   // print class
 994   st->print(BULLET"klass: ");
 995   obj->klass()->print_value_on(st);
 996   st->print(BULLET"flags: "); _misc_flags.print_on(st); st->cr();
 997   st->cr();
 998 }
 999 
1000 void Klass::oop_print_value_on(oop obj, outputStream* st) {
1001   // print title
1002   ResourceMark rm;              // Cannot print in debug mode without this
1003   st->print("%s", internal_name());
1004   obj->print_address_on(st);
1005 }
1006 
1007 // Verification
1008 
1009 void Klass::verify_on(outputStream* st) {
1010 
1011   // This can be expensive, but it is worth checking that this klass is actually
1012   // in the CLD graph but not in production.
1013   assert(Metaspace::contains((address)this), "Should be");
1014 
1015   guarantee(this->is_klass(),"should be klass");
1016 
1017   if (super() != nullptr) {
1018     guarantee(super()->is_klass(), "should be klass");
1019   }
1020   if (secondary_super_cache() != nullptr) {
1021     Klass* ko = secondary_super_cache();
1022     guarantee(ko->is_klass(), "should be klass");
1023   }
1024   for ( uint i = 0; i < primary_super_limit(); i++ ) {
1025     Klass* ko = _primary_supers[i];
1026     if (ko != nullptr) {
1027       guarantee(ko->is_klass(), "should be klass");
1028     }
1029   }
1030 
1031   if (java_mirror_no_keepalive() != nullptr) {
1032     guarantee(java_lang_Class::is_instance(java_mirror_no_keepalive()), "should be instance");
1033   }
1034 }
1035 
1036 void Klass::oop_verify_on(oop obj, outputStream* st) {
1037   guarantee(oopDesc::is_oop(obj),  "should be oop");
1038   guarantee(obj->klass()->is_klass(), "klass field is not a klass");
1039 }
1040 
1041 bool Klass::is_valid(Klass* k) {
1042   if (!is_aligned(k, sizeof(MetaWord))) return false;
1043   if ((size_t)k < os::min_page_size()) return false;
1044 
1045   if (!os::is_readable_range(k, k + 1)) return false;
1046   if (!Metaspace::contains(k)) return false;
1047 
1048   if (!Symbol::is_valid(k->name())) return false;
1049   return ClassLoaderDataGraph::is_valid(k->class_loader_data());
1050 }
1051 
1052 Method* Klass::method_at_vtable(int index)  {
1053 #ifndef PRODUCT
1054   assert(index >= 0, "valid vtable index");
1055   if (DebugVtables) {
1056     verify_vtable_index(index);
1057   }
1058 #endif
1059   return start_of_vtable()[index].method();
1060 }
1061 
1062 
1063 #ifndef PRODUCT
1064 
1065 bool Klass::verify_vtable_index(int i) {
1066   int limit = vtable_length()/vtableEntry::size();
1067   assert(i >= 0 && i < limit, "index %d out of bounds %d", i, limit);
1068   return true;
1069 }
1070 
1071 #endif // PRODUCT
1072 
1073 // Caller needs ResourceMark
1074 // joint_in_module_of_loader provides an optimization if 2 classes are in
1075 // the same module to succinctly print out relevant information about their
1076 // module name and class loader's name_and_id for error messages.
1077 // Format:
1078 //   <fully-qualified-external-class-name1> and <fully-qualified-external-class-name2>
1079 //                      are in module <module-name>[@<version>]
1080 //                      of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1081 const char* Klass::joint_in_module_of_loader(const Klass* class2, bool include_parent_loader) const {
1082   assert(module() == class2->module(), "classes do not have the same module");
1083   const char* class1_name = external_name();
1084   size_t len = strlen(class1_name) + 1;
1085 
1086   const char* class2_description = class2->class_in_module_of_loader(true, include_parent_loader);
1087   len += strlen(class2_description);
1088 
1089   len += strlen(" and ");
1090 
1091   char* joint_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1092 
1093   // Just return the FQN if error when allocating string
1094   if (joint_description == nullptr) {
1095     return class1_name;
1096   }
1097 
1098   jio_snprintf(joint_description, len, "%s and %s",
1099                class1_name,
1100                class2_description);
1101 
1102   return joint_description;
1103 }
1104 
1105 // Caller needs ResourceMark
1106 // class_in_module_of_loader provides a standard way to include
1107 // relevant information about a class, such as its module name as
1108 // well as its class loader's name_and_id, in error messages and logging.
1109 // Format:
1110 //   <fully-qualified-external-class-name> is in module <module-name>[@<version>]
1111 //                                         of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1112 const char* Klass::class_in_module_of_loader(bool use_are, bool include_parent_loader) const {
1113   // 1. fully qualified external name of class
1114   const char* klass_name = external_name();
1115   size_t len = strlen(klass_name) + 1;
1116 
1117   // 2. module name + @version
1118   const char* module_name = "";
1119   const char* version = "";
1120   bool has_version = false;
1121   bool module_is_named = false;
1122   const char* module_name_phrase = "";
1123   const Klass* bottom_klass = is_objArray_klass() ?
1124                                 ObjArrayKlass::cast(this)->bottom_klass() : this;
1125   if (bottom_klass->is_instance_klass()) {
1126     ModuleEntry* module = InstanceKlass::cast(bottom_klass)->module();
1127     if (module->is_named()) {
1128       module_is_named = true;
1129       module_name_phrase = "module ";
1130       module_name = module->name()->as_C_string();
1131       len += strlen(module_name);
1132       // Use version if exists and is not a jdk module
1133       if (module->should_show_version()) {
1134         has_version = true;
1135         version = module->version()->as_C_string();
1136         // Include stlen(version) + 1 for the "@"
1137         len += strlen(version) + 1;
1138       }
1139     } else {
1140       module_name = UNNAMED_MODULE;
1141       len += UNNAMED_MODULE_LEN;
1142     }
1143   } else {
1144     // klass is an array of primitives, module is java.base
1145     module_is_named = true;
1146     module_name_phrase = "module ";
1147     module_name = JAVA_BASE_NAME;
1148     len += JAVA_BASE_NAME_LEN;
1149   }
1150 
1151   // 3. class loader's name_and_id
1152   ClassLoaderData* cld = class_loader_data();
1153   assert(cld != nullptr, "class_loader_data should not be null");
1154   const char* loader_name_and_id = cld->loader_name_and_id();
1155   len += strlen(loader_name_and_id);
1156 
1157   // 4. include parent loader information
1158   const char* parent_loader_phrase = "";
1159   const char* parent_loader_name_and_id = "";
1160   if (include_parent_loader &&
1161       !cld->is_builtin_class_loader_data()) {
1162     oop parent_loader = java_lang_ClassLoader::parent(class_loader());
1163     ClassLoaderData *parent_cld = ClassLoaderData::class_loader_data_or_null(parent_loader);
1164     // The parent loader's ClassLoaderData could be null if it is
1165     // a delegating class loader that has never defined a class.
1166     // In this case the loader's name must be obtained via the parent loader's oop.
1167     if (parent_cld == nullptr) {
1168       oop cl_name_and_id = java_lang_ClassLoader::nameAndId(parent_loader);
1169       if (cl_name_and_id != nullptr) {
1170         parent_loader_name_and_id = java_lang_String::as_utf8_string(cl_name_and_id);
1171       }
1172     } else {
1173       parent_loader_name_and_id = parent_cld->loader_name_and_id();
1174     }
1175     parent_loader_phrase = ", parent loader ";
1176     len += strlen(parent_loader_phrase) + strlen(parent_loader_name_and_id);
1177   }
1178 
1179   // Start to construct final full class description string
1180   len += ((use_are) ? strlen(" are in ") : strlen(" is in "));
1181   len += strlen(module_name_phrase) + strlen(" of loader ");
1182 
1183   char* class_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1184 
1185   // Just return the FQN if error when allocating string
1186   if (class_description == nullptr) {
1187     return klass_name;
1188   }
1189 
1190   jio_snprintf(class_description, len, "%s %s in %s%s%s%s of loader %s%s%s",
1191                klass_name,
1192                (use_are) ? "are" : "is",
1193                module_name_phrase,
1194                module_name,
1195                (has_version) ? "@" : "",
1196                (has_version) ? version : "",
1197                loader_name_and_id,
1198                parent_loader_phrase,
1199                parent_loader_name_and_id);
1200 
1201   return class_description;
1202 }
1203 
1204 class LookupStats : StackObj {
1205  private:
1206   uint _no_of_samples;
1207   uint _worst;
1208   uint _worst_count;
1209   uint _average;
1210   uint _best;
1211   uint _best_count;
1212  public:
1213   LookupStats() : _no_of_samples(0), _worst(0), _worst_count(0), _average(0), _best(INT_MAX), _best_count(0) {}
1214 
1215   ~LookupStats() {
1216     assert(_best <= _worst || _no_of_samples == 0, "sanity");
1217   }
1218 
1219   void sample(uint value) {
1220     ++_no_of_samples;
1221     _average += value;
1222 
1223     if (_worst < value) {
1224       _worst = value;
1225       _worst_count = 1;
1226     } else if (_worst == value) {
1227       ++_worst_count;
1228     }
1229 
1230     if (_best > value) {
1231       _best = value;
1232       _best_count = 1;
1233     } else if (_best == value) {
1234       ++_best_count;
1235     }
1236   }
1237 
1238   void print_on(outputStream* st) const {
1239     st->print("best: %2d (%4.1f%%)", _best, (100.0 * _best_count) / _no_of_samples);
1240     if (_best_count < _no_of_samples) {
1241       st->print("; average: %4.1f; worst: %2d (%4.1f%%)",
1242                 (1.0 * _average) / _no_of_samples,
1243                 _worst, (100.0 * _worst_count) / _no_of_samples);
1244     }
1245   }
1246 };
1247 
1248 static void print_positive_lookup_stats(Array<Klass*>* secondary_supers, uintx bitmap, outputStream* st) {
1249   int num_of_supers = secondary_supers->length();
1250 
1251   LookupStats s;
1252   for (int i = 0; i < num_of_supers; i++) {
1253     Klass* secondary_super = secondary_supers->at(i);
1254     int home_slot = Klass::compute_home_slot(secondary_super, bitmap);
1255     uint score = 1 + ((i - home_slot) & Klass::SECONDARY_SUPERS_TABLE_MASK);
1256     s.sample(score);
1257   }
1258   st->print("positive_lookup: "); s.print_on(st);
1259 }
1260 
1261 static uint compute_distance_to_nearest_zero(int slot, uintx bitmap) {
1262   assert(~bitmap != 0, "no zeroes");
1263   uintx start = rotate_right(bitmap, slot);
1264   return count_trailing_zeros(~start);
1265 }
1266 
1267 static void print_negative_lookup_stats(uintx bitmap, outputStream* st) {
1268   LookupStats s;
1269   for (int slot = 0; slot < Klass::SECONDARY_SUPERS_TABLE_SIZE; slot++) {
1270     uint score = compute_distance_to_nearest_zero(slot, bitmap);
1271     s.sample(score);
1272   }
1273   st->print("negative_lookup: "); s.print_on(st);
1274 }
1275 
1276 void Klass::print_secondary_supers_on(outputStream* st) const {
1277   if (secondary_supers() != nullptr) {
1278     st->print("  - "); st->print("%d elements;", _secondary_supers->length());
1279     st->print_cr(" bitmap: " UINTX_FORMAT_X_0 ";", _secondary_supers_bitmap);
1280     if (_secondary_supers_bitmap != SECONDARY_SUPERS_BITMAP_EMPTY &&
1281         _secondary_supers_bitmap != SECONDARY_SUPERS_BITMAP_FULL) {
1282       st->print("  - "); print_positive_lookup_stats(secondary_supers(),
1283                                                      _secondary_supers_bitmap, st); st->cr();
1284       st->print("  - "); print_negative_lookup_stats(_secondary_supers_bitmap, st); st->cr();
1285     }
1286   } else {
1287     st->print("null");
1288   }
1289 }
1290 
1291 void Klass::on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg) {
1292   ResourceMark rm;
1293   super->print();
1294   sub->print();
1295   fatal("%s: %s implements %s: linear_search: %d; table_lookup: %d",
1296         msg, sub->external_name(), super->external_name(), linear_result, table_result);
1297 }