1 /*
   2  * Copyright (c) 2001, 2020, 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 "classfile/systemDictionary.hpp"
  27 #include "gc/shared/allocTracer.hpp"
  28 #include "gc/shared/barrierSet.hpp"
  29 #include "gc/shared/collectedHeap.hpp"
  30 #include "gc/shared/collectedHeap.inline.hpp"
  31 #include "gc/shared/gcLocker.inline.hpp"
  32 #include "gc/shared/gcHeapSummary.hpp"
  33 #include "gc/shared/gcTrace.hpp"
  34 #include "gc/shared/gcTraceTime.inline.hpp"
  35 #include "gc/shared/gcVMOperations.hpp"
  36 #include "gc/shared/gcWhen.hpp"
  37 #include "gc/shared/memAllocator.hpp"
  38 #include "logging/log.hpp"
  39 #include "memory/metaspace.hpp"
  40 #include "memory/resourceArea.hpp"
  41 #include "memory/universe.hpp"
  42 #include "oops/instanceMirrorKlass.hpp"
  43 #include "oops/oop.inline.hpp"
  44 #include "runtime/handles.inline.hpp"
  45 #include "runtime/init.hpp"
  46 #include "runtime/thread.inline.hpp"
  47 #include "runtime/threadSMR.hpp"
  48 #include "runtime/vmThread.hpp"
  49 #include "services/heapDumper.hpp"
  50 #include "utilities/align.hpp"
  51 #include "utilities/copy.hpp"
  52 
  53 class ClassLoaderData;
  54 
  55 size_t CollectedHeap::_filler_array_max_size = 0;
  56 
  57 template <>
  58 void EventLogBase<GCMessage>::print(outputStream* st, GCMessage& m) {
  59   st->print_cr("GC heap %s", m.is_before ? "before" : "after");
  60   st->print_raw(m);
  61 }
  62 
  63 void GCHeapLog::log_heap(CollectedHeap* heap, bool before) {
  64   if (!should_log()) {
  65     return;
  66   }
  67 
  68   double timestamp = fetch_timestamp();
  69   MutexLocker ml(&_mutex, Mutex::_no_safepoint_check_flag);
  70   int index = compute_log_index();
  71   _records[index].thread = NULL; // Its the GC thread so it's not that interesting.
  72   _records[index].timestamp = timestamp;
  73   _records[index].data.is_before = before;
  74   stringStream st(_records[index].data.buffer(), _records[index].data.size());
  75 
  76   st.print_cr("{Heap %s GC invocations=%u (full %u):",
  77                  before ? "before" : "after",
  78                  heap->total_collections(),
  79                  heap->total_full_collections());
  80 
  81   heap->print_on(&st);
  82   st.print_cr("}");
  83 }
  84 
  85 size_t CollectedHeap::unused() const {
  86   MutexLocker ml(Heap_lock);
  87   return capacity() - used();
  88 }
  89 
  90 VirtualSpaceSummary CollectedHeap::create_heap_space_summary() {
  91   size_t capacity_in_words = capacity() / HeapWordSize;
  92 
  93   return VirtualSpaceSummary(
  94     _reserved.start(), _reserved.start() + capacity_in_words, _reserved.end());
  95 }
  96 
  97 GCHeapSummary CollectedHeap::create_heap_summary() {
  98   VirtualSpaceSummary heap_space = create_heap_space_summary();
  99   return GCHeapSummary(heap_space, used());
 100 }
 101 
 102 MetaspaceSummary CollectedHeap::create_metaspace_summary() {
 103   const MetaspaceSizes meta_space(
 104       MetaspaceUtils::committed_bytes(),
 105       MetaspaceUtils::used_bytes(),
 106       MetaspaceUtils::reserved_bytes());
 107   const MetaspaceSizes data_space(
 108       MetaspaceUtils::committed_bytes(Metaspace::NonClassType),
 109       MetaspaceUtils::used_bytes(Metaspace::NonClassType),
 110       MetaspaceUtils::reserved_bytes(Metaspace::NonClassType));
 111   const MetaspaceSizes class_space(
 112       MetaspaceUtils::committed_bytes(Metaspace::ClassType),
 113       MetaspaceUtils::used_bytes(Metaspace::ClassType),
 114       MetaspaceUtils::reserved_bytes(Metaspace::ClassType));
 115 
 116   const MetaspaceChunkFreeListSummary& ms_chunk_free_list_summary =
 117     MetaspaceUtils::chunk_free_list_summary(Metaspace::NonClassType);
 118   const MetaspaceChunkFreeListSummary& class_chunk_free_list_summary =
 119     MetaspaceUtils::chunk_free_list_summary(Metaspace::ClassType);
 120 
 121   return MetaspaceSummary(MetaspaceGC::capacity_until_GC(), meta_space, data_space, class_space,
 122                           ms_chunk_free_list_summary, class_chunk_free_list_summary);
 123 }
 124 
 125 void CollectedHeap::run_task_at_safepoint(AbstractGangTask* task, uint num_workers) {
 126   WorkGang* gang = get_safepoint_workers();
 127   if (gang == NULL) {
 128     // GC doesn't support parallel worker threads.
 129     // Execute in this thread with worker id 0.
 130     task->work(0);
 131   } else {
 132     gang->run_task(task, num_workers);
 133   }
 134 }
 135 
 136 void CollectedHeap::print_heap_before_gc() {
 137   Universe::print_heap_before_gc();
 138   if (_gc_heap_log != NULL) {
 139     _gc_heap_log->log_heap_before(this);
 140   }
 141 }
 142 
 143 void CollectedHeap::print_heap_after_gc() {
 144   Universe::print_heap_after_gc();
 145   if (_gc_heap_log != NULL) {
 146     _gc_heap_log->log_heap_after(this);
 147   }
 148 }
 149 
 150 void CollectedHeap::print() const { print_on(tty); }
 151 
 152 void CollectedHeap::print_on_error(outputStream* st) const {
 153   st->print_cr("Heap:");
 154   print_extended_on(st);
 155   st->cr();
 156 
 157   BarrierSet* bs = BarrierSet::barrier_set();
 158   if (bs != NULL) {
 159     bs->print_on(st);
 160   }
 161 }
 162 
 163 void CollectedHeap::trace_heap(GCWhen::Type when, const GCTracer* gc_tracer) {
 164   const GCHeapSummary& heap_summary = create_heap_summary();
 165   gc_tracer->report_gc_heap_summary(when, heap_summary);
 166 
 167   const MetaspaceSummary& metaspace_summary = create_metaspace_summary();
 168   gc_tracer->report_metaspace_summary(when, metaspace_summary);
 169 }
 170 
 171 void CollectedHeap::trace_heap_before_gc(const GCTracer* gc_tracer) {
 172   trace_heap(GCWhen::BeforeGC, gc_tracer);
 173 }
 174 
 175 void CollectedHeap::trace_heap_after_gc(const GCTracer* gc_tracer) {
 176   trace_heap(GCWhen::AfterGC, gc_tracer);
 177 }
 178 
 179 // Default implementation, for collectors that don't support the feature.
 180 bool CollectedHeap::supports_concurrent_gc_breakpoints() const {
 181   return false;
 182 }
 183 
 184 bool CollectedHeap::is_oop(oop object) const {
 185   if (!is_object_aligned(object)) {
 186     return false;
 187   }
 188 
 189   if (!is_in(object)) {
 190     return false;
 191   }
 192 
 193   if (is_in(object->klass_or_null())) {
 194     return false;
 195   }
 196 
 197   return true;
 198 }
 199 
 200 // Memory state functions.
 201 
 202 
 203 CollectedHeap::CollectedHeap() :
 204   _is_gc_active(false),
 205   _last_whole_heap_examined_time_ns(os::javaTimeNanos()),
 206   _total_collections(0),
 207   _total_full_collections(0),
 208   _gc_cause(GCCause::_no_gc),
 209   _gc_lastcause(GCCause::_no_gc)
 210 {
 211   const size_t max_len = size_t(arrayOopDesc::max_array_length(T_INT));
 212   const size_t elements_per_word = HeapWordSize / sizeof(jint);
 213   _filler_array_max_size = align_object_size(filler_array_hdr_size() +
 214                                              max_len / elements_per_word);
 215 
 216   NOT_PRODUCT(_promotion_failure_alot_count = 0;)
 217   NOT_PRODUCT(_promotion_failure_alot_gc_number = 0;)
 218 
 219   if (UsePerfData) {
 220     EXCEPTION_MARK;
 221 
 222     // create the gc cause jvmstat counters
 223     _perf_gc_cause = PerfDataManager::create_string_variable(SUN_GC, "cause",
 224                              80, GCCause::to_string(_gc_cause), CHECK);
 225 
 226     _perf_gc_lastcause =
 227                 PerfDataManager::create_string_variable(SUN_GC, "lastCause",
 228                              80, GCCause::to_string(_gc_lastcause), CHECK);
 229   }
 230 
 231   // Create the ring log
 232   if (LogEvents) {
 233     _gc_heap_log = new GCHeapLog();
 234   } else {
 235     _gc_heap_log = NULL;
 236   }
 237 }
 238 
 239 // This interface assumes that it's being called by the
 240 // vm thread. It collects the heap assuming that the
 241 // heap lock is already held and that we are executing in
 242 // the context of the vm thread.
 243 void CollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {
 244   Thread* thread = Thread::current();
 245   assert(thread->is_VM_thread(), "Precondition#1");
 246   assert(Heap_lock->is_locked(), "Precondition#2");
 247   GCCauseSetter gcs(this, cause);
 248   switch (cause) {
 249     case GCCause::_heap_inspection:
 250     case GCCause::_heap_dump:
 251     case GCCause::_metadata_GC_threshold : {
 252       HandleMark hm(thread);
 253       do_full_collection(false);        // don't clear all soft refs
 254       break;
 255     }
 256     case GCCause::_archive_time_gc:
 257     case GCCause::_metadata_GC_clear_soft_refs: {
 258       HandleMark hm(thread);
 259       do_full_collection(true);         // do clear all soft refs
 260       break;
 261     }
 262     default:
 263       ShouldNotReachHere(); // Unexpected use of this function
 264   }
 265 }
 266 
 267 MetaWord* CollectedHeap::satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
 268                                                             size_t word_size,
 269                                                             Metaspace::MetadataType mdtype) {
 270   uint loop_count = 0;
 271   uint gc_count = 0;
 272   uint full_gc_count = 0;
 273 
 274   assert(!Heap_lock->owned_by_self(), "Should not be holding the Heap_lock");
 275 
 276   do {
 277     MetaWord* result = loader_data->metaspace_non_null()->allocate(word_size, mdtype);
 278     if (result != NULL) {
 279       return result;
 280     }
 281 
 282     if (GCLocker::is_active_and_needs_gc()) {
 283       // If the GCLocker is active, just expand and allocate.
 284       // If that does not succeed, wait if this thread is not
 285       // in a critical section itself.
 286       result = loader_data->metaspace_non_null()->expand_and_allocate(word_size, mdtype);
 287       if (result != NULL) {
 288         return result;
 289       }
 290       JavaThread* jthr = JavaThread::current();
 291       if (!jthr->in_critical()) {
 292         // Wait for JNI critical section to be exited
 293         GCLocker::stall_until_clear();
 294         // The GC invoked by the last thread leaving the critical
 295         // section will be a young collection and a full collection
 296         // is (currently) needed for unloading classes so continue
 297         // to the next iteration to get a full GC.
 298         continue;
 299       } else {
 300         if (CheckJNICalls) {
 301           fatal("Possible deadlock due to allocating while"
 302                 " in jni critical section");
 303         }
 304         return NULL;
 305       }
 306     }
 307 
 308     {  // Need lock to get self consistent gc_count's
 309       MutexLocker ml(Heap_lock);
 310       gc_count      = Universe::heap()->total_collections();
 311       full_gc_count = Universe::heap()->total_full_collections();
 312     }
 313 
 314     // Generate a VM operation
 315     VM_CollectForMetadataAllocation op(loader_data,
 316                                        word_size,
 317                                        mdtype,
 318                                        gc_count,
 319                                        full_gc_count,
 320                                        GCCause::_metadata_GC_threshold);
 321     VMThread::execute(&op);
 322 
 323     // If GC was locked out, try again. Check before checking success because the
 324     // prologue could have succeeded and the GC still have been locked out.
 325     if (op.gc_locked()) {
 326       continue;
 327     }
 328 
 329     if (op.prologue_succeeded()) {
 330       return op.result();
 331     }
 332     loop_count++;
 333     if ((QueuedAllocationWarningCount > 0) &&
 334         (loop_count % QueuedAllocationWarningCount == 0)) {
 335       log_warning(gc, ergo)("satisfy_failed_metadata_allocation() retries %d times,"
 336                             " size=" SIZE_FORMAT, loop_count, word_size);
 337     }
 338   } while (true);  // Until a GC is done
 339 }
 340 
 341 MemoryUsage CollectedHeap::memory_usage() {
 342   return MemoryUsage(InitialHeapSize, used(), capacity(), max_capacity());
 343 }
 344 
 345 
 346 #ifndef PRODUCT
 347 void CollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) {
 348   if (CheckMemoryInitialization && ZapUnusedHeapArea) {
 349     // please note mismatch between size (in 32/64 bit words), and ju_addr that always point to a 32 bit word
 350     for (juint* ju_addr = reinterpret_cast<juint*>(addr); ju_addr < reinterpret_cast<juint*>(addr + size); ++ju_addr) {
 351       assert(*ju_addr == badHeapWordVal, "Found non badHeapWordValue in pre-allocation check");
 352     }
 353   }
 354 }
 355 #endif // PRODUCT
 356 
 357 size_t CollectedHeap::max_tlab_size() const {
 358   // TLABs can't be bigger than we can fill with a int[Integer.MAX_VALUE].
 359   // This restriction could be removed by enabling filling with multiple arrays.
 360   // If we compute that the reasonable way as
 361   //    header_size + ((sizeof(jint) * max_jint) / HeapWordSize)
 362   // we'll overflow on the multiply, so we do the divide first.
 363   // We actually lose a little by dividing first,
 364   // but that just makes the TLAB  somewhat smaller than the biggest array,
 365   // which is fine, since we'll be able to fill that.
 366   size_t max_int_size = typeArrayOopDesc::header_size(T_INT) +
 367               sizeof(jint) *
 368               ((juint) max_jint / (size_t) HeapWordSize);
 369   return align_down(max_int_size, MinObjAlignment);
 370 }
 371 
 372 size_t CollectedHeap::filler_array_hdr_size() {
 373   return align_object_offset(arrayOopDesc::header_size(T_INT)); // align to Long
 374 }
 375 
 376 size_t CollectedHeap::filler_array_min_size() {
 377   return align_object_size(filler_array_hdr_size()); // align to MinObjAlignment
 378 }
 379 
 380 #ifdef ASSERT
 381 void CollectedHeap::fill_args_check(HeapWord* start, size_t words)
 382 {
 383   assert(words >= min_fill_size(), "too small to fill");
 384   assert(is_object_aligned(words), "unaligned size");
 385 }
 386 
 387 void CollectedHeap::zap_filler_array(HeapWord* start, size_t words, bool zap)
 388 {
 389   if (ZapFillerObjects && zap) {
 390     Copy::fill_to_words(start + filler_array_hdr_size(),
 391                         words - filler_array_hdr_size(), 0XDEAFBABE);
 392   }
 393 }
 394 #endif // ASSERT
 395 
 396 void
 397 CollectedHeap::fill_with_array(HeapWord* start, size_t words, bool zap)
 398 {
 399   assert(words >= filler_array_min_size(), "too small for an array");
 400   assert(words <= filler_array_max_size(), "too big for a single object");
 401 
 402   const size_t payload_size = words - filler_array_hdr_size();
 403   const size_t len = payload_size * HeapWordSize / sizeof(jint);
 404   assert((int)len >= 0, "size too large " SIZE_FORMAT " becomes %d", words, (int)len);
 405 
 406   ObjArrayAllocator allocator(Universe::intArrayKlassObj(), words, (int)len, /* do_zero */ false);
 407   allocator.initialize(start);
 408   DEBUG_ONLY(zap_filler_array(start, words, zap);)
 409 }
 410 
 411 void
 412 CollectedHeap::fill_with_object_impl(HeapWord* start, size_t words, bool zap)
 413 {
 414   assert(words <= filler_array_max_size(), "too big for a single object");
 415 
 416   if (words >= filler_array_min_size()) {
 417     fill_with_array(start, words, zap);
 418   } else if (words > 0) {
 419     assert(words == min_fill_size(), "unaligned size");
 420     ObjAllocator allocator(SystemDictionary::Object_klass(), words);
 421     allocator.initialize(start);
 422   }
 423 }
 424 
 425 void CollectedHeap::fill_with_object(HeapWord* start, size_t words, bool zap)
 426 {
 427   DEBUG_ONLY(fill_args_check(start, words);)
 428   HandleMark hm(Thread::current());  // Free handles before leaving.
 429   fill_with_object_impl(start, words, zap);
 430 }
 431 
 432 void CollectedHeap::fill_with_objects(HeapWord* start, size_t words, bool zap)
 433 {
 434   DEBUG_ONLY(fill_args_check(start, words);)
 435   HandleMark hm(Thread::current());  // Free handles before leaving.
 436 
 437   // Multiple objects may be required depending on the filler array maximum size. Fill
 438   // the range up to that with objects that are filler_array_max_size sized. The
 439   // remainder is filled with a single object.
 440   const size_t min = min_fill_size();
 441   const size_t max = filler_array_max_size();
 442   while (words > max) {
 443     const size_t cur = (words - max) >= min ? max : max - min;
 444     fill_with_array(start, cur, zap);
 445     start += cur;
 446     words -= cur;
 447   }
 448 
 449   fill_with_object_impl(start, words, zap);
 450 }
 451 
 452 void CollectedHeap::fill_with_dummy_object(HeapWord* start, HeapWord* end, bool zap) {
 453   CollectedHeap::fill_with_object(start, end, zap);
 454 }
 455 
 456 size_t CollectedHeap::min_dummy_object_size() const {
 457   return oopDesc::header_size();
 458 }
 459 
 460 size_t CollectedHeap::tlab_alloc_reserve() const {
 461   size_t min_size = min_dummy_object_size();
 462   return min_size > (size_t)MinObjAlignment ? align_object_size(min_size) : 0;
 463 }
 464 
 465 HeapWord* CollectedHeap::allocate_new_tlab(size_t min_size,
 466                                            size_t requested_size,
 467                                            size_t* actual_size) {
 468   guarantee(false, "thread-local allocation buffers not supported");
 469   return NULL;
 470 }
 471 
 472 void CollectedHeap::ensure_parsability(bool retire_tlabs) {
 473   assert(SafepointSynchronize::is_at_safepoint() || !is_init_completed(),
 474          "Should only be called at a safepoint or at start-up");
 475 
 476   ThreadLocalAllocStats stats;
 477 
 478   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next();) {
 479     BarrierSet::barrier_set()->make_parsable(thread);
 480     if (UseTLAB) {
 481       if (retire_tlabs) {
 482         thread->tlab().retire(&stats);
 483       } else {
 484         thread->tlab().make_parsable();
 485       }
 486     }
 487   }
 488 
 489   stats.publish();
 490 }
 491 
 492 void CollectedHeap::resize_all_tlabs() {
 493   assert(SafepointSynchronize::is_at_safepoint() || !is_init_completed(),
 494          "Should only resize tlabs at safepoint");
 495 
 496   if (UseTLAB && ResizeTLAB) {
 497     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
 498       thread->tlab().resize();
 499     }
 500   }
 501 }
 502 
 503 jlong CollectedHeap::millis_since_last_whole_heap_examined() {
 504   return (os::javaTimeNanos() - _last_whole_heap_examined_time_ns) / NANOSECS_PER_MILLISEC;
 505 }
 506 
 507 void CollectedHeap::record_whole_heap_examined_timestamp() {
 508   _last_whole_heap_examined_time_ns = os::javaTimeNanos();
 509 }
 510 
 511 void CollectedHeap::full_gc_dump(GCTimer* timer, bool before) {
 512   assert(timer != NULL, "timer is null");
 513   if ((HeapDumpBeforeFullGC && before) || (HeapDumpAfterFullGC && !before)) {
 514     GCTraceTime(Info, gc) tm(before ? "Heap Dump (before full gc)" : "Heap Dump (after full gc)", timer);
 515     HeapDumper::dump_heap();
 516   }
 517 
 518   LogTarget(Trace, gc, classhisto) lt;
 519   if (lt.is_enabled()) {
 520     GCTraceTime(Trace, gc, classhisto) tm(before ? "Class Histogram (before full gc)" : "Class Histogram (after full gc)", timer);
 521     ResourceMark rm;
 522     LogStream ls(lt);
 523     VM_GC_HeapInspection inspector(&ls, false /* ! full gc */);
 524     inspector.doit();
 525   }
 526 }
 527 
 528 void CollectedHeap::pre_full_gc_dump(GCTimer* timer) {
 529   full_gc_dump(timer, true);
 530 }
 531 
 532 void CollectedHeap::post_full_gc_dump(GCTimer* timer) {
 533   full_gc_dump(timer, false);
 534 }
 535 
 536 void CollectedHeap::initialize_reserved_region(const ReservedHeapSpace& rs) {
 537   // It is important to do this in a way such that concurrent readers can't
 538   // temporarily think something is in the heap.  (Seen this happen in asserts.)
 539   _reserved.set_word_size(0);
 540   _reserved.set_start((HeapWord*)rs.base());
 541   _reserved.set_end((HeapWord*)rs.end());
 542 }
 543 
 544 void CollectedHeap::post_initialize() {
 545   initialize_serviceability();
 546 }
 547 
 548 #ifndef PRODUCT
 549 
 550 bool CollectedHeap::promotion_should_fail(volatile size_t* count) {
 551   // Access to count is not atomic; the value does not have to be exact.
 552   if (PromotionFailureALot) {
 553     const size_t gc_num = total_collections();
 554     const size_t elapsed_gcs = gc_num - _promotion_failure_alot_gc_number;
 555     if (elapsed_gcs >= PromotionFailureALotInterval) {
 556       // Test for unsigned arithmetic wrap-around.
 557       if (++*count >= PromotionFailureALotCount) {
 558         *count = 0;
 559         return true;
 560       }
 561     }
 562   }
 563   return false;
 564 }
 565 
 566 bool CollectedHeap::promotion_should_fail() {
 567   return promotion_should_fail(&_promotion_failure_alot_count);
 568 }
 569 
 570 void CollectedHeap::reset_promotion_should_fail(volatile size_t* count) {
 571   if (PromotionFailureALot) {
 572     _promotion_failure_alot_gc_number = total_collections();
 573     *count = 0;
 574   }
 575 }
 576 
 577 void CollectedHeap::reset_promotion_should_fail() {
 578   reset_promotion_should_fail(&_promotion_failure_alot_count);
 579 }
 580 
 581 #endif  // #ifndef PRODUCT
 582 
 583 bool CollectedHeap::supports_object_pinning() const {
 584   return false;
 585 }
 586 
 587 oop CollectedHeap::pin_object(JavaThread* thread, oop obj) {
 588   ShouldNotReachHere();
 589   return NULL;
 590 }
 591 
 592 void CollectedHeap::unpin_object(JavaThread* thread, oop obj) {
 593   ShouldNotReachHere();
 594 }
 595 
 596 void CollectedHeap::deduplicate_string(oop str) {
 597   // Do nothing, unless overridden in subclass.
 598 }
 599 
 600 uint32_t CollectedHeap::hash_oop(oop obj) const {
 601   const uintptr_t addr = cast_from_oop<uintptr_t>(obj);
 602   return static_cast<uint32_t>(addr >> LogMinObjAlignment);
 603 }