1 /*
   2  * Copyright (c) 2001, 2018, 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/gcWhen.hpp"
  36 #include "gc/shared/memAllocator.hpp"
  37 #include "gc/shared/vmGCOperations.hpp"
  38 #include "logging/log.hpp"
  39 #include "memory/metaspace.hpp"
  40 #include "memory/resourceArea.hpp"
  41 #include "oops/instanceMirrorKlass.hpp"
  42 #include "oops/oop.inline.hpp"
  43 #include "runtime/handles.inline.hpp"
  44 #include "runtime/init.hpp"
  45 #include "runtime/thread.inline.hpp"
  46 #include "runtime/threadSMR.hpp"
  47 #include "runtime/vmThread.hpp"
  48 #include "services/heapDumper.hpp"
  49 #include "utilities/align.hpp"
  50 #include "utilities/copy.hpp"
  51 
  52 class ClassLoaderData;
  53 
  54 #ifdef ASSERT
  55 int CollectedHeap::_fire_out_of_memory_count = 0;
  56 #endif
  57 
  58 size_t CollectedHeap::_filler_array_max_size = 0;
  59 
  60 template <>
  61 void EventLogBase<GCMessage>::print(outputStream* st, GCMessage& m) {
  62   st->print_cr("GC heap %s", m.is_before ? "before" : "after");
  63   st->print_raw(m);
  64 }
  65 
  66 void GCHeapLog::log_heap(CollectedHeap* heap, bool before) {
  67   if (!should_log()) {
  68     return;
  69   }
  70 
  71   double timestamp = fetch_timestamp();
  72   MutexLockerEx ml(&_mutex, Mutex::_no_safepoint_check_flag);
  73   int index = compute_log_index();
  74   _records[index].thread = NULL; // Its the GC thread so it's not that interesting.
  75   _records[index].timestamp = timestamp;
  76   _records[index].data.is_before = before;
  77   stringStream st(_records[index].data.buffer(), _records[index].data.size());
  78 
  79   st.print_cr("{Heap %s GC invocations=%u (full %u):",
  80                  before ? "before" : "after",
  81                  heap->total_collections(),
  82                  heap->total_full_collections());
  83 
  84   heap->print_on(&st);
  85   st.print_cr("}");
  86 }
  87 
  88 VirtualSpaceSummary CollectedHeap::create_heap_space_summary() {
  89   size_t capacity_in_words = capacity() / HeapWordSize;
  90 
  91   return VirtualSpaceSummary(
  92     reserved_region().start(), reserved_region().start() + capacity_in_words, reserved_region().end());
  93 }
  94 
  95 GCHeapSummary CollectedHeap::create_heap_summary() {
  96   VirtualSpaceSummary heap_space = create_heap_space_summary();
  97   return GCHeapSummary(heap_space, used());
  98 }
  99 
 100 MetaspaceSummary CollectedHeap::create_metaspace_summary() {
 101   const MetaspaceSizes meta_space(
 102       MetaspaceUtils::committed_bytes(),
 103       MetaspaceUtils::used_bytes(),
 104       MetaspaceUtils::reserved_bytes());
 105   const MetaspaceSizes data_space(
 106       MetaspaceUtils::committed_bytes(Metaspace::NonClassType),
 107       MetaspaceUtils::used_bytes(Metaspace::NonClassType),
 108       MetaspaceUtils::reserved_bytes(Metaspace::NonClassType));
 109   const MetaspaceSizes class_space(
 110       MetaspaceUtils::committed_bytes(Metaspace::ClassType),
 111       MetaspaceUtils::used_bytes(Metaspace::ClassType),
 112       MetaspaceUtils::reserved_bytes(Metaspace::ClassType));
 113 
 114   const MetaspaceChunkFreeListSummary& ms_chunk_free_list_summary =
 115     MetaspaceUtils::chunk_free_list_summary(Metaspace::NonClassType);
 116   const MetaspaceChunkFreeListSummary& class_chunk_free_list_summary =
 117     MetaspaceUtils::chunk_free_list_summary(Metaspace::ClassType);
 118 
 119   return MetaspaceSummary(MetaspaceGC::capacity_until_GC(), meta_space, data_space, class_space,
 120                           ms_chunk_free_list_summary, class_chunk_free_list_summary);
 121 }
 122 
 123 void CollectedHeap::print_heap_before_gc() {
 124   Universe::print_heap_before_gc();
 125   if (_gc_heap_log != NULL) {
 126     _gc_heap_log->log_heap_before(this);
 127   }
 128 }
 129 
 130 void CollectedHeap::print_heap_after_gc() {
 131   Universe::print_heap_after_gc();
 132   if (_gc_heap_log != NULL) {
 133     _gc_heap_log->log_heap_after(this);
 134   }
 135 }
 136 
 137 void CollectedHeap::print_on_error(outputStream* st) const {
 138   st->print_cr("Heap:");
 139   print_extended_on(st);
 140   st->cr();
 141 
 142   BarrierSet::barrier_set()->print_on(st);
 143 }
 144 
 145 void CollectedHeap::trace_heap(GCWhen::Type when, const GCTracer* gc_tracer) {
 146   const GCHeapSummary& heap_summary = create_heap_summary();
 147   gc_tracer->report_gc_heap_summary(when, heap_summary);
 148 
 149   const MetaspaceSummary& metaspace_summary = create_metaspace_summary();
 150   gc_tracer->report_metaspace_summary(when, metaspace_summary);
 151 }
 152 
 153 void CollectedHeap::trace_heap_before_gc(const GCTracer* gc_tracer) {
 154   trace_heap(GCWhen::BeforeGC, gc_tracer);
 155 }
 156 
 157 void CollectedHeap::trace_heap_after_gc(const GCTracer* gc_tracer) {
 158   trace_heap(GCWhen::AfterGC, gc_tracer);
 159 }
 160 
 161 // WhiteBox API support for concurrent collectors.  These are the
 162 // default implementations, for collectors which don't support this
 163 // feature.
 164 bool CollectedHeap::supports_concurrent_phase_control() const {
 165   return false;
 166 }
 167 
 168 const char* const* CollectedHeap::concurrent_phases() const {
 169   static const char* const result[] = { NULL };
 170   return result;
 171 }
 172 
 173 bool CollectedHeap::request_concurrent_phase(const char* phase) {
 174   return false;
 175 }
 176 
 177 bool CollectedHeap::is_oop(oop object) const {
 178   if (!check_obj_alignment(object)) {
 179     return false;
 180   }
 181 
 182   if (!is_in_reserved(object)) {
 183     return false;
 184   }
 185 
 186   if (is_in_reserved(object->klass_or_null())) {
 187     return false;
 188   }
 189 
 190   return true;
 191 }
 192 
 193 // Memory state functions.
 194 
 195 
 196 CollectedHeap::CollectedHeap() :
 197   _is_gc_active(false),
 198   _total_collections(0),
 199   _total_full_collections(0),
 200   _gc_cause(GCCause::_no_gc),
 201   _gc_lastcause(GCCause::_no_gc)
 202 {
 203   const size_t max_len = size_t(arrayOopDesc::max_array_length(T_INT));
 204   const size_t elements_per_word = HeapWordSize / sizeof(jint);
 205   _filler_array_max_size = align_object_size(filler_array_hdr_size() +
 206                                              max_len / elements_per_word);
 207 
 208   NOT_PRODUCT(_promotion_failure_alot_count = 0;)
 209   NOT_PRODUCT(_promotion_failure_alot_gc_number = 0;)
 210 
 211   if (UsePerfData) {
 212     EXCEPTION_MARK;
 213 
 214     // create the gc cause jvmstat counters
 215     _perf_gc_cause = PerfDataManager::create_string_variable(SUN_GC, "cause",
 216                              80, GCCause::to_string(_gc_cause), CHECK);
 217 
 218     _perf_gc_lastcause =
 219                 PerfDataManager::create_string_variable(SUN_GC, "lastCause",
 220                              80, GCCause::to_string(_gc_lastcause), CHECK);
 221   }
 222 
 223   // Create the ring log
 224   if (LogEvents) {
 225     _gc_heap_log = new GCHeapLog();
 226   } else {
 227     _gc_heap_log = NULL;
 228   }
 229 }
 230 
 231 // This interface assumes that it's being called by the
 232 // vm thread. It collects the heap assuming that the
 233 // heap lock is already held and that we are executing in
 234 // the context of the vm thread.
 235 void CollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {
 236   assert(Thread::current()->is_VM_thread(), "Precondition#1");
 237   assert(Heap_lock->is_locked(), "Precondition#2");
 238   GCCauseSetter gcs(this, cause);
 239   switch (cause) {
 240     case GCCause::_heap_inspection:
 241     case GCCause::_heap_dump:
 242     case GCCause::_metadata_GC_threshold : {
 243       HandleMark hm;
 244       do_full_collection(false);        // don't clear all soft refs
 245       break;
 246     }
 247     case GCCause::_metadata_GC_clear_soft_refs: {
 248       HandleMark hm;
 249       do_full_collection(true);         // do clear all soft refs
 250       break;
 251     }
 252     default:
 253       ShouldNotReachHere(); // Unexpected use of this function
 254   }
 255 }
 256 
 257 MetaWord* CollectedHeap::satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
 258                                                             size_t word_size,
 259                                                             Metaspace::MetadataType mdtype) {
 260   uint loop_count = 0;
 261   uint gc_count = 0;
 262   uint full_gc_count = 0;
 263 
 264   assert(!Heap_lock->owned_by_self(), "Should not be holding the Heap_lock");
 265 
 266   do {
 267     MetaWord* result = loader_data->metaspace_non_null()->allocate(word_size, mdtype);
 268     if (result != NULL) {
 269       return result;
 270     }
 271 
 272     if (GCLocker::is_active_and_needs_gc()) {
 273       // If the GCLocker is active, just expand and allocate.
 274       // If that does not succeed, wait if this thread is not
 275       // in a critical section itself.
 276       result = loader_data->metaspace_non_null()->expand_and_allocate(word_size, mdtype);
 277       if (result != NULL) {
 278         return result;
 279       }
 280       JavaThread* jthr = JavaThread::current();
 281       if (!jthr->in_critical()) {
 282         // Wait for JNI critical section to be exited
 283         GCLocker::stall_until_clear();
 284         // The GC invoked by the last thread leaving the critical
 285         // section will be a young collection and a full collection
 286         // is (currently) needed for unloading classes so continue
 287         // to the next iteration to get a full GC.
 288         continue;
 289       } else {
 290         if (CheckJNICalls) {
 291           fatal("Possible deadlock due to allocating while"
 292                 " in jni critical section");
 293         }
 294         return NULL;
 295       }
 296     }
 297 
 298     {  // Need lock to get self consistent gc_count's
 299       MutexLocker ml(Heap_lock);
 300       gc_count      = Universe::heap()->total_collections();
 301       full_gc_count = Universe::heap()->total_full_collections();
 302     }
 303 
 304     // Generate a VM operation
 305     VM_CollectForMetadataAllocation op(loader_data,
 306                                        word_size,
 307                                        mdtype,
 308                                        gc_count,
 309                                        full_gc_count,
 310                                        GCCause::_metadata_GC_threshold);
 311     VMThread::execute(&op);
 312 
 313     // If GC was locked out, try again. Check before checking success because the
 314     // prologue could have succeeded and the GC still have been locked out.
 315     if (op.gc_locked()) {
 316       continue;
 317     }
 318 
 319     if (op.prologue_succeeded()) {
 320       return op.result();
 321     }
 322     loop_count++;
 323     if ((QueuedAllocationWarningCount > 0) &&
 324         (loop_count % QueuedAllocationWarningCount == 0)) {
 325       log_warning(gc, ergo)("satisfy_failed_metadata_allocation() retries %d times,"
 326                             " size=" SIZE_FORMAT, loop_count, word_size);
 327     }
 328   } while (true);  // Until a GC is done
 329 }
 330 
 331 MemoryUsage CollectedHeap::memory_usage() {
 332   return MemoryUsage(InitialHeapSize, used(), capacity(), max_capacity());
 333 }
 334 
 335 
 336 #ifndef PRODUCT
 337 void CollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr, size_t size) {
 338   if (CheckMemoryInitialization && ZapUnusedHeapArea) {
 339     for (size_t slot = 0; slot < size; slot += 1) {
 340       assert((*(intptr_t*) (addr + slot)) == ((intptr_t) badHeapWordVal),
 341              "Found non badHeapWordValue in pre-allocation check");
 342     }
 343   }
 344 }
 345 #endif // PRODUCT
 346 
 347 size_t CollectedHeap::max_tlab_size() const {
 348   // TLABs can't be bigger than we can fill with a int[Integer.MAX_VALUE].
 349   // This restriction could be removed by enabling filling with multiple arrays.
 350   // If we compute that the reasonable way as
 351   //    header_size + ((sizeof(jint) * max_jint) / HeapWordSize)
 352   // we'll overflow on the multiply, so we do the divide first.
 353   // We actually lose a little by dividing first,
 354   // but that just makes the TLAB  somewhat smaller than the biggest array,
 355   // which is fine, since we'll be able to fill that.
 356   size_t max_int_size = typeArrayOopDesc::header_size(T_INT) +
 357               sizeof(jint) *
 358               ((juint) max_jint / (size_t) HeapWordSize);
 359   return align_down(max_int_size, MinObjAlignment);
 360 }
 361 
 362 size_t CollectedHeap::filler_array_hdr_size() {
 363   return align_object_offset(arrayOopDesc::header_size(T_INT)); // align to Long
 364 }
 365 
 366 size_t CollectedHeap::filler_array_min_size() {
 367   return align_object_size(filler_array_hdr_size()); // align to MinObjAlignment
 368 }
 369 
 370 #ifdef ASSERT
 371 void CollectedHeap::fill_args_check(HeapWord* start, size_t words)
 372 {
 373   assert(words >= min_fill_size(), "too small to fill");
 374   assert(is_object_aligned(words), "unaligned size");
 375   assert(Universe::heap()->is_in_reserved(start), "not in heap");
 376   assert(Universe::heap()->is_in_reserved(start + words - 1), "not in heap");
 377 }
 378 
 379 void CollectedHeap::zap_filler_array(HeapWord* start, size_t words, bool zap)
 380 {
 381   if (ZapFillerObjects && zap) {
 382     Copy::fill_to_words(start + filler_array_hdr_size(),
 383                         words - filler_array_hdr_size(), 0XDEAFBABE);
 384   }
 385 }
 386 #endif // ASSERT
 387 
 388 void
 389 CollectedHeap::fill_with_array(HeapWord* start, size_t words, bool zap)
 390 {
 391   assert(words >= filler_array_min_size(), "too small for an array");
 392   assert(words <= filler_array_max_size(), "too big for a single object");
 393 
 394   const size_t payload_size = words - filler_array_hdr_size();
 395   const size_t len = payload_size * HeapWordSize / sizeof(jint);
 396   assert((int)len >= 0, "size too large " SIZE_FORMAT " becomes %d", words, (int)len);
 397 
 398   ObjArrayAllocator allocator(Universe::intArrayKlassObj(), words, (int)len, /* do_zero */ false);
 399   allocator.initialize(start);
 400   DEBUG_ONLY(zap_filler_array(start, words, zap);)
 401 }
 402 
 403 void
 404 CollectedHeap::fill_with_object_impl(HeapWord* start, size_t words, bool zap)
 405 {
 406   assert(words <= filler_array_max_size(), "too big for a single object");
 407 
 408   if (words >= filler_array_min_size()) {
 409     fill_with_array(start, words, zap);
 410   } else if (words > 0) {
 411     assert(words == min_fill_size(), "unaligned size");
 412     ObjAllocator allocator(SystemDictionary::Object_klass(), words);
 413     allocator.initialize(start);
 414   }
 415 }
 416 
 417 void CollectedHeap::fill_with_object(HeapWord* start, size_t words, bool zap)
 418 {
 419   DEBUG_ONLY(fill_args_check(start, words);)
 420   HandleMark hm;  // Free handles before leaving.
 421   fill_with_object_impl(start, words, zap);
 422 }
 423 
 424 void CollectedHeap::fill_with_objects(HeapWord* start, size_t words, bool zap)
 425 {
 426   DEBUG_ONLY(fill_args_check(start, words);)
 427   HandleMark hm;  // Free handles before leaving.
 428 
 429   // Multiple objects may be required depending on the filler array maximum size. Fill
 430   // the range up to that with objects that are filler_array_max_size sized. The
 431   // remainder is filled with a single object.
 432   const size_t min = min_fill_size();
 433   const size_t max = filler_array_max_size();
 434   while (words > max) {
 435     const size_t cur = (words - max) >= min ? max : max - min;
 436     fill_with_array(start, cur, zap);
 437     start += cur;
 438     words -= cur;
 439   }
 440 
 441   fill_with_object_impl(start, words, zap);
 442 }
 443 
 444 void CollectedHeap::fill_with_dummy_object(HeapWord* start, HeapWord* end, bool zap) {
 445   CollectedHeap::fill_with_object(start, end, zap);
 446 }
 447 
 448 HeapWord* CollectedHeap::allocate_new_tlab(size_t min_size,
 449                                            size_t requested_size,
 450                                            size_t* actual_size) {
 451   guarantee(false, "thread-local allocation buffers not supported");
 452   return NULL;
 453 }
 454 
 455 oop CollectedHeap::obj_allocate(Klass* klass, int size, TRAPS) {
 456   ObjAllocator allocator(klass, size, THREAD);
 457   return allocator.allocate();
 458 }
 459 
 460 oop CollectedHeap::array_allocate(Klass* klass, int size, int length, bool do_zero, TRAPS) {
 461   ObjArrayAllocator allocator(klass, size, length, do_zero, THREAD);
 462   return allocator.allocate();
 463 }
 464 
 465 oop CollectedHeap::class_allocate(Klass* klass, int size, TRAPS) {
 466   ClassAllocator allocator(klass, size, THREAD);
 467   return allocator.allocate();
 468 }
 469 
 470 void CollectedHeap::ensure_parsability(bool retire_tlabs) {
 471   // The second disjunct in the assertion below makes a concession
 472   // for the start-up verification done while the VM is being
 473   // created. Callers be careful that you know that mutators
 474   // aren't going to interfere -- for instance, this is permissible
 475   // if we are still single-threaded and have either not yet
 476   // started allocating (nothing much to verify) or we have
 477   // started allocating but are now a full-fledged JavaThread
 478   // (and have thus made our TLAB's) available for filling.
 479   assert(SafepointSynchronize::is_at_safepoint() || !is_init_completed(),
 480          "Should only be called at a safepoint or at start-up"
 481          " otherwise concurrent mutator activity may make heap "
 482          " unparsable again");
 483 
 484   if (UseTLAB && retire_tlabs) {
 485     // Accumulate statistics before retiring
 486     ThreadLocalAllocBuffer::accumulate_statistics_before_gc();
 487   }
 488 
 489   // The main thread starts allocating via a TLAB even before it
 490   // has added itself to the threads list at vm boot-up.
 491   JavaThreadIteratorWithHandle jtiwh;
 492   assert(jtiwh.length() > 0,
 493          "Attempt to fill tlabs before main thread has been added"
 494          " to threads list is doomed to failure!");
 495   BarrierSet *bs = BarrierSet::barrier_set();
 496   for (; JavaThread *thread = jtiwh.next(); ) {
 497      if (UseTLAB) {
 498        thread->tlab().make_parsable(retire_tlabs);
 499      }
 500      bs->make_parsable(thread);
 501   }
 502 }
 503 
 504 void CollectedHeap::resize_all_tlabs() {
 505   assert(SafepointSynchronize::is_at_safepoint() || !is_init_completed(),
 506          "Should only resize tlabs at safepoint");


 507 
 508   if (UseTLAB && ResizeTLAB) {
 509     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
 510       thread->tlab().resize();
 511     }
 512   }
 513 }
 514 
 515 void CollectedHeap::full_gc_dump(GCTimer* timer, bool before) {
 516   assert(timer != NULL, "timer is null");
 517   if ((HeapDumpBeforeFullGC && before) || (HeapDumpAfterFullGC && !before)) {
 518     GCTraceTime(Info, gc) tm(before ? "Heap Dump (before full gc)" : "Heap Dump (after full gc)", timer);
 519     HeapDumper::dump_heap();
 520   }
 521 
 522   LogTarget(Trace, gc, classhisto) lt;
 523   if (lt.is_enabled()) {
 524     GCTraceTime(Trace, gc, classhisto) tm(before ? "Class Histogram (before full gc)" : "Class Histogram (after full gc)", timer);
 525     ResourceMark rm;
 526     LogStream ls(lt);
 527     VM_GC_HeapInspection inspector(&ls, false /* ! full gc */);
 528     inspector.doit();
 529   }
 530 }
 531 
 532 void CollectedHeap::pre_full_gc_dump(GCTimer* timer) {
 533   full_gc_dump(timer, true);
 534 }
 535 
 536 void CollectedHeap::post_full_gc_dump(GCTimer* timer) {
 537   full_gc_dump(timer, false);
 538 }
 539 
 540 void CollectedHeap::initialize_reserved_region(HeapWord *start, HeapWord *end) {
 541   // It is important to do this in a way such that concurrent readers can't
 542   // temporarily think something is in the heap.  (Seen this happen in asserts.)
 543   _reserved.set_word_size(0);
 544   _reserved.set_start(start);
 545   _reserved.set_end(end);
 546 }
 547 
 548 void CollectedHeap::post_initialize() {
 549   initialize_serviceability();
 550 }
 551 
 552 #ifndef PRODUCT
 553 
 554 bool CollectedHeap::promotion_should_fail(volatile size_t* count) {
 555   // Access to count is not atomic; the value does not have to be exact.
 556   if (PromotionFailureALot) {
 557     const size_t gc_num = total_collections();
 558     const size_t elapsed_gcs = gc_num - _promotion_failure_alot_gc_number;
 559     if (elapsed_gcs >= PromotionFailureALotInterval) {
 560       // Test for unsigned arithmetic wrap-around.
 561       if (++*count >= PromotionFailureALotCount) {
 562         *count = 0;
 563         return true;
 564       }
 565     }
 566   }
 567   return false;
 568 }
 569 
 570 bool CollectedHeap::promotion_should_fail() {
 571   return promotion_should_fail(&_promotion_failure_alot_count);
 572 }
 573 
 574 void CollectedHeap::reset_promotion_should_fail(volatile size_t* count) {
 575   if (PromotionFailureALot) {
 576     _promotion_failure_alot_gc_number = total_collections();
 577     *count = 0;
 578   }
 579 }
 580 
 581 void CollectedHeap::reset_promotion_should_fail() {
 582   reset_promotion_should_fail(&_promotion_failure_alot_count);
 583 }
 584 
 585 #endif  // #ifndef PRODUCT
 586 
 587 bool CollectedHeap::supports_object_pinning() const {
 588   return false;
 589 }
 590 
 591 oop CollectedHeap::pin_object(JavaThread* thread, oop obj) {
 592   ShouldNotReachHere();
 593   return NULL;
 594 }
 595 
 596 void CollectedHeap::unpin_object(JavaThread* thread, oop obj) {
 597   ShouldNotReachHere();
 598 }
 599 
 600 void CollectedHeap::deduplicate_string(oop str) {
 601   // Do nothing, unless overridden in subclass.
 602 }
--- EOF ---