1 /*
   2  * Copyright (c) 2000, 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 "aot/aotLoader.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/stringTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "classfile/vmSymbols.hpp"
  31 #include "code/codeCache.hpp"
  32 #include "code/icBuffer.hpp"
  33 #include "gc/shared/adaptiveSizePolicy.hpp"
  34 #include "gc/shared/cardTableRS.hpp"
  35 #include "gc/shared/collectedHeap.inline.hpp"
  36 #include "gc/shared/collectorCounters.hpp"
  37 #include "gc/shared/gcId.hpp"
  38 #include "gc/shared/gcLocker.inline.hpp"
  39 #include "gc/shared/gcTrace.hpp"
  40 #include "gc/shared/gcTraceTime.inline.hpp"
  41 #include "gc/shared/genCollectedHeap.hpp"
  42 #include "gc/shared/genOopClosures.inline.hpp"
  43 #include "gc/shared/generationSpec.hpp"
  44 #include "gc/shared/space.hpp"
  45 #include "gc/shared/strongRootsScope.hpp"
  46 #include "gc/shared/vmGCOperations.hpp"
  47 #include "gc/shared/weakProcessor.hpp"
  48 #include "gc/shared/workgroup.hpp"
  49 #include "memory/filemap.hpp"
  50 #include "memory/resourceArea.hpp"
  51 #include "oops/oop.inline.hpp"
  52 #include "runtime/biasedLocking.hpp"
  53 #include "runtime/handles.hpp"
  54 #include "runtime/handles.inline.hpp"
  55 #include "runtime/java.hpp"
  56 #include "runtime/vmThread.hpp"
  57 #include "services/management.hpp"
  58 #include "services/memoryService.hpp"
  59 #include "utilities/debug.hpp"
  60 #include "utilities/formatBuffer.hpp"
  61 #include "utilities/macros.hpp"
  62 #include "utilities/stack.inline.hpp"
  63 #include "utilities/vmError.hpp"
  64 
  65 GenCollectedHeap::GenCollectedHeap(GenCollectorPolicy *policy) :
  66   CollectedHeap(),
  67   _rem_set(NULL),
  68   _gen_policy(policy),
  69   _soft_ref_gen_policy(),
  70   _process_strong_tasks(new SubTasksDone(GCH_PS_NumElements)),
  71   _full_collections_completed(0)
  72 {
  73   assert(policy != NULL, "Sanity check");
  74 }
  75 
  76 jint GenCollectedHeap::initialize() {
  77   // While there are no constraints in the GC code that HeapWordSize
  78   // be any particular value, there are multiple other areas in the
  79   // system which believe this to be true (e.g. oop->object_size in some
  80   // cases incorrectly returns the size in wordSize units rather than
  81   // HeapWordSize).
  82   guarantee(HeapWordSize == wordSize, "HeapWordSize must equal wordSize");
  83 
  84   // Allocate space for the heap.
  85 
  86   char* heap_address;
  87   ReservedSpace heap_rs;
  88 
  89   size_t heap_alignment = collector_policy()->heap_alignment();
  90 
  91   heap_address = allocate(heap_alignment, &heap_rs);
  92 
  93   if (!heap_rs.is_reserved()) {
  94     vm_shutdown_during_initialization(
  95       "Could not reserve enough space for object heap");
  96     return JNI_ENOMEM;
  97   }
  98 
  99   initialize_reserved_region((HeapWord*)heap_rs.base(), (HeapWord*)(heap_rs.base() + heap_rs.size()));
 100 
 101   _rem_set = new CardTableRS(reserved_region());
 102   set_barrier_set(rem_set()->bs());
 103 
 104   ReservedSpace young_rs = heap_rs.first_part(gen_policy()->young_gen_spec()->max_size(), false, false);
 105   _young_gen = gen_policy()->young_gen_spec()->init(young_rs, rem_set());
 106   heap_rs = heap_rs.last_part(gen_policy()->young_gen_spec()->max_size());
 107 
 108   ReservedSpace old_rs = heap_rs.first_part(gen_policy()->old_gen_spec()->max_size(), false, false);
 109   _old_gen = gen_policy()->old_gen_spec()->init(old_rs, rem_set());
 110   clear_incremental_collection_failed();
 111 
 112   return JNI_OK;
 113 }
 114 
 115 void GenCollectedHeap::initialize_size_policy(size_t init_eden_size,
 116                                               size_t init_promo_size,
 117                                               size_t init_survivor_size) {
 118   const double max_gc_pause_sec = ((double) MaxGCPauseMillis) / 1000.0;
 119   _size_policy = new AdaptiveSizePolicy(init_eden_size,
 120                                         init_promo_size,
 121                                         init_survivor_size,
 122                                         max_gc_pause_sec,
 123                                         GCTimeRatio);
 124 }
 125 
 126 char* GenCollectedHeap::allocate(size_t alignment,
 127                                  ReservedSpace* heap_rs){
 128   // Now figure out the total size.
 129   const size_t pageSize = UseLargePages ? os::large_page_size() : os::vm_page_size();
 130   assert(alignment % pageSize == 0, "Must be");
 131 
 132   GenerationSpec* young_spec = gen_policy()->young_gen_spec();
 133   GenerationSpec* old_spec = gen_policy()->old_gen_spec();
 134 
 135   // Check for overflow.
 136   size_t total_reserved = young_spec->max_size() + old_spec->max_size();
 137   if (total_reserved < young_spec->max_size()) {
 138     vm_exit_during_initialization("The size of the object heap + VM data exceeds "
 139                                   "the maximum representable size");
 140   }
 141   assert(total_reserved % alignment == 0,
 142          "Gen size; total_reserved=" SIZE_FORMAT ", alignment="
 143          SIZE_FORMAT, total_reserved, alignment);
 144 
 145   *heap_rs = Universe::reserve_heap(total_reserved, alignment);
 146 
 147   os::trace_page_sizes("Heap",
 148                        collector_policy()->min_heap_byte_size(),
 149                        total_reserved,
 150                        alignment,
 151                        heap_rs->base(),
 152                        heap_rs->size());
 153 
 154   return heap_rs->base();
 155 }
 156 
 157 void GenCollectedHeap::post_initialize() {
 158   CollectedHeap::post_initialize();
 159   ref_processing_init();
 160   check_gen_kinds();
 161   DefNewGeneration* def_new_gen = (DefNewGeneration*)_young_gen;
 162 
 163   initialize_size_policy(def_new_gen->eden()->capacity(),
 164                          _old_gen->capacity(),
 165                          def_new_gen->from()->capacity());
 166 
 167   _gen_policy->initialize_gc_policy_counters();
 168 }
 169 
 170 void GenCollectedHeap::ref_processing_init() {
 171   _young_gen->ref_processor_init();
 172   _old_gen->ref_processor_init();
 173 }
 174 
 175 size_t GenCollectedHeap::capacity() const {
 176   return _young_gen->capacity() + _old_gen->capacity();
 177 }
 178 
 179 size_t GenCollectedHeap::used() const {
 180   return _young_gen->used() + _old_gen->used();
 181 }
 182 
 183 void GenCollectedHeap::save_used_regions() {
 184   _old_gen->save_used_region();
 185   _young_gen->save_used_region();
 186 }
 187 
 188 size_t GenCollectedHeap::max_capacity() const {
 189   return _young_gen->max_capacity() + _old_gen->max_capacity();
 190 }
 191 
 192 // Update the _full_collections_completed counter
 193 // at the end of a stop-world full GC.
 194 unsigned int GenCollectedHeap::update_full_collections_completed() {
 195   MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 196   assert(_full_collections_completed <= _total_full_collections,
 197          "Can't complete more collections than were started");
 198   _full_collections_completed = _total_full_collections;
 199   ml.notify_all();
 200   return _full_collections_completed;
 201 }
 202 
 203 // Update the _full_collections_completed counter, as appropriate,
 204 // at the end of a concurrent GC cycle. Note the conditional update
 205 // below to allow this method to be called by a concurrent collector
 206 // without synchronizing in any manner with the VM thread (which
 207 // may already have initiated a STW full collection "concurrently").
 208 unsigned int GenCollectedHeap::update_full_collections_completed(unsigned int count) {
 209   MonitorLockerEx ml(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
 210   assert((_full_collections_completed <= _total_full_collections) &&
 211          (count <= _total_full_collections),
 212          "Can't complete more collections than were started");
 213   if (count > _full_collections_completed) {
 214     _full_collections_completed = count;
 215     ml.notify_all();
 216   }
 217   return _full_collections_completed;
 218 }
 219 
 220 // Return true if any of the following is true:
 221 // . the allocation won't fit into the current young gen heap
 222 // . gc locker is occupied (jni critical section)
 223 // . heap memory is tight -- the most recent previous collection
 224 //   was a full collection because a partial collection (would
 225 //   have) failed and is likely to fail again
 226 bool GenCollectedHeap::should_try_older_generation_allocation(size_t word_size) const {
 227   size_t young_capacity = young_gen()->capacity_before_gc();
 228   return    (word_size > heap_word_size(young_capacity))
 229          || GCLocker::is_active_and_needs_gc()
 230          || incremental_collection_failed();
 231 }
 232 
 233 HeapWord* GenCollectedHeap::expand_heap_and_allocate(size_t size, bool   is_tlab) {
 234   HeapWord* result = NULL;
 235   if (old_gen()->should_allocate(size, is_tlab)) {
 236     result = old_gen()->expand_and_allocate(size, is_tlab);
 237   }
 238   if (result == NULL) {
 239     if (young_gen()->should_allocate(size, is_tlab)) {
 240       result = young_gen()->expand_and_allocate(size, is_tlab);
 241     }
 242   }
 243   assert(result == NULL || is_in_reserved(result), "result not in heap");
 244   return result;
 245 }
 246 
 247 HeapWord* GenCollectedHeap::mem_allocate_work(size_t size,
 248                                               bool is_tlab,
 249                                               bool* gc_overhead_limit_was_exceeded) {
 250   debug_only(check_for_valid_allocation_state());
 251   assert(no_gc_in_progress(), "Allocation during gc not allowed");
 252 
 253   // In general gc_overhead_limit_was_exceeded should be false so
 254   // set it so here and reset it to true only if the gc time
 255   // limit is being exceeded as checked below.
 256   *gc_overhead_limit_was_exceeded = false;
 257 
 258   HeapWord* result = NULL;
 259 
 260   // Loop until the allocation is satisfied, or unsatisfied after GC.
 261   for (uint try_count = 1, gclocker_stalled_count = 0; /* return or throw */; try_count += 1) {
 262     HandleMark hm; // Discard any handles allocated in each iteration.
 263 
 264     // First allocation attempt is lock-free.
 265     Generation *young = young_gen();
 266     assert(young->supports_inline_contig_alloc(),
 267       "Otherwise, must do alloc within heap lock");
 268     if (young->should_allocate(size, is_tlab)) {
 269       result = young->par_allocate(size, is_tlab);
 270       if (result != NULL) {
 271         assert(is_in_reserved(result), "result not in heap");
 272         return result;
 273       }
 274     }
 275     uint gc_count_before;  // Read inside the Heap_lock locked region.
 276     {
 277       MutexLocker ml(Heap_lock);
 278       log_trace(gc, alloc)("GenCollectedHeap::mem_allocate_work: attempting locked slow path allocation");
 279       // Note that only large objects get a shot at being
 280       // allocated in later generations.
 281       bool first_only = ! should_try_older_generation_allocation(size);
 282 
 283       result = attempt_allocation(size, is_tlab, first_only);
 284       if (result != NULL) {
 285         assert(is_in_reserved(result), "result not in heap");
 286         return result;
 287       }
 288 
 289       if (GCLocker::is_active_and_needs_gc()) {
 290         if (is_tlab) {
 291           return NULL;  // Caller will retry allocating individual object.
 292         }
 293         if (!is_maximal_no_gc()) {
 294           // Try and expand heap to satisfy request.
 295           result = expand_heap_and_allocate(size, is_tlab);
 296           // Result could be null if we are out of space.
 297           if (result != NULL) {
 298             return result;
 299           }
 300         }
 301 
 302         if (gclocker_stalled_count > GCLockerRetryAllocationCount) {
 303           return NULL; // We didn't get to do a GC and we didn't get any memory.
 304         }
 305 
 306         // If this thread is not in a jni critical section, we stall
 307         // the requestor until the critical section has cleared and
 308         // GC allowed. When the critical section clears, a GC is
 309         // initiated by the last thread exiting the critical section; so
 310         // we retry the allocation sequence from the beginning of the loop,
 311         // rather than causing more, now probably unnecessary, GC attempts.
 312         JavaThread* jthr = JavaThread::current();
 313         if (!jthr->in_critical()) {
 314           MutexUnlocker mul(Heap_lock);
 315           // Wait for JNI critical section to be exited
 316           GCLocker::stall_until_clear();
 317           gclocker_stalled_count += 1;
 318           continue;
 319         } else {
 320           if (CheckJNICalls) {
 321             fatal("Possible deadlock due to allocating while"
 322                   " in jni critical section");
 323           }
 324           return NULL;
 325         }
 326       }
 327 
 328       // Read the gc count while the heap lock is held.
 329       gc_count_before = total_collections();
 330     }
 331 
 332     VM_GenCollectForAllocation op(size, is_tlab, gc_count_before);
 333     VMThread::execute(&op);
 334     if (op.prologue_succeeded()) {
 335       result = op.result();
 336       if (op.gc_locked()) {
 337          assert(result == NULL, "must be NULL if gc_locked() is true");
 338          continue;  // Retry and/or stall as necessary.
 339       }
 340 
 341       // Allocation has failed and a collection
 342       // has been done.  If the gc time limit was exceeded the
 343       // this time, return NULL so that an out-of-memory
 344       // will be thrown.  Clear gc_overhead_limit_exceeded
 345       // so that the overhead exceeded does not persist.
 346 
 347       const bool limit_exceeded = size_policy()->gc_overhead_limit_exceeded();
 348       const bool softrefs_clear = soft_ref_policy()->all_soft_refs_clear();
 349 
 350       if (limit_exceeded && softrefs_clear) {
 351         *gc_overhead_limit_was_exceeded = true;
 352         size_policy()->set_gc_overhead_limit_exceeded(false);
 353         if (op.result() != NULL) {
 354           CollectedHeap::fill_with_object(op.result(), size);
 355         }
 356         return NULL;
 357       }
 358       assert(result == NULL || is_in_reserved(result),
 359              "result not in heap");
 360       return result;
 361     }
 362 
 363     // Give a warning if we seem to be looping forever.
 364     if ((QueuedAllocationWarningCount > 0) &&
 365         (try_count % QueuedAllocationWarningCount == 0)) {
 366           log_warning(gc, ergo)("GenCollectedHeap::mem_allocate_work retries %d times,"
 367                                 " size=" SIZE_FORMAT " %s", try_count, size, is_tlab ? "(TLAB)" : "");
 368     }
 369   }
 370 }
 371 
 372 #ifndef PRODUCT
 373 // Override of memory state checking method in CollectedHeap:
 374 // Some collectors (CMS for example) can't have badHeapWordVal written
 375 // in the first two words of an object. (For instance , in the case of
 376 // CMS these words hold state used to synchronize between certain
 377 // (concurrent) GC steps and direct allocating mutators.)
 378 // The skip_header_HeapWords() method below, allows us to skip
 379 // over the requisite number of HeapWord's. Note that (for
 380 // generational collectors) this means that those many words are
 381 // skipped in each object, irrespective of the generation in which
 382 // that object lives. The resultant loss of precision seems to be
 383 // harmless and the pain of avoiding that imprecision appears somewhat
 384 // higher than we are prepared to pay for such rudimentary debugging
 385 // support.
 386 void GenCollectedHeap::check_for_non_bad_heap_word_value(HeapWord* addr,
 387                                                          size_t size) {
 388   if (CheckMemoryInitialization && ZapUnusedHeapArea) {
 389     // We are asked to check a size in HeapWords,
 390     // but the memory is mangled in juint words.
 391     juint* start = (juint*) (addr + skip_header_HeapWords());
 392     juint* end   = (juint*) (addr + size);
 393     for (juint* slot = start; slot < end; slot += 1) {
 394       assert(*slot == badHeapWordVal,
 395              "Found non badHeapWordValue in pre-allocation check");
 396     }
 397   }
 398 }
 399 #endif
 400 
 401 HeapWord* GenCollectedHeap::attempt_allocation(size_t size,
 402                                                bool is_tlab,
 403                                                bool first_only) {
 404   HeapWord* res = NULL;
 405 
 406   if (_young_gen->should_allocate(size, is_tlab)) {
 407     res = _young_gen->allocate(size, is_tlab);
 408     if (res != NULL || first_only) {
 409       return res;
 410     }
 411   }
 412 
 413   if (_old_gen->should_allocate(size, is_tlab)) {
 414     res = _old_gen->allocate(size, is_tlab);
 415   }
 416 
 417   return res;
 418 }
 419 
 420 HeapWord* GenCollectedHeap::mem_allocate(size_t size,
 421                                          bool* gc_overhead_limit_was_exceeded) {
 422   return mem_allocate_work(size,
 423                            false /* is_tlab */,
 424                            gc_overhead_limit_was_exceeded);
 425 }
 426 
 427 bool GenCollectedHeap::must_clear_all_soft_refs() {
 428   return _gc_cause == GCCause::_metadata_GC_clear_soft_refs ||
 429          _gc_cause == GCCause::_wb_full_gc;
 430 }
 431 
 432 void GenCollectedHeap::collect_generation(Generation* gen, bool full, size_t size,
 433                                           bool is_tlab, bool run_verification, bool clear_soft_refs,
 434                                           bool restore_marks_for_biased_locking) {
 435   FormatBuffer<> title("Collect gen: %s", gen->short_name());
 436   GCTraceTime(Trace, gc, phases) t1(title);
 437   TraceCollectorStats tcs(gen->counters());
 438   TraceMemoryManagerStats tmms(gen->gc_manager(), gc_cause());
 439 
 440   gen->stat_record()->invocations++;
 441   gen->stat_record()->accumulated_time.start();
 442 
 443   // Must be done anew before each collection because
 444   // a previous collection will do mangling and will
 445   // change top of some spaces.
 446   record_gen_tops_before_GC();
 447 
 448   log_trace(gc)("%s invoke=%d size=" SIZE_FORMAT, heap()->is_young_gen(gen) ? "Young" : "Old", gen->stat_record()->invocations, size * HeapWordSize);
 449 
 450   if (run_verification && VerifyBeforeGC) {
 451     HandleMark hm;  // Discard invalid handles created during verification
 452     Universe::verify("Before GC");
 453   }
 454   COMPILER2_PRESENT(DerivedPointerTable::clear());
 455 
 456   if (restore_marks_for_biased_locking) {
 457     // We perform this mark word preservation work lazily
 458     // because it's only at this point that we know whether we
 459     // absolutely have to do it; we want to avoid doing it for
 460     // scavenge-only collections where it's unnecessary
 461     BiasedLocking::preserve_marks();
 462   }
 463 
 464   // Do collection work
 465   {
 466     // Note on ref discovery: For what appear to be historical reasons,
 467     // GCH enables and disabled (by enqueing) refs discovery.
 468     // In the future this should be moved into the generation's
 469     // collect method so that ref discovery and enqueueing concerns
 470     // are local to a generation. The collect method could return
 471     // an appropriate indication in the case that notification on
 472     // the ref lock was needed. This will make the treatment of
 473     // weak refs more uniform (and indeed remove such concerns
 474     // from GCH). XXX
 475 
 476     HandleMark hm;  // Discard invalid handles created during gc
 477     save_marks();   // save marks for all gens
 478     // We want to discover references, but not process them yet.
 479     // This mode is disabled in process_discovered_references if the
 480     // generation does some collection work, or in
 481     // enqueue_discovered_references if the generation returns
 482     // without doing any work.
 483     ReferenceProcessor* rp = gen->ref_processor();
 484     // If the discovery of ("weak") refs in this generation is
 485     // atomic wrt other collectors in this configuration, we
 486     // are guaranteed to have empty discovered ref lists.
 487     if (rp->discovery_is_atomic()) {
 488       rp->enable_discovery();
 489       rp->setup_policy(clear_soft_refs);
 490     } else {
 491       // collect() below will enable discovery as appropriate
 492     }
 493     gen->collect(full, clear_soft_refs, size, is_tlab);
 494     if (!rp->enqueuing_is_done()) {
 495       ReferenceProcessorPhaseTimes pt(NULL, rp->num_q());
 496       rp->enqueue_discovered_references(NULL, &pt);
 497       pt.print_enqueue_phase();
 498     } else {
 499       rp->set_enqueuing_is_done(false);
 500     }
 501     rp->verify_no_references_recorded();
 502   }
 503 
 504   COMPILER2_PRESENT(DerivedPointerTable::update_pointers());
 505 
 506   gen->stat_record()->accumulated_time.stop();
 507 
 508   update_gc_stats(gen, full);
 509 
 510   if (run_verification && VerifyAfterGC) {
 511     HandleMark hm;  // Discard invalid handles created during verification
 512     Universe::verify("After GC");
 513   }
 514 }
 515 
 516 void GenCollectedHeap::do_collection(bool           full,
 517                                      bool           clear_all_soft_refs,
 518                                      size_t         size,
 519                                      bool           is_tlab,
 520                                      GenerationType max_generation) {
 521   ResourceMark rm;
 522   DEBUG_ONLY(Thread* my_thread = Thread::current();)
 523 
 524   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
 525   assert(my_thread->is_VM_thread() ||
 526          my_thread->is_ConcurrentGC_thread(),
 527          "incorrect thread type capability");
 528   assert(Heap_lock->is_locked(),
 529          "the requesting thread should have the Heap_lock");
 530   guarantee(!is_gc_active(), "collection is not reentrant");
 531 
 532   if (GCLocker::check_active_before_gc()) {
 533     return; // GC is disabled (e.g. JNI GetXXXCritical operation)
 534   }
 535 
 536   GCIdMark gc_id_mark;
 537 
 538   const bool do_clear_all_soft_refs = clear_all_soft_refs ||
 539                           soft_ref_policy()->should_clear_all_soft_refs();
 540 
 541   ClearedAllSoftRefs casr(do_clear_all_soft_refs, soft_ref_policy());
 542 
 543   const size_t metadata_prev_used = MetaspaceAux::used_bytes();
 544 
 545   print_heap_before_gc();
 546 
 547   {
 548     FlagSetting fl(_is_gc_active, true);
 549 
 550     bool complete = full && (max_generation == OldGen);
 551     bool old_collects_young = complete && !ScavengeBeforeFullGC;
 552     bool do_young_collection = !old_collects_young && _young_gen->should_collect(full, size, is_tlab);
 553 
 554     FormatBuffer<> gc_string("%s", "Pause ");
 555     if (do_young_collection) {
 556       gc_string.append("Young");
 557     } else {
 558       gc_string.append("Full");
 559     }
 560 
 561     GCTraceCPUTime tcpu;
 562     GCTraceTime(Info, gc) t(gc_string, NULL, gc_cause(), true);
 563 
 564     gc_prologue(complete);
 565     increment_total_collections(complete);
 566 
 567     size_t young_prev_used = _young_gen->used();
 568     size_t old_prev_used = _old_gen->used();
 569 
 570     bool run_verification = total_collections() >= VerifyGCStartAt;
 571 
 572     bool prepared_for_verification = false;
 573     bool collected_old = false;
 574 
 575     if (do_young_collection) {
 576       if (run_verification && VerifyGCLevel <= 0 && VerifyBeforeGC) {
 577         prepare_for_verify();
 578         prepared_for_verification = true;
 579       }
 580 
 581       collect_generation(_young_gen,
 582                          full,
 583                          size,
 584                          is_tlab,
 585                          run_verification && VerifyGCLevel <= 0,
 586                          do_clear_all_soft_refs,
 587                          false);
 588 
 589       if (size > 0 && (!is_tlab || _young_gen->supports_tlab_allocation()) &&
 590           size * HeapWordSize <= _young_gen->unsafe_max_alloc_nogc()) {
 591         // Allocation request was met by young GC.
 592         size = 0;
 593       }
 594     }
 595 
 596     bool must_restore_marks_for_biased_locking = false;
 597 
 598     if (max_generation == OldGen && _old_gen->should_collect(full, size, is_tlab)) {
 599       if (!complete) {
 600         // The full_collections increment was missed above.
 601         increment_total_full_collections();
 602       }
 603 
 604       if (!prepared_for_verification && run_verification &&
 605           VerifyGCLevel <= 1 && VerifyBeforeGC) {
 606         prepare_for_verify();
 607       }
 608 
 609       if (do_young_collection) {
 610         // We did a young GC. Need a new GC id for the old GC.
 611         GCIdMark gc_id_mark;
 612         GCTraceTime(Info, gc) t("Pause Full", NULL, gc_cause(), true);
 613         collect_generation(_old_gen, full, size, is_tlab, run_verification && VerifyGCLevel <= 1, do_clear_all_soft_refs, true);
 614       } else {
 615         // No young GC done. Use the same GC id as was set up earlier in this method.
 616         collect_generation(_old_gen, full, size, is_tlab, run_verification && VerifyGCLevel <= 1, do_clear_all_soft_refs, true);
 617       }
 618 
 619       must_restore_marks_for_biased_locking = true;
 620       collected_old = true;
 621     }
 622 
 623     // Update "complete" boolean wrt what actually transpired --
 624     // for instance, a promotion failure could have led to
 625     // a whole heap collection.
 626     complete = complete || collected_old;
 627 
 628     print_heap_change(young_prev_used, old_prev_used);
 629     MetaspaceAux::print_metaspace_change(metadata_prev_used);
 630 
 631     // Adjust generation sizes.
 632     if (collected_old) {
 633       _old_gen->compute_new_size();
 634     }
 635     _young_gen->compute_new_size();
 636 
 637     if (complete) {
 638       // Delete metaspaces for unloaded class loaders and clean up loader_data graph
 639       ClassLoaderDataGraph::purge();
 640       MetaspaceAux::verify_metrics();
 641       // Resize the metaspace capacity after full collections
 642       MetaspaceGC::compute_new_size();
 643       update_full_collections_completed();
 644     }
 645 
 646     // Track memory usage and detect low memory after GC finishes
 647     MemoryService::track_memory_usage();
 648 
 649     gc_epilogue(complete);
 650 
 651     if (must_restore_marks_for_biased_locking) {
 652       BiasedLocking::restore_marks();
 653     }
 654   }
 655 
 656   print_heap_after_gc();
 657 
 658 #ifdef TRACESPINNING
 659   ParallelTaskTerminator::print_termination_counts();
 660 #endif
 661 }
 662 
 663 void GenCollectedHeap::register_nmethod(nmethod* nm) {
 664   CodeCache::register_scavenge_root_nmethod(nm);
 665 }
 666 
 667 void GenCollectedHeap::verify_nmethod(nmethod* nm) {
 668   CodeCache::verify_scavenge_root_nmethod(nm);
 669 }
 670 
 671 HeapWord* GenCollectedHeap::satisfy_failed_allocation(size_t size, bool is_tlab) {
 672   GCCauseSetter x(this, GCCause::_allocation_failure);
 673   HeapWord* result = NULL;
 674 
 675   assert(size != 0, "Precondition violated");
 676   if (GCLocker::is_active_and_needs_gc()) {
 677     // GC locker is active; instead of a collection we will attempt
 678     // to expand the heap, if there's room for expansion.
 679     if (!is_maximal_no_gc()) {
 680       result = expand_heap_and_allocate(size, is_tlab);
 681     }
 682     return result;   // Could be null if we are out of space.
 683   } else if (!incremental_collection_will_fail(false /* don't consult_young */)) {
 684     // Do an incremental collection.
 685     do_collection(false,                     // full
 686                   false,                     // clear_all_soft_refs
 687                   size,                      // size
 688                   is_tlab,                   // is_tlab
 689                   GenCollectedHeap::OldGen); // max_generation
 690   } else {
 691     log_trace(gc)(" :: Trying full because partial may fail :: ");
 692     // Try a full collection; see delta for bug id 6266275
 693     // for the original code and why this has been simplified
 694     // with from-space allocation criteria modified and
 695     // such allocation moved out of the safepoint path.
 696     do_collection(true,                      // full
 697                   false,                     // clear_all_soft_refs
 698                   size,                      // size
 699                   is_tlab,                   // is_tlab
 700                   GenCollectedHeap::OldGen); // max_generation
 701   }
 702 
 703   result = attempt_allocation(size, is_tlab, false /*first_only*/);
 704 
 705   if (result != NULL) {
 706     assert(is_in_reserved(result), "result not in heap");
 707     return result;
 708   }
 709 
 710   // OK, collection failed, try expansion.
 711   result = expand_heap_and_allocate(size, is_tlab);
 712   if (result != NULL) {
 713     return result;
 714   }
 715 
 716   // If we reach this point, we're really out of memory. Try every trick
 717   // we can to reclaim memory. Force collection of soft references. Force
 718   // a complete compaction of the heap. Any additional methods for finding
 719   // free memory should be here, especially if they are expensive. If this
 720   // attempt fails, an OOM exception will be thrown.
 721   {
 722     UIntFlagSetting flag_change(MarkSweepAlwaysCompactCount, 1); // Make sure the heap is fully compacted
 723 
 724     do_collection(true,                      // full
 725                   true,                      // clear_all_soft_refs
 726                   size,                      // size
 727                   is_tlab,                   // is_tlab
 728                   GenCollectedHeap::OldGen); // max_generation
 729   }
 730 
 731   result = attempt_allocation(size, is_tlab, false /* first_only */);
 732   if (result != NULL) {
 733     assert(is_in_reserved(result), "result not in heap");
 734     return result;
 735   }
 736 
 737   assert(!soft_ref_policy()->should_clear_all_soft_refs(),
 738     "Flag should have been handled and cleared prior to this point");
 739 
 740   // What else?  We might try synchronous finalization later.  If the total
 741   // space available is large enough for the allocation, then a more
 742   // complete compaction phase than we've tried so far might be
 743   // appropriate.
 744   return NULL;
 745 }
 746 
 747 #ifdef ASSERT
 748 class AssertNonScavengableClosure: public OopClosure {
 749 public:
 750   virtual void do_oop(oop* p) {
 751     assert(!GenCollectedHeap::heap()->is_in_partial_collection(*p),
 752       "Referent should not be scavengable.");  }
 753   virtual void do_oop(narrowOop* p) { ShouldNotReachHere(); }
 754 };
 755 static AssertNonScavengableClosure assert_is_non_scavengable_closure;
 756 #endif
 757 
 758 void GenCollectedHeap::process_roots(StrongRootsScope* scope,
 759                                      ScanningOption so,
 760                                      OopClosure* strong_roots,
 761                                      OopClosure* weak_roots,
 762                                      CLDClosure* strong_cld_closure,
 763                                      CLDClosure* weak_cld_closure,
 764                                      CodeBlobToOopClosure* code_roots) {
 765   // General roots.
 766   assert(Threads::thread_claim_parity() != 0, "must have called prologue code");
 767   assert(code_roots != NULL, "code root closure should always be set");
 768   // _n_termination for _process_strong_tasks should be set up stream
 769   // in a method not running in a GC worker.  Otherwise the GC worker
 770   // could be trying to change the termination condition while the task
 771   // is executing in another GC worker.
 772 
 773   if (!_process_strong_tasks->is_task_claimed(GCH_PS_ClassLoaderDataGraph_oops_do)) {
 774     ClassLoaderDataGraph::roots_cld_do(strong_cld_closure, weak_cld_closure);
 775   }
 776 
 777   // Only process code roots from thread stacks if we aren't visiting the entire CodeCache anyway
 778   CodeBlobToOopClosure* roots_from_code_p = (so & SO_AllCodeCache) ? NULL : code_roots;
 779 
 780   bool is_par = scope->n_threads() > 1;
 781   Threads::possibly_parallel_oops_do(is_par, strong_roots, roots_from_code_p);
 782 
 783   if (!_process_strong_tasks->is_task_claimed(GCH_PS_Universe_oops_do)) {
 784     Universe::oops_do(strong_roots);
 785   }
 786   // Global (strong) JNI handles
 787   if (!_process_strong_tasks->is_task_claimed(GCH_PS_JNIHandles_oops_do)) {
 788     JNIHandles::oops_do(strong_roots);
 789   }
 790 
 791   if (!_process_strong_tasks->is_task_claimed(GCH_PS_ObjectSynchronizer_oops_do)) {
 792     ObjectSynchronizer::oops_do(strong_roots);
 793   }
 794   if (!_process_strong_tasks->is_task_claimed(GCH_PS_Management_oops_do)) {
 795     Management::oops_do(strong_roots);
 796   }
 797   if (!_process_strong_tasks->is_task_claimed(GCH_PS_jvmti_oops_do)) {
 798     JvmtiExport::oops_do(strong_roots);
 799   }
 800   if (UseAOT && !_process_strong_tasks->is_task_claimed(GCH_PS_aot_oops_do)) {
 801     AOTLoader::oops_do(strong_roots);
 802   }
 803 
 804   if (!_process_strong_tasks->is_task_claimed(GCH_PS_SystemDictionary_oops_do)) {
 805     SystemDictionary::roots_oops_do(strong_roots, weak_roots);
 806   }
 807 
 808   if (!_process_strong_tasks->is_task_claimed(GCH_PS_CodeCache_oops_do)) {
 809     if (so & SO_ScavengeCodeCache) {
 810       assert(code_roots != NULL, "must supply closure for code cache");
 811 
 812       // We only visit parts of the CodeCache when scavenging.
 813       CodeCache::scavenge_root_nmethods_do(code_roots);
 814     }
 815     if (so & SO_AllCodeCache) {
 816       assert(code_roots != NULL, "must supply closure for code cache");
 817 
 818       // CMSCollector uses this to do intermediate-strength collections.
 819       // We scan the entire code cache, since CodeCache::do_unloading is not called.
 820       CodeCache::blobs_do(code_roots);
 821     }
 822     // Verify that the code cache contents are not subject to
 823     // movement by a scavenging collection.
 824     DEBUG_ONLY(CodeBlobToOopClosure assert_code_is_non_scavengable(&assert_is_non_scavengable_closure, !CodeBlobToOopClosure::FixRelocations));
 825     DEBUG_ONLY(CodeCache::asserted_non_scavengable_nmethods_do(&assert_code_is_non_scavengable));
 826   }
 827 }
 828 
 829 void GenCollectedHeap::process_string_table_roots(StrongRootsScope* scope,
 830                                                   OopClosure* root_closure) {
 831   assert(root_closure != NULL, "Must be set");
 832   // All threads execute the following. A specific chunk of buckets
 833   // from the StringTable are the individual tasks.
 834   if (scope->n_threads() > 1) {
 835     StringTable::possibly_parallel_oops_do(root_closure);
 836   } else {
 837     StringTable::oops_do(root_closure);
 838   }
 839 }
 840 
 841 void GenCollectedHeap::young_process_roots(StrongRootsScope* scope,
 842                                            OopsInGenClosure* root_closure,
 843                                            OopsInGenClosure* old_gen_closure,
 844                                            CLDClosure* cld_closure) {
 845   MarkingCodeBlobClosure mark_code_closure(root_closure, CodeBlobToOopClosure::FixRelocations);
 846 
 847   process_roots(scope, SO_ScavengeCodeCache, root_closure, root_closure,
 848                 cld_closure, cld_closure, &mark_code_closure);
 849   process_string_table_roots(scope, root_closure);
 850 
 851   if (!_process_strong_tasks->is_task_claimed(GCH_PS_younger_gens)) {
 852     root_closure->reset_generation();
 853   }
 854 
 855   // When collection is parallel, all threads get to cooperate to do
 856   // old generation scanning.
 857   old_gen_closure->set_generation(_old_gen);
 858   rem_set()->younger_refs_iterate(_old_gen, old_gen_closure, scope->n_threads());
 859   old_gen_closure->reset_generation();
 860 
 861   _process_strong_tasks->all_tasks_completed(scope->n_threads());
 862 }
 863 
 864 void GenCollectedHeap::full_process_roots(StrongRootsScope* scope,
 865                                           bool is_adjust_phase,
 866                                           ScanningOption so,
 867                                           bool only_strong_roots,
 868                                           OopsInGenClosure* root_closure,
 869                                           CLDClosure* cld_closure) {
 870   MarkingCodeBlobClosure mark_code_closure(root_closure, is_adjust_phase);
 871   OopsInGenClosure* weak_roots = only_strong_roots ? NULL : root_closure;
 872   CLDClosure* weak_cld_closure = only_strong_roots ? NULL : cld_closure;
 873 
 874   process_roots(scope, so, root_closure, weak_roots, cld_closure, weak_cld_closure, &mark_code_closure);
 875   if (is_adjust_phase) {
 876     // We never treat the string table as roots during marking
 877     // for the full gc, so we only need to process it during
 878     // the adjust phase.
 879     process_string_table_roots(scope, root_closure);
 880   }
 881 
 882   _process_strong_tasks->all_tasks_completed(scope->n_threads());
 883 }
 884 
 885 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure) {
 886   WeakProcessor::oops_do(root_closure);
 887   _young_gen->ref_processor()->weak_oops_do(root_closure);
 888   _old_gen->ref_processor()->weak_oops_do(root_closure);
 889 }
 890 
 891 #define GCH_SINCE_SAVE_MARKS_ITERATE_DEFN(OopClosureType, nv_suffix)    \
 892 void GenCollectedHeap::                                                 \
 893 oop_since_save_marks_iterate(GenerationType gen,                        \
 894                              OopClosureType* cur,                       \
 895                              OopClosureType* older) {                   \
 896   if (gen == YoungGen) {                              \
 897     _young_gen->oop_since_save_marks_iterate##nv_suffix(cur);           \
 898     _old_gen->oop_since_save_marks_iterate##nv_suffix(older);           \
 899   } else {                                                              \
 900     _old_gen->oop_since_save_marks_iterate##nv_suffix(cur);             \
 901   }                                                                     \
 902 }
 903 
 904 ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DEFN)
 905 
 906 #undef GCH_SINCE_SAVE_MARKS_ITERATE_DEFN
 907 
 908 bool GenCollectedHeap::no_allocs_since_save_marks() {
 909   return _young_gen->no_allocs_since_save_marks() &&
 910          _old_gen->no_allocs_since_save_marks();
 911 }
 912 
 913 bool GenCollectedHeap::supports_inline_contig_alloc() const {
 914   return _young_gen->supports_inline_contig_alloc();
 915 }
 916 
 917 HeapWord* volatile* GenCollectedHeap::top_addr() const {
 918   return _young_gen->top_addr();
 919 }
 920 
 921 HeapWord** GenCollectedHeap::end_addr() const {
 922   return _young_gen->end_addr();
 923 }
 924 
 925 // public collection interfaces
 926 
 927 void GenCollectedHeap::collect(GCCause::Cause cause) {
 928   if (cause == GCCause::_wb_young_gc) {
 929     // Young collection for the WhiteBox API.
 930     collect(cause, YoungGen);
 931   } else {
 932 #ifdef ASSERT
 933   if (cause == GCCause::_scavenge_alot) {
 934     // Young collection only.
 935     collect(cause, YoungGen);
 936   } else {
 937     // Stop-the-world full collection.
 938     collect(cause, OldGen);
 939   }
 940 #else
 941     // Stop-the-world full collection.
 942     collect(cause, OldGen);
 943 #endif
 944   }
 945 }
 946 
 947 void GenCollectedHeap::collect(GCCause::Cause cause, GenerationType max_generation) {
 948   // The caller doesn't have the Heap_lock
 949   assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
 950   MutexLocker ml(Heap_lock);
 951   collect_locked(cause, max_generation);
 952 }
 953 
 954 void GenCollectedHeap::collect_locked(GCCause::Cause cause) {
 955   // The caller has the Heap_lock
 956   assert(Heap_lock->owned_by_self(), "this thread should own the Heap_lock");
 957   collect_locked(cause, OldGen);
 958 }
 959 
 960 // this is the private collection interface
 961 // The Heap_lock is expected to be held on entry.
 962 
 963 void GenCollectedHeap::collect_locked(GCCause::Cause cause, GenerationType max_generation) {
 964   // Read the GC count while holding the Heap_lock
 965   unsigned int gc_count_before      = total_collections();
 966   unsigned int full_gc_count_before = total_full_collections();
 967   {
 968     MutexUnlocker mu(Heap_lock);  // give up heap lock, execute gets it back
 969     VM_GenCollectFull op(gc_count_before, full_gc_count_before,
 970                          cause, max_generation);
 971     VMThread::execute(&op);
 972   }
 973 }
 974 
 975 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) {
 976    do_full_collection(clear_all_soft_refs, OldGen);
 977 }
 978 
 979 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
 980                                           GenerationType last_generation) {
 981   GenerationType local_last_generation;
 982   if (!incremental_collection_will_fail(false /* don't consult_young */) &&
 983       gc_cause() == GCCause::_gc_locker) {
 984     local_last_generation = YoungGen;
 985   } else {
 986     local_last_generation = last_generation;
 987   }
 988 
 989   do_collection(true,                   // full
 990                 clear_all_soft_refs,    // clear_all_soft_refs
 991                 0,                      // size
 992                 false,                  // is_tlab
 993                 local_last_generation); // last_generation
 994   // Hack XXX FIX ME !!!
 995   // A scavenge may not have been attempted, or may have
 996   // been attempted and failed, because the old gen was too full
 997   if (local_last_generation == YoungGen && gc_cause() == GCCause::_gc_locker &&
 998       incremental_collection_will_fail(false /* don't consult_young */)) {
 999     log_debug(gc, jni)("GC locker: Trying a full collection because scavenge failed");
1000     // This time allow the old gen to be collected as well
1001     do_collection(true,                // full
1002                   clear_all_soft_refs, // clear_all_soft_refs
1003                   0,                   // size
1004                   false,               // is_tlab
1005                   OldGen);             // last_generation
1006   }
1007 }
1008 
1009 bool GenCollectedHeap::is_in_young(oop p) {
1010   bool result = ((HeapWord*)p) < _old_gen->reserved().start();
1011   assert(result == _young_gen->is_in_reserved(p),
1012          "incorrect test - result=%d, p=" INTPTR_FORMAT, result, p2i((void*)p));
1013   return result;
1014 }
1015 
1016 // Returns "TRUE" iff "p" points into the committed areas of the heap.
1017 bool GenCollectedHeap::is_in(const void* p) const {
1018   return _young_gen->is_in(p) || _old_gen->is_in(p);
1019 }
1020 
1021 #ifdef ASSERT
1022 // Don't implement this by using is_in_young().  This method is used
1023 // in some cases to check that is_in_young() is correct.
1024 bool GenCollectedHeap::is_in_partial_collection(const void* p) {
1025   assert(is_in_reserved(p) || p == NULL,
1026     "Does not work if address is non-null and outside of the heap");
1027   return p < _young_gen->reserved().end() && p != NULL;
1028 }
1029 #endif
1030 
1031 void GenCollectedHeap::oop_iterate_no_header(OopClosure* cl) {
1032   NoHeaderExtendedOopClosure no_header_cl(cl);
1033   oop_iterate(&no_header_cl);
1034 }
1035 
1036 void GenCollectedHeap::oop_iterate(ExtendedOopClosure* cl) {
1037   _young_gen->oop_iterate(cl);
1038   _old_gen->oop_iterate(cl);
1039 }
1040 
1041 void GenCollectedHeap::object_iterate(ObjectClosure* cl) {
1042   _young_gen->object_iterate(cl);
1043   _old_gen->object_iterate(cl);
1044 }
1045 
1046 void GenCollectedHeap::safe_object_iterate(ObjectClosure* cl) {
1047   _young_gen->safe_object_iterate(cl);
1048   _old_gen->safe_object_iterate(cl);
1049 }
1050 
1051 Space* GenCollectedHeap::space_containing(const void* addr) const {
1052   Space* res = _young_gen->space_containing(addr);
1053   if (res != NULL) {
1054     return res;
1055   }
1056   res = _old_gen->space_containing(addr);
1057   assert(res != NULL, "Could not find containing space");
1058   return res;
1059 }
1060 
1061 HeapWord* GenCollectedHeap::block_start(const void* addr) const {
1062   assert(is_in_reserved(addr), "block_start of address outside of heap");
1063   if (_young_gen->is_in_reserved(addr)) {
1064     assert(_young_gen->is_in(addr), "addr should be in allocated part of generation");
1065     return _young_gen->block_start(addr);
1066   }
1067 
1068   assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address");
1069   assert(_old_gen->is_in(addr), "addr should be in allocated part of generation");
1070   return _old_gen->block_start(addr);
1071 }
1072 
1073 size_t GenCollectedHeap::block_size(const HeapWord* addr) const {
1074   assert(is_in_reserved(addr), "block_size of address outside of heap");
1075   if (_young_gen->is_in_reserved(addr)) {
1076     assert(_young_gen->is_in(addr), "addr should be in allocated part of generation");
1077     return _young_gen->block_size(addr);
1078   }
1079 
1080   assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address");
1081   assert(_old_gen->is_in(addr), "addr should be in allocated part of generation");
1082   return _old_gen->block_size(addr);
1083 }
1084 
1085 bool GenCollectedHeap::block_is_obj(const HeapWord* addr) const {
1086   assert(is_in_reserved(addr), "block_is_obj of address outside of heap");
1087   assert(block_start(addr) == addr, "addr must be a block start");
1088   if (_young_gen->is_in_reserved(addr)) {
1089     return _young_gen->block_is_obj(addr);
1090   }
1091 
1092   assert(_old_gen->is_in_reserved(addr), "Some generation should contain the address");
1093   return _old_gen->block_is_obj(addr);
1094 }
1095 
1096 bool GenCollectedHeap::supports_tlab_allocation() const {
1097   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
1098   return _young_gen->supports_tlab_allocation();
1099 }
1100 
1101 size_t GenCollectedHeap::tlab_capacity(Thread* thr) const {
1102   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
1103   if (_young_gen->supports_tlab_allocation()) {
1104     return _young_gen->tlab_capacity();
1105   }
1106   return 0;
1107 }
1108 
1109 size_t GenCollectedHeap::tlab_used(Thread* thr) const {
1110   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
1111   if (_young_gen->supports_tlab_allocation()) {
1112     return _young_gen->tlab_used();
1113   }
1114   return 0;
1115 }
1116 
1117 size_t GenCollectedHeap::unsafe_max_tlab_alloc(Thread* thr) const {
1118   assert(!_old_gen->supports_tlab_allocation(), "Old gen supports TLAB allocation?!");
1119   if (_young_gen->supports_tlab_allocation()) {
1120     return _young_gen->unsafe_max_tlab_alloc();
1121   }
1122   return 0;
1123 }
1124 
1125 HeapWord* GenCollectedHeap::allocate_new_tlab(size_t size) {
1126   bool gc_overhead_limit_was_exceeded;
1127   return mem_allocate_work(size /* size */,
1128                            true /* is_tlab */,
1129                            &gc_overhead_limit_was_exceeded);
1130 }
1131 
1132 // Requires "*prev_ptr" to be non-NULL.  Deletes and a block of minimal size
1133 // from the list headed by "*prev_ptr".
1134 static ScratchBlock *removeSmallestScratch(ScratchBlock **prev_ptr) {
1135   bool first = true;
1136   size_t min_size = 0;   // "first" makes this conceptually infinite.
1137   ScratchBlock **smallest_ptr, *smallest;
1138   ScratchBlock  *cur = *prev_ptr;
1139   while (cur) {
1140     assert(*prev_ptr == cur, "just checking");
1141     if (first || cur->num_words < min_size) {
1142       smallest_ptr = prev_ptr;
1143       smallest     = cur;
1144       min_size     = smallest->num_words;
1145       first        = false;
1146     }
1147     prev_ptr = &cur->next;
1148     cur     =  cur->next;
1149   }
1150   smallest      = *smallest_ptr;
1151   *smallest_ptr = smallest->next;
1152   return smallest;
1153 }
1154 
1155 // Sort the scratch block list headed by res into decreasing size order,
1156 // and set "res" to the result.
1157 static void sort_scratch_list(ScratchBlock*& list) {
1158   ScratchBlock* sorted = NULL;
1159   ScratchBlock* unsorted = list;
1160   while (unsorted) {
1161     ScratchBlock *smallest = removeSmallestScratch(&unsorted);
1162     smallest->next  = sorted;
1163     sorted          = smallest;
1164   }
1165   list = sorted;
1166 }
1167 
1168 ScratchBlock* GenCollectedHeap::gather_scratch(Generation* requestor,
1169                                                size_t max_alloc_words) {
1170   ScratchBlock* res = NULL;
1171   _young_gen->contribute_scratch(res, requestor, max_alloc_words);
1172   _old_gen->contribute_scratch(res, requestor, max_alloc_words);
1173   sort_scratch_list(res);
1174   return res;
1175 }
1176 
1177 void GenCollectedHeap::release_scratch() {
1178   _young_gen->reset_scratch();
1179   _old_gen->reset_scratch();
1180 }
1181 
1182 class GenPrepareForVerifyClosure: public GenCollectedHeap::GenClosure {
1183   void do_generation(Generation* gen) {
1184     gen->prepare_for_verify();
1185   }
1186 };
1187 
1188 void GenCollectedHeap::prepare_for_verify() {
1189   ensure_parsability(false);        // no need to retire TLABs
1190   GenPrepareForVerifyClosure blk;
1191   generation_iterate(&blk, false);
1192 }
1193 
1194 void GenCollectedHeap::generation_iterate(GenClosure* cl,
1195                                           bool old_to_young) {
1196   if (old_to_young) {
1197     cl->do_generation(_old_gen);
1198     cl->do_generation(_young_gen);
1199   } else {
1200     cl->do_generation(_young_gen);
1201     cl->do_generation(_old_gen);
1202   }
1203 }
1204 
1205 bool GenCollectedHeap::is_maximal_no_gc() const {
1206   return _young_gen->is_maximal_no_gc() && _old_gen->is_maximal_no_gc();
1207 }
1208 
1209 void GenCollectedHeap::save_marks() {
1210   _young_gen->save_marks();
1211   _old_gen->save_marks();
1212 }
1213 
1214 GenCollectedHeap* GenCollectedHeap::heap() {
1215   CollectedHeap* heap = Universe::heap();
1216   assert(heap != NULL, "Uninitialized access to GenCollectedHeap::heap()");
1217   assert(heap->kind() == CollectedHeap::SerialHeap ||
1218          heap->kind() == CollectedHeap::CMSHeap, "Not a GenCollectedHeap");
1219   return (GenCollectedHeap*) heap;
1220 }
1221 
1222 void GenCollectedHeap::prepare_for_compaction() {
1223   // Start by compacting into same gen.
1224   CompactPoint cp(_old_gen);
1225   _old_gen->prepare_for_compaction(&cp);
1226   _young_gen->prepare_for_compaction(&cp);
1227 }
1228 
1229 void GenCollectedHeap::verify(VerifyOption option /* ignored */) {
1230   log_debug(gc, verify)("%s", _old_gen->name());
1231   _old_gen->verify();
1232 
1233   log_debug(gc, verify)("%s", _old_gen->name());
1234   _young_gen->verify();
1235 
1236   log_debug(gc, verify)("RemSet");
1237   rem_set()->verify();
1238 }
1239 
1240 void GenCollectedHeap::print_on(outputStream* st) const {
1241   _young_gen->print_on(st);
1242   _old_gen->print_on(st);
1243   MetaspaceAux::print_on(st);
1244 }
1245 
1246 void GenCollectedHeap::gc_threads_do(ThreadClosure* tc) const {
1247 }
1248 
1249 void GenCollectedHeap::print_gc_threads_on(outputStream* st) const {
1250 }
1251 
1252 void GenCollectedHeap::print_tracing_info() const {
1253   if (log_is_enabled(Debug, gc, heap, exit)) {
1254     LogStreamHandle(Debug, gc, heap, exit) lsh;
1255     _young_gen->print_summary_info_on(&lsh);
1256     _old_gen->print_summary_info_on(&lsh);
1257   }
1258 }
1259 
1260 void GenCollectedHeap::print_heap_change(size_t young_prev_used, size_t old_prev_used) const {
1261   log_info(gc, heap)("%s: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1262                      _young_gen->short_name(), young_prev_used / K, _young_gen->used() /K, _young_gen->capacity() /K);
1263   log_info(gc, heap)("%s: " SIZE_FORMAT "K->" SIZE_FORMAT "K("  SIZE_FORMAT "K)",
1264                      _old_gen->short_name(), old_prev_used / K, _old_gen->used() /K, _old_gen->capacity() /K);
1265 }
1266 
1267 class GenGCPrologueClosure: public GenCollectedHeap::GenClosure {
1268  private:
1269   bool _full;
1270  public:
1271   void do_generation(Generation* gen) {
1272     gen->gc_prologue(_full);
1273   }
1274   GenGCPrologueClosure(bool full) : _full(full) {};
1275 };
1276 
1277 void GenCollectedHeap::gc_prologue(bool full) {
1278   assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
1279 
1280   // Fill TLAB's and such
1281   CollectedHeap::accumulate_statistics_all_tlabs();
1282   ensure_parsability(true);   // retire TLABs
1283 
1284   // Walk generations
1285   GenGCPrologueClosure blk(full);
1286   generation_iterate(&blk, false);  // not old-to-young.
1287 };
1288 
1289 class GenGCEpilogueClosure: public GenCollectedHeap::GenClosure {
1290  private:
1291   bool _full;
1292  public:
1293   void do_generation(Generation* gen) {
1294     gen->gc_epilogue(_full);
1295   }
1296   GenGCEpilogueClosure(bool full) : _full(full) {};
1297 };
1298 
1299 void GenCollectedHeap::gc_epilogue(bool full) {
1300 #if COMPILER2_OR_JVMCI
1301   assert(DerivedPointerTable::is_empty(), "derived pointer present");
1302   size_t actual_gap = pointer_delta((HeapWord*) (max_uintx-3), *(end_addr()));
1303   guarantee(is_client_compilation_mode_vm() || actual_gap > (size_t)FastAllocateSizeLimit, "inline allocation wraps");
1304 #endif // COMPILER2_OR_JVMCI
1305 
1306   resize_all_tlabs();
1307 
1308   GenGCEpilogueClosure blk(full);
1309   generation_iterate(&blk, false);  // not old-to-young.
1310 
1311   if (!CleanChunkPoolAsync) {
1312     Chunk::clean_chunk_pool();
1313   }
1314 
1315   MetaspaceCounters::update_performance_counters();
1316   CompressedClassSpaceCounters::update_performance_counters();
1317 };
1318 
1319 #ifndef PRODUCT
1320 class GenGCSaveTopsBeforeGCClosure: public GenCollectedHeap::GenClosure {
1321  private:
1322  public:
1323   void do_generation(Generation* gen) {
1324     gen->record_spaces_top();
1325   }
1326 };
1327 
1328 void GenCollectedHeap::record_gen_tops_before_GC() {
1329   if (ZapUnusedHeapArea) {
1330     GenGCSaveTopsBeforeGCClosure blk;
1331     generation_iterate(&blk, false);  // not old-to-young.
1332   }
1333 }
1334 #endif  // not PRODUCT
1335 
1336 class GenEnsureParsabilityClosure: public GenCollectedHeap::GenClosure {
1337  public:
1338   void do_generation(Generation* gen) {
1339     gen->ensure_parsability();
1340   }
1341 };
1342 
1343 void GenCollectedHeap::ensure_parsability(bool retire_tlabs) {
1344   CollectedHeap::ensure_parsability(retire_tlabs);
1345   GenEnsureParsabilityClosure ep_cl;
1346   generation_iterate(&ep_cl, false);
1347 }
1348 
1349 oop GenCollectedHeap::handle_failed_promotion(Generation* old_gen,
1350                                               oop obj,
1351                                               size_t obj_size) {
1352   guarantee(old_gen == _old_gen, "We only get here with an old generation");
1353   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1354   HeapWord* result = NULL;
1355 
1356   result = old_gen->expand_and_allocate(obj_size, false);
1357 
1358   if (result != NULL) {
1359     Copy::aligned_disjoint_words((HeapWord*)obj, result, obj_size);
1360   }
1361   return oop(result);
1362 }
1363 
1364 class GenTimeOfLastGCClosure: public GenCollectedHeap::GenClosure {
1365   jlong _time;   // in ms
1366   jlong _now;    // in ms
1367 
1368  public:
1369   GenTimeOfLastGCClosure(jlong now) : _time(now), _now(now) { }
1370 
1371   jlong time() { return _time; }
1372 
1373   void do_generation(Generation* gen) {
1374     _time = MIN2(_time, gen->time_of_last_gc(_now));
1375   }
1376 };
1377 
1378 jlong GenCollectedHeap::millis_since_last_gc() {
1379   // javaTimeNanos() is guaranteed to be monotonically non-decreasing
1380   // provided the underlying platform provides such a time source
1381   // (and it is bug free). So we still have to guard against getting
1382   // back a time later than 'now'.
1383   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1384   GenTimeOfLastGCClosure tolgc_cl(now);
1385   // iterate over generations getting the oldest
1386   // time that a generation was collected
1387   generation_iterate(&tolgc_cl, false);
1388 
1389   jlong retVal = now - tolgc_cl.time();
1390   if (retVal < 0) {
1391     log_warning(gc)("millis_since_last_gc() would return : " JLONG_FORMAT
1392        ". returning zero instead.", retVal);
1393     return 0;
1394   }
1395   return retVal;
1396 }