1 /*
   2  * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
   3  * Copyright (c) 2013, 2022, Red Hat, Inc. All rights reserved.
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This code is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License version 2 only, as
   8  * published by the Free Software Foundation.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  *
  24  */
  25 
  26 #include "precompiled.hpp"
  27 #include "memory/allocation.hpp"
  28 #include "memory/universe.hpp"
  29 
  30 #include "gc/shared/gcArguments.hpp"
  31 #include "gc/shared/gcTimer.hpp"
  32 #include "gc/shared/gcTraceTime.inline.hpp"
  33 #include "gc/shared/locationPrinter.inline.hpp"
  34 #include "gc/shared/memAllocator.hpp"
  35 #include "gc/shared/plab.hpp"
  36 #include "gc/shared/tlab_globals.hpp"
  37 
  38 #include "gc/shenandoah/shenandoahBarrierSet.hpp"
  39 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
  40 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
  41 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
  42 #include "gc/shenandoah/shenandoahConcurrentMark.hpp"
  43 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
  44 #include "gc/shenandoah/shenandoahControlThread.hpp"
  45 #include "gc/shenandoah/shenandoahFreeSet.hpp"
  46 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
  47 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  48 #include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
  49 #include "gc/shenandoah/shenandoahHeapRegionSet.hpp"
  50 #include "gc/shenandoah/shenandoahInitLogger.hpp"
  51 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
  52 #include "gc/shenandoah/shenandoahMemoryPool.hpp"
  53 #include "gc/shenandoah/shenandoahMetrics.hpp"
  54 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
  55 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
  56 #include "gc/shenandoah/shenandoahPacer.inline.hpp"
  57 #include "gc/shenandoah/shenandoahPadding.hpp"
  58 #include "gc/shenandoah/shenandoahParallelCleaning.inline.hpp"
  59 #include "gc/shenandoah/shenandoahReferenceProcessor.hpp"
  60 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  61 #include "gc/shenandoah/shenandoahSTWMark.hpp"
  62 #include "gc/shenandoah/shenandoahUtils.hpp"
  63 #include "gc/shenandoah/shenandoahVerifier.hpp"
  64 #include "gc/shenandoah/shenandoahCodeRoots.hpp"
  65 #include "gc/shenandoah/shenandoahVMOperations.hpp"
  66 #include "gc/shenandoah/shenandoahWorkGroup.hpp"
  67 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
  68 #include "gc/shenandoah/mode/shenandoahIUMode.hpp"
  69 #include "gc/shenandoah/mode/shenandoahPassiveMode.hpp"
  70 #include "gc/shenandoah/mode/shenandoahSATBMode.hpp"
  71 #if INCLUDE_JFR
  72 #include "gc/shenandoah/shenandoahJfrSupport.hpp"
  73 #endif
  74 
  75 #include "classfile/systemDictionary.hpp"
  76 #include "code/codeCache.hpp"
  77 #include "memory/classLoaderMetaspace.hpp"
  78 #include "memory/metaspaceUtils.hpp"
  79 #include "oops/compressedOops.inline.hpp"
  80 #include "prims/jvmtiTagMap.hpp"
  81 #include "runtime/atomic.hpp"
  82 #include "runtime/globals.hpp"
  83 #include "runtime/interfaceSupport.inline.hpp"
  84 #include "runtime/java.hpp"
  85 #include "runtime/orderAccess.hpp"
  86 #include "runtime/safepointMechanism.hpp"
  87 #include "runtime/vmThread.hpp"
  88 #include "services/mallocTracker.hpp"
  89 #include "services/memTracker.hpp"
  90 #include "utilities/events.hpp"
  91 #include "utilities/powerOfTwo.hpp"
  92 
  93 class ShenandoahPretouchHeapTask : public WorkerTask {
  94 private:
  95   ShenandoahRegionIterator _regions;
  96   const size_t _page_size;
  97 public:
  98   ShenandoahPretouchHeapTask(size_t page_size) :
  99     WorkerTask("Shenandoah Pretouch Heap"),
 100     _page_size(page_size) {}
 101 
 102   virtual void work(uint worker_id) {
 103     ShenandoahHeapRegion* r = _regions.next();
 104     while (r != nullptr) {
 105       if (r->is_committed()) {
 106         os::pretouch_memory(r->bottom(), r->end(), _page_size);
 107       }
 108       r = _regions.next();
 109     }
 110   }
 111 };
 112 
 113 class ShenandoahPretouchBitmapTask : public WorkerTask {
 114 private:
 115   ShenandoahRegionIterator _regions;
 116   char* _bitmap_base;
 117   const size_t _bitmap_size;
 118   const size_t _page_size;
 119 public:
 120   ShenandoahPretouchBitmapTask(char* bitmap_base, size_t bitmap_size, size_t page_size) :
 121     WorkerTask("Shenandoah Pretouch Bitmap"),
 122     _bitmap_base(bitmap_base),
 123     _bitmap_size(bitmap_size),
 124     _page_size(page_size) {}
 125 
 126   virtual void work(uint worker_id) {
 127     ShenandoahHeapRegion* r = _regions.next();
 128     while (r != nullptr) {
 129       size_t start = r->index()       * ShenandoahHeapRegion::region_size_bytes() / MarkBitMap::heap_map_factor();
 130       size_t end   = (r->index() + 1) * ShenandoahHeapRegion::region_size_bytes() / MarkBitMap::heap_map_factor();
 131       assert (end <= _bitmap_size, "end is sane: " SIZE_FORMAT " < " SIZE_FORMAT, end, _bitmap_size);
 132 
 133       if (r->is_committed()) {
 134         os::pretouch_memory(_bitmap_base + start, _bitmap_base + end, _page_size);
 135       }
 136 
 137       r = _regions.next();
 138     }
 139   }
 140 };
 141 
 142 jint ShenandoahHeap::initialize() {
 143   //
 144   // Figure out heap sizing
 145   //
 146 
 147   size_t init_byte_size = InitialHeapSize;
 148   size_t min_byte_size  = MinHeapSize;
 149   size_t max_byte_size  = MaxHeapSize;
 150   size_t heap_alignment = HeapAlignment;
 151 
 152   size_t reg_size_bytes = ShenandoahHeapRegion::region_size_bytes();
 153 
 154   Universe::check_alignment(max_byte_size,  reg_size_bytes, "Shenandoah heap");
 155   Universe::check_alignment(init_byte_size, reg_size_bytes, "Shenandoah heap");
 156 
 157   _num_regions = ShenandoahHeapRegion::region_count();
 158   assert(_num_regions == (max_byte_size / reg_size_bytes),
 159          "Regions should cover entire heap exactly: " SIZE_FORMAT " != " SIZE_FORMAT "/" SIZE_FORMAT,
 160          _num_regions, max_byte_size, reg_size_bytes);
 161 
 162   // Now we know the number of regions, initialize the heuristics.
 163   initialize_heuristics();
 164 
 165   size_t num_committed_regions = init_byte_size / reg_size_bytes;
 166   num_committed_regions = MIN2(num_committed_regions, _num_regions);
 167   assert(num_committed_regions <= _num_regions, "sanity");
 168   _initial_size = num_committed_regions * reg_size_bytes;
 169 
 170   size_t num_min_regions = min_byte_size / reg_size_bytes;
 171   num_min_regions = MIN2(num_min_regions, _num_regions);
 172   assert(num_min_regions <= _num_regions, "sanity");
 173   _minimum_size = num_min_regions * reg_size_bytes;
 174 
 175   // Default to max heap size.
 176   _soft_max_size = _num_regions * reg_size_bytes;
 177 
 178   _committed = _initial_size;
 179 
 180   size_t heap_page_size   = UseLargePages ? os::large_page_size() : os::vm_page_size();
 181   size_t bitmap_page_size = UseLargePages ? os::large_page_size() : os::vm_page_size();
 182   size_t region_page_size = UseLargePages ? os::large_page_size() : os::vm_page_size();
 183 
 184   //
 185   // Reserve and commit memory for heap
 186   //
 187 
 188   ReservedHeapSpace heap_rs = Universe::reserve_heap(max_byte_size, heap_alignment);
 189   initialize_reserved_region(heap_rs);
 190   _heap_region = MemRegion((HeapWord*)heap_rs.base(), heap_rs.size() / HeapWordSize);
 191   _heap_region_special = heap_rs.special();
 192 
 193   assert((((size_t) base()) & ShenandoahHeapRegion::region_size_bytes_mask()) == 0,
 194          "Misaligned heap: " PTR_FORMAT, p2i(base()));
 195 
 196 #if SHENANDOAH_OPTIMIZED_MARKTASK
 197   // The optimized ShenandoahMarkTask takes some bits away from the full object bits.
 198   // Fail if we ever attempt to address more than we can.
 199   if ((uintptr_t)heap_rs.end() >= ShenandoahMarkTask::max_addressable()) {
 200     FormatBuffer<512> buf("Shenandoah reserved [" PTR_FORMAT ", " PTR_FORMAT") for the heap, \n"
 201                           "but max object address is " PTR_FORMAT ". Try to reduce heap size, or try other \n"
 202                           "VM options that allocate heap at lower addresses (HeapBaseMinAddress, AllocateHeapAt, etc).",
 203                 p2i(heap_rs.base()), p2i(heap_rs.end()), ShenandoahMarkTask::max_addressable());
 204     vm_exit_during_initialization("Fatal Error", buf);
 205   }
 206 #endif
 207 
 208   ReservedSpace sh_rs = heap_rs.first_part(max_byte_size);
 209   if (!_heap_region_special) {
 210     os::commit_memory_or_exit(sh_rs.base(), _initial_size, heap_alignment, false,
 211                               "Cannot commit heap memory");
 212   }
 213 
 214   //
 215   // Reserve and commit memory for bitmap(s)
 216   //
 217 
 218   _bitmap_size = ShenandoahMarkBitMap::compute_size(heap_rs.size());
 219   _bitmap_size = align_up(_bitmap_size, bitmap_page_size);
 220 
 221   size_t bitmap_bytes_per_region = reg_size_bytes / ShenandoahMarkBitMap::heap_map_factor();
 222 
 223   guarantee(bitmap_bytes_per_region != 0,
 224             "Bitmap bytes per region should not be zero");
 225   guarantee(is_power_of_2(bitmap_bytes_per_region),
 226             "Bitmap bytes per region should be power of two: " SIZE_FORMAT, bitmap_bytes_per_region);
 227 
 228   if (bitmap_page_size > bitmap_bytes_per_region) {
 229     _bitmap_regions_per_slice = bitmap_page_size / bitmap_bytes_per_region;
 230     _bitmap_bytes_per_slice = bitmap_page_size;
 231   } else {
 232     _bitmap_regions_per_slice = 1;
 233     _bitmap_bytes_per_slice = bitmap_bytes_per_region;
 234   }
 235 
 236   guarantee(_bitmap_regions_per_slice >= 1,
 237             "Should have at least one region per slice: " SIZE_FORMAT,
 238             _bitmap_regions_per_slice);
 239 
 240   guarantee(((_bitmap_bytes_per_slice) % bitmap_page_size) == 0,
 241             "Bitmap slices should be page-granular: bps = " SIZE_FORMAT ", page size = " SIZE_FORMAT,
 242             _bitmap_bytes_per_slice, bitmap_page_size);
 243 
 244   ReservedSpace bitmap(_bitmap_size, bitmap_page_size);
 245   MemTracker::record_virtual_memory_type(bitmap.base(), mtGC);
 246   _bitmap_region = MemRegion((HeapWord*) bitmap.base(), bitmap.size() / HeapWordSize);
 247   _bitmap_region_special = bitmap.special();
 248 
 249   size_t bitmap_init_commit = _bitmap_bytes_per_slice *
 250                               align_up(num_committed_regions, _bitmap_regions_per_slice) / _bitmap_regions_per_slice;
 251   bitmap_init_commit = MIN2(_bitmap_size, bitmap_init_commit);
 252   if (!_bitmap_region_special) {
 253     os::commit_memory_or_exit((char *) _bitmap_region.start(), bitmap_init_commit, bitmap_page_size, false,
 254                               "Cannot commit bitmap memory");
 255   }
 256 
 257   _marking_context = new ShenandoahMarkingContext(_heap_region, _bitmap_region, _num_regions, _max_workers);
 258 
 259   if (ShenandoahVerify) {
 260     ReservedSpace verify_bitmap(_bitmap_size, bitmap_page_size);
 261     if (!verify_bitmap.special()) {
 262       os::commit_memory_or_exit(verify_bitmap.base(), verify_bitmap.size(), bitmap_page_size, false,
 263                                 "Cannot commit verification bitmap memory");
 264     }
 265     MemTracker::record_virtual_memory_type(verify_bitmap.base(), mtGC);
 266     MemRegion verify_bitmap_region = MemRegion((HeapWord *) verify_bitmap.base(), verify_bitmap.size() / HeapWordSize);
 267     _verification_bit_map.initialize(_heap_region, verify_bitmap_region);
 268     _verifier = new ShenandoahVerifier(this, &_verification_bit_map);
 269   }
 270 
 271   // Reserve aux bitmap for use in object_iterate(). We don't commit it here.
 272   ReservedSpace aux_bitmap(_bitmap_size, bitmap_page_size);
 273   MemTracker::record_virtual_memory_type(aux_bitmap.base(), mtGC);
 274   _aux_bitmap_region = MemRegion((HeapWord*) aux_bitmap.base(), aux_bitmap.size() / HeapWordSize);
 275   _aux_bitmap_region_special = aux_bitmap.special();
 276   _aux_bit_map.initialize(_heap_region, _aux_bitmap_region);
 277 
 278   //
 279   // Create regions and region sets
 280   //
 281   size_t region_align = align_up(sizeof(ShenandoahHeapRegion), SHENANDOAH_CACHE_LINE_SIZE);
 282   size_t region_storage_size = align_up(region_align * _num_regions, region_page_size);
 283   region_storage_size = align_up(region_storage_size, os::vm_allocation_granularity());
 284 
 285   ReservedSpace region_storage(region_storage_size, region_page_size);
 286   MemTracker::record_virtual_memory_type(region_storage.base(), mtGC);
 287   if (!region_storage.special()) {
 288     os::commit_memory_or_exit(region_storage.base(), region_storage_size, region_page_size, false,
 289                               "Cannot commit region memory");
 290   }
 291 
 292   // Try to fit the collection set bitmap at lower addresses. This optimizes code generation for cset checks.
 293   // Go up until a sensible limit (subject to encoding constraints) and try to reserve the space there.
 294   // If not successful, bite a bullet and allocate at whatever address.
 295   {
 296     size_t cset_align = MAX2<size_t>(os::vm_page_size(), os::vm_allocation_granularity());
 297     size_t cset_size = align_up(((size_t) sh_rs.base() + sh_rs.size()) >> ShenandoahHeapRegion::region_size_bytes_shift(), cset_align);
 298 
 299     uintptr_t min = round_up_power_of_2(cset_align);
 300     uintptr_t max = (1u << 30u);
 301 
 302     for (uintptr_t addr = min; addr <= max; addr <<= 1u) {
 303       char* req_addr = (char*)addr;
 304       assert(is_aligned(req_addr, cset_align), "Should be aligned");
 305       ReservedSpace cset_rs(cset_size, cset_align, os::vm_page_size(), req_addr);
 306       if (cset_rs.is_reserved()) {
 307         assert(cset_rs.base() == req_addr, "Allocated where requested: " PTR_FORMAT ", " PTR_FORMAT, p2i(cset_rs.base()), addr);
 308         _collection_set = new ShenandoahCollectionSet(this, cset_rs, sh_rs.base());
 309         break;
 310       }
 311     }
 312 
 313     if (_collection_set == nullptr) {
 314       ReservedSpace cset_rs(cset_size, cset_align, os::vm_page_size());
 315       _collection_set = new ShenandoahCollectionSet(this, cset_rs, sh_rs.base());
 316     }
 317   }
 318 
 319   _regions = NEW_C_HEAP_ARRAY(ShenandoahHeapRegion*, _num_regions, mtGC);
 320   _free_set = new ShenandoahFreeSet(this, _num_regions);
 321 
 322   {
 323     ShenandoahHeapLocker locker(lock());
 324 
 325     for (size_t i = 0; i < _num_regions; i++) {
 326       HeapWord* start = (HeapWord*)sh_rs.base() + ShenandoahHeapRegion::region_size_words() * i;
 327       bool is_committed = i < num_committed_regions;
 328       void* loc = region_storage.base() + i * region_align;
 329 
 330       ShenandoahHeapRegion* r = new (loc) ShenandoahHeapRegion(start, i, is_committed);
 331       assert(is_aligned(r, SHENANDOAH_CACHE_LINE_SIZE), "Sanity");
 332 
 333       _marking_context->initialize_top_at_mark_start(r);
 334       _regions[i] = r;
 335       assert(!collection_set()->is_in(i), "New region should not be in collection set");
 336     }
 337 
 338     // Initialize to complete
 339     _marking_context->mark_complete();
 340 
 341     _free_set->rebuild();
 342   }
 343 
 344   if (AlwaysPreTouch) {
 345     // For NUMA, it is important to pre-touch the storage under bitmaps with worker threads,
 346     // before initialize() below zeroes it with initializing thread. For any given region,
 347     // we touch the region and the corresponding bitmaps from the same thread.
 348     ShenandoahPushWorkerScope scope(workers(), _max_workers, false);
 349 
 350     _pretouch_heap_page_size = heap_page_size;
 351     _pretouch_bitmap_page_size = bitmap_page_size;
 352 
 353 #ifdef LINUX
 354     // UseTransparentHugePages would madvise that backing memory can be coalesced into huge
 355     // pages. But, the kernel needs to know that every small page is used, in order to coalesce
 356     // them into huge one. Therefore, we need to pretouch with smaller pages.
 357     if (UseTransparentHugePages) {
 358       _pretouch_heap_page_size = (size_t)os::vm_page_size();
 359       _pretouch_bitmap_page_size = (size_t)os::vm_page_size();
 360     }
 361 #endif
 362 
 363     // OS memory managers may want to coalesce back-to-back pages. Make their jobs
 364     // simpler by pre-touching continuous spaces (heap and bitmap) separately.
 365 
 366     ShenandoahPretouchBitmapTask bcl(bitmap.base(), _bitmap_size, _pretouch_bitmap_page_size);
 367     _workers->run_task(&bcl);
 368 
 369     ShenandoahPretouchHeapTask hcl(_pretouch_heap_page_size);
 370     _workers->run_task(&hcl);
 371   }
 372 
 373   //
 374   // Initialize the rest of GC subsystems
 375   //
 376 
 377   _liveness_cache = NEW_C_HEAP_ARRAY(ShenandoahLiveData*, _max_workers, mtGC);
 378   for (uint worker = 0; worker < _max_workers; worker++) {
 379     _liveness_cache[worker] = NEW_C_HEAP_ARRAY(ShenandoahLiveData, _num_regions, mtGC);
 380     Copy::fill_to_bytes(_liveness_cache[worker], _num_regions * sizeof(ShenandoahLiveData));
 381   }
 382 
 383   // There should probably be Shenandoah-specific options for these,
 384   // just as there are G1-specific options.
 385   {
 386     ShenandoahSATBMarkQueueSet& satbqs = ShenandoahBarrierSet::satb_mark_queue_set();
 387     satbqs.set_process_completed_buffers_threshold(20); // G1SATBProcessCompletedThreshold
 388     satbqs.set_buffer_enqueue_threshold_percentage(60); // G1SATBBufferEnqueueingThresholdPercent
 389   }
 390 
 391   _monitoring_support = new ShenandoahMonitoringSupport(this);
 392   _phase_timings = new ShenandoahPhaseTimings(max_workers());
 393   ShenandoahCodeRoots::initialize();
 394 
 395   if (ShenandoahPacing) {
 396     _pacer = new ShenandoahPacer(this);
 397     _pacer->setup_for_idle();
 398   } else {
 399     _pacer = nullptr;
 400   }
 401 
 402   _control_thread = new ShenandoahControlThread();
 403 
 404   ShenandoahInitLogger::print();
 405 
 406   return JNI_OK;
 407 }
 408 
 409 void ShenandoahHeap::initialize_mode() {
 410   if (ShenandoahGCMode != nullptr) {
 411     if (strcmp(ShenandoahGCMode, "satb") == 0) {
 412       _gc_mode = new ShenandoahSATBMode();
 413     } else if (strcmp(ShenandoahGCMode, "iu") == 0) {
 414       _gc_mode = new ShenandoahIUMode();
 415     } else if (strcmp(ShenandoahGCMode, "passive") == 0) {
 416       _gc_mode = new ShenandoahPassiveMode();
 417     } else {
 418       vm_exit_during_initialization("Unknown -XX:ShenandoahGCMode option");
 419     }
 420   } else {
 421     vm_exit_during_initialization("Unknown -XX:ShenandoahGCMode option (null)");
 422   }
 423   _gc_mode->initialize_flags();
 424   if (_gc_mode->is_diagnostic() && !UnlockDiagnosticVMOptions) {
 425     vm_exit_during_initialization(
 426             err_msg("GC mode \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
 427                     _gc_mode->name()));
 428   }
 429   if (_gc_mode->is_experimental() && !UnlockExperimentalVMOptions) {
 430     vm_exit_during_initialization(
 431             err_msg("GC mode \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
 432                     _gc_mode->name()));
 433   }
 434 }
 435 
 436 void ShenandoahHeap::initialize_heuristics() {
 437   assert(_gc_mode != nullptr, "Must be initialized");
 438   _heuristics = _gc_mode->initialize_heuristics();
 439 
 440   if (_heuristics->is_diagnostic() && !UnlockDiagnosticVMOptions) {
 441     vm_exit_during_initialization(
 442             err_msg("Heuristics \"%s\" is diagnostic, and must be enabled via -XX:+UnlockDiagnosticVMOptions.",
 443                     _heuristics->name()));
 444   }
 445   if (_heuristics->is_experimental() && !UnlockExperimentalVMOptions) {
 446     vm_exit_during_initialization(
 447             err_msg("Heuristics \"%s\" is experimental, and must be enabled via -XX:+UnlockExperimentalVMOptions.",
 448                     _heuristics->name()));
 449   }
 450 }
 451 
 452 #ifdef _MSC_VER
 453 #pragma warning( push )
 454 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 455 #endif
 456 
 457 ShenandoahHeap::ShenandoahHeap(ShenandoahCollectorPolicy* policy) :
 458   CollectedHeap(),
 459   _initial_size(0),
 460   _used(0),
 461   _committed(0),
 462   _bytes_allocated_since_gc_start(0),
 463   _max_workers(MAX2(ConcGCThreads, ParallelGCThreads)),
 464   _workers(nullptr),
 465   _safepoint_workers(nullptr),
 466   _heap_region_special(false),
 467   _num_regions(0),
 468   _regions(nullptr),
 469   _update_refs_iterator(this),
 470   _control_thread(nullptr),
 471   _shenandoah_policy(policy),
 472   _gc_mode(nullptr),
 473   _heuristics(nullptr),
 474   _free_set(nullptr),
 475   _pacer(nullptr),
 476   _verifier(nullptr),
 477   _phase_timings(nullptr),
 478   _monitoring_support(nullptr),
 479   _memory_pool(nullptr),
 480   _stw_memory_manager("Shenandoah Pauses"),
 481   _cycle_memory_manager("Shenandoah Cycles"),
 482   _gc_timer(new ConcurrentGCTimer()),
 483   _soft_ref_policy(),
 484   _log_min_obj_alignment_in_bytes(LogMinObjAlignmentInBytes),
 485   _ref_processor(new ShenandoahReferenceProcessor(MAX2(_max_workers, 1U))),
 486   _marking_context(nullptr),
 487   _bitmap_size(0),
 488   _bitmap_regions_per_slice(0),
 489   _bitmap_bytes_per_slice(0),
 490   _bitmap_region_special(false),
 491   _aux_bitmap_region_special(false),
 492   _liveness_cache(nullptr),
 493   _collection_set(nullptr)
 494 {
 495   // Initialize GC mode early, so we can adjust barrier support
 496   initialize_mode();
 497   BarrierSet::set_barrier_set(new ShenandoahBarrierSet(this));
 498 
 499   _max_workers = MAX2(_max_workers, 1U);
 500   _workers = new ShenandoahWorkerThreads("Shenandoah GC Threads", _max_workers);
 501   if (_workers == nullptr) {
 502     vm_exit_during_initialization("Failed necessary allocation.");
 503   } else {
 504     _workers->initialize_workers();
 505   }
 506 
 507   if (ParallelGCThreads > 1) {
 508     _safepoint_workers = new ShenandoahWorkerThreads("Safepoint Cleanup Thread",
 509                                                 ParallelGCThreads);
 510     _safepoint_workers->initialize_workers();
 511   }
 512 }
 513 
 514 #ifdef _MSC_VER
 515 #pragma warning( pop )
 516 #endif
 517 
 518 class ShenandoahResetBitmapTask : public WorkerTask {
 519 private:
 520   ShenandoahRegionIterator _regions;
 521 
 522 public:
 523   ShenandoahResetBitmapTask() :
 524     WorkerTask("Shenandoah Reset Bitmap") {}
 525 
 526   void work(uint worker_id) {
 527     ShenandoahHeapRegion* region = _regions.next();
 528     ShenandoahHeap* heap = ShenandoahHeap::heap();
 529     ShenandoahMarkingContext* const ctx = heap->marking_context();
 530     while (region != nullptr) {
 531       if (heap->is_bitmap_slice_committed(region)) {
 532         ctx->clear_bitmap(region);
 533       }
 534       region = _regions.next();
 535     }
 536   }
 537 };
 538 
 539 void ShenandoahHeap::reset_mark_bitmap() {
 540   assert_gc_workers(_workers->active_workers());
 541   mark_incomplete_marking_context();
 542 
 543   ShenandoahResetBitmapTask task;
 544   _workers->run_task(&task);
 545 }
 546 
 547 void ShenandoahHeap::print_on(outputStream* st) const {
 548   st->print_cr("Shenandoah Heap");
 549   st->print_cr(" " SIZE_FORMAT "%s max, " SIZE_FORMAT "%s soft max, " SIZE_FORMAT "%s committed, " SIZE_FORMAT "%s used",
 550                byte_size_in_proper_unit(max_capacity()), proper_unit_for_byte_size(max_capacity()),
 551                byte_size_in_proper_unit(soft_max_capacity()), proper_unit_for_byte_size(soft_max_capacity()),
 552                byte_size_in_proper_unit(committed()),    proper_unit_for_byte_size(committed()),
 553                byte_size_in_proper_unit(used()),         proper_unit_for_byte_size(used()));
 554   st->print_cr(" " SIZE_FORMAT " x " SIZE_FORMAT"%s regions",
 555                num_regions(),
 556                byte_size_in_proper_unit(ShenandoahHeapRegion::region_size_bytes()),
 557                proper_unit_for_byte_size(ShenandoahHeapRegion::region_size_bytes()));
 558 
 559   st->print("Status: ");
 560   if (has_forwarded_objects())                 st->print("has forwarded objects, ");
 561   if (is_concurrent_mark_in_progress())        st->print("marking, ");
 562   if (is_evacuation_in_progress())             st->print("evacuating, ");
 563   if (is_update_refs_in_progress())            st->print("updating refs, ");
 564   if (is_degenerated_gc_in_progress())         st->print("degenerated gc, ");
 565   if (is_full_gc_in_progress())                st->print("full gc, ");
 566   if (is_full_gc_move_in_progress())           st->print("full gc move, ");
 567   if (is_concurrent_weak_root_in_progress())   st->print("concurrent weak roots, ");
 568   if (is_concurrent_strong_root_in_progress() &&
 569       !is_concurrent_weak_root_in_progress())  st->print("concurrent strong roots, ");
 570 
 571   if (cancelled_gc()) {
 572     st->print("cancelled");
 573   } else {
 574     st->print("not cancelled");
 575   }
 576   st->cr();
 577 
 578   st->print_cr("Reserved region:");
 579   st->print_cr(" - [" PTR_FORMAT ", " PTR_FORMAT ") ",
 580                p2i(reserved_region().start()),
 581                p2i(reserved_region().end()));
 582 
 583   ShenandoahCollectionSet* cset = collection_set();
 584   st->print_cr("Collection set:");
 585   if (cset != nullptr) {
 586     st->print_cr(" - map (vanilla): " PTR_FORMAT, p2i(cset->map_address()));
 587     st->print_cr(" - map (biased):  " PTR_FORMAT, p2i(cset->biased_map_address()));
 588   } else {
 589     st->print_cr(" (null)");
 590   }
 591 
 592   st->cr();
 593   MetaspaceUtils::print_on(st);
 594 
 595   if (Verbose) {
 596     print_heap_regions_on(st);
 597   }
 598 }
 599 
 600 class ShenandoahInitWorkerGCLABClosure : public ThreadClosure {
 601 public:
 602   void do_thread(Thread* thread) {
 603     assert(thread != nullptr, "Sanity");
 604     assert(thread->is_Worker_thread(), "Only worker thread expected");
 605     ShenandoahThreadLocalData::initialize_gclab(thread);
 606   }
 607 };
 608 
 609 void ShenandoahHeap::post_initialize() {
 610   CollectedHeap::post_initialize();
 611   MutexLocker ml(Threads_lock);
 612 
 613   ShenandoahInitWorkerGCLABClosure init_gclabs;
 614   _workers->threads_do(&init_gclabs);
 615 
 616   // gclab can not be initialized early during VM startup, as it can not determinate its max_size.
 617   // Now, we will let WorkerThreads to initialize gclab when new worker is created.
 618   _workers->set_initialize_gclab();
 619   if (_safepoint_workers != nullptr) {
 620     _safepoint_workers->threads_do(&init_gclabs);
 621     _safepoint_workers->set_initialize_gclab();
 622   }
 623 
 624   _heuristics->initialize();
 625 
 626   JFR_ONLY(ShenandoahJFRSupport::register_jfr_type_serializers());
 627 }
 628 
 629 size_t ShenandoahHeap::used() const {
 630   return Atomic::load(&_used);
 631 }
 632 
 633 size_t ShenandoahHeap::committed() const {
 634   return Atomic::load(&_committed);
 635 }
 636 
 637 void ShenandoahHeap::increase_committed(size_t bytes) {
 638   shenandoah_assert_heaplocked_or_safepoint();
 639   _committed += bytes;
 640 }
 641 
 642 void ShenandoahHeap::decrease_committed(size_t bytes) {
 643   shenandoah_assert_heaplocked_or_safepoint();
 644   _committed -= bytes;
 645 }
 646 
 647 void ShenandoahHeap::increase_used(size_t bytes) {
 648   Atomic::add(&_used, bytes, memory_order_relaxed);
 649 }
 650 
 651 void ShenandoahHeap::set_used(size_t bytes) {
 652   Atomic::store(&_used, bytes);
 653 }
 654 
 655 void ShenandoahHeap::decrease_used(size_t bytes) {
 656   assert(used() >= bytes, "never decrease heap size by more than we've left");
 657   Atomic::sub(&_used, bytes, memory_order_relaxed);
 658 }
 659 
 660 void ShenandoahHeap::increase_allocated(size_t bytes) {
 661   Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
 662 }
 663 
 664 void ShenandoahHeap::notify_mutator_alloc_words(size_t words, bool waste) {
 665   size_t bytes = words * HeapWordSize;
 666   if (!waste) {
 667     increase_used(bytes);
 668   }
 669   increase_allocated(bytes);
 670   if (ShenandoahPacing) {
 671     control_thread()->pacing_notify_alloc(words);
 672     if (waste) {
 673       pacer()->claim_for_alloc(words, true);
 674     }
 675   }
 676 }
 677 
 678 size_t ShenandoahHeap::capacity() const {
 679   return committed();
 680 }
 681 
 682 size_t ShenandoahHeap::max_capacity() const {
 683   return _num_regions * ShenandoahHeapRegion::region_size_bytes();
 684 }
 685 
 686 size_t ShenandoahHeap::soft_max_capacity() const {
 687   size_t v = Atomic::load(&_soft_max_size);
 688   assert(min_capacity() <= v && v <= max_capacity(),
 689          "Should be in bounds: " SIZE_FORMAT " <= " SIZE_FORMAT " <= " SIZE_FORMAT,
 690          min_capacity(), v, max_capacity());
 691   return v;
 692 }
 693 
 694 void ShenandoahHeap::set_soft_max_capacity(size_t v) {
 695   assert(min_capacity() <= v && v <= max_capacity(),
 696          "Should be in bounds: " SIZE_FORMAT " <= " SIZE_FORMAT " <= " SIZE_FORMAT,
 697          min_capacity(), v, max_capacity());
 698   Atomic::store(&_soft_max_size, v);
 699 }
 700 
 701 size_t ShenandoahHeap::min_capacity() const {
 702   return _minimum_size;
 703 }
 704 
 705 size_t ShenandoahHeap::initial_capacity() const {
 706   return _initial_size;
 707 }
 708 
 709 bool ShenandoahHeap::is_in(const void* p) const {
 710   HeapWord* heap_base = (HeapWord*) base();
 711   HeapWord* last_region_end = heap_base + ShenandoahHeapRegion::region_size_words() * num_regions();
 712   return p >= heap_base && p < last_region_end;
 713 }
 714 
 715 void ShenandoahHeap::op_uncommit(double shrink_before, size_t shrink_until) {
 716   assert (ShenandoahUncommit, "should be enabled");
 717 
 718   // Application allocates from the beginning of the heap, and GC allocates at
 719   // the end of it. It is more efficient to uncommit from the end, so that applications
 720   // could enjoy the near committed regions. GC allocations are much less frequent,
 721   // and therefore can accept the committing costs.
 722 
 723   size_t count = 0;
 724   for (size_t i = num_regions(); i > 0; i--) { // care about size_t underflow
 725     ShenandoahHeapRegion* r = get_region(i - 1);
 726     if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
 727       ShenandoahHeapLocker locker(lock());
 728       if (r->is_empty_committed()) {
 729         if (committed() < shrink_until + ShenandoahHeapRegion::region_size_bytes()) {
 730           break;
 731         }
 732 
 733         r->make_uncommitted();
 734         count++;
 735       }
 736     }
 737     SpinPause(); // allow allocators to take the lock
 738   }
 739 
 740   if (count > 0) {
 741     control_thread()->notify_heap_changed();
 742   }
 743 }
 744 
 745 HeapWord* ShenandoahHeap::allocate_from_gclab_slow(Thread* thread, size_t size) {
 746   // New object should fit the GCLAB size
 747   size_t min_size = MAX2(size, PLAB::min_size());
 748 
 749   // Figure out size of new GCLAB, looking back at heuristics. Expand aggressively.
 750   size_t new_size = ShenandoahThreadLocalData::gclab_size(thread) * 2;
 751   new_size = MIN2(new_size, PLAB::max_size());
 752   new_size = MAX2(new_size, PLAB::min_size());
 753 
 754   // Record new heuristic value even if we take any shortcut. This captures
 755   // the case when moderately-sized objects always take a shortcut. At some point,
 756   // heuristics should catch up with them.
 757   ShenandoahThreadLocalData::set_gclab_size(thread, new_size);
 758 
 759   if (new_size < size) {
 760     // New size still does not fit the object. Fall back to shared allocation.
 761     // This avoids retiring perfectly good GCLABs, when we encounter a large object.
 762     return nullptr;
 763   }
 764 
 765   // Retire current GCLAB, and allocate a new one.
 766   PLAB* gclab = ShenandoahThreadLocalData::gclab(thread);
 767   gclab->retire();
 768 
 769   size_t actual_size = 0;
 770   HeapWord* gclab_buf = allocate_new_gclab(min_size, new_size, &actual_size);
 771   if (gclab_buf == nullptr) {
 772     return nullptr;
 773   }
 774 
 775   assert (size <= actual_size, "allocation should fit");
 776 
 777   if (ZeroTLAB) {
 778     // ..and clear it.
 779     Copy::zero_to_words(gclab_buf, actual_size);
 780   } else {
 781     // ...and zap just allocated object.
 782 #ifdef ASSERT
 783     // Skip mangling the space corresponding to the object header to
 784     // ensure that the returned space is not considered parsable by
 785     // any concurrent GC thread.
 786     size_t hdr_size = oopDesc::header_size();
 787     Copy::fill_to_words(gclab_buf + hdr_size, actual_size - hdr_size, badHeapWordVal);
 788 #endif // ASSERT
 789   }
 790   gclab->set_buf(gclab_buf, actual_size);
 791   return gclab->allocate(size);
 792 }
 793 
 794 HeapWord* ShenandoahHeap::allocate_new_tlab(size_t min_size,
 795                                             size_t requested_size,
 796                                             size_t* actual_size) {
 797   ShenandoahAllocRequest req = ShenandoahAllocRequest::for_tlab(min_size, requested_size);
 798   HeapWord* res = allocate_memory(req);
 799   if (res != nullptr) {
 800     *actual_size = req.actual_size();
 801   } else {
 802     *actual_size = 0;
 803   }
 804   return res;
 805 }
 806 
 807 HeapWord* ShenandoahHeap::allocate_new_gclab(size_t min_size,
 808                                              size_t word_size,
 809                                              size_t* actual_size) {
 810   ShenandoahAllocRequest req = ShenandoahAllocRequest::for_gclab(min_size, word_size);
 811   HeapWord* res = allocate_memory(req);
 812   if (res != nullptr) {
 813     *actual_size = req.actual_size();
 814   } else {
 815     *actual_size = 0;
 816   }
 817   return res;
 818 }
 819 
 820 HeapWord* ShenandoahHeap::allocate_memory(ShenandoahAllocRequest& req) {
 821   intptr_t pacer_epoch = 0;
 822   bool in_new_region = false;
 823   HeapWord* result = nullptr;
 824 
 825   if (req.is_mutator_alloc()) {
 826     if (ShenandoahPacing) {
 827       pacer()->pace_for_alloc(req.size());
 828       pacer_epoch = pacer()->epoch();
 829     }
 830 
 831     if (!ShenandoahAllocFailureALot || !should_inject_alloc_failure()) {
 832       result = allocate_memory_under_lock(req, in_new_region);
 833     }
 834 
 835     // Allocation failed, block until control thread reacted, then retry allocation.
 836     //
 837     // It might happen that one of the threads requesting allocation would unblock
 838     // way later after GC happened, only to fail the second allocation, because
 839     // other threads have already depleted the free storage. In this case, a better
 840     // strategy is to try again, as long as GC makes progress.
 841     //
 842     // Then, we need to make sure the allocation was retried after at least one
 843     // Full GC, which means we want to try more than ShenandoahFullGCThreshold times.
 844 
 845     size_t tries = 0;
 846 
 847     while (result == nullptr && _progress_last_gc.is_set()) {
 848       tries++;
 849       control_thread()->handle_alloc_failure(req);
 850       result = allocate_memory_under_lock(req, in_new_region);
 851     }
 852 
 853     while (result == nullptr && tries <= ShenandoahFullGCThreshold) {
 854       tries++;
 855       control_thread()->handle_alloc_failure(req);
 856       result = allocate_memory_under_lock(req, in_new_region);
 857     }
 858 
 859   } else {
 860     assert(req.is_gc_alloc(), "Can only accept GC allocs here");
 861     result = allocate_memory_under_lock(req, in_new_region);
 862     // Do not call handle_alloc_failure() here, because we cannot block.
 863     // The allocation failure would be handled by the LRB slowpath with handle_alloc_failure_evac().
 864   }
 865 
 866   if (in_new_region) {
 867     control_thread()->notify_heap_changed();
 868   }
 869 
 870   if (result != nullptr) {
 871     size_t requested = req.size();
 872     size_t actual = req.actual_size();
 873 
 874     assert (req.is_lab_alloc() || (requested == actual),
 875             "Only LAB allocations are elastic: %s, requested = " SIZE_FORMAT ", actual = " SIZE_FORMAT,
 876             ShenandoahAllocRequest::alloc_type_to_string(req.type()), requested, actual);
 877 
 878     if (req.is_mutator_alloc()) {
 879       notify_mutator_alloc_words(actual, false);
 880 
 881       // If we requested more than we were granted, give the rest back to pacer.
 882       // This only matters if we are in the same pacing epoch: do not try to unpace
 883       // over the budget for the other phase.
 884       if (ShenandoahPacing && (pacer_epoch > 0) && (requested > actual)) {
 885         pacer()->unpace_for_alloc(pacer_epoch, requested - actual);
 886       }
 887     } else {
 888       increase_used(actual*HeapWordSize);
 889     }
 890   }
 891 
 892   return result;
 893 }
 894 
 895 HeapWord* ShenandoahHeap::allocate_memory_under_lock(ShenandoahAllocRequest& req, bool& in_new_region) {
 896   ShenandoahHeapLocker locker(lock());
 897   return _free_set->allocate(req, in_new_region);
 898 }
 899 
 900 HeapWord* ShenandoahHeap::mem_allocate(size_t size,
 901                                         bool*  gc_overhead_limit_was_exceeded) {
 902   ShenandoahAllocRequest req = ShenandoahAllocRequest::for_shared(size);
 903   return allocate_memory(req);
 904 }
 905 
 906 MetaWord* ShenandoahHeap::satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
 907                                                              size_t size,
 908                                                              Metaspace::MetadataType mdtype) {
 909   MetaWord* result;
 910 
 911   // Inform metaspace OOM to GC heuristics if class unloading is possible.
 912   if (heuristics()->can_unload_classes()) {
 913     ShenandoahHeuristics* h = heuristics();
 914     h->record_metaspace_oom();
 915   }
 916 
 917   // Expand and retry allocation
 918   result = loader_data->metaspace_non_null()->expand_and_allocate(size, mdtype);
 919   if (result != nullptr) {
 920     return result;
 921   }
 922 
 923   // Start full GC
 924   collect(GCCause::_metadata_GC_clear_soft_refs);
 925 
 926   // Retry allocation
 927   result = loader_data->metaspace_non_null()->allocate(size, mdtype);
 928   if (result != nullptr) {
 929     return result;
 930   }
 931 
 932   // Expand and retry allocation
 933   result = loader_data->metaspace_non_null()->expand_and_allocate(size, mdtype);
 934   if (result != nullptr) {
 935     return result;
 936   }
 937 
 938   // Out of memory
 939   return nullptr;
 940 }
 941 
 942 class ShenandoahConcurrentEvacuateRegionObjectClosure : public ObjectClosure {
 943 private:
 944   ShenandoahHeap* const _heap;
 945   Thread* const _thread;
 946 public:
 947   ShenandoahConcurrentEvacuateRegionObjectClosure(ShenandoahHeap* heap) :
 948     _heap(heap), _thread(Thread::current()) {}
 949 
 950   void do_object(oop p) {
 951     shenandoah_assert_marked(nullptr, p);
 952     if (!p->is_forwarded()) {
 953       _heap->evacuate_object(p, _thread);
 954     }
 955   }
 956 };
 957 
 958 class ShenandoahEvacuationTask : public WorkerTask {
 959 private:
 960   ShenandoahHeap* const _sh;
 961   ShenandoahCollectionSet* const _cs;
 962   bool _concurrent;
 963 public:
 964   ShenandoahEvacuationTask(ShenandoahHeap* sh,
 965                            ShenandoahCollectionSet* cs,
 966                            bool concurrent) :
 967     WorkerTask("Shenandoah Evacuation"),
 968     _sh(sh),
 969     _cs(cs),
 970     _concurrent(concurrent)
 971   {}
 972 
 973   void work(uint worker_id) {
 974     if (_concurrent) {
 975       ShenandoahConcurrentWorkerSession worker_session(worker_id);
 976       ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
 977       ShenandoahEvacOOMScope oom_evac_scope;
 978       do_work();
 979     } else {
 980       ShenandoahParallelWorkerSession worker_session(worker_id);
 981       ShenandoahEvacOOMScope oom_evac_scope;
 982       do_work();
 983     }
 984   }
 985 
 986 private:
 987   void do_work() {
 988     ShenandoahConcurrentEvacuateRegionObjectClosure cl(_sh);
 989     ShenandoahHeapRegion* r;
 990     while ((r =_cs->claim_next()) != nullptr) {
 991       assert(r->has_live(), "Region " SIZE_FORMAT " should have been reclaimed early", r->index());
 992       _sh->marked_object_iterate(r, &cl);
 993 
 994       if (ShenandoahPacing) {
 995         _sh->pacer()->report_evac(r->used() >> LogHeapWordSize);
 996       }
 997 
 998       if (_sh->check_cancelled_gc_and_yield(_concurrent)) {
 999         break;
1000       }
1001     }
1002   }
1003 };
1004 
1005 void ShenandoahHeap::evacuate_collection_set(bool concurrent) {
1006   ShenandoahEvacuationTask task(this, _collection_set, concurrent);
1007   workers()->run_task(&task);
1008 }
1009 
1010 void ShenandoahHeap::trash_cset_regions() {
1011   ShenandoahHeapLocker locker(lock());
1012 
1013   ShenandoahCollectionSet* set = collection_set();
1014   ShenandoahHeapRegion* r;
1015   set->clear_current_index();
1016   while ((r = set->next()) != nullptr) {
1017     r->make_trash();
1018   }
1019   collection_set()->clear();
1020 }
1021 
1022 void ShenandoahHeap::print_heap_regions_on(outputStream* st) const {
1023   st->print_cr("Heap Regions:");
1024   st->print_cr("EU=empty-uncommitted, EC=empty-committed, R=regular, H=humongous start, HC=humongous continuation, CS=collection set, T=trash, P=pinned");
1025   st->print_cr("BTE=bottom/top/end, U=used, T=TLAB allocs, G=GCLAB allocs, S=shared allocs, L=live data");
1026   st->print_cr("R=root, CP=critical pins, TAMS=top-at-mark-start, UWM=update watermark");
1027   st->print_cr("SN=alloc sequence number");
1028 
1029   for (size_t i = 0; i < num_regions(); i++) {
1030     get_region(i)->print_on(st);
1031   }
1032 }
1033 
1034 void ShenandoahHeap::trash_humongous_region_at(ShenandoahHeapRegion* start) {
1035   assert(start->is_humongous_start(), "reclaim regions starting with the first one");
1036 
1037   oop humongous_obj = cast_to_oop(start->bottom());
1038   size_t size = humongous_obj->size();
1039   size_t required_regions = ShenandoahHeapRegion::required_regions(size * HeapWordSize);
1040   size_t index = start->index() + required_regions - 1;
1041 
1042   assert(!start->has_live(), "liveness must be zero");
1043 
1044   for(size_t i = 0; i < required_regions; i++) {
1045     // Reclaim from tail. Otherwise, assertion fails when printing region to trace log,
1046     // as it expects that every region belongs to a humongous region starting with a humongous start region.
1047     ShenandoahHeapRegion* region = get_region(index --);
1048 
1049     assert(region->is_humongous(), "expect correct humongous start or continuation");
1050     assert(!region->is_cset(), "Humongous region should not be in collection set");
1051 
1052     region->make_trash_immediate();
1053   }
1054 }
1055 
1056 class ShenandoahCheckCleanGCLABClosure : public ThreadClosure {
1057 public:
1058   ShenandoahCheckCleanGCLABClosure() {}
1059   void do_thread(Thread* thread) {
1060     PLAB* gclab = ShenandoahThreadLocalData::gclab(thread);
1061     assert(gclab != nullptr, "GCLAB should be initialized for %s", thread->name());
1062     assert(gclab->words_remaining() == 0, "GCLAB should not need retirement");
1063   }
1064 };
1065 
1066 class ShenandoahRetireGCLABClosure : public ThreadClosure {
1067 private:
1068   bool const _resize;
1069 public:
1070   ShenandoahRetireGCLABClosure(bool resize) : _resize(resize) {}
1071   void do_thread(Thread* thread) {
1072     PLAB* gclab = ShenandoahThreadLocalData::gclab(thread);
1073     assert(gclab != nullptr, "GCLAB should be initialized for %s", thread->name());
1074     gclab->retire();
1075     if (_resize && ShenandoahThreadLocalData::gclab_size(thread) > 0) {
1076       ShenandoahThreadLocalData::set_gclab_size(thread, 0);
1077     }
1078   }
1079 };
1080 
1081 void ShenandoahHeap::labs_make_parsable() {
1082   assert(UseTLAB, "Only call with UseTLAB");
1083 
1084   ShenandoahRetireGCLABClosure cl(false);
1085 
1086   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
1087     ThreadLocalAllocBuffer& tlab = t->tlab();
1088     tlab.make_parsable();
1089     cl.do_thread(t);
1090   }
1091 
1092   workers()->threads_do(&cl);
1093 }
1094 
1095 void ShenandoahHeap::tlabs_retire(bool resize) {
1096   assert(UseTLAB, "Only call with UseTLAB");
1097   assert(!resize || ResizeTLAB, "Only call for resize when ResizeTLAB is enabled");
1098 
1099   ThreadLocalAllocStats stats;
1100 
1101   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
1102     ThreadLocalAllocBuffer& tlab = t->tlab();
1103     tlab.retire(&stats);
1104     if (resize) {
1105       tlab.resize();
1106     }
1107   }
1108 
1109   stats.publish();
1110 
1111 #ifdef ASSERT
1112   ShenandoahCheckCleanGCLABClosure cl;
1113   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
1114     cl.do_thread(t);
1115   }
1116   workers()->threads_do(&cl);
1117 #endif
1118 }
1119 
1120 void ShenandoahHeap::gclabs_retire(bool resize) {
1121   assert(UseTLAB, "Only call with UseTLAB");
1122   assert(!resize || ResizeTLAB, "Only call for resize when ResizeTLAB is enabled");
1123 
1124   ShenandoahRetireGCLABClosure cl(resize);
1125   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
1126     cl.do_thread(t);
1127   }
1128   workers()->threads_do(&cl);
1129 
1130   if (safepoint_workers() != nullptr) {
1131     safepoint_workers()->threads_do(&cl);
1132   }
1133 }
1134 
1135 // Returns size in bytes
1136 size_t ShenandoahHeap::unsafe_max_tlab_alloc(Thread *thread) const {
1137   if (ShenandoahElasticTLAB) {
1138     // With Elastic TLABs, return the max allowed size, and let the allocation path
1139     // figure out the safe size for current allocation.
1140     return ShenandoahHeapRegion::max_tlab_size_bytes();
1141   } else {
1142     return MIN2(_free_set->unsafe_peek_free(), ShenandoahHeapRegion::max_tlab_size_bytes());
1143   }
1144 }
1145 
1146 size_t ShenandoahHeap::max_tlab_size() const {
1147   // Returns size in words
1148   return ShenandoahHeapRegion::max_tlab_size_words();
1149 }
1150 
1151 void ShenandoahHeap::collect(GCCause::Cause cause) {
1152   control_thread()->request_gc(cause);
1153 }
1154 
1155 void ShenandoahHeap::do_full_collection(bool clear_all_soft_refs) {
1156   //assert(false, "Shouldn't need to do full collections");
1157 }
1158 
1159 HeapWord* ShenandoahHeap::block_start(const void* addr) const {
1160   ShenandoahHeapRegion* r = heap_region_containing(addr);
1161   if (r != nullptr) {
1162     return r->block_start(addr);
1163   }
1164   return nullptr;
1165 }
1166 
1167 bool ShenandoahHeap::block_is_obj(const HeapWord* addr) const {
1168   ShenandoahHeapRegion* r = heap_region_containing(addr);
1169   return r->block_is_obj(addr);
1170 }
1171 
1172 bool ShenandoahHeap::print_location(outputStream* st, void* addr) const {
1173   return BlockLocationPrinter<ShenandoahHeap>::print_location(st, addr);
1174 }
1175 
1176 void ShenandoahHeap::prepare_for_verify() {
1177   if (SafepointSynchronize::is_at_safepoint() && UseTLAB) {
1178     labs_make_parsable();
1179   }
1180 }
1181 
1182 void ShenandoahHeap::gc_threads_do(ThreadClosure* tcl) const {
1183   tcl->do_thread(_control_thread);
1184   workers()->threads_do(tcl);
1185   if (_safepoint_workers != nullptr) {
1186     _safepoint_workers->threads_do(tcl);
1187   }
1188 }
1189 
1190 void ShenandoahHeap::print_tracing_info() const {
1191   LogTarget(Info, gc, stats) lt;
1192   if (lt.is_enabled()) {
1193     ResourceMark rm;
1194     LogStream ls(lt);
1195 
1196     phase_timings()->print_global_on(&ls);
1197 
1198     ls.cr();
1199     ls.cr();
1200 
1201     shenandoah_policy()->print_gc_stats(&ls);
1202 
1203     ls.cr();
1204     ls.cr();
1205   }
1206 }
1207 
1208 void ShenandoahHeap::verify(VerifyOption vo) {
1209   if (ShenandoahSafepoint::is_at_shenandoah_safepoint()) {
1210     if (ShenandoahVerify) {
1211       verifier()->verify_generic(vo);
1212     } else {
1213       // TODO: Consider allocating verification bitmaps on demand,
1214       // and turn this on unconditionally.
1215     }
1216   }
1217 }
1218 size_t ShenandoahHeap::tlab_capacity(Thread *thr) const {
1219   return _free_set->capacity();
1220 }
1221 
1222 class ObjectIterateScanRootClosure : public BasicOopIterateClosure {
1223 private:
1224   MarkBitMap* _bitmap;
1225   ShenandoahScanObjectStack* _oop_stack;
1226   ShenandoahHeap* const _heap;
1227   ShenandoahMarkingContext* const _marking_context;
1228 
1229   template <class T>
1230   void do_oop_work(T* p) {
1231     T o = RawAccess<>::oop_load(p);
1232     if (!CompressedOops::is_null(o)) {
1233       oop obj = CompressedOops::decode_not_null(o);
1234       if (_heap->is_concurrent_weak_root_in_progress() && !_marking_context->is_marked(obj)) {
1235         // There may be dead oops in weak roots in concurrent root phase, do not touch them.
1236         return;
1237       }
1238       obj = ShenandoahBarrierSet::barrier_set()->load_reference_barrier(obj);
1239 
1240       assert(oopDesc::is_oop(obj), "must be a valid oop");
1241       if (!_bitmap->is_marked(obj)) {
1242         _bitmap->mark(obj);
1243         _oop_stack->push(obj);
1244       }
1245     }
1246   }
1247 public:
1248   ObjectIterateScanRootClosure(MarkBitMap* bitmap, ShenandoahScanObjectStack* oop_stack) :
1249     _bitmap(bitmap), _oop_stack(oop_stack), _heap(ShenandoahHeap::heap()),
1250     _marking_context(_heap->marking_context()) {}
1251   void do_oop(oop* p)       { do_oop_work(p); }
1252   void do_oop(narrowOop* p) { do_oop_work(p); }
1253 };
1254 
1255 /*
1256  * This is public API, used in preparation of object_iterate().
1257  * Since we don't do linear scan of heap in object_iterate() (see comment below), we don't
1258  * need to make the heap parsable. For Shenandoah-internal linear heap scans that we can
1259  * control, we call SH::tlabs_retire, SH::gclabs_retire.
1260  */
1261 void ShenandoahHeap::ensure_parsability(bool retire_tlabs) {
1262   // No-op.
1263 }
1264 
1265 /*
1266  * Iterates objects in the heap. This is public API, used for, e.g., heap dumping.
1267  *
1268  * We cannot safely iterate objects by doing a linear scan at random points in time. Linear
1269  * scanning needs to deal with dead objects, which may have dead Klass* pointers (e.g.
1270  * calling oopDesc::size() would crash) or dangling reference fields (crashes) etc. Linear
1271  * scanning therefore depends on having a valid marking bitmap to support it. However, we only
1272  * have a valid marking bitmap after successful marking. In particular, we *don't* have a valid
1273  * marking bitmap during marking, after aborted marking or during/after cleanup (when we just
1274  * wiped the bitmap in preparation for next marking).
1275  *
1276  * For all those reasons, we implement object iteration as a single marking traversal, reporting
1277  * objects as we mark+traverse through the heap, starting from GC roots. JVMTI IterateThroughHeap
1278  * is allowed to report dead objects, but is not required to do so.
1279  */
1280 void ShenandoahHeap::object_iterate(ObjectClosure* cl) {
1281   // Reset bitmap
1282   if (!prepare_aux_bitmap_for_iteration())
1283     return;
1284 
1285   ShenandoahScanObjectStack oop_stack;
1286   ObjectIterateScanRootClosure oops(&_aux_bit_map, &oop_stack);
1287   // Seed the stack with root scan
1288   scan_roots_for_iteration(&oop_stack, &oops);
1289 
1290   // Work through the oop stack to traverse heap
1291   while (! oop_stack.is_empty()) {
1292     oop obj = oop_stack.pop();
1293     assert(oopDesc::is_oop(obj), "must be a valid oop");
1294     cl->do_object(obj);
1295     obj->oop_iterate(&oops);
1296   }
1297 
1298   assert(oop_stack.is_empty(), "should be empty");
1299   // Reclaim bitmap
1300   reclaim_aux_bitmap_for_iteration();
1301 }
1302 
1303 bool ShenandoahHeap::prepare_aux_bitmap_for_iteration() {
1304   assert(SafepointSynchronize::is_at_safepoint(), "safe iteration is only available during safepoints");
1305 
1306   if (!_aux_bitmap_region_special && !os::commit_memory((char*)_aux_bitmap_region.start(), _aux_bitmap_region.byte_size(), false)) {
1307     log_warning(gc)("Could not commit native memory for auxiliary marking bitmap for heap iteration");
1308     return false;
1309   }
1310   // Reset bitmap
1311   _aux_bit_map.clear();
1312   return true;
1313 }
1314 
1315 void ShenandoahHeap::scan_roots_for_iteration(ShenandoahScanObjectStack* oop_stack, ObjectIterateScanRootClosure* oops) {
1316   // Process GC roots according to current GC cycle
1317   // This populates the work stack with initial objects
1318   // It is important to relinquish the associated locks before diving
1319   // into heap dumper
1320   uint n_workers = safepoint_workers() != nullptr ? safepoint_workers()->active_workers() : 1;
1321   ShenandoahHeapIterationRootScanner rp(n_workers);
1322   rp.roots_do(oops);
1323 }
1324 
1325 void ShenandoahHeap::reclaim_aux_bitmap_for_iteration() {
1326   if (!_aux_bitmap_region_special && !os::uncommit_memory((char*)_aux_bitmap_region.start(), _aux_bitmap_region.byte_size())) {
1327     log_warning(gc)("Could not uncommit native memory for auxiliary marking bitmap for heap iteration");
1328   }
1329 }
1330 
1331 // Closure for parallelly iterate objects
1332 class ShenandoahObjectIterateParScanClosure : public BasicOopIterateClosure {
1333 private:
1334   MarkBitMap* _bitmap;
1335   ShenandoahObjToScanQueue* _queue;
1336   ShenandoahHeap* const _heap;
1337   ShenandoahMarkingContext* const _marking_context;
1338 
1339   template <class T>
1340   void do_oop_work(T* p) {
1341     T o = RawAccess<>::oop_load(p);
1342     if (!CompressedOops::is_null(o)) {
1343       oop obj = CompressedOops::decode_not_null(o);
1344       if (_heap->is_concurrent_weak_root_in_progress() && !_marking_context->is_marked(obj)) {
1345         // There may be dead oops in weak roots in concurrent root phase, do not touch them.
1346         return;
1347       }
1348       obj = ShenandoahBarrierSet::barrier_set()->load_reference_barrier(obj);
1349 
1350       assert(oopDesc::is_oop(obj), "Must be a valid oop");
1351       if (_bitmap->par_mark(obj)) {
1352         _queue->push(ShenandoahMarkTask(obj));
1353       }
1354     }
1355   }
1356 public:
1357   ShenandoahObjectIterateParScanClosure(MarkBitMap* bitmap, ShenandoahObjToScanQueue* q) :
1358     _bitmap(bitmap), _queue(q), _heap(ShenandoahHeap::heap()),
1359     _marking_context(_heap->marking_context()) {}
1360   void do_oop(oop* p)       { do_oop_work(p); }
1361   void do_oop(narrowOop* p) { do_oop_work(p); }
1362 };
1363 
1364 // Object iterator for parallel heap iteraion.
1365 // The root scanning phase happenes in construction as a preparation of
1366 // parallel marking queues.
1367 // Every worker processes it's own marking queue. work-stealing is used
1368 // to balance workload.
1369 class ShenandoahParallelObjectIterator : public ParallelObjectIteratorImpl {
1370 private:
1371   uint                         _num_workers;
1372   bool                         _init_ready;
1373   MarkBitMap*                  _aux_bit_map;
1374   ShenandoahHeap*              _heap;
1375   ShenandoahScanObjectStack    _roots_stack; // global roots stack
1376   ShenandoahObjToScanQueueSet* _task_queues;
1377 public:
1378   ShenandoahParallelObjectIterator(uint num_workers, MarkBitMap* bitmap) :
1379         _num_workers(num_workers),
1380         _init_ready(false),
1381         _aux_bit_map(bitmap),
1382         _heap(ShenandoahHeap::heap()) {
1383     // Initialize bitmap
1384     _init_ready = _heap->prepare_aux_bitmap_for_iteration();
1385     if (!_init_ready) {
1386       return;
1387     }
1388 
1389     ObjectIterateScanRootClosure oops(_aux_bit_map, &_roots_stack);
1390     _heap->scan_roots_for_iteration(&_roots_stack, &oops);
1391 
1392     _init_ready = prepare_worker_queues();
1393   }
1394 
1395   ~ShenandoahParallelObjectIterator() {
1396     // Reclaim bitmap
1397     _heap->reclaim_aux_bitmap_for_iteration();
1398     // Reclaim queue for workers
1399     if (_task_queues!= nullptr) {
1400       for (uint i = 0; i < _num_workers; ++i) {
1401         ShenandoahObjToScanQueue* q = _task_queues->queue(i);
1402         if (q != nullptr) {
1403           delete q;
1404           _task_queues->register_queue(i, nullptr);
1405         }
1406       }
1407       delete _task_queues;
1408       _task_queues = nullptr;
1409     }
1410   }
1411 
1412   virtual void object_iterate(ObjectClosure* cl, uint worker_id) {
1413     if (_init_ready) {
1414       object_iterate_parallel(cl, worker_id, _task_queues);
1415     }
1416   }
1417 
1418 private:
1419   // Divide global root_stack into worker queues
1420   bool prepare_worker_queues() {
1421     _task_queues = new ShenandoahObjToScanQueueSet((int) _num_workers);
1422     // Initialize queues for every workers
1423     for (uint i = 0; i < _num_workers; ++i) {
1424       ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
1425       _task_queues->register_queue(i, task_queue);
1426     }
1427     // Divide roots among the workers. Assume that object referencing distribution
1428     // is related with root kind, use round-robin to make every worker have same chance
1429     // to process every kind of roots
1430     size_t roots_num = _roots_stack.size();
1431     if (roots_num == 0) {
1432       // No work to do
1433       return false;
1434     }
1435 
1436     for (uint j = 0; j < roots_num; j++) {
1437       uint stack_id = j % _num_workers;
1438       oop obj = _roots_stack.pop();
1439       _task_queues->queue(stack_id)->push(ShenandoahMarkTask(obj));
1440     }
1441     return true;
1442   }
1443 
1444   void object_iterate_parallel(ObjectClosure* cl,
1445                                uint worker_id,
1446                                ShenandoahObjToScanQueueSet* queue_set) {
1447     assert(SafepointSynchronize::is_at_safepoint(), "safe iteration is only available during safepoints");
1448     assert(queue_set != nullptr, "task queue must not be null");
1449 
1450     ShenandoahObjToScanQueue* q = queue_set->queue(worker_id);
1451     assert(q != nullptr, "object iterate queue must not be null");
1452 
1453     ShenandoahMarkTask t;
1454     ShenandoahObjectIterateParScanClosure oops(_aux_bit_map, q);
1455 
1456     // Work through the queue to traverse heap.
1457     // Steal when there is no task in queue.
1458     while (q->pop(t) || queue_set->steal(worker_id, t)) {
1459       oop obj = t.obj();
1460       assert(oopDesc::is_oop(obj), "must be a valid oop");
1461       cl->do_object(obj);
1462       obj->oop_iterate(&oops);
1463     }
1464     assert(q->is_empty(), "should be empty");
1465   }
1466 };
1467 
1468 ParallelObjectIteratorImpl* ShenandoahHeap::parallel_object_iterator(uint workers) {
1469   return new ShenandoahParallelObjectIterator(workers, &_aux_bit_map);
1470 }
1471 
1472 // Keep alive an object that was loaded with AS_NO_KEEPALIVE.
1473 void ShenandoahHeap::keep_alive(oop obj) {
1474   if (is_concurrent_mark_in_progress() && (obj != nullptr)) {
1475     ShenandoahBarrierSet::barrier_set()->enqueue(obj);
1476   }
1477 }
1478 
1479 void ShenandoahHeap::heap_region_iterate(ShenandoahHeapRegionClosure* blk) const {
1480   for (size_t i = 0; i < num_regions(); i++) {
1481     ShenandoahHeapRegion* current = get_region(i);
1482     blk->heap_region_do(current);
1483   }
1484 }
1485 
1486 class ShenandoahParallelHeapRegionTask : public WorkerTask {
1487 private:
1488   ShenandoahHeap* const _heap;
1489   ShenandoahHeapRegionClosure* const _blk;
1490 
1491   shenandoah_padding(0);
1492   volatile size_t _index;
1493   shenandoah_padding(1);
1494 
1495 public:
1496   ShenandoahParallelHeapRegionTask(ShenandoahHeapRegionClosure* blk) :
1497           WorkerTask("Shenandoah Parallel Region Operation"),
1498           _heap(ShenandoahHeap::heap()), _blk(blk), _index(0) {}
1499 
1500   void work(uint worker_id) {
1501     ShenandoahParallelWorkerSession worker_session(worker_id);
1502     size_t stride = ShenandoahParallelRegionStride;
1503 
1504     size_t max = _heap->num_regions();
1505     while (Atomic::load(&_index) < max) {
1506       size_t cur = Atomic::fetch_then_add(&_index, stride, memory_order_relaxed);
1507       size_t start = cur;
1508       size_t end = MIN2(cur + stride, max);
1509       if (start >= max) break;
1510 
1511       for (size_t i = cur; i < end; i++) {
1512         ShenandoahHeapRegion* current = _heap->get_region(i);
1513         _blk->heap_region_do(current);
1514       }
1515     }
1516   }
1517 };
1518 
1519 void ShenandoahHeap::parallel_heap_region_iterate(ShenandoahHeapRegionClosure* blk) const {
1520   assert(blk->is_thread_safe(), "Only thread-safe closures here");
1521   if (num_regions() > ShenandoahParallelRegionStride) {
1522     ShenandoahParallelHeapRegionTask task(blk);
1523     workers()->run_task(&task);
1524   } else {
1525     heap_region_iterate(blk);
1526   }
1527 }
1528 
1529 class ShenandoahInitMarkUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
1530 private:
1531   ShenandoahMarkingContext* const _ctx;
1532 public:
1533   ShenandoahInitMarkUpdateRegionStateClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
1534 
1535   void heap_region_do(ShenandoahHeapRegion* r) {
1536     assert(!r->has_live(), "Region " SIZE_FORMAT " should have no live data", r->index());
1537     if (r->is_active()) {
1538       // Check if region needs updating its TAMS. We have updated it already during concurrent
1539       // reset, so it is very likely we don't need to do another write here.
1540       if (_ctx->top_at_mark_start(r) != r->top()) {
1541         _ctx->capture_top_at_mark_start(r);
1542       }
1543     } else {
1544       assert(_ctx->top_at_mark_start(r) == r->top(),
1545              "Region " SIZE_FORMAT " should already have correct TAMS", r->index());
1546     }
1547   }
1548 
1549   bool is_thread_safe() { return true; }
1550 };
1551 
1552 class ShenandoahRendezvousClosure : public HandshakeClosure {
1553 public:
1554   inline ShenandoahRendezvousClosure() : HandshakeClosure("ShenandoahRendezvous") {}
1555   inline void do_thread(Thread* thread) {}
1556 };
1557 
1558 void ShenandoahHeap::rendezvous_threads() {
1559   ShenandoahRendezvousClosure cl;
1560   Handshake::execute(&cl);
1561 }
1562 
1563 void ShenandoahHeap::recycle_trash() {
1564   free_set()->recycle_trash();
1565 }
1566 
1567 class ShenandoahResetUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
1568 private:
1569   ShenandoahMarkingContext* const _ctx;
1570 public:
1571   ShenandoahResetUpdateRegionStateClosure() : _ctx(ShenandoahHeap::heap()->marking_context()) {}
1572 
1573   void heap_region_do(ShenandoahHeapRegion* r) {
1574     if (r->is_active()) {
1575       // Reset live data and set TAMS optimistically. We would recheck these under the pause
1576       // anyway to capture any updates that happened since now.
1577       r->clear_live_data();
1578       _ctx->capture_top_at_mark_start(r);
1579     }
1580   }
1581 
1582   bool is_thread_safe() { return true; }
1583 };
1584 
1585 void ShenandoahHeap::prepare_gc() {
1586   reset_mark_bitmap();
1587 
1588   ShenandoahResetUpdateRegionStateClosure cl;
1589   parallel_heap_region_iterate(&cl);
1590 }
1591 
1592 class ShenandoahFinalMarkUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
1593 private:
1594   ShenandoahMarkingContext* const _ctx;
1595   ShenandoahHeapLock* const _lock;
1596 
1597 public:
1598   ShenandoahFinalMarkUpdateRegionStateClosure() :
1599     _ctx(ShenandoahHeap::heap()->complete_marking_context()), _lock(ShenandoahHeap::heap()->lock()) {}
1600 
1601   void heap_region_do(ShenandoahHeapRegion* r) {
1602     if (r->is_active()) {
1603       // All allocations past TAMS are implicitly live, adjust the region data.
1604       // Bitmaps/TAMS are swapped at this point, so we need to poll complete bitmap.
1605       HeapWord *tams = _ctx->top_at_mark_start(r);
1606       HeapWord *top = r->top();
1607       if (top > tams) {
1608         r->increase_live_data_alloc_words(pointer_delta(top, tams));
1609       }
1610 
1611       // We are about to select the collection set, make sure it knows about
1612       // current pinning status. Also, this allows trashing more regions that
1613       // now have their pinning status dropped.
1614       if (r->is_pinned()) {
1615         if (r->pin_count() == 0) {
1616           ShenandoahHeapLocker locker(_lock);
1617           r->make_unpinned();
1618         }
1619       } else {
1620         if (r->pin_count() > 0) {
1621           ShenandoahHeapLocker locker(_lock);
1622           r->make_pinned();
1623         }
1624       }
1625 
1626       // Remember limit for updating refs. It's guaranteed that we get no
1627       // from-space-refs written from here on.
1628       r->set_update_watermark_at_safepoint(r->top());
1629     } else {
1630       assert(!r->has_live(), "Region " SIZE_FORMAT " should have no live data", r->index());
1631       assert(_ctx->top_at_mark_start(r) == r->top(),
1632              "Region " SIZE_FORMAT " should have correct TAMS", r->index());
1633     }
1634   }
1635 
1636   bool is_thread_safe() { return true; }
1637 };
1638 
1639 void ShenandoahHeap::prepare_regions_and_collection_set(bool concurrent) {
1640   assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
1641   {
1642     ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_update_region_states :
1643                                          ShenandoahPhaseTimings::degen_gc_final_update_region_states);
1644     ShenandoahFinalMarkUpdateRegionStateClosure cl;
1645     parallel_heap_region_iterate(&cl);
1646 
1647     assert_pinned_region_status();
1648   }
1649 
1650   {
1651     ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::choose_cset :
1652                                          ShenandoahPhaseTimings::degen_gc_choose_cset);
1653     ShenandoahHeapLocker locker(lock());
1654     _collection_set->clear();
1655     heuristics()->choose_collection_set(_collection_set);
1656   }
1657 
1658   {
1659     ShenandoahGCPhase phase(concurrent ? ShenandoahPhaseTimings::final_rebuild_freeset :
1660                                          ShenandoahPhaseTimings::degen_gc_final_rebuild_freeset);
1661     ShenandoahHeapLocker locker(lock());
1662     _free_set->rebuild();
1663   }
1664 }
1665 
1666 void ShenandoahHeap::do_class_unloading() {
1667   _unloader.unload();
1668 }
1669 
1670 void ShenandoahHeap::stw_weak_refs(bool full_gc) {
1671   // Weak refs processing
1672   ShenandoahPhaseTimings::Phase phase = full_gc ? ShenandoahPhaseTimings::full_gc_weakrefs
1673                                                 : ShenandoahPhaseTimings::degen_gc_weakrefs;
1674   ShenandoahTimingsTracker t(phase);
1675   ShenandoahGCWorkerPhase worker_phase(phase);
1676   ref_processor()->process_references(phase, workers(), false /* concurrent */);
1677 }
1678 
1679 void ShenandoahHeap::prepare_update_heap_references(bool concurrent) {
1680   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "must be at safepoint");
1681 
1682   // Evacuation is over, no GCLABs are needed anymore. GCLABs are under URWM, so we need to
1683   // make them parsable for update code to work correctly. Plus, we can compute new sizes
1684   // for future GCLABs here.
1685   if (UseTLAB) {
1686     ShenandoahGCPhase phase(concurrent ?
1687                             ShenandoahPhaseTimings::init_update_refs_manage_gclabs :
1688                             ShenandoahPhaseTimings::degen_gc_init_update_refs_manage_gclabs);
1689     gclabs_retire(ResizeTLAB);
1690   }
1691 
1692   _update_refs_iterator.reset();
1693 }
1694 
1695 void ShenandoahHeap::set_gc_state_all_threads(char state) {
1696   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
1697     ShenandoahThreadLocalData::set_gc_state(t, state);
1698   }
1699 }
1700 
1701 void ShenandoahHeap::set_gc_state_mask(uint mask, bool value) {
1702   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Should really be Shenandoah safepoint");
1703   _gc_state.set_cond(mask, value);
1704   set_gc_state_all_threads(_gc_state.raw_value());
1705 }
1706 
1707 void ShenandoahHeap::set_concurrent_mark_in_progress(bool in_progress) {
1708   assert(!has_forwarded_objects(), "Not expected before/after mark phase");
1709   set_gc_state_mask(MARKING, in_progress);
1710   ShenandoahBarrierSet::satb_mark_queue_set().set_active_all_threads(in_progress, !in_progress);
1711 }
1712 
1713 void ShenandoahHeap::set_evacuation_in_progress(bool in_progress) {
1714   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Only call this at safepoint");
1715   set_gc_state_mask(EVACUATION, in_progress);
1716 }
1717 
1718 void ShenandoahHeap::set_concurrent_strong_root_in_progress(bool in_progress) {
1719   if (in_progress) {
1720     _concurrent_strong_root_in_progress.set();
1721   } else {
1722     _concurrent_strong_root_in_progress.unset();
1723   }
1724 }
1725 
1726 void ShenandoahHeap::set_concurrent_weak_root_in_progress(bool cond) {
1727   set_gc_state_mask(WEAK_ROOTS, cond);
1728 }
1729 
1730 GCTracer* ShenandoahHeap::tracer() {
1731   return shenandoah_policy()->tracer();
1732 }
1733 
1734 size_t ShenandoahHeap::tlab_used(Thread* thread) const {
1735   return _free_set->used();
1736 }
1737 
1738 bool ShenandoahHeap::try_cancel_gc() {
1739   jbyte prev = _cancelled_gc.cmpxchg(CANCELLED, CANCELLABLE);
1740   return prev == CANCELLABLE;
1741 }
1742 
1743 void ShenandoahHeap::cancel_gc(GCCause::Cause cause) {
1744   if (try_cancel_gc()) {
1745     FormatBuffer<> msg("Cancelling GC: %s", GCCause::to_string(cause));
1746     log_info(gc)("%s", msg.buffer());
1747     Events::log(Thread::current(), "%s", msg.buffer());
1748   }
1749 }
1750 
1751 uint ShenandoahHeap::max_workers() {
1752   return _max_workers;
1753 }
1754 
1755 void ShenandoahHeap::stop() {
1756   // The shutdown sequence should be able to terminate when GC is running.
1757 
1758   // Step 0. Notify policy to disable event recording.
1759   _shenandoah_policy->record_shutdown();
1760 
1761   // Step 1. Notify control thread that we are in shutdown.
1762   // Note that we cannot do that with stop(), because stop() is blocking and waits for the actual shutdown.
1763   // Doing stop() here would wait for the normal GC cycle to complete, never falling through to cancel below.
1764   control_thread()->prepare_for_graceful_shutdown();
1765 
1766   // Step 2. Notify GC workers that we are cancelling GC.
1767   cancel_gc(GCCause::_shenandoah_stop_vm);
1768 
1769   // Step 3. Wait until GC worker exits normally.
1770   control_thread()->stop();
1771 }
1772 
1773 void ShenandoahHeap::stw_unload_classes(bool full_gc) {
1774   if (!unload_classes()) return;
1775   // Unload classes and purge SystemDictionary.
1776   {
1777     ShenandoahPhaseTimings::Phase phase = full_gc ?
1778                                           ShenandoahPhaseTimings::full_gc_purge_class_unload :
1779                                           ShenandoahPhaseTimings::degen_gc_purge_class_unload;
1780     ShenandoahIsAliveSelector is_alive;
1781     CodeCache::UnloadingScope scope(is_alive.is_alive_closure());
1782     ShenandoahGCPhase gc_phase(phase);
1783     ShenandoahGCWorkerPhase worker_phase(phase);
1784     bool purged_class = SystemDictionary::do_unloading(gc_timer());
1785 
1786     uint num_workers = _workers->active_workers();
1787     ShenandoahClassUnloadingTask unlink_task(phase, num_workers, purged_class);
1788     _workers->run_task(&unlink_task);
1789   }
1790 
1791   {
1792     ShenandoahGCPhase phase(full_gc ?
1793                             ShenandoahPhaseTimings::full_gc_purge_cldg :
1794                             ShenandoahPhaseTimings::degen_gc_purge_cldg);
1795     ClassLoaderDataGraph::purge(/*at_safepoint*/true);
1796   }
1797   // Resize and verify metaspace
1798   MetaspaceGC::compute_new_size();
1799   DEBUG_ONLY(MetaspaceUtils::verify();)
1800 }
1801 
1802 // Weak roots are either pre-evacuated (final mark) or updated (final updaterefs),
1803 // so they should not have forwarded oops.
1804 // However, we do need to "null" dead oops in the roots, if can not be done
1805 // in concurrent cycles.
1806 void ShenandoahHeap::stw_process_weak_roots(bool full_gc) {
1807   uint num_workers = _workers->active_workers();
1808   ShenandoahPhaseTimings::Phase timing_phase = full_gc ?
1809                                                ShenandoahPhaseTimings::full_gc_purge_weak_par :
1810                                                ShenandoahPhaseTimings::degen_gc_purge_weak_par;
1811   ShenandoahGCPhase phase(timing_phase);
1812   ShenandoahGCWorkerPhase worker_phase(timing_phase);
1813   // Cleanup weak roots
1814   if (has_forwarded_objects()) {
1815     ShenandoahForwardedIsAliveClosure is_alive;
1816     ShenandoahUpdateRefsClosure keep_alive;
1817     ShenandoahParallelWeakRootsCleaningTask<ShenandoahForwardedIsAliveClosure, ShenandoahUpdateRefsClosure>
1818       cleaning_task(timing_phase, &is_alive, &keep_alive, num_workers);
1819     _workers->run_task(&cleaning_task);
1820   } else {
1821     ShenandoahIsAliveClosure is_alive;
1822 #ifdef ASSERT
1823     ShenandoahAssertNotForwardedClosure verify_cl;
1824     ShenandoahParallelWeakRootsCleaningTask<ShenandoahIsAliveClosure, ShenandoahAssertNotForwardedClosure>
1825       cleaning_task(timing_phase, &is_alive, &verify_cl, num_workers);
1826 #else
1827     ShenandoahParallelWeakRootsCleaningTask<ShenandoahIsAliveClosure, DoNothingClosure>
1828       cleaning_task(timing_phase, &is_alive, &do_nothing_cl, num_workers);
1829 #endif
1830     _workers->run_task(&cleaning_task);
1831   }
1832 }
1833 
1834 void ShenandoahHeap::parallel_cleaning(bool full_gc) {
1835   assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
1836   assert(is_stw_gc_in_progress(), "Only for Degenerated and Full GC");
1837   ShenandoahGCPhase phase(full_gc ?
1838                           ShenandoahPhaseTimings::full_gc_purge :
1839                           ShenandoahPhaseTimings::degen_gc_purge);
1840   stw_weak_refs(full_gc);
1841   stw_process_weak_roots(full_gc);
1842   stw_unload_classes(full_gc);
1843 }
1844 
1845 void ShenandoahHeap::set_has_forwarded_objects(bool cond) {
1846   set_gc_state_mask(HAS_FORWARDED, cond);
1847 }
1848 
1849 void ShenandoahHeap::set_unload_classes(bool uc) {
1850   _unload_classes.set_cond(uc);
1851 }
1852 
1853 bool ShenandoahHeap::unload_classes() const {
1854   return _unload_classes.is_set();
1855 }
1856 
1857 address ShenandoahHeap::in_cset_fast_test_addr() {
1858   ShenandoahHeap* heap = ShenandoahHeap::heap();
1859   assert(heap->collection_set() != nullptr, "Sanity");
1860   return (address) heap->collection_set()->biased_map_address();
1861 }
1862 
1863 address ShenandoahHeap::cancelled_gc_addr() {
1864   return (address) ShenandoahHeap::heap()->_cancelled_gc.addr_of();
1865 }
1866 
1867 address ShenandoahHeap::gc_state_addr() {
1868   return (address) ShenandoahHeap::heap()->_gc_state.addr_of();
1869 }
1870 
1871 size_t ShenandoahHeap::bytes_allocated_since_gc_start() {
1872   return Atomic::load(&_bytes_allocated_since_gc_start);
1873 }
1874 
1875 void ShenandoahHeap::reset_bytes_allocated_since_gc_start() {
1876   Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
1877 }
1878 
1879 void ShenandoahHeap::set_degenerated_gc_in_progress(bool in_progress) {
1880   _degenerated_gc_in_progress.set_cond(in_progress);
1881 }
1882 
1883 void ShenandoahHeap::set_full_gc_in_progress(bool in_progress) {
1884   _full_gc_in_progress.set_cond(in_progress);
1885 }
1886 
1887 void ShenandoahHeap::set_full_gc_move_in_progress(bool in_progress) {
1888   assert (is_full_gc_in_progress(), "should be");
1889   _full_gc_move_in_progress.set_cond(in_progress);
1890 }
1891 
1892 void ShenandoahHeap::set_update_refs_in_progress(bool in_progress) {
1893   set_gc_state_mask(UPDATEREFS, in_progress);
1894 }
1895 
1896 void ShenandoahHeap::register_nmethod(nmethod* nm) {
1897   ShenandoahCodeRoots::register_nmethod(nm);
1898 }
1899 
1900 void ShenandoahHeap::unregister_nmethod(nmethod* nm) {
1901   ShenandoahCodeRoots::unregister_nmethod(nm);
1902 }
1903 
1904 void ShenandoahHeap::pin_object(JavaThread* thr, oop o) {
1905   heap_region_containing(o)->record_pin();
1906 }
1907 
1908 void ShenandoahHeap::unpin_object(JavaThread* thr, oop o) {
1909   ShenandoahHeapRegion* r = heap_region_containing(o);
1910   assert(r != nullptr, "Sanity");
1911   assert(r->pin_count() > 0, "Region " SIZE_FORMAT " should have non-zero pins", r->index());
1912   r->record_unpin();
1913 }
1914 
1915 void ShenandoahHeap::sync_pinned_region_status() {
1916   ShenandoahHeapLocker locker(lock());
1917 
1918   for (size_t i = 0; i < num_regions(); i++) {
1919     ShenandoahHeapRegion *r = get_region(i);
1920     if (r->is_active()) {
1921       if (r->is_pinned()) {
1922         if (r->pin_count() == 0) {
1923           r->make_unpinned();
1924         }
1925       } else {
1926         if (r->pin_count() > 0) {
1927           r->make_pinned();
1928         }
1929       }
1930     }
1931   }
1932 
1933   assert_pinned_region_status();
1934 }
1935 
1936 #ifdef ASSERT
1937 void ShenandoahHeap::assert_pinned_region_status() {
1938   for (size_t i = 0; i < num_regions(); i++) {
1939     ShenandoahHeapRegion* r = get_region(i);
1940     assert((r->is_pinned() && r->pin_count() > 0) || (!r->is_pinned() && r->pin_count() == 0),
1941            "Region " SIZE_FORMAT " pinning status is inconsistent", i);
1942   }
1943 }
1944 #endif
1945 
1946 ConcurrentGCTimer* ShenandoahHeap::gc_timer() const {
1947   return _gc_timer;
1948 }
1949 
1950 void ShenandoahHeap::prepare_concurrent_roots() {
1951   assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
1952   assert(!is_stw_gc_in_progress(), "Only concurrent GC");
1953   set_concurrent_strong_root_in_progress(!collection_set()->is_empty());
1954   set_concurrent_weak_root_in_progress(true);
1955   if (unload_classes()) {
1956     _unloader.prepare();
1957   }
1958 }
1959 
1960 void ShenandoahHeap::finish_concurrent_roots() {
1961   assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
1962   assert(!is_stw_gc_in_progress(), "Only concurrent GC");
1963   if (unload_classes()) {
1964     _unloader.finish();
1965   }
1966 }
1967 
1968 #ifdef ASSERT
1969 void ShenandoahHeap::assert_gc_workers(uint nworkers) {
1970   assert(nworkers > 0 && nworkers <= max_workers(), "Sanity");
1971 
1972   if (ShenandoahSafepoint::is_at_shenandoah_safepoint()) {
1973     if (UseDynamicNumberOfGCThreads) {
1974       assert(nworkers <= ParallelGCThreads, "Cannot use more than it has");
1975     } else {
1976       // Use ParallelGCThreads inside safepoints
1977       assert(nworkers == ParallelGCThreads, "Use ParallelGCThreads within safepoints");
1978     }
1979   } else {
1980     if (UseDynamicNumberOfGCThreads) {
1981       assert(nworkers <= ConcGCThreads, "Cannot use more than it has");
1982     } else {
1983       // Use ConcGCThreads outside safepoints
1984       assert(nworkers == ConcGCThreads, "Use ConcGCThreads outside safepoints");
1985     }
1986   }
1987 }
1988 #endif
1989 
1990 ShenandoahVerifier* ShenandoahHeap::verifier() {
1991   guarantee(ShenandoahVerify, "Should be enabled");
1992   assert (_verifier != nullptr, "sanity");
1993   return _verifier;
1994 }
1995 
1996 template<bool CONCURRENT>
1997 class ShenandoahUpdateHeapRefsTask : public WorkerTask {
1998 private:
1999   ShenandoahHeap* _heap;
2000   ShenandoahRegionIterator* _regions;
2001 public:
2002   ShenandoahUpdateHeapRefsTask(ShenandoahRegionIterator* regions) :
2003     WorkerTask("Shenandoah Update References"),
2004     _heap(ShenandoahHeap::heap()),
2005     _regions(regions) {
2006   }
2007 
2008   void work(uint worker_id) {
2009     if (CONCURRENT) {
2010       ShenandoahConcurrentWorkerSession worker_session(worker_id);
2011       ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
2012       do_work<ShenandoahConcUpdateRefsClosure>();
2013     } else {
2014       ShenandoahParallelWorkerSession worker_session(worker_id);
2015       do_work<ShenandoahSTWUpdateRefsClosure>();
2016     }
2017   }
2018 
2019 private:
2020   template<class T>
2021   void do_work() {
2022     T cl;
2023     ShenandoahHeapRegion* r = _regions->next();
2024     ShenandoahMarkingContext* const ctx = _heap->complete_marking_context();
2025     while (r != nullptr) {
2026       HeapWord* update_watermark = r->get_update_watermark();
2027       assert (update_watermark >= r->bottom(), "sanity");
2028       if (r->is_active() && !r->is_cset()) {
2029         _heap->marked_object_oop_iterate(r, &cl, update_watermark);
2030       }
2031       if (ShenandoahPacing) {
2032         _heap->pacer()->report_updaterefs(pointer_delta(update_watermark, r->bottom()));
2033       }
2034       if (_heap->check_cancelled_gc_and_yield(CONCURRENT)) {
2035         return;
2036       }
2037       r = _regions->next();
2038     }
2039   }
2040 };
2041 
2042 void ShenandoahHeap::update_heap_references(bool concurrent) {
2043   assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
2044 
2045   if (concurrent) {
2046     ShenandoahUpdateHeapRefsTask<true> task(&_update_refs_iterator);
2047     workers()->run_task(&task);
2048   } else {
2049     ShenandoahUpdateHeapRefsTask<false> task(&_update_refs_iterator);
2050     workers()->run_task(&task);
2051   }
2052 }
2053 
2054 
2055 class ShenandoahFinalUpdateRefsUpdateRegionStateClosure : public ShenandoahHeapRegionClosure {
2056 private:
2057   ShenandoahHeapLock* const _lock;
2058 
2059 public:
2060   ShenandoahFinalUpdateRefsUpdateRegionStateClosure() : _lock(ShenandoahHeap::heap()->lock()) {}
2061 
2062   void heap_region_do(ShenandoahHeapRegion* r) {
2063     // Drop unnecessary "pinned" state from regions that does not have CP marks
2064     // anymore, as this would allow trashing them.
2065 
2066     if (r->is_active()) {
2067       if (r->is_pinned()) {
2068         if (r->pin_count() == 0) {
2069           ShenandoahHeapLocker locker(_lock);
2070           r->make_unpinned();
2071         }
2072       } else {
2073         if (r->pin_count() > 0) {
2074           ShenandoahHeapLocker locker(_lock);
2075           r->make_pinned();
2076         }
2077       }
2078     }
2079   }
2080 
2081   bool is_thread_safe() { return true; }
2082 };
2083 
2084 void ShenandoahHeap::update_heap_region_states(bool concurrent) {
2085   assert(SafepointSynchronize::is_at_safepoint(), "Must be at a safepoint");
2086   assert(!is_full_gc_in_progress(), "Only for concurrent and degenerated GC");
2087 
2088   {
2089     ShenandoahGCPhase phase(concurrent ?
2090                             ShenandoahPhaseTimings::final_update_refs_update_region_states :
2091                             ShenandoahPhaseTimings::degen_gc_final_update_refs_update_region_states);
2092     ShenandoahFinalUpdateRefsUpdateRegionStateClosure cl;
2093     parallel_heap_region_iterate(&cl);
2094 
2095     assert_pinned_region_status();
2096   }
2097 
2098   {
2099     ShenandoahGCPhase phase(concurrent ?
2100                             ShenandoahPhaseTimings::final_update_refs_trash_cset :
2101                             ShenandoahPhaseTimings::degen_gc_final_update_refs_trash_cset);
2102     trash_cset_regions();
2103   }
2104 }
2105 
2106 void ShenandoahHeap::rebuild_free_set(bool concurrent) {
2107   {
2108     ShenandoahGCPhase phase(concurrent ?
2109                             ShenandoahPhaseTimings::final_update_refs_rebuild_freeset :
2110                             ShenandoahPhaseTimings::degen_gc_final_update_refs_rebuild_freeset);
2111     ShenandoahHeapLocker locker(lock());
2112     _free_set->rebuild();
2113   }
2114 }
2115 
2116 void ShenandoahHeap::print_extended_on(outputStream *st) const {
2117   print_on(st);
2118   print_heap_regions_on(st);
2119 }
2120 
2121 bool ShenandoahHeap::is_bitmap_slice_committed(ShenandoahHeapRegion* r, bool skip_self) {
2122   size_t slice = r->index() / _bitmap_regions_per_slice;
2123 
2124   size_t regions_from = _bitmap_regions_per_slice * slice;
2125   size_t regions_to   = MIN2(num_regions(), _bitmap_regions_per_slice * (slice + 1));
2126   for (size_t g = regions_from; g < regions_to; g++) {
2127     assert (g / _bitmap_regions_per_slice == slice, "same slice");
2128     if (skip_self && g == r->index()) continue;
2129     if (get_region(g)->is_committed()) {
2130       return true;
2131     }
2132   }
2133   return false;
2134 }
2135 
2136 bool ShenandoahHeap::commit_bitmap_slice(ShenandoahHeapRegion* r) {
2137   shenandoah_assert_heaplocked();
2138 
2139   // Bitmaps in special regions do not need commits
2140   if (_bitmap_region_special) {
2141     return true;
2142   }
2143 
2144   if (is_bitmap_slice_committed(r, true)) {
2145     // Some other region from the group is already committed, meaning the bitmap
2146     // slice is already committed, we exit right away.
2147     return true;
2148   }
2149 
2150   // Commit the bitmap slice:
2151   size_t slice = r->index() / _bitmap_regions_per_slice;
2152   size_t off = _bitmap_bytes_per_slice * slice;
2153   size_t len = _bitmap_bytes_per_slice;
2154   char* start = (char*) _bitmap_region.start() + off;
2155 
2156   if (!os::commit_memory(start, len, false)) {
2157     return false;
2158   }
2159 
2160   if (AlwaysPreTouch) {
2161     os::pretouch_memory(start, start + len, _pretouch_bitmap_page_size);
2162   }
2163 
2164   return true;
2165 }
2166 
2167 bool ShenandoahHeap::uncommit_bitmap_slice(ShenandoahHeapRegion *r) {
2168   shenandoah_assert_heaplocked();
2169 
2170   // Bitmaps in special regions do not need uncommits
2171   if (_bitmap_region_special) {
2172     return true;
2173   }
2174 
2175   if (is_bitmap_slice_committed(r, true)) {
2176     // Some other region from the group is still committed, meaning the bitmap
2177     // slice is should stay committed, exit right away.
2178     return true;
2179   }
2180 
2181   // Uncommit the bitmap slice:
2182   size_t slice = r->index() / _bitmap_regions_per_slice;
2183   size_t off = _bitmap_bytes_per_slice * slice;
2184   size_t len = _bitmap_bytes_per_slice;
2185   if (!os::uncommit_memory((char*)_bitmap_region.start() + off, len)) {
2186     return false;
2187   }
2188   return true;
2189 }
2190 
2191 void ShenandoahHeap::safepoint_synchronize_begin() {
2192   if (ShenandoahSuspendibleWorkers) {
2193     SuspendibleThreadSet::synchronize();
2194   }
2195 }
2196 
2197 void ShenandoahHeap::safepoint_synchronize_end() {
2198   if (ShenandoahSuspendibleWorkers) {
2199     SuspendibleThreadSet::desynchronize();
2200   }
2201 }
2202 
2203 void ShenandoahHeap::entry_uncommit(double shrink_before, size_t shrink_until) {
2204   static const char *msg = "Concurrent uncommit";
2205   ShenandoahConcurrentPhase gc_phase(msg, ShenandoahPhaseTimings::conc_uncommit, true /* log_heap_usage */);
2206   EventMark em("%s", msg);
2207 
2208   op_uncommit(shrink_before, shrink_until);
2209 }
2210 
2211 void ShenandoahHeap::try_inject_alloc_failure() {
2212   if (ShenandoahAllocFailureALot && !cancelled_gc() && ((os::random() % 1000) > 950)) {
2213     _inject_alloc_failure.set();
2214     os::naked_short_sleep(1);
2215     if (cancelled_gc()) {
2216       log_info(gc)("Allocation failure was successfully injected");
2217     }
2218   }
2219 }
2220 
2221 bool ShenandoahHeap::should_inject_alloc_failure() {
2222   return _inject_alloc_failure.is_set() && _inject_alloc_failure.try_unset();
2223 }
2224 
2225 void ShenandoahHeap::initialize_serviceability() {
2226   _memory_pool = new ShenandoahMemoryPool(this);
2227   _cycle_memory_manager.add_pool(_memory_pool);
2228   _stw_memory_manager.add_pool(_memory_pool);
2229 }
2230 
2231 GrowableArray<GCMemoryManager*> ShenandoahHeap::memory_managers() {
2232   GrowableArray<GCMemoryManager*> memory_managers(2);
2233   memory_managers.append(&_cycle_memory_manager);
2234   memory_managers.append(&_stw_memory_manager);
2235   return memory_managers;
2236 }
2237 
2238 GrowableArray<MemoryPool*> ShenandoahHeap::memory_pools() {
2239   GrowableArray<MemoryPool*> memory_pools(1);
2240   memory_pools.append(_memory_pool);
2241   return memory_pools;
2242 }
2243 
2244 MemoryUsage ShenandoahHeap::memory_usage() {
2245   return _memory_pool->get_memory_usage();
2246 }
2247 
2248 ShenandoahRegionIterator::ShenandoahRegionIterator() :
2249   _heap(ShenandoahHeap::heap()),
2250   _index(0) {}
2251 
2252 ShenandoahRegionIterator::ShenandoahRegionIterator(ShenandoahHeap* heap) :
2253   _heap(heap),
2254   _index(0) {}
2255 
2256 void ShenandoahRegionIterator::reset() {
2257   _index = 0;
2258 }
2259 
2260 bool ShenandoahRegionIterator::has_next() const {
2261   return _index < _heap->num_regions();
2262 }
2263 
2264 char ShenandoahHeap::gc_state() const {
2265   return _gc_state.raw_value();
2266 }
2267 
2268 ShenandoahLiveData* ShenandoahHeap::get_liveness_cache(uint worker_id) {
2269 #ifdef ASSERT
2270   assert(_liveness_cache != nullptr, "sanity");
2271   assert(worker_id < _max_workers, "sanity");
2272   for (uint i = 0; i < num_regions(); i++) {
2273     assert(_liveness_cache[worker_id][i] == 0, "liveness cache should be empty");
2274   }
2275 #endif
2276   return _liveness_cache[worker_id];
2277 }
2278 
2279 void ShenandoahHeap::flush_liveness_cache(uint worker_id) {
2280   assert(worker_id < _max_workers, "sanity");
2281   assert(_liveness_cache != nullptr, "sanity");
2282   ShenandoahLiveData* ld = _liveness_cache[worker_id];
2283   for (uint i = 0; i < num_regions(); i++) {
2284     ShenandoahLiveData live = ld[i];
2285     if (live > 0) {
2286       ShenandoahHeapRegion* r = get_region(i);
2287       r->increase_live_data_gc_words(live);
2288       ld[i] = 0;
2289     }
2290   }
2291 }
2292 
2293 bool ShenandoahHeap::requires_barriers(stackChunkOop obj) const {
2294   if (is_idle()) return false;
2295 
2296   // Objects allocated after marking start are implicitly alive, don't need any barriers during
2297   // marking phase.
2298   if (is_concurrent_mark_in_progress() &&
2299      !marking_context()->allocated_after_mark_start(obj)) {
2300     return true;
2301   }
2302 
2303   // Can not guarantee obj is deeply good.
2304   if (has_forwarded_objects()) {
2305     return true;
2306   }
2307 
2308   return false;
2309 }