1 /*
   2  * Copyright (c) 2013, 2019, Red Hat, Inc. All rights reserved.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This code is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  11  * version 2 for more details (a copy is included in the LICENSE file that
  12  * accompanied this code).
  13  *
  14  * You should have received a copy of the GNU General Public License version
  15  * 2 along with this work; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  17  *
  18  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  19  * or visit www.oracle.com if you need additional information or have any
  20  * questions.
  21  *
  22  */
  23 
  24 #include "precompiled.hpp"
  25 
  26 #include "classfile/symbolTable.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "code/codeCache.hpp"
  29 
  30 #include "gc/shared/weakProcessor.inline.hpp"
  31 #include "gc/shared/gcTimer.hpp"
  32 #include "gc/shared/referenceProcessor.hpp"
  33 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  34 
  35 #include "gc/shenandoah/shenandoahBarrierSet.inline.hpp"
  36 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
  37 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
  38 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
  39 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  40 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  41 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
  42 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
  43 #include "gc/shenandoah/shenandoahTimingTracker.hpp"
  44 #include "gc/shenandoah/shenandoahUtils.hpp"
  45 
  46 #include "memory/iterator.inline.hpp"
  47 #include "memory/metaspace.hpp"
  48 #include "memory/resourceArea.hpp"
  49 #include "oops/oop.inline.hpp"
  50 #include "runtime/handles.inline.hpp"
  51 
  52 template<UpdateRefsMode UPDATE_REFS>
  53 class ShenandoahInitMarkRootsClosure : public OopClosure {
  54 private:
  55   ShenandoahObjToScanQueue* _queue;
  56   ShenandoahHeap* _heap;
  57   ShenandoahMarkingContext* const _mark_context;
  58 
  59   template <class T>
  60   inline void do_oop_work(T* p) {
  61     ShenandoahConcurrentMark::mark_through_ref<T, UPDATE_REFS, NO_DEDUP>(p, _heap, _queue, _mark_context);
  62   }
  63 
  64 public:
  65   ShenandoahInitMarkRootsClosure(ShenandoahObjToScanQueue* q) :
  66     _queue(q),
  67     _heap(ShenandoahHeap::heap()),
  68     _mark_context(_heap->marking_context()) {};
  69 
  70   void do_oop(narrowOop* p) { do_oop_work(p); }
  71   void do_oop(oop* p)       { do_oop_work(p); }
  72 };
  73 
  74 ShenandoahMarkRefsSuperClosure::ShenandoahMarkRefsSuperClosure(ShenandoahObjToScanQueue* q, ReferenceProcessor* rp) :
  75   MetadataVisitingOopIterateClosure(rp),
  76   _queue(q),
  77   _heap(ShenandoahHeap::heap()),
  78   _mark_context(_heap->marking_context())
  79 { }
  80 
  81 template<UpdateRefsMode UPDATE_REFS>
  82 class ShenandoahInitMarkRootsTask : public AbstractGangTask {
  83 private:
  84   ShenandoahAllRootScanner* _rp;
  85   bool _process_refs;
  86 public:
  87   ShenandoahInitMarkRootsTask(ShenandoahAllRootScanner* rp, bool process_refs) :
  88     AbstractGangTask("Shenandoah init mark roots task"),
  89     _rp(rp),
  90     _process_refs(process_refs) {
  91   }
  92 
  93   void work(uint worker_id) {
  94     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
  95     ShenandoahParallelWorkerSession worker_session(worker_id);
  96 
  97     ShenandoahHeap* heap = ShenandoahHeap::heap();
  98     ShenandoahObjToScanQueueSet* queues = heap->concurrent_mark()->task_queues();
  99     assert(queues->get_reserved() > worker_id, "Queue has not been reserved for worker id: %d", worker_id);
 100 
 101     ShenandoahObjToScanQueue* q = queues->queue(worker_id);
 102 
 103     ShenandoahInitMarkRootsClosure<UPDATE_REFS> mark_cl(q);
 104     do_work(heap, &mark_cl, worker_id);
 105   }
 106 
 107 private:
 108   void do_work(ShenandoahHeap* heap, OopClosure* oops, uint worker_id) {
 109     // The rationale for selecting the roots to scan is as follows:
 110     //   a. With unload_classes = true, we only want to scan the actual strong roots from the
 111     //      code cache. This will allow us to identify the dead classes, unload them, *and*
 112     //      invalidate the relevant code cache blobs. This could be only done together with
 113     //      class unloading.
 114     //   b. With unload_classes = false, we have to nominally retain all the references from code
 115     //      cache, because there could be the case of embedded class/oop in the generated code,
 116     //      which we will never visit during mark. Without code cache invalidation, as in (a),
 117     //      we risk executing that code cache blob, and crashing.
 118     if (heap->unload_classes()) {
 119       _rp->strong_roots_do(worker_id, oops);
 120     } else {
 121       _rp->roots_do(worker_id, oops);
 122     }
 123   }
 124 };
 125 
 126 class ShenandoahUpdateRootsTask : public AbstractGangTask {
 127 private:
 128   ShenandoahRootUpdater*  _root_updater;
 129 public:
 130   ShenandoahUpdateRootsTask(ShenandoahRootUpdater* root_updater) :
 131     AbstractGangTask("Shenandoah update roots task"),
 132     _root_updater(root_updater) {
 133   }
 134 
 135   void work(uint worker_id) {
 136     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 137     ShenandoahParallelWorkerSession worker_session(worker_id);
 138 
 139     ShenandoahHeap* heap = ShenandoahHeap::heap();
 140     ShenandoahUpdateRefsClosure cl;
 141     AlwaysTrueClosure always_true;
 142     _root_updater->roots_do<AlwaysTrueClosure, ShenandoahUpdateRefsClosure>(worker_id, &always_true, &cl);
 143   }
 144 };
 145 
 146 class ShenandoahConcurrentMarkingTask : public AbstractGangTask {
 147 private:
 148   ShenandoahConcurrentMark* _cm;
 149   ShenandoahTaskTerminator* _terminator;
 150 
 151 public:
 152   ShenandoahConcurrentMarkingTask(ShenandoahConcurrentMark* cm, ShenandoahTaskTerminator* terminator) :
 153     AbstractGangTask("Root Region Scan"), _cm(cm), _terminator(terminator) {
 154   }
 155 
 156   void work(uint worker_id) {
 157     ShenandoahHeap* heap = ShenandoahHeap::heap();
 158     ShenandoahConcurrentWorkerSession worker_session(worker_id);
 159     ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
 160     ShenandoahObjToScanQueue* q = _cm->get_queue(worker_id);
 161     ReferenceProcessor* rp;
 162     if (heap->process_references()) {
 163       rp = heap->ref_processor();
 164       shenandoah_assert_rp_isalive_installed();
 165     } else {
 166       rp = NULL;
 167     }
 168 
 169     _cm->concurrent_scan_code_roots(worker_id, rp);
 170     _cm->mark_loop(worker_id, _terminator, rp,
 171                    true, // cancellable
 172                    ShenandoahStringDedup::is_enabled()); // perform string dedup
 173   }
 174 };
 175 
 176 class ShenandoahSATBThreadsClosure : public ThreadClosure {
 177 private:
 178   ShenandoahSATBBufferClosure* _satb_cl;
 179   uintx _claim_token;
 180 
 181 public:
 182   ShenandoahSATBThreadsClosure(ShenandoahSATBBufferClosure* satb_cl) :
 183     _satb_cl(satb_cl),
 184     _claim_token(Threads::thread_claim_token()) {}
 185 
 186   void do_thread(Thread* thread) {
 187     if (thread->claim_threads_do(true, _claim_token)) {
 188       ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
 189     }
 190   }
 191 };
 192 
 193 class ShenandoahFinalMarkingTask : public AbstractGangTask {
 194 private:
 195   ShenandoahConcurrentMark* _cm;
 196   ShenandoahTaskTerminator* _terminator;
 197   bool _dedup_string;
 198 
 199 public:
 200   ShenandoahFinalMarkingTask(ShenandoahConcurrentMark* cm, ShenandoahTaskTerminator* terminator, bool dedup_string) :
 201     AbstractGangTask("Shenandoah Final Marking"), _cm(cm), _terminator(terminator), _dedup_string(dedup_string) {
 202   }
 203 
 204   void work(uint worker_id) {
 205     ShenandoahHeap* heap = ShenandoahHeap::heap();
 206 
 207     ShenandoahParallelWorkerSession worker_session(worker_id);
 208     // First drain remaining SATB buffers.
 209     // Notice that this is not strictly necessary for mark-compact. But since
 210     // it requires a StrongRootsScope around the task, we need to claim the
 211     // threads, and performance-wise it doesn't really matter. Adds about 1ms to
 212     // full-gc.
 213     {
 214       ShenandoahObjToScanQueue* q = _cm->get_queue(worker_id);
 215       ShenandoahSATBBufferClosure cl(q);
 216       SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
 217       while (satb_mq_set.apply_closure_to_completed_buffer(&cl));
 218       ShenandoahSATBThreadsClosure tc(&cl);
 219       Threads::threads_do(&tc);
 220     }
 221 
 222     ReferenceProcessor* rp;
 223     if (heap->process_references()) {
 224       rp = heap->ref_processor();
 225       shenandoah_assert_rp_isalive_installed();
 226     } else {
 227       rp = NULL;
 228     }
 229 
 230     if (heap->is_degenerated_gc_in_progress()) {
 231       // Degenerated cycle may bypass concurrent cycle, so code roots might not be scanned,
 232       // let's check here.
 233       _cm->concurrent_scan_code_roots(worker_id, rp);
 234     }
 235 
 236     _cm->mark_loop(worker_id, _terminator, rp,
 237                    false, // not cancellable
 238                    _dedup_string);
 239 
 240     assert(_cm->task_queues()->is_empty(), "Should be empty");
 241   }
 242 };
 243 
 244 void ShenandoahConcurrentMark::mark_roots(ShenandoahPhaseTimings::Phase root_phase) {
 245   assert(Thread::current()->is_VM_thread(), "can only do this in VMThread");
 246   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 247 
 248   ShenandoahHeap* heap = ShenandoahHeap::heap();
 249 
 250   ShenandoahGCPhase phase(root_phase);
 251 
 252   WorkGang* workers = heap->workers();
 253   uint nworkers = workers->active_workers();
 254 
 255   assert(nworkers <= task_queues()->size(), "Just check");
 256 
 257   ShenandoahAllRootScanner root_proc(nworkers, root_phase);
 258   TASKQUEUE_STATS_ONLY(task_queues()->reset_taskqueue_stats());
 259   task_queues()->reserve(nworkers);
 260 
 261   if (heap->has_forwarded_objects()) {
 262     ShenandoahInitMarkRootsTask<RESOLVE> mark_roots(&root_proc, _heap->process_references());
 263     workers->run_task(&mark_roots);
 264   } else {
 265     // No need to update references, which means the heap is stable.
 266     // Can save time not walking through forwarding pointers.
 267     ShenandoahInitMarkRootsTask<NONE> mark_roots(&root_proc, _heap->process_references());
 268     workers->run_task(&mark_roots);
 269   }
 270 
 271   if (ShenandoahConcurrentScanCodeRoots) {
 272     clear_claim_codecache();
 273   }
 274 }
 275 
 276 void ShenandoahConcurrentMark::update_roots(ShenandoahPhaseTimings::Phase root_phase) {
 277   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 278 
 279   bool update_code_cache = true; // initialize to safer value
 280   switch (root_phase) {
 281     case ShenandoahPhaseTimings::update_roots:
 282     case ShenandoahPhaseTimings::final_update_refs_roots:
 283       update_code_cache = false;
 284       break;
 285     case ShenandoahPhaseTimings::full_gc_roots:
 286     case ShenandoahPhaseTimings::degen_gc_update_roots:
 287       update_code_cache = true;
 288       break;
 289     default:
 290       ShouldNotReachHere();
 291   }
 292 
 293   ShenandoahGCPhase phase(root_phase);
 294 
 295 #if defined(COMPILER2) || INCLUDE_JVMCI
 296   DerivedPointerTable::clear();
 297 #endif
 298 
 299   uint nworkers = _heap->workers()->active_workers();
 300 
 301   ShenandoahRootUpdater root_updater(nworkers, root_phase, update_code_cache);
 302   ShenandoahUpdateRootsTask update_roots(&root_updater);
 303   _heap->workers()->run_task(&update_roots);
 304 
 305 #if defined(COMPILER2) || INCLUDE_JVMCI
 306   DerivedPointerTable::update_pointers();
 307 #endif
 308 }
 309 
 310 class ShenandoahUpdateThreadRootsTask : public AbstractGangTask {
 311 private:
 312   ShenandoahThreadRoots           _thread_roots;
 313   ShenandoahPhaseTimings::Phase   _phase;
 314 public:
 315   ShenandoahUpdateThreadRootsTask(bool is_par, ShenandoahPhaseTimings::Phase phase) :
 316     AbstractGangTask("Shenandoah Update Thread Roots"),
 317     _thread_roots(is_par),
 318     _phase(phase) {
 319     ShenandoahHeap::heap()->phase_timings()->record_workers_start(_phase);
 320   }
 321 
 322   ~ShenandoahUpdateThreadRootsTask() {
 323     ShenandoahHeap::heap()->phase_timings()->record_workers_end(_phase);
 324   }
 325   void work(uint worker_id) {
 326     ShenandoahUpdateRefsClosure cl;
 327     _thread_roots.oops_do(&cl, NULL, worker_id);
 328   }
 329 };
 330 
 331 void ShenandoahConcurrentMark::update_thread_roots(ShenandoahPhaseTimings::Phase root_phase) {
 332   WorkGang* workers = _heap->workers();
 333   bool is_par = workers->active_workers() > 1;
 334   ShenandoahUpdateThreadRootsTask task(is_par, root_phase);
 335   workers->run_task(&task);
 336 }
 337 
 338 void ShenandoahConcurrentMark::initialize(uint workers) {
 339   _heap = ShenandoahHeap::heap();
 340 
 341   uint num_queues = MAX2(workers, 1U);
 342 
 343   _task_queues = new ShenandoahObjToScanQueueSet((int) num_queues);
 344 
 345   for (uint i = 0; i < num_queues; ++i) {
 346     ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
 347     task_queue->initialize();
 348     _task_queues->register_queue(i, task_queue);
 349   }
 350 }
 351 
 352 void ShenandoahConcurrentMark::concurrent_scan_code_roots(uint worker_id, ReferenceProcessor* rp) {
 353   if (ShenandoahConcurrentScanCodeRoots && claim_codecache()) {
 354     ShenandoahObjToScanQueue* q = task_queues()->queue(worker_id);
 355     if (!_heap->unload_classes()) {
 356       MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 357       // TODO: We can not honor StringDeduplication here, due to lock ranking
 358       // inversion. So, we may miss some deduplication candidates.
 359       if (_heap->has_forwarded_objects()) {
 360         ShenandoahMarkResolveRefsClosure cl(q, rp);
 361         CodeBlobToOopClosure blobs(&cl, !CodeBlobToOopClosure::FixRelocations);
 362         CodeCache::blobs_do(&blobs);
 363       } else {
 364         ShenandoahMarkRefsClosure cl(q, rp);
 365         CodeBlobToOopClosure blobs(&cl, !CodeBlobToOopClosure::FixRelocations);
 366         CodeCache::blobs_do(&blobs);
 367       }
 368     }
 369   }
 370 }
 371 
 372 void ShenandoahConcurrentMark::mark_from_roots() {
 373   WorkGang* workers = _heap->workers();
 374   uint nworkers = workers->active_workers();
 375 
 376   ShenandoahGCPhase conc_mark_phase(ShenandoahPhaseTimings::conc_mark);
 377 
 378   if (_heap->process_references()) {
 379     ReferenceProcessor* rp = _heap->ref_processor();
 380     rp->set_active_mt_degree(nworkers);
 381 
 382     // enable ("weak") refs discovery
 383     rp->enable_discovery(true /*verify_no_refs*/);
 384     rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
 385   }
 386 
 387   shenandoah_assert_rp_isalive_not_installed();
 388   ShenandoahIsAliveSelector is_alive;
 389   ReferenceProcessorIsAliveMutator fix_isalive(_heap->ref_processor(), is_alive.is_alive_closure());
 390 
 391   task_queues()->reserve(nworkers);
 392 
 393   {
 394     ShenandoahTerminationTracker term(ShenandoahPhaseTimings::conc_termination);
 395     ShenandoahTaskTerminator terminator(nworkers, task_queues());
 396     ShenandoahConcurrentMarkingTask task(this, &terminator);
 397     workers->run_task(&task);
 398   }
 399 
 400   assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty when not cancelled");
 401 }
 402 
 403 void ShenandoahConcurrentMark::finish_mark_from_roots(bool full_gc) {
 404   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 405 
 406   uint nworkers = _heap->workers()->active_workers();
 407 
 408   // Finally mark everything else we've got in our queues during the previous steps.
 409   // It does two different things for concurrent vs. mark-compact GC:
 410   // - For concurrent GC, it starts with empty task queues, drains the remaining
 411   //   SATB buffers, and then completes the marking closure.
 412   // - For mark-compact GC, it starts out with the task queues seeded by initial
 413   //   root scan, and completes the closure, thus marking through all live objects
 414   // The implementation is the same, so it's shared here.
 415   {
 416     ShenandoahGCPhase phase(full_gc ?
 417                             ShenandoahPhaseTimings::full_gc_mark_finish_queues :
 418                             ShenandoahPhaseTimings::finish_queues);
 419     task_queues()->reserve(nworkers);
 420 
 421     shenandoah_assert_rp_isalive_not_installed();
 422     ShenandoahIsAliveSelector is_alive;
 423     ReferenceProcessorIsAliveMutator fix_isalive(_heap->ref_processor(), is_alive.is_alive_closure());
 424 
 425     ShenandoahTerminationTracker termination_tracker(full_gc ?
 426                                                      ShenandoahPhaseTimings::full_gc_mark_termination :
 427                                                      ShenandoahPhaseTimings::termination);
 428 
 429     StrongRootsScope scope(nworkers);
 430     ShenandoahTaskTerminator terminator(nworkers, task_queues());
 431     ShenandoahFinalMarkingTask task(this, &terminator, ShenandoahStringDedup::is_enabled());
 432     _heap->workers()->run_task(&task);
 433   }
 434 
 435   assert(task_queues()->is_empty(), "Should be empty");
 436 
 437   // When we're done marking everything, we process weak references.
 438   if (_heap->process_references()) {
 439     weak_refs_work(full_gc);
 440   }
 441 
 442   weak_roots_work();
 443 
 444   // And finally finish class unloading
 445   if (_heap->unload_classes()) {
 446     _heap->unload_classes_and_cleanup_tables(full_gc);
 447   } else if (ShenandoahStringDedup::is_enabled()) {
 448     ShenandoahIsAliveSelector alive;
 449     BoolObjectClosure* is_alive = alive.is_alive_closure();
 450     ShenandoahStringDedup::unlink_or_oops_do(is_alive, NULL, false);
 451   }
 452   assert(task_queues()->is_empty(), "Should be empty");
 453   TASKQUEUE_STATS_ONLY(task_queues()->print_taskqueue_stats());
 454   TASKQUEUE_STATS_ONLY(task_queues()->reset_taskqueue_stats());
 455 
 456   // Resize Metaspace
 457   MetaspaceGC::compute_new_size();
 458 }
 459 
 460 // Weak Reference Closures
 461 class ShenandoahCMDrainMarkingStackClosure: public VoidClosure {
 462   uint _worker_id;
 463   ShenandoahTaskTerminator* _terminator;
 464   bool _reset_terminator;
 465 
 466 public:
 467   ShenandoahCMDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
 468     _worker_id(worker_id),
 469     _terminator(t),
 470     _reset_terminator(reset_terminator) {
 471   }
 472 
 473   void do_void() {
 474     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 475 
 476     ShenandoahHeap* sh = ShenandoahHeap::heap();
 477     ShenandoahConcurrentMark* scm = sh->concurrent_mark();
 478     assert(sh->process_references(), "why else would we be here?");
 479     ReferenceProcessor* rp = sh->ref_processor();
 480 
 481     shenandoah_assert_rp_isalive_installed();
 482 
 483     scm->mark_loop(_worker_id, _terminator, rp,
 484                    false,   // not cancellable
 485                    false);  // do not do strdedup
 486 
 487     if (_reset_terminator) {
 488       _terminator->reset_for_reuse();
 489     }
 490   }
 491 };
 492 
 493 class ShenandoahCMKeepAliveClosure : public OopClosure {
 494 private:
 495   ShenandoahObjToScanQueue* _queue;
 496   ShenandoahHeap* _heap;
 497   ShenandoahMarkingContext* const _mark_context;
 498 
 499   template <class T>
 500   inline void do_oop_work(T* p) {
 501     ShenandoahConcurrentMark::mark_through_ref<T, NONE, NO_DEDUP>(p, _heap, _queue, _mark_context);
 502   }
 503 
 504 public:
 505   ShenandoahCMKeepAliveClosure(ShenandoahObjToScanQueue* q) :
 506     _queue(q),
 507     _heap(ShenandoahHeap::heap()),
 508     _mark_context(_heap->marking_context()) {}
 509 
 510   void do_oop(narrowOop* p) { do_oop_work(p); }
 511   void do_oop(oop* p)       { do_oop_work(p); }
 512 };
 513 
 514 class ShenandoahCMKeepAliveUpdateClosure : public OopClosure {
 515 private:
 516   ShenandoahObjToScanQueue* _queue;
 517   ShenandoahHeap* _heap;
 518   ShenandoahMarkingContext* const _mark_context;
 519 
 520   template <class T>
 521   inline void do_oop_work(T* p) {
 522     ShenandoahConcurrentMark::mark_through_ref<T, SIMPLE, NO_DEDUP>(p, _heap, _queue, _mark_context);
 523   }
 524 
 525 public:
 526   ShenandoahCMKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
 527     _queue(q),
 528     _heap(ShenandoahHeap::heap()),
 529     _mark_context(_heap->marking_context()) {}
 530 
 531   void do_oop(narrowOop* p) { do_oop_work(p); }
 532   void do_oop(oop* p)       { do_oop_work(p); }
 533 };
 534 
 535 class ShenandoahWeakUpdateClosure : public OopClosure {
 536 private:
 537   ShenandoahHeap* const _heap;
 538 
 539   template <class T>
 540   inline void do_oop_work(T* p) {
 541     oop o = _heap->maybe_update_with_forwarded(p);
 542     shenandoah_assert_marked_except(p, o, o == NULL);
 543   }
 544 
 545 public:
 546   ShenandoahWeakUpdateClosure() : _heap(ShenandoahHeap::heap()) {}
 547 
 548   void do_oop(narrowOop* p) { do_oop_work(p); }
 549   void do_oop(oop* p)       { do_oop_work(p); }
 550 };
 551 
 552 class ShenandoahWeakAssertNotForwardedClosure : public OopClosure {
 553 private:
 554   template <class T>
 555   inline void do_oop_work(T* p) {
 556 #ifdef ASSERT
 557     T o = RawAccess<>::oop_load(p);
 558     if (!CompressedOops::is_null(o)) {
 559       oop obj = CompressedOops::decode_not_null(o);
 560       shenandoah_assert_not_forwarded(p, obj);
 561     }
 562 #endif
 563   }
 564 
 565 public:
 566   ShenandoahWeakAssertNotForwardedClosure() {}
 567 
 568   void do_oop(narrowOop* p) { do_oop_work(p); }
 569   void do_oop(oop* p)       { do_oop_work(p); }
 570 };
 571 
 572 class ShenandoahRefProcTaskProxy : public AbstractGangTask {
 573 private:
 574   AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
 575   ShenandoahTaskTerminator* _terminator;
 576 
 577 public:
 578   ShenandoahRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
 579                              ShenandoahTaskTerminator* t) :
 580     AbstractGangTask("Process reference objects in parallel"),
 581     _proc_task(proc_task),
 582     _terminator(t) {
 583   }
 584 
 585   void work(uint worker_id) {
 586     ResourceMark rm;
 587     HandleMark hm;
 588     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 589     ShenandoahHeap* heap = ShenandoahHeap::heap();
 590     ShenandoahCMDrainMarkingStackClosure complete_gc(worker_id, _terminator);
 591     if (heap->has_forwarded_objects()) {
 592       ShenandoahForwardedIsAliveClosure is_alive;
 593       ShenandoahCMKeepAliveUpdateClosure keep_alive(heap->concurrent_mark()->get_queue(worker_id));
 594       _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
 595     } else {
 596       ShenandoahIsAliveClosure is_alive;
 597       ShenandoahCMKeepAliveClosure keep_alive(heap->concurrent_mark()->get_queue(worker_id));
 598       _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
 599     }
 600   }
 601 };
 602 
 603 class ShenandoahRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
 604 private:
 605   WorkGang* _workers;
 606 
 607 public:
 608   ShenandoahRefProcTaskExecutor(WorkGang* workers) :
 609     _workers(workers) {
 610   }
 611 
 612   // Executes a task using worker threads.
 613   void execute(ProcessTask& task, uint ergo_workers) {
 614     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 615 
 616     ShenandoahHeap* heap = ShenandoahHeap::heap();
 617     ShenandoahConcurrentMark* cm = heap->concurrent_mark();
 618     ShenandoahPushWorkerQueuesScope scope(_workers, cm->task_queues(),
 619                                           ergo_workers,
 620                                           /* do_check = */ false);
 621     uint nworkers = _workers->active_workers();
 622     cm->task_queues()->reserve(nworkers);
 623     ShenandoahTaskTerminator terminator(nworkers, cm->task_queues());
 624     ShenandoahRefProcTaskProxy proc_task_proxy(task, &terminator);
 625     _workers->run_task(&proc_task_proxy);
 626   }
 627 };
 628 
 629 void ShenandoahConcurrentMark::weak_refs_work(bool full_gc) {
 630   assert(_heap->process_references(), "sanity");
 631 
 632   ShenandoahPhaseTimings::Phase phase_root =
 633           full_gc ?
 634           ShenandoahPhaseTimings::full_gc_weakrefs :
 635           ShenandoahPhaseTimings::weakrefs;
 636 
 637   ShenandoahGCPhase phase(phase_root);
 638 
 639   ReferenceProcessor* rp = _heap->ref_processor();
 640 
 641   // NOTE: We cannot shortcut on has_discovered_references() here, because
 642   // we will miss marking JNI Weak refs then, see implementation in
 643   // ReferenceProcessor::process_discovered_references.
 644   weak_refs_work_doit(full_gc);
 645 
 646   rp->verify_no_references_recorded();
 647   assert(!rp->discovery_enabled(), "Post condition");
 648 
 649 }
 650 
 651 // Process leftover weak oops: update them, if needed or assert they do not
 652 // need updating otherwise.
 653 // Weak processor API requires us to visit the oops, even if we are not doing
 654 // anything to them.
 655 void ShenandoahConcurrentMark::weak_roots_work() {
 656   WorkGang* workers = _heap->workers();
 657   OopClosure* keep_alive = &do_nothing_cl;
 658 #ifdef ASSERT
 659   ShenandoahWeakAssertNotForwardedClosure verify_cl;
 660   keep_alive = &verify_cl;
 661 #endif
 662   ShenandoahIsAliveClosure is_alive;
 663   WeakProcessor::weak_oops_do(workers, &is_alive, keep_alive, 1);
 664 }
 665 
 666 void ShenandoahConcurrentMark::weak_refs_work_doit(bool full_gc) {
 667   ReferenceProcessor* rp = _heap->ref_processor();
 668 
 669   ShenandoahPhaseTimings::Phase phase_process =
 670           full_gc ?
 671           ShenandoahPhaseTimings::full_gc_weakrefs_process :
 672           ShenandoahPhaseTimings::weakrefs_process;
 673 
 674   ShenandoahPhaseTimings::Phase phase_process_termination =
 675           full_gc ?
 676           ShenandoahPhaseTimings::full_gc_weakrefs_termination :
 677           ShenandoahPhaseTimings::weakrefs_termination;
 678 
 679   shenandoah_assert_rp_isalive_not_installed();
 680   ShenandoahIsAliveSelector is_alive;
 681   ReferenceProcessorIsAliveMutator fix_isalive(rp, is_alive.is_alive_closure());
 682 
 683   WorkGang* workers = _heap->workers();
 684   uint nworkers = workers->active_workers();
 685 
 686   rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
 687   rp->set_active_mt_degree(nworkers);
 688 
 689   assert(task_queues()->is_empty(), "Should be empty");
 690 
 691   // complete_gc and keep_alive closures instantiated here are only needed for
 692   // single-threaded path in RP. They share the queue 0 for tracking work, which
 693   // simplifies implementation. Since RP may decide to call complete_gc several
 694   // times, we need to be able to reuse the terminator.
 695   uint serial_worker_id = 0;
 696   ShenandoahTaskTerminator terminator(1, task_queues());
 697   ShenandoahCMDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
 698 
 699   ShenandoahRefProcTaskExecutor executor(workers);
 700 
 701   ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
 702 
 703   {
 704     ShenandoahGCPhase phase(phase_process);
 705     ShenandoahTerminationTracker phase_term(phase_process_termination);
 706 
 707     if (_heap->has_forwarded_objects()) {
 708       ShenandoahCMKeepAliveUpdateClosure keep_alive(get_queue(serial_worker_id));
 709       rp->process_discovered_references(is_alive.is_alive_closure(), &keep_alive,
 710                                         &complete_gc, &executor,
 711                                         &pt);
 712 
 713     } else {
 714       ShenandoahCMKeepAliveClosure keep_alive(get_queue(serial_worker_id));
 715       rp->process_discovered_references(is_alive.is_alive_closure(), &keep_alive,
 716                                         &complete_gc, &executor,
 717                                         &pt);
 718 
 719     }
 720 
 721     pt.print_all_references();
 722 
 723     assert(task_queues()->is_empty(), "Should be empty");
 724   }
 725 }
 726 
 727 class ShenandoahCancelledGCYieldClosure : public YieldClosure {
 728 private:
 729   ShenandoahHeap* const _heap;
 730 public:
 731   ShenandoahCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
 732   virtual bool should_return() { return _heap->cancelled_gc(); }
 733 };
 734 
 735 class ShenandoahPrecleanCompleteGCClosure : public VoidClosure {
 736 public:
 737   void do_void() {
 738     ShenandoahHeap* sh = ShenandoahHeap::heap();
 739     ShenandoahConcurrentMark* scm = sh->concurrent_mark();
 740     assert(sh->process_references(), "why else would we be here?");
 741     ShenandoahTaskTerminator terminator(1, scm->task_queues());
 742 
 743     ReferenceProcessor* rp = sh->ref_processor();
 744     shenandoah_assert_rp_isalive_installed();
 745 
 746     scm->mark_loop(0, &terminator, rp,
 747                    false, // not cancellable
 748                    false); // do not do strdedup
 749   }
 750 };
 751 
 752 class ShenandoahPrecleanKeepAliveUpdateClosure : public OopClosure {
 753 private:
 754   ShenandoahObjToScanQueue* _queue;
 755   ShenandoahHeap* _heap;
 756   ShenandoahMarkingContext* const _mark_context;
 757 
 758   template <class T>
 759   inline void do_oop_work(T* p) {
 760     ShenandoahConcurrentMark::mark_through_ref<T, CONCURRENT, NO_DEDUP>(p, _heap, _queue, _mark_context);
 761   }
 762 
 763 public:
 764   ShenandoahPrecleanKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
 765     _queue(q),
 766     _heap(ShenandoahHeap::heap()),
 767     _mark_context(_heap->marking_context()) {}
 768 
 769   void do_oop(narrowOop* p) { do_oop_work(p); }
 770   void do_oop(oop* p)       { do_oop_work(p); }
 771 };
 772 
 773 class ShenandoahPrecleanTask : public AbstractGangTask {
 774 private:
 775   ReferenceProcessor* _rp;
 776 
 777 public:
 778   ShenandoahPrecleanTask(ReferenceProcessor* rp) :
 779           AbstractGangTask("Precleaning task"),
 780           _rp(rp) {}
 781 
 782   void work(uint worker_id) {
 783     assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
 784     ShenandoahParallelWorkerSession worker_session(worker_id);
 785 
 786     ShenandoahHeap* sh = ShenandoahHeap::heap();
 787 
 788     ShenandoahObjToScanQueue* q = sh->concurrent_mark()->get_queue(worker_id);
 789 
 790     ShenandoahCancelledGCYieldClosure yield;
 791     ShenandoahPrecleanCompleteGCClosure complete_gc;
 792 
 793     if (sh->has_forwarded_objects()) {
 794       ShenandoahForwardedIsAliveClosure is_alive;
 795       ShenandoahPrecleanKeepAliveUpdateClosure keep_alive(q);
 796       ResourceMark rm;
 797       _rp->preclean_discovered_references(&is_alive, &keep_alive,
 798                                           &complete_gc, &yield,
 799                                           NULL);
 800     } else {
 801       ShenandoahIsAliveClosure is_alive;
 802       ShenandoahCMKeepAliveClosure keep_alive(q);
 803       ResourceMark rm;
 804       _rp->preclean_discovered_references(&is_alive, &keep_alive,
 805                                           &complete_gc, &yield,
 806                                           NULL);
 807     }
 808   }
 809 };
 810 
 811 void ShenandoahConcurrentMark::preclean_weak_refs() {
 812   // Pre-cleaning weak references before diving into STW makes sense at the
 813   // end of concurrent mark. This will filter out the references which referents
 814   // are alive. Note that ReferenceProcessor already filters out these on reference
 815   // discovery, and the bulk of work is done here. This phase processes leftovers
 816   // that missed the initial filtering, i.e. when referent was marked alive after
 817   // reference was discovered by RP.
 818 
 819   assert(_heap->process_references(), "sanity");
 820 
 821   // Shortcut if no references were discovered to avoid winding up threads.
 822   ReferenceProcessor* rp = _heap->ref_processor();
 823   if (!rp->has_discovered_references()) {
 824     return;
 825   }
 826 
 827   assert(task_queues()->is_empty(), "Should be empty");
 828 
 829   ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
 830 
 831   shenandoah_assert_rp_isalive_not_installed();
 832   ShenandoahIsAliveSelector is_alive;
 833   ReferenceProcessorIsAliveMutator fix_isalive(rp, is_alive.is_alive_closure());
 834 
 835   // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
 836   // queues and other goodies. When upstream ReferenceProcessor starts supporting
 837   // parallel precleans, we can extend this to more threads.
 838   WorkGang* workers = _heap->workers();
 839   uint nworkers = workers->active_workers();
 840   assert(nworkers == 1, "This code uses only a single worker");
 841   task_queues()->reserve(nworkers);
 842 
 843   ShenandoahPrecleanTask task(rp);
 844   workers->run_task(&task);
 845 
 846   assert(task_queues()->is_empty(), "Should be empty");
 847 }
 848 
 849 void ShenandoahConcurrentMark::cancel() {
 850   // Clean up marking stacks.
 851   ShenandoahObjToScanQueueSet* queues = task_queues();
 852   queues->clear();
 853 
 854   // Cancel SATB buffers.
 855   ShenandoahBarrierSet::satb_mark_queue_set().abandon_partial_marking();
 856 }
 857 
 858 ShenandoahObjToScanQueue* ShenandoahConcurrentMark::get_queue(uint worker_id) {
 859   assert(task_queues()->get_reserved() > worker_id, "No reserved queue for worker id: %d", worker_id);
 860   return _task_queues->queue(worker_id);
 861 }
 862 
 863 template <bool CANCELLABLE>
 864 void ShenandoahConcurrentMark::mark_loop_prework(uint w, ShenandoahTaskTerminator *t, ReferenceProcessor *rp,
 865                                                  bool strdedup) {
 866   ShenandoahObjToScanQueue* q = get_queue(w);
 867 
 868   jushort* ld = _heap->get_liveness_cache(w);
 869 
 870   // TODO: We can clean up this if we figure out how to do templated oop closures that
 871   // play nice with specialized_oop_iterators.
 872   if (_heap->unload_classes()) {
 873     if (_heap->has_forwarded_objects()) {
 874       if (strdedup) {
 875         ShenandoahMarkUpdateRefsMetadataDedupClosure cl(q, rp);
 876         mark_loop_work<ShenandoahMarkUpdateRefsMetadataDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 877       } else {
 878         ShenandoahMarkUpdateRefsMetadataClosure cl(q, rp);
 879         mark_loop_work<ShenandoahMarkUpdateRefsMetadataClosure, CANCELLABLE>(&cl, ld, w, t);
 880       }
 881     } else {
 882       if (strdedup) {
 883         ShenandoahMarkRefsMetadataDedupClosure cl(q, rp);
 884         mark_loop_work<ShenandoahMarkRefsMetadataDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 885       } else {
 886         ShenandoahMarkRefsMetadataClosure cl(q, rp);
 887         mark_loop_work<ShenandoahMarkRefsMetadataClosure, CANCELLABLE>(&cl, ld, w, t);
 888       }
 889     }
 890   } else {
 891     if (_heap->has_forwarded_objects()) {
 892       if (strdedup) {
 893         ShenandoahMarkUpdateRefsDedupClosure cl(q, rp);
 894         mark_loop_work<ShenandoahMarkUpdateRefsDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 895       } else {
 896         ShenandoahMarkUpdateRefsClosure cl(q, rp);
 897         mark_loop_work<ShenandoahMarkUpdateRefsClosure, CANCELLABLE>(&cl, ld, w, t);
 898       }
 899     } else {
 900       if (strdedup) {
 901         ShenandoahMarkRefsDedupClosure cl(q, rp);
 902         mark_loop_work<ShenandoahMarkRefsDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 903       } else {
 904         ShenandoahMarkRefsClosure cl(q, rp);
 905         mark_loop_work<ShenandoahMarkRefsClosure, CANCELLABLE>(&cl, ld, w, t);
 906       }
 907     }
 908   }
 909 
 910   _heap->flush_liveness_cache(w);
 911 }
 912 
 913 template <class T, bool CANCELLABLE>
 914 void ShenandoahConcurrentMark::mark_loop_work(T* cl, jushort* live_data, uint worker_id, ShenandoahTaskTerminator *terminator) {
 915   uintx stride = ShenandoahMarkLoopStride;
 916 
 917   ShenandoahHeap* heap = ShenandoahHeap::heap();
 918   ShenandoahObjToScanQueueSet* queues = task_queues();
 919   ShenandoahObjToScanQueue* q;
 920   ShenandoahMarkTask t;
 921 
 922   /*
 923    * Process outstanding queues, if any.
 924    *
 925    * There can be more queues than workers. To deal with the imbalance, we claim
 926    * extra queues first. Since marking can push new tasks into the queue associated
 927    * with this worker id, we come back to process this queue in the normal loop.
 928    */
 929   assert(queues->get_reserved() == heap->workers()->active_workers(),
 930          "Need to reserve proper number of queues: reserved: %u, active: %u", queues->get_reserved(), heap->workers()->active_workers());
 931 
 932   q = queues->claim_next();
 933   while (q != NULL) {
 934     if (CANCELLABLE && heap->check_cancelled_gc_and_yield()) {
 935       return;
 936     }
 937 
 938     for (uint i = 0; i < stride; i++) {
 939       if (q->pop(t)) {
 940         do_task<T>(q, cl, live_data, &t);
 941       } else {
 942         assert(q->is_empty(), "Must be empty");
 943         q = queues->claim_next();
 944         break;
 945       }
 946     }
 947   }
 948   q = get_queue(worker_id);
 949 
 950   ShenandoahSATBBufferClosure drain_satb(q);
 951   SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
 952 
 953   /*
 954    * Normal marking loop:
 955    */
 956   while (true) {
 957     if (CANCELLABLE && heap->check_cancelled_gc_and_yield()) {
 958       return;
 959     }
 960 
 961     while (satb_mq_set.completed_buffers_num() > 0) {
 962       satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
 963     }
 964 
 965     uint work = 0;
 966     for (uint i = 0; i < stride; i++) {
 967       if (q->pop(t) ||
 968           queues->steal(worker_id, t)) {
 969         do_task<T>(q, cl, live_data, &t);
 970         work++;
 971       } else {
 972         break;
 973       }
 974     }
 975 
 976     if (work == 0) {
 977       // No work encountered in current stride, try to terminate.
 978       // Need to leave the STS here otherwise it might block safepoints.
 979       ShenandoahSuspendibleThreadSetLeaver stsl(CANCELLABLE && ShenandoahSuspendibleWorkers);
 980       ShenandoahTerminationTimingsTracker term_tracker(worker_id);
 981       ShenandoahTerminatorTerminator tt(heap);
 982       if (terminator->offer_termination(&tt)) return;
 983     }
 984   }
 985 }
 986 
 987 bool ShenandoahConcurrentMark::claim_codecache() {
 988   assert(ShenandoahConcurrentScanCodeRoots, "must not be called otherwise");
 989   return _claimed_codecache.try_set();
 990 }
 991 
 992 void ShenandoahConcurrentMark::clear_claim_codecache() {
 993   assert(ShenandoahConcurrentScanCodeRoots, "must not be called otherwise");
 994   _claimed_codecache.unset();
 995 }