1 /*
   2  * Copyright (c) 2013, 2020, Red Hat, Inc. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 
  31 #include "gc/shared/weakProcessor.inline.hpp"
  32 #include "gc/shared/gcTimer.hpp"
  33 #include "gc/shared/gcTrace.hpp"
  34 #include "gc/shared/referenceProcessor.hpp"
  35 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
  36 #include "gc/shared/strongRootsScope.hpp"
  37 
  38 #include "gc/shenandoah/shenandoahBarrierSet.inline.hpp"
  39 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
  40 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
  41 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
  42 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
  43 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
  44 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
  45 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
  46 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
  47 #include "gc/shenandoah/shenandoahUtils.hpp"
  48 
  49 #include "memory/iterator.inline.hpp"
  50 #include "memory/metaspace.hpp"
  51 #include "memory/resourceArea.hpp"
  52 #include "oops/oop.inline.hpp"
  53 #include "runtime/handles.inline.hpp"
  54 
  55 template<UpdateRefsMode UPDATE_REFS>
  56 class ShenandoahInitMarkRootsClosure : public OopClosure {
  57 private:
  58   ShenandoahObjToScanQueue* _queue;
  59   ShenandoahHeap* _heap;
  60   ShenandoahMarkingContext* const _mark_context;
  61 
  62   template <class T>
  63   inline void do_oop_work(T* p) {
  64     ShenandoahConcurrentMark::mark_through_ref<T, UPDATE_REFS, NO_DEDUP>(p, _heap, _queue, _mark_context);
  65   }
  66 
  67 public:
  68   ShenandoahInitMarkRootsClosure(ShenandoahObjToScanQueue* q) :
  69     _queue(q),
  70     _heap(ShenandoahHeap::heap()),
  71     _mark_context(_heap->marking_context()) {};
  72 
  73   void do_oop(narrowOop* p) { do_oop_work(p); }
  74   void do_oop(oop* p)       { do_oop_work(p); }
  75 };
  76 
  77 ShenandoahMarkRefsSuperClosure::ShenandoahMarkRefsSuperClosure(ShenandoahObjToScanQueue* q, ReferenceProcessor* rp) :
  78   MetadataVisitingOopIterateClosure(rp),
  79   _queue(q),
  80   _heap(ShenandoahHeap::heap()),
  81   _mark_context(_heap->marking_context())
  82 { }
  83 
  84 template<UpdateRefsMode UPDATE_REFS>
  85 class ShenandoahInitMarkRootsTask : public AbstractGangTask {
  86 private:
  87   ShenandoahRootScanner* _rp;
  88 public:
  89   ShenandoahInitMarkRootsTask(ShenandoahRootScanner* rp) :
  90     AbstractGangTask("Shenandoah init mark roots task"),
  91     _rp(rp) {
  92   }
  93 
  94   void work(uint worker_id) {
  95     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
  96     ShenandoahParallelWorkerSession worker_session(worker_id);
  97 
  98     ShenandoahHeap* heap = ShenandoahHeap::heap();
  99     ShenandoahObjToScanQueueSet* queues = heap->concurrent_mark()->task_queues();
 100     assert(queues->get_reserved() > worker_id, "Queue has not been reserved for worker id: %d", worker_id);
 101 
 102     ShenandoahObjToScanQueue* q = queues->queue(worker_id);
 103 
 104     ShenandoahInitMarkRootsClosure<UPDATE_REFS> mark_cl(q);
 105     do_work(heap, &mark_cl, worker_id);
 106   }
 107 
 108 private:
 109   void do_work(ShenandoahHeap* heap, OopClosure* oops, uint worker_id) {
 110     // The rationale for selecting the roots to scan is as follows:
 111     //   a. With unload_classes = true, we only want to scan the actual strong roots from the
 112     //      code cache. This will allow us to identify the dead classes, unload them, *and*
 113     //      invalidate the relevant code cache blobs. This could be only done together with
 114     //      class unloading.
 115     //   b. With unload_classes = false, we have to nominally retain all the references from code
 116     //      cache, because there could be the case of embedded class/oop in the generated code,
 117     //      which we will never visit during mark. Without code cache invalidation, as in (a),
 118     //      we risk executing that code cache blob, and crashing.
 119     if (heap->unload_classes()) {
 120       _rp->strong_roots_do(worker_id, oops);
 121     } else {
 122       _rp->roots_do(worker_id, oops);
 123     }
 124   }
 125 };
 126 
 127 class ShenandoahUpdateRootsTask : public AbstractGangTask {
 128 private:
 129   ShenandoahRootUpdater*  _root_updater;
 130   bool                    _check_alive;
 131 public:
 132   ShenandoahUpdateRootsTask(ShenandoahRootUpdater* root_updater, bool check_alive) :
 133     AbstractGangTask("Shenandoah update roots task"),
 134     _root_updater(root_updater),
 135     _check_alive(check_alive){
 136   }
 137 
 138   void work(uint worker_id) {
 139     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 140     ShenandoahParallelWorkerSession worker_session(worker_id);
 141 
 142     ShenandoahHeap* heap = ShenandoahHeap::heap();
 143     ShenandoahUpdateRefsClosure cl;
 144     if (_check_alive) {
 145       ShenandoahForwardedIsAliveClosure is_alive;
 146       _root_updater->roots_do<ShenandoahForwardedIsAliveClosure, ShenandoahUpdateRefsClosure>(worker_id, &is_alive, &cl);
 147     } else {
 148       AlwaysTrueClosure always_true;;
 149       _root_updater->roots_do<AlwaysTrueClosure, ShenandoahUpdateRefsClosure>(worker_id, &always_true, &cl);
 150     }
 151   }
 152 };
 153 
 154 class ShenandoahConcurrentMarkingTask : public AbstractGangTask {
 155 private:
 156   ShenandoahConcurrentMark* _cm;
 157   TaskTerminator* _terminator;
 158 
 159 public:
 160   ShenandoahConcurrentMarkingTask(ShenandoahConcurrentMark* cm, TaskTerminator* terminator) :
 161     AbstractGangTask("Root Region Scan"), _cm(cm), _terminator(terminator) {
 162   }
 163 
 164   void work(uint worker_id) {
 165     ShenandoahHeap* heap = ShenandoahHeap::heap();
 166     ShenandoahConcurrentWorkerSession worker_session(worker_id);
 167     ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
 168     ShenandoahObjToScanQueue* q = _cm->get_queue(worker_id);
 169     ReferenceProcessor* rp;
 170     if (heap->process_references()) {
 171       rp = heap->ref_processor();
 172       shenandoah_assert_rp_isalive_installed();
 173     } else {
 174       rp = NULL;
 175     }
 176 
 177     _cm->concurrent_scan_code_roots(worker_id, rp);
 178     _cm->mark_loop(worker_id, _terminator, rp,
 179                    true, // cancellable
 180                    ShenandoahStringDedup::is_enabled()); // perform string dedup
 181   }
 182 };
 183 
 184 class ShenandoahSATBAndRemarkCodeRootsThreadsClosure : public ThreadClosure {
 185 private:
 186   ShenandoahSATBBufferClosure* _satb_cl;
 187   OopClosure*            const _cl;
 188   MarkingCodeBlobClosure*      _code_cl;
 189   uintx _claim_token;
 190 
 191 public:
 192   ShenandoahSATBAndRemarkCodeRootsThreadsClosure(ShenandoahSATBBufferClosure* satb_cl, OopClosure* cl, MarkingCodeBlobClosure* code_cl) :
 193     _satb_cl(satb_cl), _cl(cl), _code_cl(code_cl),
 194     _claim_token(Threads::thread_claim_token()) {}
 195 
 196   void do_thread(Thread* thread) {
 197     if (thread->claim_threads_do(true, _claim_token)) {
 198       ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
 199       if (thread->is_Java_thread()) {
 200         if (_cl != NULL) {
 201           ResourceMark rm;
 202           thread->oops_do(_cl, _code_cl);
 203         } else if (_code_cl != NULL) {
 204           // In theory it should not be neccessary to explicitly walk the nmethods to find roots for concurrent marking
 205           // however the liveness of oops reachable from nmethods have very complex lifecycles:
 206           // * Alive if on the stack of an executing method
 207           // * Weakly reachable otherwise
 208           // Some objects reachable from nmethods, such as the class loader (or klass_holder) of the receiver should be
 209           // live by the SATB invariant but other oops recorded in nmethods may behave differently.
 210           JavaThread* jt = (JavaThread*)thread;
 211           jt->nmethods_do(_code_cl);
 212         }
 213       }
 214     }
 215   }
 216 };
 217 
 218 class ShenandoahFinalMarkingTask : public AbstractGangTask {
 219 private:
 220   ShenandoahConcurrentMark* _cm;
 221   TaskTerminator*           _terminator;
 222   bool _dedup_string;
 223 
 224 public:
 225   ShenandoahFinalMarkingTask(ShenandoahConcurrentMark* cm, TaskTerminator* terminator, bool dedup_string) :
 226     AbstractGangTask("Shenandoah Final Marking"), _cm(cm), _terminator(terminator), _dedup_string(dedup_string) {
 227   }
 228 
 229   void work(uint worker_id) {
 230     ShenandoahHeap* heap = ShenandoahHeap::heap();
 231 
 232     ShenandoahParallelWorkerSession worker_session(worker_id);
 233     ReferenceProcessor* rp;
 234     if (heap->process_references()) {
 235       rp = heap->ref_processor();
 236       shenandoah_assert_rp_isalive_installed();
 237     } else {
 238       rp = NULL;
 239     }
 240 
 241     // First drain remaining SATB buffers.
 242     // Notice that this is not strictly necessary for mark-compact. But since
 243     // it requires a StrongRootsScope around the task, we need to claim the
 244     // threads, and performance-wise it doesn't really matter. Adds about 1ms to
 245     // full-gc.
 246     {
 247       ShenandoahObjToScanQueue* q = _cm->get_queue(worker_id);
 248 
 249       ShenandoahSATBBufferClosure cl(q);
 250       SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
 251       while (satb_mq_set.apply_closure_to_completed_buffer(&cl));
 252       bool do_nmethods = heap->unload_classes() && !ShenandoahConcurrentRoots::can_do_concurrent_class_unloading();
 253       if (heap->has_forwarded_objects()) {
 254         ShenandoahMarkResolveRefsClosure resolve_mark_cl(q, rp);
 255         MarkingCodeBlobClosure blobsCl(&resolve_mark_cl, !CodeBlobToOopClosure::FixRelocations);
 256         ShenandoahSATBAndRemarkCodeRootsThreadsClosure tc(&cl,
 257                                                           ShenandoahStoreValEnqueueBarrier ? &resolve_mark_cl : NULL,
 258                                                           do_nmethods ? &blobsCl : NULL);
 259         Threads::threads_do(&tc);
 260       } else {
 261         ShenandoahMarkRefsClosure mark_cl(q, rp);
 262         MarkingCodeBlobClosure blobsCl(&mark_cl, !CodeBlobToOopClosure::FixRelocations);
 263         ShenandoahSATBAndRemarkCodeRootsThreadsClosure tc(&cl,
 264                                                           ShenandoahStoreValEnqueueBarrier ? &mark_cl : NULL,
 265                                                           do_nmethods ? &blobsCl : NULL);
 266         Threads::threads_do(&tc);
 267       }
 268     }
 269 
 270     if (heap->is_degenerated_gc_in_progress() || heap->is_full_gc_in_progress()) {
 271       // Full GC does not execute concurrent cycle.
 272       // Degenerated cycle may bypass concurrent cycle.
 273       // So code roots might not be scanned, let's scan here.
 274       _cm->concurrent_scan_code_roots(worker_id, rp);
 275     }
 276 
 277     _cm->mark_loop(worker_id, _terminator, rp,
 278                    false, // not cancellable
 279                    _dedup_string);
 280 
 281     assert(_cm->task_queues()->is_empty(), "Should be empty");
 282   }
 283 };
 284 
 285 void ShenandoahConcurrentMark::mark_roots(ShenandoahPhaseTimings::Phase root_phase) {
 286   assert(Thread::current()->is_VM_thread(), "can only do this in VMThread");
 287   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 288 
 289   ShenandoahHeap* heap = ShenandoahHeap::heap();
 290 
 291   ShenandoahGCPhase phase(root_phase);
 292 
 293   WorkGang* workers = heap->workers();
 294   uint nworkers = workers->active_workers();
 295 
 296   assert(nworkers <= task_queues()->size(), "Just check");
 297 
 298   ShenandoahRootScanner root_proc(nworkers, root_phase);
 299   TASKQUEUE_STATS_ONLY(task_queues()->reset_taskqueue_stats());
 300   task_queues()->reserve(nworkers);
 301 
 302   if (heap->has_forwarded_objects()) {
 303     ShenandoahInitMarkRootsTask<RESOLVE> mark_roots(&root_proc);
 304     workers->run_task(&mark_roots);
 305   } else {
 306     // No need to update references, which means the heap is stable.
 307     // Can save time not walking through forwarding pointers.
 308     ShenandoahInitMarkRootsTask<NONE> mark_roots(&root_proc);
 309     workers->run_task(&mark_roots);
 310   }
 311 
 312   clear_claim_codecache();
 313 }
 314 
 315 void ShenandoahConcurrentMark::update_roots(ShenandoahPhaseTimings::Phase root_phase) {
 316   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 317   assert(root_phase == ShenandoahPhaseTimings::full_gc_update_roots ||
 318          root_phase == ShenandoahPhaseTimings::degen_gc_update_roots,
 319          "Only for these phases");
 320 
 321   ShenandoahGCPhase phase(root_phase);
 322 
 323   bool check_alive = root_phase == ShenandoahPhaseTimings::degen_gc_update_roots;
 324 
 325 #if COMPILER2_OR_JVMCI
 326   DerivedPointerTable::clear();
 327 #endif
 328 
 329   uint nworkers = _heap->workers()->active_workers();
 330 
 331   ShenandoahRootUpdater root_updater(nworkers, root_phase);
 332   ShenandoahUpdateRootsTask update_roots(&root_updater, check_alive);
 333   _heap->workers()->run_task(&update_roots);
 334 
 335 #if COMPILER2_OR_JVMCI
 336   DerivedPointerTable::update_pointers();
 337 #endif
 338 }
 339 
 340 class ShenandoahUpdateThreadRootsTask : public AbstractGangTask {
 341 private:
 342   ShenandoahThreadRoots           _thread_roots;
 343   ShenandoahPhaseTimings::Phase   _phase;
 344   ShenandoahGCWorkerPhase         _worker_phase;
 345 public:
 346   ShenandoahUpdateThreadRootsTask(bool is_par, ShenandoahPhaseTimings::Phase phase) :
 347     AbstractGangTask("Shenandoah Update Thread Roots"),
 348     _thread_roots(phase, is_par),
 349     _phase(phase),
 350     _worker_phase(phase) {}
 351 
 352   void work(uint worker_id) {
 353     ShenandoahParallelWorkerSession worker_session(worker_id);
 354     ShenandoahUpdateRefsClosure cl;
 355     _thread_roots.oops_do(&cl, NULL, worker_id);
 356   }
 357 };
 358 
 359 void ShenandoahConcurrentMark::update_thread_roots(ShenandoahPhaseTimings::Phase root_phase) {
 360   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 361 
 362   ShenandoahGCPhase phase(root_phase);
 363 
 364 #if COMPILER2_OR_JVMCI
 365   DerivedPointerTable::clear();
 366 #endif
 367 
 368   WorkGang* workers = _heap->workers();
 369   bool is_par = workers->active_workers() > 1;
 370 
 371   ShenandoahUpdateThreadRootsTask task(is_par, root_phase);
 372   workers->run_task(&task);
 373 
 374 #if COMPILER2_OR_JVMCI
 375   DerivedPointerTable::update_pointers();
 376 #endif
 377 }
 378 
 379 void ShenandoahConcurrentMark::initialize(uint workers) {
 380   _heap = ShenandoahHeap::heap();
 381 
 382   uint num_queues = MAX2(workers, 1U);
 383 
 384   _task_queues = new ShenandoahObjToScanQueueSet((int) num_queues);
 385 
 386   for (uint i = 0; i < num_queues; ++i) {
 387     ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
 388     task_queue->initialize();
 389     _task_queues->register_queue(i, task_queue);
 390   }
 391 }
 392 
 393 void ShenandoahConcurrentMark::concurrent_scan_code_roots(uint worker_id, ReferenceProcessor* rp) {
 394   if (_heap->unload_classes()) {
 395     return;
 396   }
 397 
 398   if (claim_codecache()) {
 399     ShenandoahObjToScanQueue* q = task_queues()->queue(worker_id);
 400     MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 401     // TODO: We can not honor StringDeduplication here, due to lock ranking
 402     // inversion. So, we may miss some deduplication candidates.
 403     if (_heap->has_forwarded_objects()) {
 404       ShenandoahMarkResolveRefsClosure cl(q, rp);
 405       CodeBlobToOopClosure blobs(&cl, !CodeBlobToOopClosure::FixRelocations);
 406       CodeCache::blobs_do(&blobs);
 407     } else {
 408       ShenandoahMarkRefsClosure cl(q, rp);
 409       CodeBlobToOopClosure blobs(&cl, !CodeBlobToOopClosure::FixRelocations);
 410       CodeCache::blobs_do(&blobs);
 411     }
 412   }
 413 }
 414 
 415 void ShenandoahConcurrentMark::mark_from_roots() {
 416   WorkGang* workers = _heap->workers();
 417   uint nworkers = workers->active_workers();
 418 
 419   if (_heap->process_references()) {
 420     ReferenceProcessor* rp = _heap->ref_processor();
 421     rp->set_active_mt_degree(nworkers);
 422 
 423     // enable ("weak") refs discovery
 424     rp->enable_discovery(true /*verify_no_refs*/);
 425     rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
 426   }
 427 
 428   shenandoah_assert_rp_isalive_not_installed();
 429   ShenandoahIsAliveSelector is_alive;
 430   ReferenceProcessorIsAliveMutator fix_isalive(_heap->ref_processor(), is_alive.is_alive_closure());
 431 
 432   task_queues()->reserve(nworkers);
 433 
 434   {
 435     TaskTerminator terminator(nworkers, task_queues());
 436     ShenandoahConcurrentMarkingTask task(this, &terminator);
 437     workers->run_task(&task);
 438   }
 439 
 440   assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty when not cancelled");
 441 }
 442 
 443 void ShenandoahConcurrentMark::finish_mark_from_roots(bool full_gc) {
 444   assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 445 
 446   uint nworkers = _heap->workers()->active_workers();
 447 
 448   // Finally mark everything else we've got in our queues during the previous steps.
 449   // It does two different things for concurrent vs. mark-compact GC:
 450   // - For concurrent GC, it starts with empty task queues, drains the remaining
 451   //   SATB buffers, and then completes the marking closure.
 452   // - For mark-compact GC, it starts out with the task queues seeded by initial
 453   //   root scan, and completes the closure, thus marking through all live objects
 454   // The implementation is the same, so it's shared here.
 455   {
 456     ShenandoahGCPhase phase(full_gc ?
 457                             ShenandoahPhaseTimings::full_gc_mark_finish_queues :
 458                             ShenandoahPhaseTimings::finish_queues);
 459     task_queues()->reserve(nworkers);
 460 
 461     shenandoah_assert_rp_isalive_not_installed();
 462     ShenandoahIsAliveSelector is_alive;
 463     ReferenceProcessorIsAliveMutator fix_isalive(_heap->ref_processor(), is_alive.is_alive_closure());
 464 
 465     StrongRootsScope scope(nworkers);
 466     TaskTerminator terminator(nworkers, task_queues());
 467     ShenandoahFinalMarkingTask task(this, &terminator, ShenandoahStringDedup::is_enabled());
 468     _heap->workers()->run_task(&task);
 469   }
 470 
 471   assert(task_queues()->is_empty(), "Should be empty");
 472 
 473   // When we're done marking everything, we process weak references.
 474   if (_heap->process_references()) {
 475     weak_refs_work(full_gc);
 476   }
 477 
 478   assert(task_queues()->is_empty(), "Should be empty");
 479   TASKQUEUE_STATS_ONLY(task_queues()->print_taskqueue_stats());
 480   TASKQUEUE_STATS_ONLY(task_queues()->reset_taskqueue_stats());
 481 }
 482 
 483 // Weak Reference Closures
 484 class ShenandoahCMDrainMarkingStackClosure: public VoidClosure {
 485   uint _worker_id;
 486   TaskTerminator* _terminator;
 487   bool _reset_terminator;
 488 
 489 public:
 490   ShenandoahCMDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
 491     _worker_id(worker_id),
 492     _terminator(t),
 493     _reset_terminator(reset_terminator) {
 494   }
 495 
 496   void do_void() {
 497     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 498 
 499     ShenandoahHeap* sh = ShenandoahHeap::heap();
 500     ShenandoahConcurrentMark* scm = sh->concurrent_mark();
 501     assert(sh->process_references(), "why else would we be here?");
 502     ReferenceProcessor* rp = sh->ref_processor();
 503 
 504     shenandoah_assert_rp_isalive_installed();
 505 
 506     scm->mark_loop(_worker_id, _terminator, rp,
 507                    false,   // not cancellable
 508                    false);  // do not do strdedup
 509 
 510     if (_reset_terminator) {
 511       _terminator->reset_for_reuse();
 512     }
 513   }
 514 };
 515 
 516 class ShenandoahCMKeepAliveClosure : public OopClosure {
 517 private:
 518   ShenandoahObjToScanQueue* _queue;
 519   ShenandoahHeap* _heap;
 520   ShenandoahMarkingContext* const _mark_context;
 521 
 522   template <class T>
 523   inline void do_oop_work(T* p) {
 524     ShenandoahConcurrentMark::mark_through_ref<T, NONE, NO_DEDUP>(p, _heap, _queue, _mark_context);
 525   }
 526 
 527 public:
 528   ShenandoahCMKeepAliveClosure(ShenandoahObjToScanQueue* q) :
 529     _queue(q),
 530     _heap(ShenandoahHeap::heap()),
 531     _mark_context(_heap->marking_context()) {}
 532 
 533   void do_oop(narrowOop* p) { do_oop_work(p); }
 534   void do_oop(oop* p)       { do_oop_work(p); }
 535 };
 536 
 537 class ShenandoahCMKeepAliveUpdateClosure : public OopClosure {
 538 private:
 539   ShenandoahObjToScanQueue* _queue;
 540   ShenandoahHeap* _heap;
 541   ShenandoahMarkingContext* const _mark_context;
 542 
 543   template <class T>
 544   inline void do_oop_work(T* p) {
 545     ShenandoahConcurrentMark::mark_through_ref<T, SIMPLE, NO_DEDUP>(p, _heap, _queue, _mark_context);
 546   }
 547 
 548 public:
 549   ShenandoahCMKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
 550     _queue(q),
 551     _heap(ShenandoahHeap::heap()),
 552     _mark_context(_heap->marking_context()) {}
 553 
 554   void do_oop(narrowOop* p) { do_oop_work(p); }
 555   void do_oop(oop* p)       { do_oop_work(p); }
 556 };
 557 
 558 class ShenandoahWeakUpdateClosure : public OopClosure {
 559 private:
 560   ShenandoahHeap* const _heap;
 561 
 562   template <class T>
 563   inline void do_oop_work(T* p) {
 564     oop o = _heap->maybe_update_with_forwarded(p);
 565     shenandoah_assert_marked_except(p, o, o == NULL);
 566   }
 567 
 568 public:
 569   ShenandoahWeakUpdateClosure() : _heap(ShenandoahHeap::heap()) {}
 570 
 571   void do_oop(narrowOop* p) { do_oop_work(p); }
 572   void do_oop(oop* p)       { do_oop_work(p); }
 573 };
 574 
 575 class ShenandoahRefProcTaskProxy : public AbstractGangTask {
 576 private:
 577   AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
 578   TaskTerminator* _terminator;
 579 
 580 public:
 581   ShenandoahRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
 582                              TaskTerminator* t) :
 583     AbstractGangTask("Process reference objects in parallel"),
 584     _proc_task(proc_task),
 585     _terminator(t) {
 586   }
 587 
 588   void work(uint worker_id) {
 589     ResourceMark rm;
 590     HandleMark hm;
 591     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 592     ShenandoahHeap* heap = ShenandoahHeap::heap();
 593     ShenandoahParallelWorkerSession worker_session(worker_id);
 594     ShenandoahCMDrainMarkingStackClosure complete_gc(worker_id, _terminator);
 595     if (heap->has_forwarded_objects()) {
 596       ShenandoahForwardedIsAliveClosure is_alive;
 597       ShenandoahCMKeepAliveUpdateClosure keep_alive(heap->concurrent_mark()->get_queue(worker_id));
 598       _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
 599     } else {
 600       ShenandoahIsAliveClosure is_alive;
 601       ShenandoahCMKeepAliveClosure keep_alive(heap->concurrent_mark()->get_queue(worker_id));
 602       _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
 603     }
 604   }
 605 };
 606 
 607 class ShenandoahRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
 608 private:
 609   WorkGang* _workers;
 610 
 611 public:
 612   ShenandoahRefProcTaskExecutor(WorkGang* workers) :
 613     _workers(workers) {
 614   }
 615 
 616   // Executes a task using worker threads.
 617   void execute(ProcessTask& task, uint ergo_workers) {
 618     assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
 619 
 620     ShenandoahHeap* heap = ShenandoahHeap::heap();
 621     ShenandoahConcurrentMark* cm = heap->concurrent_mark();
 622     ShenandoahPushWorkerQueuesScope scope(_workers, cm->task_queues(),
 623                                           ergo_workers,
 624                                           /* do_check = */ false);
 625     uint nworkers = _workers->active_workers();
 626     cm->task_queues()->reserve(nworkers);
 627     TaskTerminator terminator(nworkers, cm->task_queues());
 628     ShenandoahRefProcTaskProxy proc_task_proxy(task, &terminator);
 629     _workers->run_task(&proc_task_proxy);
 630   }
 631 };
 632 
 633 void ShenandoahConcurrentMark::weak_refs_work(bool full_gc) {
 634   assert(_heap->process_references(), "sanity");
 635 
 636   ShenandoahPhaseTimings::Phase phase_root =
 637           full_gc ?
 638           ShenandoahPhaseTimings::full_gc_weakrefs :
 639           ShenandoahPhaseTimings::weakrefs;
 640 
 641   ShenandoahGCPhase phase(phase_root);
 642 
 643   ReferenceProcessor* rp = _heap->ref_processor();
 644 
 645   // NOTE: We cannot shortcut on has_discovered_references() here, because
 646   // we will miss marking JNI Weak refs then, see implementation in
 647   // ReferenceProcessor::process_discovered_references.
 648   weak_refs_work_doit(full_gc);
 649 
 650   rp->verify_no_references_recorded();
 651   assert(!rp->discovery_enabled(), "Post condition");
 652 
 653 }
 654 
 655 void ShenandoahConcurrentMark::weak_refs_work_doit(bool full_gc) {
 656   ReferenceProcessor* rp = _heap->ref_processor();
 657 
 658   ShenandoahPhaseTimings::Phase phase_process =
 659           full_gc ?
 660           ShenandoahPhaseTimings::full_gc_weakrefs_process :
 661           ShenandoahPhaseTimings::weakrefs_process;
 662 
 663   shenandoah_assert_rp_isalive_not_installed();
 664   ShenandoahIsAliveSelector is_alive;
 665   ReferenceProcessorIsAliveMutator fix_isalive(rp, is_alive.is_alive_closure());
 666 
 667   WorkGang* workers = _heap->workers();
 668   uint nworkers = workers->active_workers();
 669 
 670   rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
 671   rp->set_active_mt_degree(nworkers);
 672 
 673   assert(task_queues()->is_empty(), "Should be empty");
 674 
 675   // complete_gc and keep_alive closures instantiated here are only needed for
 676   // single-threaded path in RP. They share the queue 0 for tracking work, which
 677   // simplifies implementation. Since RP may decide to call complete_gc several
 678   // times, we need to be able to reuse the terminator.
 679   uint serial_worker_id = 0;
 680   TaskTerminator terminator(1, task_queues());
 681   ShenandoahCMDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
 682 
 683   ShenandoahRefProcTaskExecutor executor(workers);
 684 
 685   ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
 686 
 687   {
 688     // Note: Don't emit JFR event for this phase, to avoid overflow nesting phase level.
 689     // Reference Processor emits 2 levels JFR event, that can get us over the JFR
 690     // event nesting level limits, in case of degenerated GC gets upgraded to
 691     // full GC.
 692     ShenandoahTimingsTracker phase_timing(phase_process);
 693 
 694     if (_heap->has_forwarded_objects()) {
 695       ShenandoahCMKeepAliveUpdateClosure keep_alive(get_queue(serial_worker_id));
 696       const ReferenceProcessorStats& stats =
 697         rp->process_discovered_references(is_alive.is_alive_closure(), &keep_alive,
 698                                           &complete_gc, &executor,
 699                                           &pt);
 700        _heap->tracer()->report_gc_reference_stats(stats);
 701     } else {
 702       ShenandoahCMKeepAliveClosure keep_alive(get_queue(serial_worker_id));
 703       const ReferenceProcessorStats& stats =
 704         rp->process_discovered_references(is_alive.is_alive_closure(), &keep_alive,
 705                                           &complete_gc, &executor,
 706                                           &pt);
 707       _heap->tracer()->report_gc_reference_stats(stats);
 708     }
 709 
 710     pt.print_all_references();
 711 
 712     assert(task_queues()->is_empty(), "Should be empty");
 713   }
 714 }
 715 
 716 class ShenandoahCancelledGCYieldClosure : public YieldClosure {
 717 private:
 718   ShenandoahHeap* const _heap;
 719 public:
 720   ShenandoahCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
 721   virtual bool should_return() { return _heap->cancelled_gc(); }
 722 };
 723 
 724 class ShenandoahPrecleanCompleteGCClosure : public VoidClosure {
 725 public:
 726   void do_void() {
 727     ShenandoahHeap* sh = ShenandoahHeap::heap();
 728     ShenandoahConcurrentMark* scm = sh->concurrent_mark();
 729     assert(sh->process_references(), "why else would we be here?");
 730     TaskTerminator terminator(1, scm->task_queues());
 731 
 732     ReferenceProcessor* rp = sh->ref_processor();
 733     shenandoah_assert_rp_isalive_installed();
 734 
 735     scm->mark_loop(0, &terminator, rp,
 736                    false, // not cancellable
 737                    false); // do not do strdedup
 738   }
 739 };
 740 
 741 class ShenandoahPrecleanTask : public AbstractGangTask {
 742 private:
 743   ReferenceProcessor* _rp;
 744 
 745 public:
 746   ShenandoahPrecleanTask(ReferenceProcessor* rp) :
 747           AbstractGangTask("Precleaning task"),
 748           _rp(rp) {}
 749 
 750   void work(uint worker_id) {
 751     assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
 752     ShenandoahParallelWorkerSession worker_session(worker_id);
 753 
 754     ShenandoahHeap* sh = ShenandoahHeap::heap();
 755     assert(!sh->has_forwarded_objects(), "No forwarded objects expected here");
 756 
 757     ShenandoahObjToScanQueue* q = sh->concurrent_mark()->get_queue(worker_id);
 758 
 759     ShenandoahCancelledGCYieldClosure yield;
 760     ShenandoahPrecleanCompleteGCClosure complete_gc;
 761 
 762     ShenandoahIsAliveClosure is_alive;
 763     ShenandoahCMKeepAliveClosure keep_alive(q);
 764     ResourceMark rm;
 765     _rp->preclean_discovered_references(&is_alive, &keep_alive,
 766                                         &complete_gc, &yield,
 767                                         NULL);
 768   }
 769 };
 770 
 771 void ShenandoahConcurrentMark::preclean_weak_refs() {
 772   // Pre-cleaning weak references before diving into STW makes sense at the
 773   // end of concurrent mark. This will filter out the references which referents
 774   // are alive. Note that ReferenceProcessor already filters out these on reference
 775   // discovery, and the bulk of work is done here. This phase processes leftovers
 776   // that missed the initial filtering, i.e. when referent was marked alive after
 777   // reference was discovered by RP.
 778 
 779   assert(_heap->process_references(), "sanity");
 780 
 781   // Shortcut if no references were discovered to avoid winding up threads.
 782   ReferenceProcessor* rp = _heap->ref_processor();
 783   if (!rp->has_discovered_references()) {
 784     return;
 785   }
 786 
 787   assert(task_queues()->is_empty(), "Should be empty");
 788 
 789   ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
 790 
 791   shenandoah_assert_rp_isalive_not_installed();
 792   ShenandoahIsAliveSelector is_alive;
 793   ReferenceProcessorIsAliveMutator fix_isalive(rp, is_alive.is_alive_closure());
 794 
 795   // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
 796   // queues and other goodies. When upstream ReferenceProcessor starts supporting
 797   // parallel precleans, we can extend this to more threads.
 798   WorkGang* workers = _heap->workers();
 799   uint nworkers = workers->active_workers();
 800   assert(nworkers == 1, "This code uses only a single worker");
 801   task_queues()->reserve(nworkers);
 802 
 803   ShenandoahPrecleanTask task(rp);
 804   workers->run_task(&task);
 805 
 806   assert(task_queues()->is_empty(), "Should be empty");
 807 }
 808 
 809 void ShenandoahConcurrentMark::cancel() {
 810   // Clean up marking stacks.
 811   ShenandoahObjToScanQueueSet* queues = task_queues();
 812   queues->clear();
 813 
 814   // Cancel SATB buffers.
 815   ShenandoahBarrierSet::satb_mark_queue_set().abandon_partial_marking();
 816 }
 817 
 818 ShenandoahObjToScanQueue* ShenandoahConcurrentMark::get_queue(uint worker_id) {
 819   assert(task_queues()->get_reserved() > worker_id, "No reserved queue for worker id: %d", worker_id);
 820   return _task_queues->queue(worker_id);
 821 }
 822 
 823 template <bool CANCELLABLE>
 824 void ShenandoahConcurrentMark::mark_loop_prework(uint w, TaskTerminator *t, ReferenceProcessor *rp,
 825                                                  bool strdedup) {
 826   ShenandoahObjToScanQueue* q = get_queue(w);
 827 
 828   ShenandoahLiveData* ld = _heap->get_liveness_cache(w);
 829 
 830   // TODO: We can clean up this if we figure out how to do templated oop closures that
 831   // play nice with specialized_oop_iterators.
 832   if (_heap->unload_classes()) {
 833     if (_heap->has_forwarded_objects()) {
 834       if (strdedup) {
 835         ShenandoahMarkUpdateRefsMetadataDedupClosure cl(q, rp);
 836         mark_loop_work<ShenandoahMarkUpdateRefsMetadataDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 837       } else {
 838         ShenandoahMarkUpdateRefsMetadataClosure cl(q, rp);
 839         mark_loop_work<ShenandoahMarkUpdateRefsMetadataClosure, CANCELLABLE>(&cl, ld, w, t);
 840       }
 841     } else {
 842       if (strdedup) {
 843         ShenandoahMarkRefsMetadataDedupClosure cl(q, rp);
 844         mark_loop_work<ShenandoahMarkRefsMetadataDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 845       } else {
 846         ShenandoahMarkRefsMetadataClosure cl(q, rp);
 847         mark_loop_work<ShenandoahMarkRefsMetadataClosure, CANCELLABLE>(&cl, ld, w, t);
 848       }
 849     }
 850   } else {
 851     if (_heap->has_forwarded_objects()) {
 852       if (strdedup) {
 853         ShenandoahMarkUpdateRefsDedupClosure cl(q, rp);
 854         mark_loop_work<ShenandoahMarkUpdateRefsDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 855       } else {
 856         ShenandoahMarkUpdateRefsClosure cl(q, rp);
 857         mark_loop_work<ShenandoahMarkUpdateRefsClosure, CANCELLABLE>(&cl, ld, w, t);
 858       }
 859     } else {
 860       if (strdedup) {
 861         ShenandoahMarkRefsDedupClosure cl(q, rp);
 862         mark_loop_work<ShenandoahMarkRefsDedupClosure, CANCELLABLE>(&cl, ld, w, t);
 863       } else {
 864         ShenandoahMarkRefsClosure cl(q, rp);
 865         mark_loop_work<ShenandoahMarkRefsClosure, CANCELLABLE>(&cl, ld, w, t);
 866       }
 867     }
 868   }
 869 
 870   _heap->flush_liveness_cache(w);
 871 }
 872 
 873 template <class T, bool CANCELLABLE>
 874 void ShenandoahConcurrentMark::mark_loop_work(T* cl, ShenandoahLiveData* live_data, uint worker_id, TaskTerminator *terminator) {
 875   uintx stride = ShenandoahMarkLoopStride;
 876 
 877   ShenandoahHeap* heap = ShenandoahHeap::heap();
 878   ShenandoahObjToScanQueueSet* queues = task_queues();
 879   ShenandoahObjToScanQueue* q;
 880   ShenandoahMarkTask t;
 881 
 882   /*
 883    * Process outstanding queues, if any.
 884    *
 885    * There can be more queues than workers. To deal with the imbalance, we claim
 886    * extra queues first. Since marking can push new tasks into the queue associated
 887    * with this worker id, we come back to process this queue in the normal loop.
 888    */
 889   assert(queues->get_reserved() == heap->workers()->active_workers(),
 890          "Need to reserve proper number of queues: reserved: %u, active: %u", queues->get_reserved(), heap->workers()->active_workers());
 891 
 892   q = queues->claim_next();
 893   while (q != NULL) {
 894     if (CANCELLABLE && heap->check_cancelled_gc_and_yield()) {
 895       return;
 896     }
 897 
 898     for (uint i = 0; i < stride; i++) {
 899       if (q->pop(t)) {
 900         do_task<T>(q, cl, live_data, &t);
 901       } else {
 902         assert(q->is_empty(), "Must be empty");
 903         q = queues->claim_next();
 904         break;
 905       }
 906     }
 907   }
 908   q = get_queue(worker_id);
 909 
 910   ShenandoahSATBBufferClosure drain_satb(q);
 911   SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
 912 
 913   /*
 914    * Normal marking loop:
 915    */
 916   while (true) {
 917     if (CANCELLABLE && heap->check_cancelled_gc_and_yield()) {
 918       return;
 919     }
 920 
 921     while (satb_mq_set.completed_buffers_num() > 0) {
 922       satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
 923     }
 924 
 925     uint work = 0;
 926     for (uint i = 0; i < stride; i++) {
 927       if (q->pop(t) ||
 928           queues->steal(worker_id, t)) {
 929         do_task<T>(q, cl, live_data, &t);
 930         work++;
 931       } else {
 932         break;
 933       }
 934     }
 935 
 936     if (work == 0) {
 937       // No work encountered in current stride, try to terminate.
 938       // Need to leave the STS here otherwise it might block safepoints.
 939       ShenandoahSuspendibleThreadSetLeaver stsl(CANCELLABLE && ShenandoahSuspendibleWorkers);
 940       ShenandoahTerminatorTerminator tt(heap);
 941       if (terminator->offer_termination(&tt)) return;
 942     }
 943   }
 944 }
 945 
 946 bool ShenandoahConcurrentMark::claim_codecache() {
 947   return _claimed_codecache.try_set();
 948 }
 949 
 950 void ShenandoahConcurrentMark::clear_claim_codecache() {
 951   _claimed_codecache.unset();
 952 }