1 /* 2 * Copyright (c) 2001, 2017, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP 26 #define SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP 27 28 #include "gc/shared/gcTrace.hpp" 29 #include "gc/shared/referencePolicy.hpp" 30 #include "gc/shared/referenceProcessorPhaseTimes.hpp" 31 #include "gc/shared/referenceProcessorStats.hpp" 32 #include "memory/referenceType.hpp" 33 #include "oops/instanceRefKlass.hpp" 34 35 class GCTimer; 36 37 // ReferenceProcessor class encapsulates the per-"collector" processing 38 // of java.lang.Reference objects for GC. The interface is useful for supporting 39 // a generational abstraction, in particular when there are multiple 40 // generations that are being independently collected -- possibly 41 // concurrently and/or incrementally. Note, however, that the 42 // ReferenceProcessor class abstracts away from a generational setting 43 // by using only a heap interval (called "span" below), thus allowing 44 // its use in a straightforward manner in a general, non-generational 45 // setting. 46 // 47 // The basic idea is that each ReferenceProcessor object concerns 48 // itself with ("weak") reference processing in a specific "span" 49 // of the heap of interest to a specific collector. Currently, 50 // the span is a convex interval of the heap, but, efficiency 51 // apart, there seems to be no reason it couldn't be extended 52 // (with appropriate modifications) to any "non-convex interval". 53 54 // forward references 55 class ReferencePolicy; 56 class AbstractRefProcTaskExecutor; 57 58 // List of discovered references. 59 class DiscoveredList { 60 public: 61 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { } 62 inline oop head() const; 63 HeapWord* adr_head() { 64 return UseCompressedOops ? (HeapWord*)&_compressed_head : 65 (HeapWord*)&_oop_head; 66 } 67 inline void set_head(oop o); 68 inline bool is_empty() const; 69 size_t length() { return _len; } 70 void set_length(size_t len) { _len = len; } 71 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); } 72 void dec_length(size_t dec) { _len -= dec; } 73 private: 74 // Set value depending on UseCompressedOops. This could be a template class 75 // but then we have to fix all the instantiations and declarations that use this class. 76 oop _oop_head; 77 narrowOop _compressed_head; 78 size_t _len; 79 }; 80 81 // Iterator for the list of discovered references. 82 class DiscoveredListIterator { 83 private: 84 DiscoveredList& _refs_list; 85 HeapWord* _prev_next; 86 oop _prev; 87 oop _ref; 88 HeapWord* _discovered_addr; 89 oop _next; 90 HeapWord* _referent_addr; 91 oop _referent; 92 OopClosure* _keep_alive; 93 BoolObjectClosure* _is_alive; 94 95 DEBUG_ONLY( 96 oop _first_seen; // cyclic linked list check 97 ) 98 99 NOT_PRODUCT( 100 size_t _processed; 101 size_t _removed; 102 ) 103 104 public: 105 inline DiscoveredListIterator(DiscoveredList& refs_list, 106 OopClosure* keep_alive, 107 BoolObjectClosure* is_alive); 108 109 // End Of List. 110 inline bool has_next() const { return _ref != NULL; } 111 112 // Get oop to the Reference object. 113 inline oop obj() const { return _ref; } 114 115 // Get oop to the referent object. 116 inline oop referent() const { return _referent; } 117 118 // Returns true if referent is alive. 119 inline bool is_referent_alive() const { 120 return _is_alive->do_object_b(_referent); 121 } 122 123 // Loads data for the current reference. 124 // The "allow_null_referent" argument tells us to allow for the possibility 125 // of a NULL referent in the discovered Reference object. This typically 126 // happens in the case of concurrent collectors that may have done the 127 // discovery concurrently, or interleaved, with mutator execution. 128 void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); 129 130 // Move to the next discovered reference. 131 inline void next() { 132 _prev_next = _discovered_addr; 133 _prev = _ref; 134 move_to_next(); 135 } 136 137 // Remove the current reference from the list 138 void remove(); 139 140 // Make the referent alive. 141 inline void make_referent_alive() { 142 if (UseCompressedOops) { 143 _keep_alive->do_oop((narrowOop*)_referent_addr); 144 } else { 145 _keep_alive->do_oop((oop*)_referent_addr); 146 } 147 } 148 149 // NULL out referent pointer. 150 void clear_referent(); 151 152 // Statistics 153 NOT_PRODUCT( 154 inline size_t processed() const { return _processed; } 155 inline size_t removed() const { return _removed; } 156 ) 157 158 inline void move_to_next() { 159 if (_ref == _next) { 160 // End of the list. 161 _ref = NULL; 162 } else { 163 _ref = _next; 164 } 165 assert(_ref != _first_seen, "cyclic ref_list found"); 166 NOT_PRODUCT(_processed++); 167 } 168 }; 169 170 class ReferenceProcessor : public CHeapObj<mtGC> { 171 172 private: 173 size_t total_count(DiscoveredList lists[]); 174 175 protected: 176 // The SoftReference master timestamp clock 177 static jlong _soft_ref_timestamp_clock; 178 179 MemRegion _span; // (right-open) interval of heap 180 // subject to wkref discovery 181 182 bool _discovering_refs; // true when discovery enabled 183 bool _discovery_is_atomic; // if discovery is atomic wrt 184 // other collectors in configuration 185 bool _discovery_is_mt; // true if reference discovery is MT. 186 187 bool _enqueuing_is_done; // true if all weak references enqueued 188 bool _processing_is_mt; // true during phases when 189 // reference processing is MT. 190 uint _next_id; // round-robin mod _num_q counter in 191 // support of work distribution 192 193 // For collectors that do not keep GC liveness information 194 // in the object header, this field holds a closure that 195 // helps the reference processor determine the reachability 196 // of an oop. It is currently initialized to NULL for all 197 // collectors except for CMS and G1. 198 BoolObjectClosure* _is_alive_non_header; 199 200 // Soft ref clearing policies 201 // . the default policy 202 static ReferencePolicy* _default_soft_ref_policy; 203 // . the "clear all" policy 204 static ReferencePolicy* _always_clear_soft_ref_policy; 205 // . the current policy below is either one of the above 206 ReferencePolicy* _current_soft_ref_policy; 207 208 // The discovered ref lists themselves 209 210 // The active MT'ness degree of the queues below 211 uint _num_q; 212 // The maximum MT'ness degree of the queues below 213 uint _max_num_q; 214 215 // Master array of discovered oops 216 DiscoveredList* _discovered_refs; 217 218 // Arrays of lists of oops, one per thread (pointers into master array above) 219 DiscoveredList* _discoveredSoftRefs; 220 DiscoveredList* _discoveredWeakRefs; 221 DiscoveredList* _discoveredFinalRefs; 222 DiscoveredList* _discoveredPhantomRefs; 223 224 ReferenceProcessorPhaseTimes* _phase_times; 225 226 public: 227 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); } 228 229 uint num_q() { return _num_q; } 230 uint max_num_q() { return _max_num_q; } 231 void set_active_mt_degree(uint v); 232 233 DiscoveredList* discovered_refs() { return _discovered_refs; } 234 235 ReferencePolicy* setup_policy(bool always_clear) { 236 _current_soft_ref_policy = always_clear ? 237 _always_clear_soft_ref_policy : _default_soft_ref_policy; 238 _current_soft_ref_policy->setup(); // snapshot the policy threshold 239 return _current_soft_ref_policy; 240 } 241 242 // Process references with a certain reachability level. 243 void process_discovered_reflist(DiscoveredList refs_lists[], 244 ReferencePolicy* policy, 245 bool clear_referent, 246 BoolObjectClosure* is_alive, 247 OopClosure* keep_alive, 248 VoidClosure* complete_gc, 249 AbstractRefProcTaskExecutor* task_executor, 250 GCTimer* gc_timer); 251 252 void process_phaseJNI(BoolObjectClosure* is_alive, 253 OopClosure* keep_alive, 254 VoidClosure* complete_gc); 255 256 // Work methods used by the method process_discovered_reflist 257 // Phase1: keep alive all those referents that are otherwise 258 // dead but which must be kept alive by policy (and their closure). 259 void process_phase1(DiscoveredList& refs_list, 260 ReferencePolicy* policy, 261 BoolObjectClosure* is_alive, 262 OopClosure* keep_alive, 263 VoidClosure* complete_gc); 264 // Phase2: remove all those references whose referents are 265 // reachable. 266 inline void process_phase2(DiscoveredList& refs_list, 267 BoolObjectClosure* is_alive, 268 OopClosure* keep_alive, 269 VoidClosure* complete_gc) { 270 if (discovery_is_atomic()) { 271 // complete_gc is ignored in this case for this phase 272 pp2_work(refs_list, is_alive, keep_alive); 273 } else { 274 assert(complete_gc != NULL, "Error"); 275 pp2_work_concurrent_discovery(refs_list, is_alive, 276 keep_alive, complete_gc); 277 } 278 } 279 // Work methods in support of process_phase2 280 void pp2_work(DiscoveredList& refs_list, 281 BoolObjectClosure* is_alive, 282 OopClosure* keep_alive); 283 void pp2_work_concurrent_discovery( 284 DiscoveredList& refs_list, 285 BoolObjectClosure* is_alive, 286 OopClosure* keep_alive, 287 VoidClosure* complete_gc); 288 // Phase3: process the referents by either clearing them 289 // or keeping them alive (and their closure) 290 void process_phase3(DiscoveredList& refs_list, 291 bool clear_referent, 292 BoolObjectClosure* is_alive, 293 OopClosure* keep_alive, 294 VoidClosure* complete_gc); 295 296 // Enqueue references with a certain reachability level 297 void enqueue_discovered_reflist(DiscoveredList& refs_list); 298 299 // "Preclean" all the discovered reference lists 300 // by removing references with strongly reachable referents. 301 // The first argument is a predicate on an oop that indicates 302 // its (strong) reachability and the second is a closure that 303 // may be used to incrementalize or abort the precleaning process. 304 // The caller is responsible for taking care of potential 305 // interference with concurrent operations on these lists 306 // (or predicates involved) by other threads. Currently 307 // only used by the CMS collector. 308 void preclean_discovered_references(BoolObjectClosure* is_alive, 309 OopClosure* keep_alive, 310 VoidClosure* complete_gc, 311 YieldClosure* yield, 312 GCTimer* gc_timer); 313 314 // Returns the name of the discovered reference list 315 // occupying the i / _num_q slot. 316 const char* list_name(uint i); 317 318 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor, GCTimer* gc_timer); 319 320 ReferenceProcessorPhaseTimes* phase_times() const { return _phase_times; } 321 322 protected: 323 // "Preclean" the given discovered reference list 324 // by removing references with strongly reachable referents. 325 // Currently used in support of CMS only. 326 void preclean_discovered_reflist(DiscoveredList& refs_list, 327 BoolObjectClosure* is_alive, 328 OopClosure* keep_alive, 329 VoidClosure* complete_gc, 330 YieldClosure* yield); 331 332 // round-robin mod _num_q (not: _not_ mode _max_num_q) 333 uint next_id() { 334 uint id = _next_id; 335 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery"); 336 if (++_next_id == _num_q) { 337 _next_id = 0; 338 } 339 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q); 340 return id; 341 } 342 DiscoveredList* get_discovered_list(ReferenceType rt); 343 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj, 344 HeapWord* discovered_addr); 345 346 void clear_discovered_references(DiscoveredList& refs_list); 347 348 // Calculate the number of jni handles. 349 size_t count_jni_refs(); 350 351 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN; 352 353 // Balances reference queues. 354 void balance_queues(DiscoveredList ref_lists[]); 355 356 // Update (advance) the soft ref master clock field. 357 void update_soft_ref_master_clock(); 358 359 public: 360 // Default parameters give you a vanilla reference processor. 361 ReferenceProcessor(MemRegion span, 362 bool mt_processing = false, uint mt_processing_degree = 1, 363 bool mt_discovery = false, uint mt_discovery_degree = 1, 364 bool atomic_discovery = true, 365 BoolObjectClosure* is_alive_non_header = NULL); 366 367 // RefDiscoveryPolicy values 368 enum DiscoveryPolicy { 369 ReferenceBasedDiscovery = 0, 370 ReferentBasedDiscovery = 1, 371 DiscoveryPolicyMin = ReferenceBasedDiscovery, 372 DiscoveryPolicyMax = ReferentBasedDiscovery 373 }; 374 375 static void init_statics(); 376 377 public: 378 // get and set "is_alive_non_header" field 379 BoolObjectClosure* is_alive_non_header() { 380 return _is_alive_non_header; 381 } 382 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) { 383 _is_alive_non_header = is_alive_non_header; 384 } 385 386 // get and set span 387 MemRegion span() { return _span; } 388 void set_span(MemRegion span) { _span = span; } 389 390 // start and stop weak ref discovery 391 void enable_discovery(bool check_no_refs = true); 392 void disable_discovery() { _discovering_refs = false; } 393 bool discovery_enabled() { return _discovering_refs; } 394 395 // whether discovery is atomic wrt other collectors 396 bool discovery_is_atomic() const { return _discovery_is_atomic; } 397 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; } 398 399 // whether discovery is done by multiple threads same-old-timeously 400 bool discovery_is_mt() const { return _discovery_is_mt; } 401 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; } 402 403 // Whether we are in a phase when _processing_ is MT. 404 bool processing_is_mt() const { return _processing_is_mt; } 405 void set_mt_processing(bool mt) { _processing_is_mt = mt; } 406 407 // whether all enqueueing of weak references is complete 408 bool enqueuing_is_done() { return _enqueuing_is_done; } 409 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; } 410 411 // iterate over oops 412 void weak_oops_do(OopClosure* f); // weak roots 413 414 // Balance each of the discovered lists. 415 void balance_all_queues(); 416 void verify_list(DiscoveredList& ref_list); 417 418 // Discover a Reference object, using appropriate discovery criteria 419 bool discover_reference(oop obj, ReferenceType rt); 420 421 // Has discovered references that need handling 422 bool has_discovered_references(); 423 424 // Process references found during GC (called by the garbage collector) 425 ReferenceProcessorStats 426 process_discovered_references(BoolObjectClosure* is_alive, 427 OopClosure* keep_alive, 428 VoidClosure* complete_gc, 429 AbstractRefProcTaskExecutor* task_executor, 430 GCTimer *gc_timer); 431 432 // Enqueue references at end of GC (called by the garbage collector) 433 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL, 434 GCTimer* gc_timer = NULL); 435 436 // If a discovery is in process that is being superceded, abandon it: all 437 // the discovered lists will be empty, and all the objects on them will 438 // have NULL discovered fields. Must be called only at a safepoint. 439 void abandon_partial_discovery(); 440 441 // debugging 442 void verify_no_references_recorded() PRODUCT_RETURN; 443 void verify_referent(oop obj) PRODUCT_RETURN; 444 }; 445 446 // A utility class to disable reference discovery in 447 // the scope which contains it, for given ReferenceProcessor. 448 class NoRefDiscovery: StackObj { 449 private: 450 ReferenceProcessor* _rp; 451 bool _was_discovering_refs; 452 public: 453 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) { 454 _was_discovering_refs = _rp->discovery_enabled(); 455 if (_was_discovering_refs) { 456 _rp->disable_discovery(); 457 } 458 } 459 460 ~NoRefDiscovery() { 461 if (_was_discovering_refs) { 462 _rp->enable_discovery(false /*check_no_refs*/); 463 } 464 } 465 }; 466 467 468 // A utility class to temporarily mutate the span of the 469 // given ReferenceProcessor in the scope that contains it. 470 class ReferenceProcessorSpanMutator: StackObj { 471 private: 472 ReferenceProcessor* _rp; 473 MemRegion _saved_span; 474 475 public: 476 ReferenceProcessorSpanMutator(ReferenceProcessor* rp, 477 MemRegion span): 478 _rp(rp) { 479 _saved_span = _rp->span(); 480 _rp->set_span(span); 481 } 482 483 ~ReferenceProcessorSpanMutator() { 484 _rp->set_span(_saved_span); 485 } 486 }; 487 488 // A utility class to temporarily change the MT'ness of 489 // reference discovery for the given ReferenceProcessor 490 // in the scope that contains it. 491 class ReferenceProcessorMTDiscoveryMutator: StackObj { 492 private: 493 ReferenceProcessor* _rp; 494 bool _saved_mt; 495 496 public: 497 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp, 498 bool mt): 499 _rp(rp) { 500 _saved_mt = _rp->discovery_is_mt(); 501 _rp->set_mt_discovery(mt); 502 } 503 504 ~ReferenceProcessorMTDiscoveryMutator() { 505 _rp->set_mt_discovery(_saved_mt); 506 } 507 }; 508 509 510 // A utility class to temporarily change the disposition 511 // of the "is_alive_non_header" closure field of the 512 // given ReferenceProcessor in the scope that contains it. 513 class ReferenceProcessorIsAliveMutator: StackObj { 514 private: 515 ReferenceProcessor* _rp; 516 BoolObjectClosure* _saved_cl; 517 518 public: 519 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp, 520 BoolObjectClosure* cl): 521 _rp(rp) { 522 _saved_cl = _rp->is_alive_non_header(); 523 _rp->set_is_alive_non_header(cl); 524 } 525 526 ~ReferenceProcessorIsAliveMutator() { 527 _rp->set_is_alive_non_header(_saved_cl); 528 } 529 }; 530 531 // A utility class to temporarily change the disposition 532 // of the "discovery_is_atomic" field of the 533 // given ReferenceProcessor in the scope that contains it. 534 class ReferenceProcessorAtomicMutator: StackObj { 535 private: 536 ReferenceProcessor* _rp; 537 bool _saved_atomic_discovery; 538 539 public: 540 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp, 541 bool atomic): 542 _rp(rp) { 543 _saved_atomic_discovery = _rp->discovery_is_atomic(); 544 _rp->set_atomic_discovery(atomic); 545 } 546 547 ~ReferenceProcessorAtomicMutator() { 548 _rp->set_atomic_discovery(_saved_atomic_discovery); 549 } 550 }; 551 552 553 // A utility class to temporarily change the MT processing 554 // disposition of the given ReferenceProcessor instance 555 // in the scope that contains it. 556 class ReferenceProcessorMTProcMutator: StackObj { 557 private: 558 ReferenceProcessor* _rp; 559 bool _saved_mt; 560 561 public: 562 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp, 563 bool mt): 564 _rp(rp) { 565 _saved_mt = _rp->processing_is_mt(); 566 _rp->set_mt_processing(mt); 567 } 568 569 ~ReferenceProcessorMTProcMutator() { 570 _rp->set_mt_processing(_saved_mt); 571 } 572 }; 573 574 575 // This class is an interface used to implement task execution for the 576 // reference processing. 577 class AbstractRefProcTaskExecutor { 578 public: 579 580 // Abstract tasks to execute. 581 class ProcessTask; 582 class EnqueueTask; 583 584 // Executes a task using worker threads. 585 virtual void execute(ProcessTask& task) = 0; 586 virtual void execute(EnqueueTask& task) = 0; 587 588 // Switch to single threaded mode. 589 virtual void set_single_threaded_mode() { }; 590 }; 591 592 // Abstract reference processing task to execute. 593 class AbstractRefProcTaskExecutor::ProcessTask { 594 protected: 595 ProcessTask(ReferenceProcessor& ref_processor, 596 DiscoveredList refs_lists[], 597 bool marks_oops_alive) 598 : _ref_processor(ref_processor), 599 _refs_lists(refs_lists), 600 _marks_oops_alive(marks_oops_alive) 601 { } 602 603 public: 604 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive, 605 OopClosure& keep_alive, 606 VoidClosure& complete_gc) = 0; 607 608 // Returns true if a task marks some oops as alive. 609 bool marks_oops_alive() const 610 { return _marks_oops_alive; } 611 612 protected: 613 ReferenceProcessor& _ref_processor; 614 DiscoveredList* _refs_lists; 615 const bool _marks_oops_alive; 616 }; 617 618 // Abstract reference processing task to execute. 619 class AbstractRefProcTaskExecutor::EnqueueTask { 620 protected: 621 EnqueueTask(ReferenceProcessor& ref_processor, 622 DiscoveredList refs_lists[], 623 int n_queues) 624 : _ref_processor(ref_processor), 625 _refs_lists(refs_lists), 626 _n_queues(n_queues) 627 { } 628 629 public: 630 virtual void work(unsigned int work_id) = 0; 631 632 protected: 633 ReferenceProcessor& _ref_processor; 634 DiscoveredList* _refs_lists; 635 int _n_queues; 636 }; 637 638 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP