1 /* 2 * Copyright (c) 2001, 2016, 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/referenceProcessorStats.hpp" 31 #include "memory/referenceType.hpp" 32 #include "oops/instanceRefKlass.hpp" 33 34 class GCTimer; 35 36 // ReferenceProcessor class encapsulates the per-"collector" processing 37 // of java.lang.Reference objects for GC. The interface is useful for supporting 38 // a generational abstraction, in particular when there are multiple 39 // generations that are being independently collected -- possibly 40 // concurrently and/or incrementally. Note, however, that the 41 // ReferenceProcessor class abstracts away from a generational setting 42 // by using only a heap interval (called "span" below), thus allowing 43 // its use in a straightforward manner in a general, non-generational 44 // setting. 45 // 46 // The basic idea is that each ReferenceProcessor object concerns 47 // itself with ("weak") reference processing in a specific "span" 48 // of the heap of interest to a specific collector. Currently, 49 // the span is a convex interval of the heap, but, efficiency 50 // apart, there seems to be no reason it couldn't be extended 51 // (with appropriate modifications) to any "non-convex interval". 52 53 // forward references 54 class ReferencePolicy; 55 class AbstractRefProcTaskExecutor; 56 57 // List of discovered references. 58 class DiscoveredList { 59 public: 60 DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { } 61 inline oop head() const; 62 HeapWord* adr_head() { 63 return UseCompressedOops ? (HeapWord*)&_compressed_head : 64 (HeapWord*)&_oop_head; 65 } 66 inline void set_head(oop o); 67 inline bool is_empty() const; 68 size_t length() { return _len; } 69 void set_length(size_t len) { _len = len; } 70 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); } 71 void dec_length(size_t dec) { _len -= dec; } 72 private: 73 // Set value depending on UseCompressedOops. This could be a template class 74 // but then we have to fix all the instantiations and declarations that use this class. 75 oop _oop_head; 76 narrowOop _compressed_head; 77 size_t _len; 78 }; 79 80 // Iterator for the list of discovered references. 81 class DiscoveredListIterator { 82 private: 83 DiscoveredList& _refs_list; 84 HeapWord* _prev_next; 85 oop _prev; 86 oop _ref; 87 HeapWord* _discovered_addr; 88 oop _next; 89 HeapWord* _referent_addr; 90 oop _referent; 91 OopClosure* _keep_alive; 92 BoolObjectClosure* _is_alive; 93 94 DEBUG_ONLY( 95 oop _first_seen; // cyclic linked list check 96 ) 97 98 NOT_PRODUCT( 99 size_t _processed; 100 size_t _removed; 101 ) 102 103 public: 104 inline DiscoveredListIterator(DiscoveredList& refs_list, 105 OopClosure* keep_alive, 106 BoolObjectClosure* is_alive); 107 108 // End Of List. 109 inline bool has_next() const { return _ref != NULL; } 110 111 // Get oop to the Reference object. 112 inline oop obj() const { return _ref; } 113 114 // Get oop to the referent object. 115 inline oop referent() const { return _referent; } 116 117 // Returns true if referent is alive. 118 inline bool is_referent_alive() const { 119 return _is_alive->do_object_b(_referent); 120 } 121 122 // Loads data for the current reference. 123 // The "allow_null_referent" argument tells us to allow for the possibility 124 // of a NULL referent in the discovered Reference object. This typically 125 // happens in the case of concurrent collectors that may have done the 126 // discovery concurrently, or interleaved, with mutator execution. 127 void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); 128 129 // Move to the next discovered reference. 130 inline void next() { 131 _prev_next = _discovered_addr; 132 _prev = _ref; 133 move_to_next(); 134 } 135 136 // Remove the current reference from the list 137 void remove(); 138 139 // Make the referent alive. 140 inline void make_referent_alive() { 141 if (UseCompressedOops) { 142 _keep_alive->do_oop((narrowOop*)_referent_addr); 143 } else { 144 _keep_alive->do_oop((oop*)_referent_addr); 145 } 146 } 147 148 // NULL out referent pointer. 149 void clear_referent(); 150 151 // Statistics 152 NOT_PRODUCT( 153 inline size_t processed() const { return _processed; } 154 inline size_t removed() const { return _removed; } 155 ) 156 157 inline void move_to_next() { 158 if (_ref == _next) { 159 // End of the list. 160 _ref = NULL; 161 } else { 162 _ref = _next; 163 } 164 assert(_ref != _first_seen, "cyclic ref_list found"); 165 NOT_PRODUCT(_processed++); 166 } 167 }; 168 169 class ReferenceProcessor : public CHeapObj<mtGC> { 170 171 private: 172 size_t total_count(DiscoveredList lists[]); 173 174 protected: 175 // The SoftReference master timestamp clock 176 static jlong _soft_ref_timestamp_clock; 177 178 MemRegion _span; // (right-open) interval of heap 179 // subject to wkref discovery 180 181 bool _discovering_refs; // true when discovery enabled 182 bool _discovery_is_atomic; // if discovery is atomic wrt 183 // other collectors in configuration 184 bool _discovery_is_mt; // true if reference discovery is MT. 185 186 bool _enqueuing_is_done; // true if all weak references enqueued 187 bool _processing_is_mt; // true during phases when 188 // reference processing is MT. 189 uint _next_id; // round-robin mod _num_q counter in 190 // support of work distribution 191 192 // For collectors that do not keep GC liveness information 193 // in the object header, this field holds a closure that 194 // helps the reference processor determine the reachability 195 // of an oop. It is currently initialized to NULL for all 196 // collectors except for CMS and G1. 197 BoolObjectClosure* _is_alive_non_header; 198 199 // Soft ref clearing policies 200 // . the default policy 201 static ReferencePolicy* _default_soft_ref_policy; 202 // . the "clear all" policy 203 static ReferencePolicy* _always_clear_soft_ref_policy; 204 // . the current policy below is either one of the above 205 ReferencePolicy* _current_soft_ref_policy; 206 207 // The discovered ref lists themselves 208 209 // The active MT'ness degree of the queues below 210 uint _num_q; 211 // The maximum MT'ness degree of the queues below 212 uint _max_num_q; 213 214 // Master array of discovered oops 215 DiscoveredList* _discovered_refs; 216 217 // Arrays of lists of oops, one per thread (pointers into master array above) 218 DiscoveredList* _discoveredSoftRefs; 219 DiscoveredList* _discoveredWeakRefs; 220 DiscoveredList* _discoveredFinalRefs; 221 DiscoveredList* _discoveredPhantomRefs; 222 223 public: 224 static int number_of_subclasses_of_ref() { return (REF_PHANTOM - REF_OTHER); } 225 226 uint num_q() { return _num_q; } 227 uint max_num_q() { return _max_num_q; } 228 void set_active_mt_degree(uint v); 229 230 DiscoveredList* discovered_refs() { return _discovered_refs; } 231 232 ReferencePolicy* setup_policy(bool always_clear) { 233 _current_soft_ref_policy = always_clear ? 234 _always_clear_soft_ref_policy : _default_soft_ref_policy; 235 _current_soft_ref_policy->setup(); // snapshot the policy threshold 236 return _current_soft_ref_policy; 237 } 238 239 // Process references with a certain reachability level. 240 void process_discovered_reflist(DiscoveredList refs_lists[], 241 ReferencePolicy* policy, 242 bool clear_referent, 243 BoolObjectClosure* is_alive, 244 OopClosure* keep_alive, 245 VoidClosure* complete_gc, 246 AbstractRefProcTaskExecutor* task_executor); 247 248 void process_phaseJNI(BoolObjectClosure* is_alive, 249 OopClosure* keep_alive, 250 VoidClosure* complete_gc); 251 252 size_t process_phaseHeapSampling(BoolObjectClosure* is_alive, 253 OopClosure* keep_alive, 254 VoidClosure* complete_gc, 255 AbstractRefProcTaskExecutor* task_executor); 256 257 // Work methods used by the method process_discovered_reflist 258 // Phase1: keep alive all those referents that are otherwise 259 // dead but which must be kept alive by policy (and their closure). 260 void process_phase1(DiscoveredList& refs_list, 261 ReferencePolicy* policy, 262 BoolObjectClosure* is_alive, 263 OopClosure* keep_alive, 264 VoidClosure* complete_gc); 265 // Phase2: remove all those references whose referents are 266 // reachable. 267 inline void process_phase2(DiscoveredList& refs_list, 268 BoolObjectClosure* is_alive, 269 OopClosure* keep_alive, 270 VoidClosure* complete_gc) { 271 if (discovery_is_atomic()) { 272 // complete_gc is ignored in this case for this phase 273 pp2_work(refs_list, is_alive, keep_alive); 274 } else { 275 assert(complete_gc != NULL, "Error"); 276 pp2_work_concurrent_discovery(refs_list, is_alive, 277 keep_alive, complete_gc); 278 } 279 } 280 // Work methods in support of process_phase2 281 void pp2_work(DiscoveredList& refs_list, 282 BoolObjectClosure* is_alive, 283 OopClosure* keep_alive); 284 void pp2_work_concurrent_discovery( 285 DiscoveredList& refs_list, 286 BoolObjectClosure* is_alive, 287 OopClosure* keep_alive, 288 VoidClosure* complete_gc); 289 // Phase3: process the referents by either clearing them 290 // or keeping them alive (and their closure) 291 void process_phase3(DiscoveredList& refs_list, 292 bool clear_referent, 293 BoolObjectClosure* is_alive, 294 OopClosure* keep_alive, 295 VoidClosure* complete_gc); 296 297 // Enqueue references with a certain reachability level 298 void enqueue_discovered_reflist(DiscoveredList& refs_list); 299 300 // "Preclean" all the discovered reference lists 301 // by removing references with strongly reachable referents. 302 // The first argument is a predicate on an oop that indicates 303 // its (strong) reachability and the second is a closure that 304 // may be used to incrementalize or abort the precleaning process. 305 // The caller is responsible for taking care of potential 306 // interference with concurrent operations on these lists 307 // (or predicates involved) by other threads. Currently 308 // only used by the CMS collector. 309 void preclean_discovered_references(BoolObjectClosure* is_alive, 310 OopClosure* keep_alive, 311 VoidClosure* complete_gc, 312 YieldClosure* yield, 313 GCTimer* gc_timer); 314 315 // Returns the name of the discovered reference list 316 // occupying the i / _num_q slot. 317 const char* list_name(uint i); 318 319 void enqueue_discovered_reflists(AbstractRefProcTaskExecutor* task_executor); 320 321 protected: 322 // "Preclean" the given discovered reference list 323 // by removing references with strongly reachable referents. 324 // Currently used in support of CMS only. 325 void preclean_discovered_reflist(DiscoveredList& refs_list, 326 BoolObjectClosure* is_alive, 327 OopClosure* keep_alive, 328 VoidClosure* complete_gc, 329 YieldClosure* yield); 330 331 // round-robin mod _num_q (not: _not_ mode _max_num_q) 332 uint next_id() { 333 uint id = _next_id; 334 assert(!_discovery_is_mt, "Round robin should only be used in serial discovery"); 335 if (++_next_id == _num_q) { 336 _next_id = 0; 337 } 338 assert(_next_id < _num_q, "_next_id %u _num_q %u _max_num_q %u", _next_id, _num_q, _max_num_q); 339 return id; 340 } 341 DiscoveredList* get_discovered_list(ReferenceType rt); 342 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj, 343 HeapWord* discovered_addr); 344 345 void clear_discovered_references(DiscoveredList& refs_list); 346 347 // Calculate the number of jni handles. 348 size_t count_jni_refs(); 349 350 void log_reflist_counts(DiscoveredList ref_lists[], uint active_length, size_t total_count) PRODUCT_RETURN; 351 352 // Balances reference queues. 353 void balance_queues(DiscoveredList ref_lists[]); 354 355 // Update (advance) the soft ref master clock field. 356 void update_soft_ref_master_clock(); 357 358 public: 359 // Default parameters give you a vanilla reference processor. 360 ReferenceProcessor(MemRegion span, 361 bool mt_processing = false, uint mt_processing_degree = 1, 362 bool mt_discovery = false, uint mt_discovery_degree = 1, 363 bool atomic_discovery = true, 364 BoolObjectClosure* is_alive_non_header = NULL); 365 366 // RefDiscoveryPolicy values 367 enum DiscoveryPolicy { 368 ReferenceBasedDiscovery = 0, 369 ReferentBasedDiscovery = 1, 370 DiscoveryPolicyMin = ReferenceBasedDiscovery, 371 DiscoveryPolicyMax = ReferentBasedDiscovery 372 }; 373 374 static void init_statics(); 375 376 public: 377 // get and set "is_alive_non_header" field 378 BoolObjectClosure* is_alive_non_header() { 379 return _is_alive_non_header; 380 } 381 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) { 382 _is_alive_non_header = is_alive_non_header; 383 } 384 385 // get and set span 386 MemRegion span() { return _span; } 387 void set_span(MemRegion span) { _span = span; } 388 389 // start and stop weak ref discovery 390 void enable_discovery(bool check_no_refs = true); 391 void disable_discovery() { _discovering_refs = false; } 392 bool discovery_enabled() { return _discovering_refs; } 393 394 // whether discovery is atomic wrt other collectors 395 bool discovery_is_atomic() const { return _discovery_is_atomic; } 396 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; } 397 398 // whether discovery is done by multiple threads same-old-timeously 399 bool discovery_is_mt() const { return _discovery_is_mt; } 400 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; } 401 402 // Whether we are in a phase when _processing_ is MT. 403 bool processing_is_mt() const { return _processing_is_mt; } 404 void set_mt_processing(bool mt) { _processing_is_mt = mt; } 405 406 // whether all enqueueing of weak references is complete 407 bool enqueuing_is_done() { return _enqueuing_is_done; } 408 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; } 409 410 // iterate over oops 411 void weak_oops_do(OopClosure* f); // weak roots 412 413 // Balance each of the discovered lists. 414 void balance_all_queues(); 415 void verify_list(DiscoveredList& ref_list); 416 417 // Discover a Reference object, using appropriate discovery criteria 418 bool discover_reference(oop obj, ReferenceType rt); 419 420 // Has discovered references that need handling 421 bool has_discovered_references(); 422 423 // Process references found during GC (called by the garbage collector) 424 ReferenceProcessorStats 425 process_discovered_references(BoolObjectClosure* is_alive, 426 OopClosure* keep_alive, 427 VoidClosure* complete_gc, 428 AbstractRefProcTaskExecutor* task_executor, 429 GCTimer *gc_timer); 430 431 // Enqueue references at end of GC (called by the garbage collector) 432 void enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL); 433 434 // If a discovery is in process that is being superceded, abandon it: all 435 // the discovered lists will be empty, and all the objects on them will 436 // have NULL discovered fields. Must be called only at a safepoint. 437 void abandon_partial_discovery(); 438 439 // debugging 440 void verify_no_references_recorded() PRODUCT_RETURN; 441 void verify_referent(oop obj) PRODUCT_RETURN; 442 }; 443 444 // A utility class to disable reference discovery in 445 // the scope which contains it, for given ReferenceProcessor. 446 class NoRefDiscovery: StackObj { 447 private: 448 ReferenceProcessor* _rp; 449 bool _was_discovering_refs; 450 public: 451 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) { 452 _was_discovering_refs = _rp->discovery_enabled(); 453 if (_was_discovering_refs) { 454 _rp->disable_discovery(); 455 } 456 } 457 458 ~NoRefDiscovery() { 459 if (_was_discovering_refs) { 460 _rp->enable_discovery(false /*check_no_refs*/); 461 } 462 } 463 }; 464 465 466 // A utility class to temporarily mutate the span of the 467 // given ReferenceProcessor in the scope that contains it. 468 class ReferenceProcessorSpanMutator: StackObj { 469 private: 470 ReferenceProcessor* _rp; 471 MemRegion _saved_span; 472 473 public: 474 ReferenceProcessorSpanMutator(ReferenceProcessor* rp, 475 MemRegion span): 476 _rp(rp) { 477 _saved_span = _rp->span(); 478 _rp->set_span(span); 479 } 480 481 ~ReferenceProcessorSpanMutator() { 482 _rp->set_span(_saved_span); 483 } 484 }; 485 486 // A utility class to temporarily change the MT'ness of 487 // reference discovery for the given ReferenceProcessor 488 // in the scope that contains it. 489 class ReferenceProcessorMTDiscoveryMutator: StackObj { 490 private: 491 ReferenceProcessor* _rp; 492 bool _saved_mt; 493 494 public: 495 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp, 496 bool mt): 497 _rp(rp) { 498 _saved_mt = _rp->discovery_is_mt(); 499 _rp->set_mt_discovery(mt); 500 } 501 502 ~ReferenceProcessorMTDiscoveryMutator() { 503 _rp->set_mt_discovery(_saved_mt); 504 } 505 }; 506 507 508 // A utility class to temporarily change the disposition 509 // of the "is_alive_non_header" closure field of the 510 // given ReferenceProcessor in the scope that contains it. 511 class ReferenceProcessorIsAliveMutator: StackObj { 512 private: 513 ReferenceProcessor* _rp; 514 BoolObjectClosure* _saved_cl; 515 516 public: 517 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp, 518 BoolObjectClosure* cl): 519 _rp(rp) { 520 _saved_cl = _rp->is_alive_non_header(); 521 _rp->set_is_alive_non_header(cl); 522 } 523 524 ~ReferenceProcessorIsAliveMutator() { 525 _rp->set_is_alive_non_header(_saved_cl); 526 } 527 }; 528 529 // A utility class to temporarily change the disposition 530 // of the "discovery_is_atomic" field of the 531 // given ReferenceProcessor in the scope that contains it. 532 class ReferenceProcessorAtomicMutator: StackObj { 533 private: 534 ReferenceProcessor* _rp; 535 bool _saved_atomic_discovery; 536 537 public: 538 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp, 539 bool atomic): 540 _rp(rp) { 541 _saved_atomic_discovery = _rp->discovery_is_atomic(); 542 _rp->set_atomic_discovery(atomic); 543 } 544 545 ~ReferenceProcessorAtomicMutator() { 546 _rp->set_atomic_discovery(_saved_atomic_discovery); 547 } 548 }; 549 550 551 // A utility class to temporarily change the MT processing 552 // disposition of the given ReferenceProcessor instance 553 // in the scope that contains it. 554 class ReferenceProcessorMTProcMutator: StackObj { 555 private: 556 ReferenceProcessor* _rp; 557 bool _saved_mt; 558 559 public: 560 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp, 561 bool mt): 562 _rp(rp) { 563 _saved_mt = _rp->processing_is_mt(); 564 _rp->set_mt_processing(mt); 565 } 566 567 ~ReferenceProcessorMTProcMutator() { 568 _rp->set_mt_processing(_saved_mt); 569 } 570 }; 571 572 573 // This class is an interface used to implement task execution for the 574 // reference processing. 575 class AbstractRefProcTaskExecutor { 576 public: 577 578 // Abstract tasks to execute. 579 class ProcessTask; 580 class EnqueueTask; 581 582 // Executes a task using worker threads. 583 virtual void execute(ProcessTask& task) = 0; 584 virtual void execute(EnqueueTask& task) = 0; 585 586 // Switch to single threaded mode. 587 virtual void set_single_threaded_mode() { }; 588 }; 589 590 // Abstract reference processing task to execute. 591 class AbstractRefProcTaskExecutor::ProcessTask { 592 protected: 593 ProcessTask(ReferenceProcessor& ref_processor, 594 DiscoveredList refs_lists[], 595 bool marks_oops_alive) 596 : _ref_processor(ref_processor), 597 _refs_lists(refs_lists), 598 _marks_oops_alive(marks_oops_alive) 599 { } 600 601 public: 602 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive, 603 OopClosure& keep_alive, 604 VoidClosure& complete_gc) = 0; 605 606 // Returns true if a task marks some oops as alive. 607 bool marks_oops_alive() const 608 { return _marks_oops_alive; } 609 610 protected: 611 ReferenceProcessor& _ref_processor; 612 DiscoveredList* _refs_lists; 613 const bool _marks_oops_alive; 614 }; 615 616 // Abstract reference processing task to execute. 617 class AbstractRefProcTaskExecutor::EnqueueTask { 618 protected: 619 EnqueueTask(ReferenceProcessor& ref_processor, 620 DiscoveredList refs_lists[], 621 int n_queues) 622 : _ref_processor(ref_processor), 623 _refs_lists(refs_lists), 624 _n_queues(n_queues) 625 { } 626 627 public: 628 virtual void work(unsigned int work_id) = 0; 629 630 protected: 631 ReferenceProcessor& _ref_processor; 632 DiscoveredList* _refs_lists; 633 int _n_queues; 634 }; 635 636 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP