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) { _num_q = 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 // Work methods used by the method process_discovered_reflist 253 // Phase1: keep alive all those referents that are otherwise 254 // dead but which must be kept alive by policy (and their closure). 255 void process_phase1(DiscoveredList& refs_list, 256 ReferencePolicy* policy, 257 BoolObjectClosure* is_alive, 258 OopClosure* keep_alive, 259 VoidClosure* complete_gc); 260 // Phase2: remove all those references whose referents are 261 // reachable. 262 inline void process_phase2(DiscoveredList& refs_list, 263 BoolObjectClosure* is_alive, 264 OopClosure* keep_alive, 265 VoidClosure* complete_gc) { 266 if (discovery_is_atomic()) { 267 // complete_gc is ignored in this case for this phase 268 pp2_work(refs_list, is_alive, keep_alive); 269 } else { 270 assert(complete_gc != NULL, "Error"); 271 pp2_work_concurrent_discovery(refs_list, is_alive, 272 keep_alive, complete_gc); 273 } 274 } 275 // Work methods in support of process_phase2 276 void pp2_work(DiscoveredList& refs_list, 277 BoolObjectClosure* is_alive, 278 OopClosure* keep_alive); 279 void pp2_work_concurrent_discovery( 280 DiscoveredList& refs_list, 281 BoolObjectClosure* is_alive, 282 OopClosure* keep_alive, 283 VoidClosure* complete_gc); 284 // Phase3: process the referents by either clearing them 285 // or keeping them alive (and their closure) 286 void process_phase3(DiscoveredList& refs_list, 287 bool clear_referent, 288 BoolObjectClosure* is_alive, 289 OopClosure* keep_alive, 290 VoidClosure* complete_gc); 291 292 // Enqueue references with a certain reachability level 293 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr); 294 295 // "Preclean" all the discovered reference lists 296 // by removing references with strongly reachable referents. 297 // The first argument is a predicate on an oop that indicates 298 // its (strong) reachability and the second is a closure that 299 // may be used to incrementalize or abort the precleaning process. 300 // The caller is responsible for taking care of potential 301 // interference with concurrent operations on these lists 302 // (or predicates involved) by other threads. Currently 303 // only used by the CMS collector. 304 void preclean_discovered_references(BoolObjectClosure* is_alive, 305 OopClosure* keep_alive, 306 VoidClosure* complete_gc, 307 YieldClosure* yield, 308 GCTimer* gc_timer); 309 310 // Returns the name of the discovered reference list 311 // occupying the i / _num_q slot. 312 const char* list_name(uint i); 313 314 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor); 315 316 protected: 317 // "Preclean" the given discovered reference list 318 // by removing references with strongly reachable referents. 319 // Currently used in support of CMS only. 320 void preclean_discovered_reflist(DiscoveredList& refs_list, 321 BoolObjectClosure* is_alive, 322 OopClosure* keep_alive, 323 VoidClosure* complete_gc, 324 YieldClosure* yield); 325 326 // round-robin mod _num_q (not: _not_ mode _max_num_q) 327 uint next_id() { 328 uint id = _next_id; 329 if (++_next_id == _num_q) { 330 _next_id = 0; 331 } 332 return id; 333 } 334 DiscoveredList* get_discovered_list(ReferenceType rt); 335 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj, 336 HeapWord* discovered_addr); 337 338 void clear_discovered_references(DiscoveredList& refs_list); 339 340 // Calculate the number of jni handles. 341 size_t count_jni_refs(); 342 343 void log_reflist_counts(DiscoveredList ref_lists[], size_t total_count) PRODUCT_RETURN; 344 345 // Balances reference queues. 346 void balance_queues(DiscoveredList ref_lists[]); 347 348 // Update (advance) the soft ref master clock field. 349 void update_soft_ref_master_clock(); 350 351 public: 352 // Default parameters give you a vanilla reference processor. 353 ReferenceProcessor(MemRegion span, 354 bool mt_processing = false, uint mt_processing_degree = 1, 355 bool mt_discovery = false, uint mt_discovery_degree = 1, 356 bool atomic_discovery = true, 357 BoolObjectClosure* is_alive_non_header = NULL); 358 359 // RefDiscoveryPolicy values 360 enum DiscoveryPolicy { 361 ReferenceBasedDiscovery = 0, 362 ReferentBasedDiscovery = 1, 363 DiscoveryPolicyMin = ReferenceBasedDiscovery, 364 DiscoveryPolicyMax = ReferentBasedDiscovery 365 }; 366 367 static void init_statics(); 368 369 public: 370 // get and set "is_alive_non_header" field 371 BoolObjectClosure* is_alive_non_header() { 372 return _is_alive_non_header; 373 } 374 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) { 375 _is_alive_non_header = is_alive_non_header; 376 } 377 378 // get and set span 379 MemRegion span() { return _span; } 380 void set_span(MemRegion span) { _span = span; } 381 382 // start and stop weak ref discovery 383 void enable_discovery(bool check_no_refs = true); 384 void disable_discovery() { _discovering_refs = false; } 385 bool discovery_enabled() { return _discovering_refs; } 386 387 // whether discovery is atomic wrt other collectors 388 bool discovery_is_atomic() const { return _discovery_is_atomic; } 389 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; } 390 391 // whether discovery is done by multiple threads same-old-timeously 392 bool discovery_is_mt() const { return _discovery_is_mt; } 393 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; } 394 395 // Whether we are in a phase when _processing_ is MT. 396 bool processing_is_mt() const { return _processing_is_mt; } 397 void set_mt_processing(bool mt) { _processing_is_mt = mt; } 398 399 // whether all enqueueing of weak references is complete 400 bool enqueuing_is_done() { return _enqueuing_is_done; } 401 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; } 402 403 // iterate over oops 404 void weak_oops_do(OopClosure* f); // weak roots 405 406 // Balance each of the discovered lists. 407 void balance_all_queues(); 408 void verify_list(DiscoveredList& ref_list); 409 410 // Discover a Reference object, using appropriate discovery criteria 411 bool discover_reference(oop obj, ReferenceType rt); 412 413 // Process references found during GC (called by the garbage collector) 414 ReferenceProcessorStats 415 process_discovered_references(BoolObjectClosure* is_alive, 416 OopClosure* keep_alive, 417 VoidClosure* complete_gc, 418 AbstractRefProcTaskExecutor* task_executor, 419 GCTimer *gc_timer); 420 421 // Enqueue references at end of GC (called by the garbage collector) 422 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL); 423 424 // If a discovery is in process that is being superceded, abandon it: all 425 // the discovered lists will be empty, and all the objects on them will 426 // have NULL discovered fields. Must be called only at a safepoint. 427 void abandon_partial_discovery(); 428 429 // debugging 430 void verify_no_references_recorded() PRODUCT_RETURN; 431 void verify_referent(oop obj) PRODUCT_RETURN; 432 }; 433 434 // A utility class to disable reference discovery in 435 // the scope which contains it, for given ReferenceProcessor. 436 class NoRefDiscovery: StackObj { 437 private: 438 ReferenceProcessor* _rp; 439 bool _was_discovering_refs; 440 public: 441 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) { 442 _was_discovering_refs = _rp->discovery_enabled(); 443 if (_was_discovering_refs) { 444 _rp->disable_discovery(); 445 } 446 } 447 448 ~NoRefDiscovery() { 449 if (_was_discovering_refs) { 450 _rp->enable_discovery(false /*check_no_refs*/); 451 } 452 } 453 }; 454 455 456 // A utility class to temporarily mutate the span of the 457 // given ReferenceProcessor in the scope that contains it. 458 class ReferenceProcessorSpanMutator: StackObj { 459 private: 460 ReferenceProcessor* _rp; 461 MemRegion _saved_span; 462 463 public: 464 ReferenceProcessorSpanMutator(ReferenceProcessor* rp, 465 MemRegion span): 466 _rp(rp) { 467 _saved_span = _rp->span(); 468 _rp->set_span(span); 469 } 470 471 ~ReferenceProcessorSpanMutator() { 472 _rp->set_span(_saved_span); 473 } 474 }; 475 476 // A utility class to temporarily change the MT'ness of 477 // reference discovery for the given ReferenceProcessor 478 // in the scope that contains it. 479 class ReferenceProcessorMTDiscoveryMutator: StackObj { 480 private: 481 ReferenceProcessor* _rp; 482 bool _saved_mt; 483 484 public: 485 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp, 486 bool mt): 487 _rp(rp) { 488 _saved_mt = _rp->discovery_is_mt(); 489 _rp->set_mt_discovery(mt); 490 } 491 492 ~ReferenceProcessorMTDiscoveryMutator() { 493 _rp->set_mt_discovery(_saved_mt); 494 } 495 }; 496 497 498 // A utility class to temporarily change the disposition 499 // of the "is_alive_non_header" closure field of the 500 // given ReferenceProcessor in the scope that contains it. 501 class ReferenceProcessorIsAliveMutator: StackObj { 502 private: 503 ReferenceProcessor* _rp; 504 BoolObjectClosure* _saved_cl; 505 506 public: 507 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp, 508 BoolObjectClosure* cl): 509 _rp(rp) { 510 _saved_cl = _rp->is_alive_non_header(); 511 _rp->set_is_alive_non_header(cl); 512 } 513 514 ~ReferenceProcessorIsAliveMutator() { 515 _rp->set_is_alive_non_header(_saved_cl); 516 } 517 }; 518 519 // A utility class to temporarily change the disposition 520 // of the "discovery_is_atomic" field of the 521 // given ReferenceProcessor in the scope that contains it. 522 class ReferenceProcessorAtomicMutator: StackObj { 523 private: 524 ReferenceProcessor* _rp; 525 bool _saved_atomic_discovery; 526 527 public: 528 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp, 529 bool atomic): 530 _rp(rp) { 531 _saved_atomic_discovery = _rp->discovery_is_atomic(); 532 _rp->set_atomic_discovery(atomic); 533 } 534 535 ~ReferenceProcessorAtomicMutator() { 536 _rp->set_atomic_discovery(_saved_atomic_discovery); 537 } 538 }; 539 540 541 // A utility class to temporarily change the MT processing 542 // disposition of the given ReferenceProcessor instance 543 // in the scope that contains it. 544 class ReferenceProcessorMTProcMutator: StackObj { 545 private: 546 ReferenceProcessor* _rp; 547 bool _saved_mt; 548 549 public: 550 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp, 551 bool mt): 552 _rp(rp) { 553 _saved_mt = _rp->processing_is_mt(); 554 _rp->set_mt_processing(mt); 555 } 556 557 ~ReferenceProcessorMTProcMutator() { 558 _rp->set_mt_processing(_saved_mt); 559 } 560 }; 561 562 563 // This class is an interface used to implement task execution for the 564 // reference processing. 565 class AbstractRefProcTaskExecutor { 566 public: 567 568 // Abstract tasks to execute. 569 class ProcessTask; 570 class EnqueueTask; 571 572 // Executes a task using worker threads. 573 virtual void execute(ProcessTask& task) = 0; 574 virtual void execute(EnqueueTask& task) = 0; 575 576 // Switch to single threaded mode. 577 virtual void set_single_threaded_mode() { }; 578 }; 579 580 // Abstract reference processing task to execute. 581 class AbstractRefProcTaskExecutor::ProcessTask { 582 protected: 583 ProcessTask(ReferenceProcessor& ref_processor, 584 DiscoveredList refs_lists[], 585 bool marks_oops_alive) 586 : _ref_processor(ref_processor), 587 _refs_lists(refs_lists), 588 _marks_oops_alive(marks_oops_alive) 589 { } 590 591 public: 592 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive, 593 OopClosure& keep_alive, 594 VoidClosure& complete_gc) = 0; 595 596 // Returns true if a task marks some oops as alive. 597 bool marks_oops_alive() const 598 { return _marks_oops_alive; } 599 600 protected: 601 ReferenceProcessor& _ref_processor; 602 DiscoveredList* _refs_lists; 603 const bool _marks_oops_alive; 604 }; 605 606 // Abstract reference processing task to execute. 607 class AbstractRefProcTaskExecutor::EnqueueTask { 608 protected: 609 EnqueueTask(ReferenceProcessor& ref_processor, 610 DiscoveredList refs_lists[], 611 HeapWord* pending_list_addr, 612 int n_queues) 613 : _ref_processor(ref_processor), 614 _refs_lists(refs_lists), 615 _pending_list_addr(pending_list_addr), 616 _n_queues(n_queues) 617 { } 618 619 public: 620 virtual void work(unsigned int work_id) = 0; 621 622 protected: 623 ReferenceProcessor& _ref_processor; 624 DiscoveredList* _refs_lists; 625 HeapWord* _pending_list_addr; 626 int _n_queues; 627 }; 628 629 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP