1 /* 2 * Copyright (c) 2001, 2015, 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 oop head() const { 62 return UseCompressedOops ? oopDesc::decode_heap_oop(_compressed_head) : 63 _oop_head; 64 } 65 HeapWord* adr_head() { 66 return UseCompressedOops ? (HeapWord*)&_compressed_head : 67 (HeapWord*)&_oop_head; 68 } 69 void set_head(oop o) { 70 if (UseCompressedOops) { 71 // Must compress the head ptr. 72 _compressed_head = oopDesc::encode_heap_oop(o); 73 } else { 74 _oop_head = o; 75 } 76 } 77 bool is_empty() const { return head() == NULL; } 78 size_t length() { return _len; } 79 void set_length(size_t len) { _len = len; } 80 void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); } 81 void dec_length(size_t dec) { _len -= dec; } 82 private: 83 // Set value depending on UseCompressedOops. This could be a template class 84 // but then we have to fix all the instantiations and declarations that use this class. 85 oop _oop_head; 86 narrowOop _compressed_head; 87 size_t _len; 88 }; 89 90 // Iterator for the list of discovered references. 91 class DiscoveredListIterator { 92 private: 93 DiscoveredList& _refs_list; 94 HeapWord* _prev_next; 95 oop _prev; 96 oop _ref; 97 HeapWord* _discovered_addr; 98 oop _next; 99 HeapWord* _referent_addr; 100 oop _referent; 101 OopClosure* _keep_alive; 102 BoolObjectClosure* _is_alive; 103 104 DEBUG_ONLY( 105 oop _first_seen; // cyclic linked list check 106 ) 107 108 NOT_PRODUCT( 109 size_t _processed; 110 size_t _removed; 111 ) 112 113 public: 114 inline DiscoveredListIterator(DiscoveredList& refs_list, 115 OopClosure* keep_alive, 116 BoolObjectClosure* is_alive): 117 _refs_list(refs_list), 118 _prev_next(refs_list.adr_head()), 119 _prev(NULL), 120 _ref(refs_list.head()), 121 #ifdef ASSERT 122 _first_seen(refs_list.head()), 123 #endif 124 #ifndef PRODUCT 125 _processed(0), 126 _removed(0), 127 #endif 128 _next(NULL), 129 _keep_alive(keep_alive), 130 _is_alive(is_alive) 131 { } 132 133 // End Of List. 134 inline bool has_next() const { return _ref != NULL; } 135 136 // Get oop to the Reference object. 137 inline oop obj() const { return _ref; } 138 139 // Get oop to the referent object. 140 inline oop referent() const { return _referent; } 141 142 // Returns true if referent is alive. 143 inline bool is_referent_alive() const { 144 return _is_alive->do_object_b(_referent); 145 } 146 147 // Loads data for the current reference. 148 // The "allow_null_referent" argument tells us to allow for the possibility 149 // of a NULL referent in the discovered Reference object. This typically 150 // happens in the case of concurrent collectors that may have done the 151 // discovery concurrently, or interleaved, with mutator execution. 152 void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); 153 154 // Move to the next discovered reference. 155 inline void next() { 156 _prev_next = _discovered_addr; 157 _prev = _ref; 158 move_to_next(); 159 } 160 161 // Remove the current reference from the list 162 void remove(); 163 164 // Make the referent alive. 165 inline void make_referent_alive() { 166 if (UseCompressedOops) { 167 _keep_alive->do_oop((narrowOop*)_referent_addr); 168 } else { 169 _keep_alive->do_oop((oop*)_referent_addr); 170 } 171 } 172 173 // NULL out referent pointer. 174 void clear_referent(); 175 176 // Statistics 177 NOT_PRODUCT( 178 inline size_t processed() const { return _processed; } 179 inline size_t removed() const { return _removed; } 180 ) 181 182 inline void move_to_next() { 183 if (_ref == _next) { 184 // End of the list. 185 _ref = NULL; 186 } else { 187 _ref = _next; 188 } 189 assert(_ref != _first_seen, "cyclic ref_list found"); 190 NOT_PRODUCT(_processed++); 191 } 192 }; 193 194 class ReferenceProcessor : public CHeapObj<mtGC> { 195 196 private: 197 size_t total_count(DiscoveredList lists[]); 198 199 protected: 200 // The SoftReference master timestamp clock 201 static jlong _soft_ref_timestamp_clock; 202 203 MemRegion _span; // (right-open) interval of heap 204 // subject to wkref discovery 205 206 bool _discovering_refs; // true when discovery enabled 207 bool _discovery_is_atomic; // if discovery is atomic wrt 208 // other collectors in configuration 209 bool _discovery_is_mt; // true if reference discovery is MT. 210 211 bool _enqueuing_is_done; // true if all weak references enqueued 212 bool _processing_is_mt; // true during phases when 213 // reference processing is MT. 214 uint _next_id; // round-robin mod _num_q counter in 215 // support of work distribution 216 217 // For collectors that do not keep GC liveness information 218 // in the object header, this field holds a closure that 219 // helps the reference processor determine the reachability 220 // of an oop. It is currently initialized to NULL for all 221 // collectors except for CMS and G1. 222 BoolObjectClosure* _is_alive_non_header; 223 224 // Soft ref clearing policies 225 // . the default policy 226 static ReferencePolicy* _default_soft_ref_policy; 227 // . the "clear all" policy 228 static ReferencePolicy* _always_clear_soft_ref_policy; 229 // . the current policy below is either one of the above 230 ReferencePolicy* _current_soft_ref_policy; 231 232 // The discovered ref lists themselves 233 234 // The active MT'ness degree of the queues below 235 uint _num_q; 236 // The maximum MT'ness degree of the queues below 237 uint _max_num_q; 238 239 // Master array of discovered oops 240 DiscoveredList* _discovered_refs; 241 242 // Arrays of lists of oops, one per thread (pointers into master array above) 243 DiscoveredList* _discoveredSoftRefs; 244 DiscoveredList* _discoveredWeakRefs; 245 DiscoveredList* _discoveredFinalRefs; 246 DiscoveredList* _discoveredPhantomRefs; 247 DiscoveredList* _discoveredCleanerRefs; 248 249 public: 250 static int number_of_subclasses_of_ref() { return (REF_CLEANER - REF_OTHER); } 251 252 uint num_q() { return _num_q; } 253 uint max_num_q() { return _max_num_q; } 254 void set_active_mt_degree(uint v) { _num_q = v; } 255 256 DiscoveredList* discovered_refs() { return _discovered_refs; } 257 258 ReferencePolicy* setup_policy(bool always_clear) { 259 _current_soft_ref_policy = always_clear ? 260 _always_clear_soft_ref_policy : _default_soft_ref_policy; 261 _current_soft_ref_policy->setup(); // snapshot the policy threshold 262 return _current_soft_ref_policy; 263 } 264 265 // Process references with a certain reachability level. 266 void process_discovered_reflist(DiscoveredList refs_lists[], 267 ReferencePolicy* policy, 268 bool clear_referent, 269 BoolObjectClosure* is_alive, 270 OopClosure* keep_alive, 271 VoidClosure* complete_gc, 272 AbstractRefProcTaskExecutor* task_executor); 273 274 void process_phaseJNI(BoolObjectClosure* is_alive, 275 OopClosure* keep_alive, 276 VoidClosure* complete_gc); 277 278 // Work methods used by the method process_discovered_reflist 279 // Phase1: keep alive all those referents that are otherwise 280 // dead but which must be kept alive by policy (and their closure). 281 void process_phase1(DiscoveredList& refs_list, 282 ReferencePolicy* policy, 283 BoolObjectClosure* is_alive, 284 OopClosure* keep_alive, 285 VoidClosure* complete_gc); 286 // Phase2: remove all those references whose referents are 287 // reachable. 288 inline void process_phase2(DiscoveredList& refs_list, 289 BoolObjectClosure* is_alive, 290 OopClosure* keep_alive, 291 VoidClosure* complete_gc) { 292 if (discovery_is_atomic()) { 293 // complete_gc is ignored in this case for this phase 294 pp2_work(refs_list, is_alive, keep_alive); 295 } else { 296 assert(complete_gc != NULL, "Error"); 297 pp2_work_concurrent_discovery(refs_list, is_alive, 298 keep_alive, complete_gc); 299 } 300 } 301 // Work methods in support of process_phase2 302 void pp2_work(DiscoveredList& refs_list, 303 BoolObjectClosure* is_alive, 304 OopClosure* keep_alive); 305 void pp2_work_concurrent_discovery( 306 DiscoveredList& refs_list, 307 BoolObjectClosure* is_alive, 308 OopClosure* keep_alive, 309 VoidClosure* complete_gc); 310 // Phase3: process the referents by either clearing them 311 // or keeping them alive (and their closure) 312 void process_phase3(DiscoveredList& refs_list, 313 bool clear_referent, 314 BoolObjectClosure* is_alive, 315 OopClosure* keep_alive, 316 VoidClosure* complete_gc); 317 318 // Enqueue references with a certain reachability level 319 void enqueue_discovered_reflist(DiscoveredList& refs_list, HeapWord* pending_list_addr); 320 321 // "Preclean" all the discovered reference lists 322 // by removing references with strongly reachable referents. 323 // The first argument is a predicate on an oop that indicates 324 // its (strong) reachability and the second is a closure that 325 // may be used to incrementalize or abort the precleaning process. 326 // The caller is responsible for taking care of potential 327 // interference with concurrent operations on these lists 328 // (or predicates involved) by other threads. Currently 329 // only used by the CMS collector. 330 void preclean_discovered_references(BoolObjectClosure* is_alive, 331 OopClosure* keep_alive, 332 VoidClosure* complete_gc, 333 YieldClosure* yield, 334 GCTimer* gc_timer); 335 336 // Returns the name of the discovered reference list 337 // occupying the i / _num_q slot. 338 const char* list_name(uint i); 339 340 void enqueue_discovered_reflists(HeapWord* pending_list_addr, AbstractRefProcTaskExecutor* task_executor); 341 342 protected: 343 // "Preclean" the given discovered reference list 344 // by removing references with strongly reachable referents. 345 // Currently used in support of CMS only. 346 void preclean_discovered_reflist(DiscoveredList& refs_list, 347 BoolObjectClosure* is_alive, 348 OopClosure* keep_alive, 349 VoidClosure* complete_gc, 350 YieldClosure* yield); 351 352 // round-robin mod _num_q (not: _not_ mode _max_num_q) 353 uint next_id() { 354 uint id = _next_id; 355 if (++_next_id == _num_q) { 356 _next_id = 0; 357 } 358 return id; 359 } 360 DiscoveredList* get_discovered_list(ReferenceType rt); 361 inline void add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj, 362 HeapWord* discovered_addr); 363 364 void clear_discovered_references(DiscoveredList& refs_list); 365 366 // Calculate the number of jni handles. 367 unsigned int count_jni_refs(); 368 369 // Balances reference queues. 370 void balance_queues(DiscoveredList ref_lists[]); 371 372 // Update (advance) the soft ref master clock field. 373 void update_soft_ref_master_clock(); 374 375 public: 376 // Default parameters give you a vanilla reference processor. 377 ReferenceProcessor(MemRegion span, 378 bool mt_processing = false, uint mt_processing_degree = 1, 379 bool mt_discovery = false, uint mt_discovery_degree = 1, 380 bool atomic_discovery = true, 381 BoolObjectClosure* is_alive_non_header = NULL); 382 383 // RefDiscoveryPolicy values 384 enum DiscoveryPolicy { 385 ReferenceBasedDiscovery = 0, 386 ReferentBasedDiscovery = 1, 387 DiscoveryPolicyMin = ReferenceBasedDiscovery, 388 DiscoveryPolicyMax = ReferentBasedDiscovery 389 }; 390 391 static void init_statics(); 392 393 public: 394 // get and set "is_alive_non_header" field 395 BoolObjectClosure* is_alive_non_header() { 396 return _is_alive_non_header; 397 } 398 void set_is_alive_non_header(BoolObjectClosure* is_alive_non_header) { 399 _is_alive_non_header = is_alive_non_header; 400 } 401 402 // get and set span 403 MemRegion span() { return _span; } 404 void set_span(MemRegion span) { _span = span; } 405 406 // start and stop weak ref discovery 407 void enable_discovery(bool check_no_refs = true); 408 void disable_discovery() { _discovering_refs = false; } 409 bool discovery_enabled() { return _discovering_refs; } 410 411 // whether discovery is atomic wrt other collectors 412 bool discovery_is_atomic() const { return _discovery_is_atomic; } 413 void set_atomic_discovery(bool atomic) { _discovery_is_atomic = atomic; } 414 415 // whether discovery is done by multiple threads same-old-timeously 416 bool discovery_is_mt() const { return _discovery_is_mt; } 417 void set_mt_discovery(bool mt) { _discovery_is_mt = mt; } 418 419 // Whether we are in a phase when _processing_ is MT. 420 bool processing_is_mt() const { return _processing_is_mt; } 421 void set_mt_processing(bool mt) { _processing_is_mt = mt; } 422 423 // whether all enqueueing of weak references is complete 424 bool enqueuing_is_done() { return _enqueuing_is_done; } 425 void set_enqueuing_is_done(bool v) { _enqueuing_is_done = v; } 426 427 // iterate over oops 428 void weak_oops_do(OopClosure* f); // weak roots 429 430 // Balance each of the discovered lists. 431 void balance_all_queues(); 432 void verify_list(DiscoveredList& ref_list); 433 434 // Discover a Reference object, using appropriate discovery criteria 435 bool discover_reference(oop obj, ReferenceType rt); 436 437 // Process references found during GC (called by the garbage collector) 438 ReferenceProcessorStats 439 process_discovered_references(BoolObjectClosure* is_alive, 440 OopClosure* keep_alive, 441 VoidClosure* complete_gc, 442 AbstractRefProcTaskExecutor* task_executor, 443 GCTimer *gc_timer); 444 445 // Enqueue references at end of GC (called by the garbage collector) 446 bool enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor = NULL); 447 448 // If a discovery is in process that is being superceded, abandon it: all 449 // the discovered lists will be empty, and all the objects on them will 450 // have NULL discovered fields. Must be called only at a safepoint. 451 void abandon_partial_discovery(); 452 453 // debugging 454 void verify_no_references_recorded() PRODUCT_RETURN; 455 void verify_referent(oop obj) PRODUCT_RETURN; 456 }; 457 458 // A utility class to disable reference discovery in 459 // the scope which contains it, for given ReferenceProcessor. 460 class NoRefDiscovery: StackObj { 461 private: 462 ReferenceProcessor* _rp; 463 bool _was_discovering_refs; 464 public: 465 NoRefDiscovery(ReferenceProcessor* rp) : _rp(rp) { 466 _was_discovering_refs = _rp->discovery_enabled(); 467 if (_was_discovering_refs) { 468 _rp->disable_discovery(); 469 } 470 } 471 472 ~NoRefDiscovery() { 473 if (_was_discovering_refs) { 474 _rp->enable_discovery(false /*check_no_refs*/); 475 } 476 } 477 }; 478 479 480 // A utility class to temporarily mutate the span of the 481 // given ReferenceProcessor in the scope that contains it. 482 class ReferenceProcessorSpanMutator: StackObj { 483 private: 484 ReferenceProcessor* _rp; 485 MemRegion _saved_span; 486 487 public: 488 ReferenceProcessorSpanMutator(ReferenceProcessor* rp, 489 MemRegion span): 490 _rp(rp) { 491 _saved_span = _rp->span(); 492 _rp->set_span(span); 493 } 494 495 ~ReferenceProcessorSpanMutator() { 496 _rp->set_span(_saved_span); 497 } 498 }; 499 500 // A utility class to temporarily change the MT'ness of 501 // reference discovery for the given ReferenceProcessor 502 // in the scope that contains it. 503 class ReferenceProcessorMTDiscoveryMutator: StackObj { 504 private: 505 ReferenceProcessor* _rp; 506 bool _saved_mt; 507 508 public: 509 ReferenceProcessorMTDiscoveryMutator(ReferenceProcessor* rp, 510 bool mt): 511 _rp(rp) { 512 _saved_mt = _rp->discovery_is_mt(); 513 _rp->set_mt_discovery(mt); 514 } 515 516 ~ReferenceProcessorMTDiscoveryMutator() { 517 _rp->set_mt_discovery(_saved_mt); 518 } 519 }; 520 521 522 // A utility class to temporarily change the disposition 523 // of the "is_alive_non_header" closure field of the 524 // given ReferenceProcessor in the scope that contains it. 525 class ReferenceProcessorIsAliveMutator: StackObj { 526 private: 527 ReferenceProcessor* _rp; 528 BoolObjectClosure* _saved_cl; 529 530 public: 531 ReferenceProcessorIsAliveMutator(ReferenceProcessor* rp, 532 BoolObjectClosure* cl): 533 _rp(rp) { 534 _saved_cl = _rp->is_alive_non_header(); 535 _rp->set_is_alive_non_header(cl); 536 } 537 538 ~ReferenceProcessorIsAliveMutator() { 539 _rp->set_is_alive_non_header(_saved_cl); 540 } 541 }; 542 543 // A utility class to temporarily change the disposition 544 // of the "discovery_is_atomic" field of the 545 // given ReferenceProcessor in the scope that contains it. 546 class ReferenceProcessorAtomicMutator: StackObj { 547 private: 548 ReferenceProcessor* _rp; 549 bool _saved_atomic_discovery; 550 551 public: 552 ReferenceProcessorAtomicMutator(ReferenceProcessor* rp, 553 bool atomic): 554 _rp(rp) { 555 _saved_atomic_discovery = _rp->discovery_is_atomic(); 556 _rp->set_atomic_discovery(atomic); 557 } 558 559 ~ReferenceProcessorAtomicMutator() { 560 _rp->set_atomic_discovery(_saved_atomic_discovery); 561 } 562 }; 563 564 565 // A utility class to temporarily change the MT processing 566 // disposition of the given ReferenceProcessor instance 567 // in the scope that contains it. 568 class ReferenceProcessorMTProcMutator: StackObj { 569 private: 570 ReferenceProcessor* _rp; 571 bool _saved_mt; 572 573 public: 574 ReferenceProcessorMTProcMutator(ReferenceProcessor* rp, 575 bool mt): 576 _rp(rp) { 577 _saved_mt = _rp->processing_is_mt(); 578 _rp->set_mt_processing(mt); 579 } 580 581 ~ReferenceProcessorMTProcMutator() { 582 _rp->set_mt_processing(_saved_mt); 583 } 584 }; 585 586 587 // This class is an interface used to implement task execution for the 588 // reference processing. 589 class AbstractRefProcTaskExecutor { 590 public: 591 592 // Abstract tasks to execute. 593 class ProcessTask; 594 class EnqueueTask; 595 596 // Executes a task using worker threads. 597 virtual void execute(ProcessTask& task) = 0; 598 virtual void execute(EnqueueTask& task) = 0; 599 600 // Switch to single threaded mode. 601 virtual void set_single_threaded_mode() { }; 602 }; 603 604 // Abstract reference processing task to execute. 605 class AbstractRefProcTaskExecutor::ProcessTask { 606 protected: 607 ProcessTask(ReferenceProcessor& ref_processor, 608 DiscoveredList refs_lists[], 609 bool marks_oops_alive) 610 : _ref_processor(ref_processor), 611 _refs_lists(refs_lists), 612 _marks_oops_alive(marks_oops_alive) 613 { } 614 615 public: 616 virtual void work(unsigned int work_id, BoolObjectClosure& is_alive, 617 OopClosure& keep_alive, 618 VoidClosure& complete_gc) = 0; 619 620 // Returns true if a task marks some oops as alive. 621 bool marks_oops_alive() const 622 { return _marks_oops_alive; } 623 624 protected: 625 ReferenceProcessor& _ref_processor; 626 DiscoveredList* _refs_lists; 627 const bool _marks_oops_alive; 628 }; 629 630 // Abstract reference processing task to execute. 631 class AbstractRefProcTaskExecutor::EnqueueTask { 632 protected: 633 EnqueueTask(ReferenceProcessor& ref_processor, 634 DiscoveredList refs_lists[], 635 HeapWord* pending_list_addr, 636 int n_queues) 637 : _ref_processor(ref_processor), 638 _refs_lists(refs_lists), 639 _pending_list_addr(pending_list_addr), 640 _n_queues(n_queues) 641 { } 642 643 public: 644 virtual void work(unsigned int work_id) = 0; 645 646 protected: 647 ReferenceProcessor& _ref_processor; 648 DiscoveredList* _refs_lists; 649 HeapWord* _pending_list_addr; 650 int _n_queues; 651 }; 652 653 #endif // SHARE_VM_GC_SHARED_REFERENCEPROCESSOR_HPP