1 /* 2 * Copyright (c) 1997, 2014, 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_MEMORY_GENERATION_HPP 26 #define SHARE_VM_MEMORY_GENERATION_HPP 27 28 #include "gc_implementation/shared/collectorCounters.hpp" 29 #include "memory/allocation.hpp" 30 #include "memory/memRegion.hpp" 31 #include "memory/referenceProcessor.hpp" 32 #include "memory/universe.hpp" 33 #include "memory/watermark.hpp" 34 #include "runtime/mutex.hpp" 35 #include "runtime/perfData.hpp" 36 #include "runtime/virtualspace.hpp" 37 38 // A Generation models a heap area for similarly-aged objects. 39 // It will contain one ore more spaces holding the actual objects. 40 // 41 // The Generation class hierarchy: 42 // 43 // Generation - abstract base class 44 // - DefNewGeneration - allocation area (copy collected) 45 // - ParNewGeneration - a DefNewGeneration that is collected by 46 // several threads 47 // - CardGeneration - abstract class adding offset array behavior 48 // - OneContigSpaceCardGeneration - abstract class holding a single 49 // contiguous space with card marking 50 // - TenuredGeneration - tenured (old object) space (markSweepCompact) 51 // - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation 52 // (Detlefs-Printezis refinement of 53 // Boehm-Demers-Schenker) 54 // 55 // The system configurations currently allowed are: 56 // 57 // DefNewGeneration + TenuredGeneration 58 // DefNewGeneration + ConcurrentMarkSweepGeneration 59 // 60 // ParNewGeneration + TenuredGeneration 61 // ParNewGeneration + ConcurrentMarkSweepGeneration 62 // 63 64 class DefNewGeneration; 65 class GenerationSpec; 66 class CompactibleSpace; 67 class ContiguousSpace; 68 class CompactPoint; 69 class OopsInGenClosure; 70 class OopClosure; 71 class ScanClosure; 72 class FastScanClosure; 73 class GenCollectedHeap; 74 class GenRemSet; 75 class GCStats; 76 77 // A "ScratchBlock" represents a block of memory in one generation usable by 78 // another. It represents "num_words" free words, starting at and including 79 // the address of "this". 80 struct ScratchBlock { 81 ScratchBlock* next; 82 size_t num_words; 83 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming 84 // first two fields are word-sized.) 85 }; 86 87 88 class Generation: public CHeapObj<mtGC> { 89 friend class VMStructs; 90 private: 91 jlong _time_of_last_gc; // time when last gc on this generation happened (ms) 92 MemRegion _prev_used_region; // for collectors that want to "remember" a value for 93 // used region at some specific point during collection. 94 95 protected: 96 // Minimum and maximum addresses for memory reserved (not necessarily 97 // committed) for generation. 98 // Used by card marking code. Must not overlap with address ranges of 99 // other generations. 100 MemRegion _reserved; 101 102 // Memory area reserved for generation 103 VirtualSpace _virtual_space; 104 105 // Level in the generation hierarchy. 106 int _level; 107 108 // ("Weak") Reference processing support 109 ReferenceProcessor* _ref_processor; 110 111 // Performance Counters 112 CollectorCounters* _gc_counters; 113 114 // Statistics for garbage collection 115 GCStats* _gc_stats; 116 117 // Returns the next generation in the configuration, or else NULL if this 118 // is the highest generation. 119 Generation* next_gen() const; 120 121 // Initialize the generation. 122 Generation(ReservedSpace rs, size_t initial_byte_size, int level); 123 124 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in 125 // "sp" that point into younger generations. 126 // The iteration is only over objects allocated at the start of the 127 // iterations; objects allocated as a result of applying the closure are 128 // not included. 129 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl); 130 131 public: 132 // The set of possible generation kinds. 133 enum Name { 134 ASParNew, 135 ASConcurrentMarkSweep, 136 DefNew, 137 ParNew, 138 MarkSweepCompact, 139 ConcurrentMarkSweep, 140 Other 141 }; 142 143 enum SomePublicConstants { 144 // Generations are GenGrain-aligned and have size that are multiples of 145 // GenGrain. 146 // Note: on ARM we add 1 bit for card_table_base to be properly aligned 147 // (we expect its low byte to be zero - see implementation of post_barrier) 148 LogOfGenGrain = 16 ARM_ONLY(+1), 149 GenGrain = 1 << LogOfGenGrain 150 }; 151 152 // allocate and initialize ("weak") refs processing support 153 virtual void ref_processor_init(); 154 void set_ref_processor(ReferenceProcessor* rp) { 155 assert(_ref_processor == NULL, "clobbering existing _ref_processor"); 156 _ref_processor = rp; 157 } 158 159 virtual Generation::Name kind() { return Generation::Other; } 160 GenerationSpec* spec(); 161 162 // This properly belongs in the collector, but for now this 163 // will do. 164 virtual bool refs_discovery_is_atomic() const { return true; } 165 virtual bool refs_discovery_is_mt() const { return false; } 166 167 // Space enquiries (results in bytes) 168 virtual size_t capacity() const = 0; // The maximum number of object bytes the 169 // generation can currently hold. 170 virtual size_t used() const = 0; // The number of used bytes in the gen. 171 virtual size_t free() const = 0; // The number of free bytes in the gen. 172 173 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap. 174 // Returns the total number of bytes available in a generation 175 // for the allocation of objects. 176 virtual size_t max_capacity() const; 177 178 // If this is a young generation, the maximum number of bytes that can be 179 // allocated in this generation before a GC is triggered. 180 virtual size_t capacity_before_gc() const { return 0; } 181 182 // The largest number of contiguous free bytes in the generation, 183 // including expansion (Assumes called at a safepoint.) 184 virtual size_t contiguous_available() const = 0; 185 // The largest number of contiguous free bytes in this or any higher generation. 186 virtual size_t max_contiguous_available() const; 187 188 // Returns true if promotions of the specified amount are 189 // likely to succeed without a promotion failure. 190 // Promotion of the full amount is not guaranteed but 191 // might be attempted in the worst case. 192 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const; 193 194 // For a non-young generation, this interface can be used to inform a 195 // generation that a promotion attempt into that generation failed. 196 // Typically used to enable diagnostic output for post-mortem analysis, 197 // but other uses of the interface are not ruled out. 198 virtual void promotion_failure_occurred() { /* does nothing */ } 199 200 // Return an estimate of the maximum allocation that could be performed 201 // in the generation without triggering any collection or expansion 202 // activity. It is "unsafe" because no locks are taken; the result 203 // should be treated as an approximation, not a guarantee, for use in 204 // heuristic resizing decisions. 205 virtual size_t unsafe_max_alloc_nogc() const = 0; 206 207 // Returns true if this generation cannot be expanded further 208 // without a GC. Override as appropriate. 209 virtual bool is_maximal_no_gc() const { 210 return _virtual_space.uncommitted_size() == 0; 211 } 212 213 MemRegion reserved() const { return _reserved; } 214 215 // Returns a region guaranteed to contain all the objects in the 216 // generation. 217 virtual MemRegion used_region() const { return _reserved; } 218 219 MemRegion prev_used_region() const { return _prev_used_region; } 220 virtual void save_used_region() { _prev_used_region = used_region(); } 221 222 // Returns "TRUE" iff "p" points into the committed areas in the generation. 223 // For some kinds of generations, this may be an expensive operation. 224 // To avoid performance problems stemming from its inadvertent use in 225 // product jvm's, we restrict its use to assertion checking or 226 // verification only. 227 virtual bool is_in(const void* p) const; 228 229 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */ 230 bool is_in_reserved(const void* p) const { 231 return _reserved.contains(p); 232 } 233 234 // Check that the generation kind is DefNewGeneration or a sub 235 // class of DefNewGeneration and return a DefNewGeneration* 236 DefNewGeneration* as_DefNewGeneration(); 237 238 // If some space in the generation contains the given "addr", return a 239 // pointer to that space, else return "NULL". 240 virtual Space* space_containing(const void* addr) const; 241 242 // Iteration - do not use for time critical operations 243 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0; 244 245 // Returns the first space, if any, in the generation that can participate 246 // in compaction, or else "NULL". 247 virtual CompactibleSpace* first_compaction_space() const = 0; 248 249 // Returns "true" iff this generation should be used to allocate an 250 // object of the given size. Young generations might 251 // wish to exclude very large objects, for example, since, if allocated 252 // often, they would greatly increase the frequency of young-gen 253 // collection. 254 virtual bool should_allocate(size_t word_size, bool is_tlab) { 255 bool result = false; 256 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize); 257 if (!is_tlab || supports_tlab_allocation()) { 258 result = (word_size > 0) && (word_size < overflow_limit); 259 } 260 return result; 261 } 262 263 // Allocate and returns a block of the requested size, or returns "NULL". 264 // Assumes the caller has done any necessary locking. 265 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0; 266 267 // Like "allocate", but performs any necessary locking internally. 268 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0; 269 270 // A 'younger' gen has reached an allocation limit, and uses this to notify 271 // the next older gen. The return value is a new limit, or NULL if none. The 272 // caller must do the necessary locking. 273 virtual HeapWord* allocation_limit_reached(Space* space, HeapWord* top, 274 size_t word_size) { 275 return NULL; 276 } 277 278 // Some generation may offer a region for shared, contiguous allocation, 279 // via inlined code (by exporting the address of the top and end fields 280 // defining the extent of the contiguous allocation region.) 281 282 // This function returns "true" iff the heap supports this kind of 283 // allocation. (More precisely, this means the style of allocation that 284 // increments *top_addr()" with a CAS.) (Default is "no".) 285 // A generation that supports this allocation style must use lock-free 286 // allocation for *all* allocation, since there are times when lock free 287 // allocation will be concurrent with plain "allocate" calls. 288 virtual bool supports_inline_contig_alloc() const { return false; } 289 290 // These functions return the addresses of the fields that define the 291 // boundaries of the contiguous allocation area. (These fields should be 292 // physicall near to one another.) 293 virtual HeapWord** top_addr() const { return NULL; } 294 virtual HeapWord** end_addr() const { return NULL; } 295 296 // Thread-local allocation buffers 297 virtual bool supports_tlab_allocation() const { return false; } 298 virtual size_t tlab_capacity() const { 299 guarantee(false, "Generation doesn't support thread local allocation buffers"); 300 return 0; 301 } 302 virtual size_t tlab_used() const { 303 guarantee(false, "Generation doesn't support thread local allocation buffers"); 304 return 0; 305 } 306 virtual size_t unsafe_max_tlab_alloc() const { 307 guarantee(false, "Generation doesn't support thread local allocation buffers"); 308 return 0; 309 } 310 311 // "obj" is the address of an object in a younger generation. Allocate space 312 // for "obj" in the current (or some higher) generation, and copy "obj" into 313 // the newly allocated space, if possible, returning the result (or NULL if 314 // the allocation failed). 315 // 316 // The "obj_size" argument is just obj->size(), passed along so the caller can 317 // avoid repeating the virtual call to retrieve it. 318 virtual oop promote(oop obj, size_t obj_size); 319 320 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote 321 // object "obj", whose original mark word was "m", and whose size is 322 // "word_sz". If possible, allocate space for "obj", copy obj into it 323 // (taking care to copy "m" into the mark word when done, since the mark 324 // word of "obj" may have been overwritten with a forwarding pointer, and 325 // also taking care to copy the klass pointer *last*. Returns the new 326 // object if successful, or else NULL. 327 virtual oop par_promote(int thread_num, 328 oop obj, markOop m, size_t word_sz); 329 330 // Undo, if possible, the most recent par_promote_alloc allocation by 331 // "thread_num" ("obj", of "word_sz"). 332 virtual void par_promote_alloc_undo(int thread_num, 333 HeapWord* obj, size_t word_sz); 334 335 // Informs the current generation that all par_promote_alloc's in the 336 // collection have been completed; any supporting data structures can be 337 // reset. Default is to do nothing. 338 virtual void par_promote_alloc_done(int thread_num) {} 339 340 // Informs the current generation that all oop_since_save_marks_iterates 341 // performed by "thread_num" in the current collection, if any, have been 342 // completed; any supporting data structures can be reset. Default is to 343 // do nothing. 344 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {} 345 346 // This generation will collect all younger generations 347 // during a full collection. 348 virtual bool full_collects_younger_generations() const { return false; } 349 350 // This generation does in-place marking, meaning that mark words 351 // are mutated during the marking phase and presumably reinitialized 352 // to a canonical value after the GC. This is currently used by the 353 // biased locking implementation to determine whether additional 354 // work is required during the GC prologue and epilogue. 355 virtual bool performs_in_place_marking() const { return true; } 356 357 // Returns "true" iff collect() should subsequently be called on this 358 // this generation. See comment below. 359 // This is a generic implementation which can be overridden. 360 // 361 // Note: in the current (1.4) implementation, when genCollectedHeap's 362 // incremental_collection_will_fail flag is set, all allocations are 363 // slow path (the only fast-path place to allocate is DefNew, which 364 // will be full if the flag is set). 365 // Thus, older generations which collect younger generations should 366 // test this flag and collect if it is set. 367 virtual bool should_collect(bool full, 368 size_t word_size, 369 bool is_tlab) { 370 return (full || should_allocate(word_size, is_tlab)); 371 } 372 373 // Returns true if the collection is likely to be safely 374 // completed. Even if this method returns true, a collection 375 // may not be guaranteed to succeed, and the system should be 376 // able to safely unwind and recover from that failure, albeit 377 // at some additional cost. 378 virtual bool collection_attempt_is_safe() { 379 guarantee(false, "Are you sure you want to call this method?"); 380 return true; 381 } 382 383 // Perform a garbage collection. 384 // If full is true attempt a full garbage collection of this generation. 385 // Otherwise, attempting to (at least) free enough space to support an 386 // allocation of the given "word_size". 387 virtual void collect(bool full, 388 bool clear_all_soft_refs, 389 size_t word_size, 390 bool is_tlab) = 0; 391 392 // Perform a heap collection, attempting to create (at least) enough 393 // space to support an allocation of the given "word_size". If 394 // successful, perform the allocation and return the resulting 395 // "oop" (initializing the allocated block). If the allocation is 396 // still unsuccessful, return "NULL". 397 virtual HeapWord* expand_and_allocate(size_t word_size, 398 bool is_tlab, 399 bool parallel = false) = 0; 400 401 // Some generations may require some cleanup or preparation actions before 402 // allowing a collection. The default is to do nothing. 403 virtual void gc_prologue(bool full) {}; 404 405 // Some generations may require some cleanup actions after a collection. 406 // The default is to do nothing. 407 virtual void gc_epilogue(bool full) {}; 408 409 // Save the high water marks for the used space in a generation. 410 virtual void record_spaces_top() {}; 411 412 // Some generations may need to be "fixed-up" after some allocation 413 // activity to make them parsable again. The default is to do nothing. 414 virtual void ensure_parsability() {}; 415 416 // Time (in ms) when we were last collected or now if a collection is 417 // in progress. 418 virtual jlong time_of_last_gc(jlong now) { 419 // Both _time_of_last_gc and now are set using a time source 420 // that guarantees monotonically non-decreasing values provided 421 // the underlying platform provides such a source. So we still 422 // have to guard against non-monotonicity. 423 NOT_PRODUCT( 424 if (now < _time_of_last_gc) { 425 warning("time warp: "INT64_FORMAT" to "INT64_FORMAT, (int64_t)_time_of_last_gc, (int64_t)now); 426 } 427 ) 428 return _time_of_last_gc; 429 } 430 431 virtual void update_time_of_last_gc(jlong now) { 432 _time_of_last_gc = now; 433 } 434 435 // Generations may keep statistics about collection. This 436 // method updates those statistics. current_level is 437 // the level of the collection that has most recently 438 // occurred. This allows the generation to decide what 439 // statistics are valid to collect. For example, the 440 // generation can decide to gather the amount of promoted data 441 // if the collection of the younger generations has completed. 442 GCStats* gc_stats() const { return _gc_stats; } 443 virtual void update_gc_stats(int current_level, bool full) {} 444 445 // Mark sweep support phase2 446 virtual void prepare_for_compaction(CompactPoint* cp); 447 // Mark sweep support phase3 448 virtual void adjust_pointers(); 449 // Mark sweep support phase4 450 virtual void compact(); 451 virtual void post_compact() {ShouldNotReachHere();} 452 453 // Support for CMS's rescan. In this general form we return a pointer 454 // to an abstract object that can be used, based on specific previously 455 // decided protocols, to exchange information between generations, 456 // information that may be useful for speeding up certain types of 457 // garbage collectors. A NULL value indicates to the client that 458 // no data recording is expected by the provider. The data-recorder is 459 // expected to be GC worker thread-local, with the worker index 460 // indicated by "thr_num". 461 virtual void* get_data_recorder(int thr_num) { return NULL; } 462 virtual void sample_eden_chunk() {} 463 464 // Some generations may require some cleanup actions before allowing 465 // a verification. 466 virtual void prepare_for_verify() {}; 467 468 // Accessing "marks". 469 470 // This function gives a generation a chance to note a point between 471 // collections. For example, a contiguous generation might note the 472 // beginning allocation point post-collection, which might allow some later 473 // operations to be optimized. 474 virtual void save_marks() {} 475 476 // This function allows generations to initialize any "saved marks". That 477 // is, should only be called when the generation is empty. 478 virtual void reset_saved_marks() {} 479 480 // This function is "true" iff any no allocations have occurred in the 481 // generation since the last call to "save_marks". 482 virtual bool no_allocs_since_save_marks() = 0; 483 484 // Apply "cl->apply" to (the addresses of) all reference fields in objects 485 // allocated in the current generation since the last call to "save_marks". 486 // If more objects are allocated in this generation as a result of applying 487 // the closure, iterates over reference fields in those objects as well. 488 // Calls "save_marks" at the end of the iteration. 489 // General signature... 490 virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0; 491 // ...and specializations for de-virtualization. (The general 492 // implemention of the _nv versions call the virtual version. 493 // Note that the _nv suffix is not really semantically necessary, 494 // but it avoids some not-so-useful warnings on Solaris.) 495 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \ 496 virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ 497 oop_since_save_marks_iterate_v((OopsInGenClosure*)cl); \ 498 } 499 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL) 500 501 #undef Generation_SINCE_SAVE_MARKS_DECL 502 503 // The "requestor" generation is performing some garbage collection 504 // action for which it would be useful to have scratch space. If 505 // the target is not the requestor, no gc actions will be required 506 // of the target. The requestor promises to allocate no more than 507 // "max_alloc_words" in the target generation (via promotion say, 508 // if the requestor is a young generation and the target is older). 509 // If the target generation can provide any scratch space, it adds 510 // it to "list", leaving "list" pointing to the head of the 511 // augmented list. The default is to offer no space. 512 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor, 513 size_t max_alloc_words) {} 514 515 // Give each generation an opportunity to do clean up for any 516 // contributed scratch. 517 virtual void reset_scratch() {}; 518 519 // When an older generation has been collected, and perhaps resized, 520 // this method will be invoked on all younger generations (from older to 521 // younger), allowing them to resize themselves as appropriate. 522 virtual void compute_new_size() = 0; 523 524 // Printing 525 virtual const char* name() const = 0; 526 virtual const char* short_name() const = 0; 527 528 int level() const { return _level; } 529 530 // Attributes 531 532 // True iff the given generation may only be the youngest generation. 533 virtual bool must_be_youngest() const = 0; 534 // True iff the given generation may only be the oldest generation. 535 virtual bool must_be_oldest() const = 0; 536 537 // Reference Processing accessor 538 ReferenceProcessor* const ref_processor() { return _ref_processor; } 539 540 // Iteration. 541 542 // Iterate over all the ref-containing fields of all objects in the 543 // generation, calling "cl.do_oop" on each. 544 virtual void oop_iterate(ExtendedOopClosure* cl); 545 546 // Iterate over all objects in the generation, calling "cl.do_object" on 547 // each. 548 virtual void object_iterate(ObjectClosure* cl); 549 550 // Iterate over all safe objects in the generation, calling "cl.do_object" on 551 // each. An object is safe if its references point to other objects in 552 // the heap. This defaults to object_iterate() unless overridden. 553 virtual void safe_object_iterate(ObjectClosure* cl); 554 555 // Apply "cl->do_oop" to (the address of) all and only all the ref fields 556 // in the current generation that contain pointers to objects in younger 557 // generations. Objects allocated since the last "save_marks" call are 558 // excluded. 559 virtual void younger_refs_iterate(OopsInGenClosure* cl) = 0; 560 561 // Inform a generation that it longer contains references to objects 562 // in any younger generation. [e.g. Because younger gens are empty, 563 // clear the card table.] 564 virtual void clear_remembered_set() { } 565 566 // Inform a generation that some of its objects have moved. [e.g. The 567 // generation's spaces were compacted, invalidating the card table.] 568 virtual void invalidate_remembered_set() { } 569 570 // Block abstraction. 571 572 // Returns the address of the start of the "block" that contains the 573 // address "addr". We say "blocks" instead of "object" since some heaps 574 // may not pack objects densely; a chunk may either be an object or a 575 // non-object. 576 virtual HeapWord* block_start(const void* addr) const; 577 578 // Requires "addr" to be the start of a chunk, and returns its size. 579 // "addr + size" is required to be the start of a new chunk, or the end 580 // of the active area of the heap. 581 virtual size_t block_size(const HeapWord* addr) const ; 582 583 // Requires "addr" to be the start of a block, and returns "TRUE" iff 584 // the block is an object. 585 virtual bool block_is_obj(const HeapWord* addr) const; 586 587 588 // PrintGC, PrintGCDetails support 589 void print_heap_change(size_t prev_used) const; 590 591 // PrintHeapAtGC support 592 virtual void print() const; 593 virtual void print_on(outputStream* st) const; 594 595 virtual void verify() = 0; 596 597 struct StatRecord { 598 int invocations; 599 elapsedTimer accumulated_time; 600 StatRecord() : 601 invocations(0), 602 accumulated_time(elapsedTimer()) {} 603 }; 604 private: 605 StatRecord _stat_record; 606 public: 607 StatRecord* stat_record() { return &_stat_record; } 608 609 virtual void print_summary_info(); 610 virtual void print_summary_info_on(outputStream* st); 611 612 // Performance Counter support 613 virtual void update_counters() = 0; 614 virtual CollectorCounters* counters() { return _gc_counters; } 615 }; 616 617 // Class CardGeneration is a generation that is covered by a card table, 618 // and uses a card-size block-offset array to implement block_start. 619 620 // class BlockOffsetArray; 621 // class BlockOffsetArrayContigSpace; 622 class BlockOffsetSharedArray; 623 624 class CardGeneration: public Generation { 625 friend class VMStructs; 626 protected: 627 // This is shared with other generations. 628 GenRemSet* _rs; 629 // This is local to this generation. 630 BlockOffsetSharedArray* _bts; 631 632 // current shrinking effect: this damps shrinking when the heap gets empty. 633 size_t _shrink_factor; 634 635 size_t _min_heap_delta_bytes; // Minimum amount to expand. 636 637 // Some statistics from before gc started. 638 // These are gathered in the gc_prologue (and should_collect) 639 // to control growing/shrinking policy in spite of promotions. 640 size_t _capacity_at_prologue; 641 size_t _used_at_prologue; 642 643 CardGeneration(ReservedSpace rs, size_t initial_byte_size, int level, 644 GenRemSet* remset); 645 646 public: 647 648 // Attempt to expand the generation by "bytes". Expand by at a 649 // minimum "expand_bytes". Return true if some amount (not 650 // necessarily the full "bytes") was done. 651 virtual bool expand(size_t bytes, size_t expand_bytes); 652 653 // Shrink generation with specified size (returns false if unable to shrink) 654 virtual void shrink(size_t bytes) = 0; 655 656 virtual void compute_new_size(); 657 658 virtual void clear_remembered_set(); 659 660 virtual void invalidate_remembered_set(); 661 662 virtual void prepare_for_verify(); 663 664 // Grow generation with specified size (returns false if unable to grow) 665 virtual bool grow_by(size_t bytes) = 0; 666 // Grow generation to reserved size. 667 virtual bool grow_to_reserved() = 0; 668 }; 669 670 // OneContigSpaceCardGeneration models a heap of old objects contained in a single 671 // contiguous space. 672 // 673 // Garbage collection is performed using mark-compact. 674 675 class OneContigSpaceCardGeneration: public CardGeneration { 676 friend class VMStructs; 677 // Abstractly, this is a subtype that gets access to protected fields. 678 friend class VM_PopulateDumpSharedSpace; 679 680 protected: 681 ContiguousSpace* _the_space; // actual space holding objects 682 WaterMark _last_gc; // watermark between objects allocated before 683 // and after last GC. 684 685 // Grow generation with specified size (returns false if unable to grow) 686 virtual bool grow_by(size_t bytes); 687 // Grow generation to reserved size. 688 virtual bool grow_to_reserved(); 689 // Shrink generation with specified size (returns false if unable to shrink) 690 void shrink_by(size_t bytes); 691 692 // Allocation failure 693 virtual bool expand(size_t bytes, size_t expand_bytes); 694 void shrink(size_t bytes); 695 696 // Accessing spaces 697 ContiguousSpace* the_space() const { return _the_space; } 698 699 public: 700 OneContigSpaceCardGeneration(ReservedSpace rs, size_t initial_byte_size, 701 int level, GenRemSet* remset, 702 ContiguousSpace* space) : 703 CardGeneration(rs, initial_byte_size, level, remset), 704 _the_space(space) 705 {} 706 707 inline bool is_in(const void* p) const; 708 709 // Space enquiries 710 size_t capacity() const; 711 size_t used() const; 712 size_t free() const; 713 714 MemRegion used_region() const; 715 716 size_t unsafe_max_alloc_nogc() const; 717 size_t contiguous_available() const; 718 719 // Iteration 720 void object_iterate(ObjectClosure* blk); 721 void space_iterate(SpaceClosure* blk, bool usedOnly = false); 722 723 void younger_refs_iterate(OopsInGenClosure* blk); 724 725 inline CompactibleSpace* first_compaction_space() const; 726 727 virtual inline HeapWord* allocate(size_t word_size, bool is_tlab); 728 virtual inline HeapWord* par_allocate(size_t word_size, bool is_tlab); 729 730 // Accessing marks 731 inline WaterMark top_mark(); 732 inline WaterMark bottom_mark(); 733 734 #define OneContig_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \ 735 void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl); 736 OneContig_SINCE_SAVE_MARKS_DECL(OopsInGenClosure,_v) 737 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(OneContig_SINCE_SAVE_MARKS_DECL) 738 739 void save_marks(); 740 void reset_saved_marks(); 741 bool no_allocs_since_save_marks(); 742 743 inline size_t block_size(const HeapWord* addr) const; 744 745 inline bool block_is_obj(const HeapWord* addr) const; 746 747 virtual void collect(bool full, 748 bool clear_all_soft_refs, 749 size_t size, 750 bool is_tlab); 751 HeapWord* expand_and_allocate(size_t size, 752 bool is_tlab, 753 bool parallel = false); 754 755 virtual void prepare_for_verify(); 756 757 virtual void gc_epilogue(bool full); 758 759 virtual void record_spaces_top(); 760 761 virtual void verify(); 762 virtual void print_on(outputStream* st) const; 763 }; 764 765 #endif // SHARE_VM_MEMORY_GENERATION_HPP