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