1 /* 2 * Copyright (c) 1997, 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_GENERATION_HPP 26 #define SHARE_VM_GC_SHARED_GENERATION_HPP 27 28 #include "gc/shared/collectorCounters.hpp" 29 #include "gc/shared/referenceProcessor.hpp" 30 #include "gc/shared/watermark.hpp" 31 #include "memory/allocation.hpp" 32 #include "memory/memRegion.hpp" 33 #include "memory/universe.hpp" 34 #include "memory/virtualspace.hpp" 35 #include "runtime/mutex.hpp" 36 #include "runtime/perfData.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 // 57 // ParNewGeneration + ConcurrentMarkSweepGeneration 58 // 59 60 class DefNewGeneration; 61 class GenerationSpec; 62 class CompactibleSpace; 63 class ContiguousSpace; 64 class CompactPoint; 65 class OopsInGenClosure; 66 class OopClosure; 67 class ScanClosure; 68 class FastScanClosure; 69 class GenCollectedHeap; 70 class GenRemSet; 71 class GCStats; 72 73 // A "ScratchBlock" represents a block of memory in one generation usable by 74 // another. It represents "num_words" free words, starting at and including 75 // the address of "this". 76 struct ScratchBlock { 77 ScratchBlock* next; 78 size_t num_words; 79 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming 80 // first two fields are word-sized.) 81 }; 82 83 84 class Generation: public CHeapObj<mtGC> { 85 friend class VMStructs; 86 private: 87 jlong _time_of_last_gc; // time when last gc on this generation happened (ms) 88 MemRegion _prev_used_region; // for collectors that want to "remember" a value for 89 // used region at some specific point during collection. 90 91 protected: 92 // Minimum and maximum addresses for memory reserved (not necessarily 93 // committed) for generation. 94 // Used by card marking code. Must not overlap with address ranges of 95 // other generations. 96 MemRegion _reserved; 97 98 // Memory area reserved for generation 99 VirtualSpace _virtual_space; 100 101 // Level in the generation hierarchy. 102 int _level; 103 104 // ("Weak") Reference processing support 105 ReferenceProcessor* _ref_processor; 106 107 // Performance Counters 108 CollectorCounters* _gc_counters; 109 110 // Statistics for garbage collection 111 GCStats* _gc_stats; 112 113 // Returns the next generation in the configuration, or else NULL if this 114 // is the highest generation. 115 Generation* next_gen() const; 116 117 // Initialize the generation. 118 Generation(ReservedSpace rs, size_t initial_byte_size, int level); 119 120 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in 121 // "sp" that point into younger generations. 122 // The iteration is only over objects allocated at the start of the 123 // iterations; objects allocated as a result of applying the closure are 124 // not included. 125 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl); 126 127 public: 128 // The set of possible generation kinds. 129 enum Name { 130 DefNew, 131 ParNew, 132 MarkSweepCompact, 133 ConcurrentMarkSweep, 134 Other 135 }; 136 137 enum SomePublicConstants { 138 // Generations are GenGrain-aligned and have size that are multiples of 139 // GenGrain. 140 // Note: on ARM we add 1 bit for card_table_base to be properly aligned 141 // (we expect its low byte to be zero - see implementation of post_barrier) 142 LogOfGenGrain = 16 ARM32_ONLY(+1), 143 GenGrain = 1 << LogOfGenGrain 144 }; 145 146 // allocate and initialize ("weak") refs processing support 147 virtual void ref_processor_init(); 148 void set_ref_processor(ReferenceProcessor* rp) { 149 assert(_ref_processor == NULL, "clobbering existing _ref_processor"); 150 _ref_processor = rp; 151 } 152 153 virtual Generation::Name kind() { return Generation::Other; } 154 GenerationSpec* spec(); 155 156 // This properly belongs in the collector, but for now this 157 // will do. 158 virtual bool refs_discovery_is_atomic() const { return true; } 159 virtual bool refs_discovery_is_mt() const { return false; } 160 161 // Space enquiries (results in bytes) 162 virtual size_t capacity() const = 0; // The maximum number of object bytes the 163 // generation can currently hold. 164 virtual size_t used() const = 0; // The number of used bytes in the gen. 165 virtual size_t free() const = 0; // The number of free bytes in the gen. 166 167 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap. 168 // Returns the total number of bytes available in a generation 169 // for the allocation of objects. 170 virtual size_t max_capacity() const; 171 172 // If this is a young generation, the maximum number of bytes that can be 173 // allocated in this generation before a GC is triggered. 174 virtual size_t capacity_before_gc() const { return 0; } 175 176 // The largest number of contiguous free bytes in the generation, 177 // including expansion (Assumes called at a safepoint.) 178 virtual size_t contiguous_available() const = 0; 179 // The largest number of contiguous free bytes in this or any higher generation. 180 virtual size_t max_contiguous_available() const; 181 182 // Returns true if promotions of the specified amount are 183 // likely to succeed without a promotion failure. 184 // Promotion of the full amount is not guaranteed but 185 // might be attempted in the worst case. 186 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const; 187 188 // For a non-young generation, this interface can be used to inform a 189 // generation that a promotion attempt into that generation failed. 190 // Typically used to enable diagnostic output for post-mortem analysis, 191 // but other uses of the interface are not ruled out. 192 virtual void promotion_failure_occurred() { /* does nothing */ } 193 194 // Return an estimate of the maximum allocation that could be performed 195 // in the generation without triggering any collection or expansion 196 // activity. It is "unsafe" because no locks are taken; the result 197 // should be treated as an approximation, not a guarantee, for use in 198 // heuristic resizing decisions. 199 virtual size_t unsafe_max_alloc_nogc() const = 0; 200 201 // Returns true if this generation cannot be expanded further 202 // without a GC. Override as appropriate. 203 virtual bool is_maximal_no_gc() const { 204 return _virtual_space.uncommitted_size() == 0; 205 } 206 207 MemRegion reserved() const { return _reserved; } 208 209 // Returns a region guaranteed to contain all the objects in the 210 // generation. 211 virtual MemRegion used_region() const { return _reserved; } 212 213 MemRegion prev_used_region() const { return _prev_used_region; } 214 virtual void save_used_region() { _prev_used_region = used_region(); } 215 216 // Returns "TRUE" iff "p" points into the committed areas in the generation. 217 // For some kinds of generations, this may be an expensive operation. 218 // To avoid performance problems stemming from its inadvertent use in 219 // product jvm's, we restrict its use to assertion checking or 220 // verification only. 221 virtual bool is_in(const void* p) const; 222 223 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */ 224 bool is_in_reserved(const void* p) const { 225 return _reserved.contains(p); 226 } 227 228 // If some space in the generation contains the given "addr", return a 229 // pointer to that space, else return "NULL". 230 virtual Space* space_containing(const void* addr) const; 231 232 // Iteration - do not use for time critical operations 233 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0; 234 235 // Returns the first space, if any, in the generation that can participate 236 // in compaction, or else "NULL". 237 virtual CompactibleSpace* first_compaction_space() const = 0; 238 239 // Returns "true" iff this generation should be used to allocate an 240 // object of the given size. Young generations might 241 // wish to exclude very large objects, for example, since, if allocated 242 // often, they would greatly increase the frequency of young-gen 243 // collection. 244 virtual bool should_allocate(size_t word_size, bool is_tlab) { 245 bool result = false; 246 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize); 247 if (!is_tlab || supports_tlab_allocation()) { 248 result = (word_size > 0) && (word_size < overflow_limit); 249 } 250 return result; 251 } 252 253 // Allocate and returns a block of the requested size, or returns "NULL". 254 // Assumes the caller has done any necessary locking. 255 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0; 256 257 // Like "allocate", but performs any necessary locking internally. 258 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0; 259 260 // Some generation may offer a region for shared, contiguous allocation, 261 // via inlined code (by exporting the address of the top and end fields 262 // defining the extent of the contiguous allocation region.) 263 264 // This function returns "true" iff the heap supports this kind of 265 // allocation. (More precisely, this means the style of allocation that 266 // increments *top_addr()" with a CAS.) (Default is "no".) 267 // A generation that supports this allocation style must use lock-free 268 // allocation for *all* allocation, since there are times when lock free 269 // allocation will be concurrent with plain "allocate" calls. 270 virtual bool supports_inline_contig_alloc() const { return false; } 271 272 // These functions return the addresses of the fields that define the 273 // boundaries of the contiguous allocation area. (These fields should be 274 // physically near to one another.) 275 virtual HeapWord** top_addr() const { return NULL; } 276 virtual HeapWord** end_addr() const { return NULL; } 277 278 // Thread-local allocation buffers 279 virtual bool supports_tlab_allocation() const { return false; } 280 virtual size_t tlab_capacity() const { 281 guarantee(false, "Generation doesn't support thread local allocation buffers"); 282 return 0; 283 } 284 virtual size_t tlab_used() const { 285 guarantee(false, "Generation doesn't support thread local allocation buffers"); 286 return 0; 287 } 288 virtual size_t unsafe_max_tlab_alloc() const { 289 guarantee(false, "Generation doesn't support thread local allocation buffers"); 290 return 0; 291 } 292 293 // "obj" is the address of an object in a younger generation. Allocate space 294 // for "obj" in the current (or some higher) generation, and copy "obj" into 295 // the newly allocated space, if possible, returning the result (or NULL if 296 // the allocation failed). 297 // 298 // The "obj_size" argument is just obj->size(), passed along so the caller can 299 // avoid repeating the virtual call to retrieve it. 300 virtual oop promote(oop obj, size_t obj_size); 301 302 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote 303 // object "obj", whose original mark word was "m", and whose size is 304 // "word_sz". If possible, allocate space for "obj", copy obj into it 305 // (taking care to copy "m" into the mark word when done, since the mark 306 // word of "obj" may have been overwritten with a forwarding pointer, and 307 // also taking care to copy the klass pointer *last*. Returns the new 308 // object if successful, or else NULL. 309 virtual oop par_promote(int thread_num, 310 oop obj, markOop m, size_t word_sz); 311 312 // Informs the current generation that all par_promote_alloc's in the 313 // collection have been completed; any supporting data structures can be 314 // reset. Default is to do nothing. 315 virtual void par_promote_alloc_done(int thread_num) {} 316 317 // Informs the current generation that all oop_since_save_marks_iterates 318 // performed by "thread_num" in the current collection, if any, have been 319 // completed; any supporting data structures can be reset. Default is to 320 // do nothing. 321 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {} 322 323 // This generation will collect all younger generations 324 // during a full collection. 325 virtual bool full_collects_younger_generations() const { return false; } 326 327 // This generation does in-place marking, meaning that mark words 328 // are mutated during the marking phase and presumably reinitialized 329 // to a canonical value after the GC. This is currently used by the 330 // biased locking implementation to determine whether additional 331 // work is required during the GC prologue and epilogue. 332 virtual bool performs_in_place_marking() const { return true; } 333 334 // Returns "true" iff collect() should subsequently be called on this 335 // this generation. See comment below. 336 // This is a generic implementation which can be overridden. 337 // 338 // Note: in the current (1.4) implementation, when genCollectedHeap's 339 // incremental_collection_will_fail flag is set, all allocations are 340 // slow path (the only fast-path place to allocate is DefNew, which 341 // will be full if the flag is set). 342 // Thus, older generations which collect younger generations should 343 // test this flag and collect if it is set. 344 virtual bool should_collect(bool full, 345 size_t word_size, 346 bool is_tlab) { 347 return (full || should_allocate(word_size, is_tlab)); 348 } 349 350 // Returns true if the collection is likely to be safely 351 // completed. Even if this method returns true, a collection 352 // may not be guaranteed to succeed, and the system should be 353 // able to safely unwind and recover from that failure, albeit 354 // at some additional cost. 355 virtual bool collection_attempt_is_safe() { 356 guarantee(false, "Are you sure you want to call this method?"); 357 return true; 358 } 359 360 // Perform a garbage collection. 361 // If full is true attempt a full garbage collection of this generation. 362 // Otherwise, attempting to (at least) free enough space to support an 363 // allocation of the given "word_size". 364 virtual void collect(bool full, 365 bool clear_all_soft_refs, 366 size_t word_size, 367 bool is_tlab) = 0; 368 369 // Perform a heap collection, attempting to create (at least) enough 370 // space to support an allocation of the given "word_size". If 371 // successful, perform the allocation and return the resulting 372 // "oop" (initializing the allocated block). If the allocation is 373 // still unsuccessful, return "NULL". 374 virtual HeapWord* expand_and_allocate(size_t word_size, 375 bool is_tlab, 376 bool parallel = false) = 0; 377 378 // Some generations may require some cleanup or preparation actions before 379 // allowing a collection. The default is to do nothing. 380 virtual void gc_prologue(bool full) {}; 381 382 // Some generations may require some cleanup actions after a collection. 383 // The default is to do nothing. 384 virtual void gc_epilogue(bool full) {}; 385 386 // Save the high water marks for the used space in a generation. 387 virtual void record_spaces_top() {}; 388 389 // Some generations may need to be "fixed-up" after some allocation 390 // activity to make them parsable again. The default is to do nothing. 391 virtual void ensure_parsability() {}; 392 393 // Time (in ms) when we were last collected or now if a collection is 394 // in progress. 395 virtual jlong time_of_last_gc(jlong now) { 396 // Both _time_of_last_gc and now are set using a time source 397 // that guarantees monotonically non-decreasing values provided 398 // the underlying platform provides such a source. So we still 399 // have to guard against non-monotonicity. 400 NOT_PRODUCT( 401 if (now < _time_of_last_gc) { 402 warning("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now); 403 } 404 ) 405 return _time_of_last_gc; 406 } 407 408 virtual void update_time_of_last_gc(jlong now) { 409 _time_of_last_gc = now; 410 } 411 412 // Generations may keep statistics about collection. This 413 // method updates those statistics. current_level is 414 // the level of the collection that has most recently 415 // occurred. This allows the generation to decide what 416 // statistics are valid to collect. For example, the 417 // generation can decide to gather the amount of promoted data 418 // if the collection of the younger generations has completed. 419 GCStats* gc_stats() const { return _gc_stats; } 420 virtual void update_gc_stats(int current_level, bool full) {} 421 422 // Mark sweep support phase2 423 virtual void prepare_for_compaction(CompactPoint* cp); 424 // Mark sweep support phase3 425 virtual void adjust_pointers(); 426 // Mark sweep support phase4 427 virtual void compact(); 428 virtual void post_compact() {ShouldNotReachHere();} 429 430 // Support for CMS's rescan. In this general form we return a pointer 431 // to an abstract object that can be used, based on specific previously 432 // decided protocols, to exchange information between generations, 433 // information that may be useful for speeding up certain types of 434 // garbage collectors. A NULL value indicates to the client that 435 // no data recording is expected by the provider. The data-recorder is 436 // expected to be GC worker thread-local, with the worker index 437 // indicated by "thr_num". 438 virtual void* get_data_recorder(int thr_num) { return NULL; } 439 virtual void sample_eden_chunk() {} 440 441 // Some generations may require some cleanup actions before allowing 442 // a verification. 443 virtual void prepare_for_verify() {}; 444 445 // Accessing "marks". 446 447 // This function gives a generation a chance to note a point between 448 // collections. For example, a contiguous generation might note the 449 // beginning allocation point post-collection, which might allow some later 450 // operations to be optimized. 451 virtual void save_marks() {} 452 453 // This function allows generations to initialize any "saved marks". That 454 // is, should only be called when the generation is empty. 455 virtual void reset_saved_marks() {} 456 457 // This function is "true" iff any no allocations have occurred in the 458 // generation since the last call to "save_marks". 459 virtual bool no_allocs_since_save_marks() = 0; 460 461 // Apply "cl->apply" to (the addresses of) all reference fields in objects 462 // allocated in the current generation since the last call to "save_marks". 463 // If more objects are allocated in this generation as a result of applying 464 // the closure, iterates over reference fields in those objects as well. 465 // Calls "save_marks" at the end of the iteration. 466 // General signature... 467 virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0; 468 // ...and specializations for de-virtualization. (The general 469 // implementation of the _nv versions call the virtual version. 470 // Note that the _nv suffix is not really semantically necessary, 471 // but it avoids some not-so-useful warnings on Solaris.) 472 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \ 473 virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ 474 oop_since_save_marks_iterate_v((OopsInGenClosure*)cl); \ 475 } 476 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL) 477 478 #undef Generation_SINCE_SAVE_MARKS_DECL 479 480 // The "requestor" generation is performing some garbage collection 481 // action for which it would be useful to have scratch space. If 482 // the target is not the requestor, no gc actions will be required 483 // of the target. The requestor promises to allocate no more than 484 // "max_alloc_words" in the target generation (via promotion say, 485 // if the requestor is a young generation and the target is older). 486 // If the target generation can provide any scratch space, it adds 487 // it to "list", leaving "list" pointing to the head of the 488 // augmented list. The default is to offer no space. 489 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor, 490 size_t max_alloc_words) {} 491 492 // Give each generation an opportunity to do clean up for any 493 // contributed scratch. 494 virtual void reset_scratch() {}; 495 496 // When an older generation has been collected, and perhaps resized, 497 // this method will be invoked on all younger generations (from older to 498 // younger), allowing them to resize themselves as appropriate. 499 virtual void compute_new_size() = 0; 500 501 // Printing 502 virtual const char* name() const = 0; 503 virtual const char* short_name() const = 0; 504 505 int level() const { return _level; } 506 507 // Reference Processing accessor 508 ReferenceProcessor* const ref_processor() { return _ref_processor; } 509 510 // Iteration. 511 512 // Iterate over all the ref-containing fields of all objects in the 513 // generation, calling "cl.do_oop" on each. 514 virtual void oop_iterate(ExtendedOopClosure* cl); 515 516 // Iterate over all objects in the generation, calling "cl.do_object" on 517 // each. 518 virtual void object_iterate(ObjectClosure* cl); 519 520 // Iterate over all safe objects in the generation, calling "cl.do_object" on 521 // each. An object is safe if its references point to other objects in 522 // the heap. This defaults to object_iterate() unless overridden. 523 virtual void safe_object_iterate(ObjectClosure* cl); 524 525 // Apply "cl->do_oop" to (the address of) all and only all the ref fields 526 // in the current generation that contain pointers to objects in younger 527 // generations. Objects allocated since the last "save_marks" call are 528 // excluded. 529 virtual void younger_refs_iterate(OopsInGenClosure* cl) = 0; 530 531 // Inform a generation that it longer contains references to objects 532 // in any younger generation. [e.g. Because younger gens are empty, 533 // clear the card table.] 534 virtual void clear_remembered_set() { } 535 536 // Inform a generation that some of its objects have moved. [e.g. The 537 // generation's spaces were compacted, invalidating the card table.] 538 virtual void invalidate_remembered_set() { } 539 540 // Block abstraction. 541 542 // Returns the address of the start of the "block" that contains the 543 // address "addr". We say "blocks" instead of "object" since some heaps 544 // may not pack objects densely; a chunk may either be an object or a 545 // non-object. 546 virtual HeapWord* block_start(const void* addr) const; 547 548 // Requires "addr" to be the start of a chunk, and returns its size. 549 // "addr + size" is required to be the start of a new chunk, or the end 550 // of the active area of the heap. 551 virtual size_t block_size(const HeapWord* addr) const ; 552 553 // Requires "addr" to be the start of a block, and returns "TRUE" iff 554 // the block is an object. 555 virtual bool block_is_obj(const HeapWord* addr) const; 556 557 558 // PrintGC, PrintGCDetails support 559 void print_heap_change(size_t prev_used) const; 560 561 // PrintHeapAtGC support 562 virtual void print() const; 563 virtual void print_on(outputStream* st) const; 564 565 virtual void verify() = 0; 566 567 struct StatRecord { 568 int invocations; 569 elapsedTimer accumulated_time; 570 StatRecord() : 571 invocations(0), 572 accumulated_time(elapsedTimer()) {} 573 }; 574 private: 575 StatRecord _stat_record; 576 public: 577 StatRecord* stat_record() { return &_stat_record; } 578 579 virtual void print_summary_info(); 580 virtual void print_summary_info_on(outputStream* st); 581 582 // Performance Counter support 583 virtual void update_counters() = 0; 584 virtual CollectorCounters* counters() { return _gc_counters; } 585 }; 586 587 #endif // SHARE_VM_GC_SHARED_GENERATION_HPP