1 /* 2 * Copyright (c) 1997, 2017, 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 "logging/log.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 GCMemoryManager; 62 class GenerationSpec; 63 class CompactibleSpace; 64 class ContiguousSpace; 65 class CompactPoint; 66 class OopsInGenClosure; 67 class OopClosure; 68 class ScanClosure; 69 class FastScanClosure; 70 class GenCollectedHeap; 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 class Generation: public CHeapObj<mtGC> { 84 friend class VMStructs; 85 private: 86 jlong _time_of_last_gc; // time when last gc on this generation happened (ms) 87 MemRegion _prev_used_region; // for collectors that want to "remember" a value for 88 // used region at some specific point during collection. 89 90 GCMemoryManager* _gc_manager; 91 92 protected: 93 // Minimum and maximum addresses for memory reserved (not necessarily 94 // committed) for generation. 95 // Used by card marking code. Must not overlap with address ranges of 96 // other generations. 97 MemRegion _reserved; 98 99 // Memory area reserved for generation 100 VirtualSpace _virtual_space; 101 102 // ("Weak") Reference processing support 103 SpanSubjectToDiscoveryClosure _span_based_discoverer; 104 ReferenceProcessor* _ref_processor; 105 106 // Performance Counters 107 CollectorCounters* _gc_counters; 108 109 // Statistics for garbage collection 110 GCStats* _gc_stats; 111 112 // Initialize the generation. 113 Generation(ReservedSpace rs, size_t initial_byte_size); 114 115 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in 116 // "sp" that point into younger generations. 117 // The iteration is only over objects allocated at the start of the 118 // iterations; objects allocated as a result of applying the closure are 119 // not included. 120 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads); 121 122 public: 123 // The set of possible generation kinds. 124 enum Name { 125 DefNew, 126 ParNew, 127 MarkSweepCompact, 128 ConcurrentMarkSweep, 129 Other 130 }; 131 132 enum SomePublicConstants { 133 // Generations are GenGrain-aligned and have size that are multiples of 134 // GenGrain. 135 // Note: on ARM we add 1 bit for card_table_base to be properly aligned 136 // (we expect its low byte to be zero - see implementation of post_barrier) 137 LogOfGenGrain = 16 ARM32_ONLY(+1), 138 GenGrain = 1 << LogOfGenGrain 139 }; 140 141 // allocate and initialize ("weak") refs processing support 142 virtual void ref_processor_init(); set_ref_processor(ReferenceProcessor * rp)143 void set_ref_processor(ReferenceProcessor* rp) { 144 assert(_ref_processor == NULL, "clobbering existing _ref_processor"); 145 _ref_processor = rp; 146 } 147 kind()148 virtual Generation::Name kind() { return Generation::Other; } 149 150 // This properly belongs in the collector, but for now this 151 // will do. refs_discovery_is_atomic() const152 virtual bool refs_discovery_is_atomic() const { return true; } refs_discovery_is_mt() const153 virtual bool refs_discovery_is_mt() const { return false; } 154 155 // Space inquiries (results in bytes) 156 size_t initial_size(); 157 virtual size_t capacity() const = 0; // The maximum number of object bytes the 158 // generation can currently hold. 159 virtual size_t used() const = 0; // The number of used bytes in the gen. 160 virtual size_t used_stable() const; // The number of used bytes for memory monitoring tools. 161 virtual size_t free() const = 0; // The number of free bytes in the gen. 162 163 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap. 164 // Returns the total number of bytes available in a generation 165 // for the allocation of objects. 166 virtual size_t max_capacity() const; 167 168 // If this is a young generation, the maximum number of bytes that can be 169 // allocated in this generation before a GC is triggered. capacity_before_gc() const170 virtual size_t capacity_before_gc() const { return 0; } 171 172 // The largest number of contiguous free bytes in the generation, 173 // including expansion (Assumes called at a safepoint.) 174 virtual size_t contiguous_available() const = 0; 175 // The largest number of contiguous free bytes in this or any higher generation. 176 virtual size_t max_contiguous_available() const; 177 178 // Returns true if promotions of the specified amount are 179 // likely to succeed without a promotion failure. 180 // Promotion of the full amount is not guaranteed but 181 // might be attempted in the worst case. 182 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const; 183 184 // For a non-young generation, this interface can be used to inform a 185 // generation that a promotion attempt into that generation failed. 186 // Typically used to enable diagnostic output for post-mortem analysis, 187 // but other uses of the interface are not ruled out. promotion_failure_occurred()188 virtual void promotion_failure_occurred() { /* does nothing */ } 189 190 // Return an estimate of the maximum allocation that could be performed 191 // in the generation without triggering any collection or expansion 192 // activity. It is "unsafe" because no locks are taken; the result 193 // should be treated as an approximation, not a guarantee, for use in 194 // heuristic resizing decisions. 195 virtual size_t unsafe_max_alloc_nogc() const = 0; 196 197 // Returns true if this generation cannot be expanded further 198 // without a GC. Override as appropriate. is_maximal_no_gc() const199 virtual bool is_maximal_no_gc() const { 200 return _virtual_space.uncommitted_size() == 0; 201 } 202 reserved() const203 MemRegion reserved() const { return _reserved; } 204 205 // Returns a region guaranteed to contain all the objects in the 206 // generation. used_region() const207 virtual MemRegion used_region() const { return _reserved; } 208 prev_used_region() const209 MemRegion prev_used_region() const { return _prev_used_region; } save_used_region()210 virtual void save_used_region() { _prev_used_region = used_region(); } 211 212 // Returns "TRUE" iff "p" points into the committed areas in the generation. 213 // For some kinds of generations, this may be an expensive operation. 214 // To avoid performance problems stemming from its inadvertent use in 215 // product jvm's, we restrict its use to assertion checking or 216 // verification only. 217 virtual bool is_in(const void* p) const; 218 219 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */ is_in_reserved(const void * p) const220 bool is_in_reserved(const void* p) const { 221 return _reserved.contains(p); 222 } 223 224 // If some space in the generation contains the given "addr", return a 225 // pointer to that space, else return "NULL". 226 virtual Space* space_containing(const void* addr) const; 227 228 // Iteration - do not use for time critical operations 229 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0; 230 231 // Returns the first space, if any, in the generation that can participate 232 // in compaction, or else "NULL". 233 virtual CompactibleSpace* first_compaction_space() const = 0; 234 235 // Returns "true" iff this generation should be used to allocate an 236 // object of the given size. Young generations might 237 // wish to exclude very large objects, for example, since, if allocated 238 // often, they would greatly increase the frequency of young-gen 239 // collection. should_allocate(size_t word_size,bool is_tlab)240 virtual bool should_allocate(size_t word_size, bool is_tlab) { 241 bool result = false; 242 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize); 243 if (!is_tlab || supports_tlab_allocation()) { 244 result = (word_size > 0) && (word_size < overflow_limit); 245 } 246 return result; 247 } 248 249 // Allocate and returns a block of the requested size, or returns "NULL". 250 // Assumes the caller has done any necessary locking. 251 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0; 252 253 // Like "allocate", but performs any necessary locking internally. 254 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0; 255 256 // Some generation may offer a region for shared, contiguous allocation, 257 // via inlined code (by exporting the address of the top and end fields 258 // defining the extent of the contiguous allocation region.) 259 260 // This function returns "true" iff the heap supports this kind of 261 // allocation. (More precisely, this means the style of allocation that 262 // increments *top_addr()" with a CAS.) (Default is "no".) 263 // A generation that supports this allocation style must use lock-free 264 // allocation for *all* allocation, since there are times when lock free 265 // allocation will be concurrent with plain "allocate" calls. supports_inline_contig_alloc() const266 virtual bool supports_inline_contig_alloc() const { return false; } 267 268 // These functions return the addresses of the fields that define the 269 // boundaries of the contiguous allocation area. (These fields should be 270 // physically near to one another.) top_addr() const271 virtual HeapWord* volatile* top_addr() const { return NULL; } end_addr() const272 virtual HeapWord** end_addr() const { return NULL; } 273 274 // Thread-local allocation buffers supports_tlab_allocation() const275 virtual bool supports_tlab_allocation() const { return false; } tlab_capacity() const276 virtual size_t tlab_capacity() const { 277 guarantee(false, "Generation doesn't support thread local allocation buffers"); 278 return 0; 279 } tlab_used() const280 virtual size_t tlab_used() const { 281 guarantee(false, "Generation doesn't support thread local allocation buffers"); 282 return 0; 283 } unsafe_max_tlab_alloc() const284 virtual size_t unsafe_max_tlab_alloc() const { 285 guarantee(false, "Generation doesn't support thread local allocation buffers"); 286 return 0; 287 } 288 289 // "obj" is the address of an object in a younger generation. Allocate space 290 // for "obj" in the current (or some higher) generation, and copy "obj" into 291 // the newly allocated space, if possible, returning the result (or NULL if 292 // the allocation failed). 293 // 294 // The "obj_size" argument is just obj->size(), passed along so the caller can 295 // avoid repeating the virtual call to retrieve it. 296 virtual oop promote(oop obj, size_t obj_size); 297 298 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote 299 // object "obj", whose original mark word was "m", and whose size is 300 // "word_sz". If possible, allocate space for "obj", copy obj into it 301 // (taking care to copy "m" into the mark word when done, since the mark 302 // word of "obj" may have been overwritten with a forwarding pointer, and 303 // also taking care to copy the klass pointer *last*. Returns the new 304 // object if successful, or else NULL. 305 virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz); 306 307 // Informs the current generation that all par_promote_alloc's in the 308 // collection have been completed; any supporting data structures can be 309 // reset. Default is to do nothing. par_promote_alloc_done(int thread_num)310 virtual void par_promote_alloc_done(int thread_num) {} 311 312 // Informs the current generation that all oop_since_save_marks_iterates 313 // performed by "thread_num" in the current collection, if any, have been 314 // completed; any supporting data structures can be reset. Default is to 315 // do nothing. par_oop_since_save_marks_iterate_done(int thread_num)316 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {} 317 318 // Returns "true" iff collect() should subsequently be called on this 319 // this generation. See comment below. 320 // This is a generic implementation which can be overridden. 321 // 322 // Note: in the current (1.4) implementation, when genCollectedHeap's 323 // incremental_collection_will_fail flag is set, all allocations are 324 // slow path (the only fast-path place to allocate is DefNew, which 325 // will be full if the flag is set). 326 // Thus, older generations which collect younger generations should 327 // test this flag and collect if it is set. should_collect(bool full,size_t word_size,bool is_tlab)328 virtual bool should_collect(bool full, 329 size_t word_size, 330 bool is_tlab) { 331 return (full || should_allocate(word_size, is_tlab)); 332 } 333 334 // Returns true if the collection is likely to be safely 335 // completed. Even if this method returns true, a collection 336 // may not be guaranteed to succeed, and the system should be 337 // able to safely unwind and recover from that failure, albeit 338 // at some additional cost. collection_attempt_is_safe()339 virtual bool collection_attempt_is_safe() { 340 guarantee(false, "Are you sure you want to call this method?"); 341 return true; 342 } 343 344 // Perform a garbage collection. 345 // If full is true attempt a full garbage collection of this generation. 346 // Otherwise, attempting to (at least) free enough space to support an 347 // allocation of the given "word_size". 348 virtual void collect(bool full, 349 bool clear_all_soft_refs, 350 size_t word_size, 351 bool is_tlab) = 0; 352 353 // Perform a heap collection, attempting to create (at least) enough 354 // space to support an allocation of the given "word_size". If 355 // successful, perform the allocation and return the resulting 356 // "oop" (initializing the allocated block). If the allocation is 357 // still unsuccessful, return "NULL". 358 virtual HeapWord* expand_and_allocate(size_t word_size, 359 bool is_tlab, 360 bool parallel = false) = 0; 361 362 // Some generations may require some cleanup or preparation actions before 363 // allowing a collection. The default is to do nothing. gc_prologue(bool full)364 virtual void gc_prologue(bool full) {} 365 366 // Some generations may require some cleanup actions after a collection. 367 // The default is to do nothing. gc_epilogue(bool full)368 virtual void gc_epilogue(bool full) {} 369 370 // Save the high water marks for the used space in a generation. record_spaces_top()371 virtual void record_spaces_top() {} 372 373 // Some generations may need to be "fixed-up" after some allocation 374 // activity to make them parsable again. The default is to do nothing. ensure_parsability()375 virtual void ensure_parsability() {} 376 377 // Time (in ms) when we were last collected or now if a collection is 378 // in progress. time_of_last_gc(jlong now)379 virtual jlong time_of_last_gc(jlong now) { 380 // Both _time_of_last_gc and now are set using a time source 381 // that guarantees monotonically non-decreasing values provided 382 // the underlying platform provides such a source. So we still 383 // have to guard against non-monotonicity. 384 NOT_PRODUCT( 385 if (now < _time_of_last_gc) { 386 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now); 387 } 388 ) 389 return _time_of_last_gc; 390 } 391 update_time_of_last_gc(jlong now)392 virtual void update_time_of_last_gc(jlong now) { 393 _time_of_last_gc = now; 394 } 395 396 // Generations may keep statistics about collection. This method 397 // updates those statistics. current_generation is the generation 398 // that was most recently collected. This allows the generation to 399 // decide what statistics are valid to collect. For example, the 400 // generation can decide to gather the amount of promoted data if 401 // the collection of the young generation has completed. gc_stats() const402 GCStats* gc_stats() const { return _gc_stats; } update_gc_stats(Generation * current_generation,bool full)403 virtual void update_gc_stats(Generation* current_generation, bool full) {} 404 405 #if INCLUDE_SERIALGC 406 // Mark sweep support phase2 407 virtual void prepare_for_compaction(CompactPoint* cp); 408 // Mark sweep support phase3 409 virtual void adjust_pointers(); 410 // Mark sweep support phase4 411 virtual void compact(); post_compact()412 virtual void post_compact() { ShouldNotReachHere(); } 413 #endif 414 415 // Support for CMS's rescan. In this general form we return a pointer 416 // to an abstract object that can be used, based on specific previously 417 // decided protocols, to exchange information between generations, 418 // information that may be useful for speeding up certain types of 419 // garbage collectors. A NULL value indicates to the client that 420 // no data recording is expected by the provider. The data-recorder is 421 // expected to be GC worker thread-local, with the worker index 422 // indicated by "thr_num". get_data_recorder(int thr_num)423 virtual void* get_data_recorder(int thr_num) { return NULL; } sample_eden_chunk()424 virtual void sample_eden_chunk() {} 425 426 // Some generations may require some cleanup actions before allowing 427 // a verification. prepare_for_verify()428 virtual void prepare_for_verify() {} 429 430 // Accessing "marks". 431 432 // This function gives a generation a chance to note a point between 433 // collections. For example, a contiguous generation might note the 434 // beginning allocation point post-collection, which might allow some later 435 // operations to be optimized. save_marks()436 virtual void save_marks() {} 437 438 // This function allows generations to initialize any "saved marks". That 439 // is, should only be called when the generation is empty. reset_saved_marks()440 virtual void reset_saved_marks() {} 441 442 // This function is "true" iff any no allocations have occurred in the 443 // generation since the last call to "save_marks". 444 virtual bool no_allocs_since_save_marks() = 0; 445 446 // The "requestor" generation is performing some garbage collection 447 // action for which it would be useful to have scratch space. If 448 // the target is not the requestor, no gc actions will be required 449 // of the target. The requestor promises to allocate no more than 450 // "max_alloc_words" in the target generation (via promotion say, 451 // if the requestor is a young generation and the target is older). 452 // If the target generation can provide any scratch space, it adds 453 // it to "list", leaving "list" pointing to the head of the 454 // augmented list. The default is to offer no space. contribute_scratch(ScratchBlock * & list,Generation * requestor,size_t max_alloc_words)455 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor, 456 size_t max_alloc_words) {} 457 458 // Give each generation an opportunity to do clean up for any 459 // contributed scratch. reset_scratch()460 virtual void reset_scratch() {} 461 462 // When an older generation has been collected, and perhaps resized, 463 // this method will be invoked on all younger generations (from older to 464 // younger), allowing them to resize themselves as appropriate. 465 virtual void compute_new_size() = 0; 466 467 // Printing 468 virtual const char* name() const = 0; 469 virtual const char* short_name() const = 0; 470 471 // Reference Processing accessor ref_processor()472 ReferenceProcessor* const ref_processor() { return _ref_processor; } 473 474 // Iteration. 475 476 // Iterate over all the ref-containing fields of all objects in the 477 // generation, calling "cl.do_oop" on each. 478 virtual void oop_iterate(OopIterateClosure* cl); 479 480 // Iterate over all objects in the generation, calling "cl.do_object" on 481 // each. 482 virtual void object_iterate(ObjectClosure* cl); 483 484 // Iterate over all safe objects in the generation, calling "cl.do_object" on 485 // each. An object is safe if its references point to other objects in 486 // the heap. This defaults to object_iterate() unless overridden. 487 virtual void safe_object_iterate(ObjectClosure* cl); 488 489 // Apply "cl->do_oop" to (the address of) all and only all the ref fields 490 // in the current generation that contain pointers to objects in younger 491 // generations. Objects allocated since the last "save_marks" call are 492 // excluded. 493 virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0; 494 495 // Inform a generation that it longer contains references to objects 496 // in any younger generation. [e.g. Because younger gens are empty, 497 // clear the card table.] clear_remembered_set()498 virtual void clear_remembered_set() { } 499 500 // Inform a generation that some of its objects have moved. [e.g. The 501 // generation's spaces were compacted, invalidating the card table.] invalidate_remembered_set()502 virtual void invalidate_remembered_set() { } 503 504 // Block abstraction. 505 506 // Returns the address of the start of the "block" that contains the 507 // address "addr". We say "blocks" instead of "object" since some heaps 508 // may not pack objects densely; a chunk may either be an object or a 509 // non-object. 510 virtual HeapWord* block_start(const void* addr) const; 511 512 // Requires "addr" to be the start of a chunk, and returns its size. 513 // "addr + size" is required to be the start of a new chunk, or the end 514 // of the active area of the heap. 515 virtual size_t block_size(const HeapWord* addr) const ; 516 517 // Requires "addr" to be the start of a block, and returns "TRUE" iff 518 // the block is an object. 519 virtual bool block_is_obj(const HeapWord* addr) const; 520 521 void print_heap_change(size_t prev_used) const; 522 523 virtual void print() const; 524 virtual void print_on(outputStream* st) const; 525 526 virtual void verify() = 0; 527 528 struct StatRecord { 529 int invocations; 530 elapsedTimer accumulated_time; StatRecordGeneration::StatRecord531 StatRecord() : 532 invocations(0), 533 accumulated_time(elapsedTimer()) {} 534 }; 535 private: 536 StatRecord _stat_record; 537 public: stat_record()538 StatRecord* stat_record() { return &_stat_record; } 539 540 virtual void print_summary_info_on(outputStream* st); 541 542 // Performance Counter support 543 virtual void update_counters() = 0; counters()544 virtual CollectorCounters* counters() { return _gc_counters; } 545 gc_manager() const546 GCMemoryManager* gc_manager() const { 547 assert(_gc_manager != NULL, "not initialized yet"); 548 return _gc_manager; 549 } 550 set_gc_manager(GCMemoryManager * gc_manager)551 void set_gc_manager(GCMemoryManager* gc_manager) { 552 _gc_manager = gc_manager; 553 } 554 555 }; 556 557 #endif // SHARE_VM_GC_SHARED_GENERATION_HPP 558