1 /* 2 * Copyright (c) 1997, 2019, 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_GC_SHARED_GENERATION_HPP 26 #define SHARE_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/virtualspace.hpp" 34 #include "runtime/mutex.hpp" 35 #include "runtime/perfData.hpp" 36 37 // A Generation models a heap area for similarly-aged objects. 38 // It will contain one ore more spaces holding the actual objects. 39 // 40 // The Generation class hierarchy: 41 // 42 // Generation - abstract base class 43 // - DefNewGeneration - allocation area (copy collected) 44 // - ParNewGeneration - a DefNewGeneration that is collected by 45 // several threads 46 // - CardGeneration - abstract class adding offset array behavior 47 // - TenuredGeneration - tenured (old object) space (markSweepCompact) 48 // - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation 49 // (Detlefs-Printezis refinement of 50 // Boehm-Demers-Schenker) 51 // 52 // The system configurations currently allowed are: 53 // 54 // DefNewGeneration + TenuredGeneration 55 // 56 // ParNewGeneration + ConcurrentMarkSweepGeneration 57 // 58 59 class DefNewGeneration; 60 class GCMemoryManager; 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 GCStats; 71 72 // A "ScratchBlock" represents a block of memory in one generation usable by 73 // another. It represents "num_words" free words, starting at and including 74 // the address of "this". 75 struct ScratchBlock { 76 ScratchBlock* next; 77 size_t num_words; 78 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming 79 // first two fields are word-sized.) 80 }; 81 82 class Generation: public CHeapObj<mtGC> { 83 friend class VMStructs; 84 private: 85 jlong _time_of_last_gc; // time when last gc on this generation happened (ms) 86 MemRegion _prev_used_region; // for collectors that want to "remember" a value for 87 // used region at some specific point during collection. 88 89 GCMemoryManager* _gc_manager; 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 // ("Weak") Reference processing support 102 SpanSubjectToDiscoveryClosure _span_based_discoverer; 103 ReferenceProcessor* _ref_processor; 104 105 // Performance Counters 106 CollectorCounters* _gc_counters; 107 108 // Statistics for garbage collection 109 GCStats* _gc_stats; 110 111 // Initialize the generation. 112 Generation(ReservedSpace rs, size_t initial_byte_size); 113 114 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in 115 // "sp" that point into younger generations. 116 // The iteration is only over objects allocated at the start of the 117 // iterations; objects allocated as a result of applying the closure are 118 // not included. 119 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads); 120 121 public: 122 // The set of possible generation kinds. 123 enum Name { 124 DefNew, 125 ParNew, 126 MarkSweepCompact, 127 ConcurrentMarkSweep, 128 Other 129 }; 130 131 enum SomePublicConstants { 132 // Generations are GenGrain-aligned and have size that are multiples of 133 // GenGrain. 134 // Note: on ARM we add 1 bit for card_table_base to be properly aligned 135 // (we expect its low byte to be zero - see implementation of post_barrier) 136 LogOfGenGrain = 16 ARM32_ONLY(+1), 137 GenGrain = 1 << LogOfGenGrain 138 }; 139 140 // allocate and initialize ("weak") refs processing support 141 virtual void ref_processor_init(); 142 void set_ref_processor(ReferenceProcessor* rp) { 143 assert(_ref_processor == NULL, "clobbering existing _ref_processor"); 144 _ref_processor = rp; 145 } 146 147 virtual Generation::Name kind() { return Generation::Other; } 148 149 // This properly belongs in the collector, but for now this 150 // will do. 151 virtual bool refs_discovery_is_atomic() const { return true; } 152 virtual bool refs_discovery_is_mt() const { return false; } 153 154 // Space inquiries (results in bytes) 155 size_t initial_size(); 156 virtual size_t capacity() const = 0; // The maximum number of object bytes the 157 // generation can currently hold. 158 virtual size_t used() const = 0; // The number of used bytes in the gen. 159 virtual size_t free() const = 0; // The number of free bytes in the gen. 160 161 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap. 162 // Returns the total number of bytes available in a generation 163 // for the allocation of objects. 164 virtual size_t max_capacity() const; 165 166 // If this is a young generation, the maximum number of bytes that can be 167 // allocated in this generation before a GC is triggered. 168 virtual size_t capacity_before_gc() const { return 0; } 169 170 // The largest number of contiguous free bytes in the generation, 171 // including expansion (Assumes called at a safepoint.) 172 virtual size_t contiguous_available() const = 0; 173 // The largest number of contiguous free bytes in this or any higher generation. 174 virtual size_t max_contiguous_available() const; 175 176 // Returns true if promotions of the specified amount are 177 // likely to succeed without a promotion failure. 178 // Promotion of the full amount is not guaranteed but 179 // might be attempted in the worst case. 180 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const; 181 182 // For a non-young generation, this interface can be used to inform a 183 // generation that a promotion attempt into that generation failed. 184 // Typically used to enable diagnostic output for post-mortem analysis, 185 // but other uses of the interface are not ruled out. 186 virtual void promotion_failure_occurred() { /* does nothing */ } 187 188 // Return an estimate of the maximum allocation that could be performed 189 // in the generation without triggering any collection or expansion 190 // activity. It is "unsafe" because no locks are taken; the result 191 // should be treated as an approximation, not a guarantee, for use in 192 // heuristic resizing decisions. 193 virtual size_t unsafe_max_alloc_nogc() const = 0; 194 195 // Returns true if this generation cannot be expanded further 196 // without a GC. Override as appropriate. 197 virtual bool is_maximal_no_gc() const { 198 return _virtual_space.uncommitted_size() == 0; 199 } 200 201 MemRegion reserved() const { return _reserved; } 202 203 // Returns a region guaranteed to contain all the objects in the 204 // generation. 205 virtual MemRegion used_region() const { return _reserved; } 206 207 MemRegion prev_used_region() const { return _prev_used_region; } 208 virtual void save_used_region() { _prev_used_region = used_region(); } 209 210 // Returns "TRUE" iff "p" points into the committed areas in the generation. 211 // For some kinds of generations, this may be an expensive operation. 212 // To avoid performance problems stemming from its inadvertent use in 213 // product jvm's, we restrict its use to assertion checking or 214 // verification only. 215 virtual bool is_in(const void* p) const; 216 217 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */ 218 bool is_in_reserved(const void* p) const { 219 return _reserved.contains(p); 220 } 221 222 // If some space in the generation contains the given "addr", return a 223 // pointer to that space, else return "NULL". 224 virtual Space* space_containing(const void* addr) const; 225 226 // Iteration - do not use for time critical operations 227 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0; 228 229 // Returns the first space, if any, in the generation that can participate 230 // in compaction, or else "NULL". 231 virtual CompactibleSpace* first_compaction_space() const = 0; 232 233 // Returns "true" iff this generation should be used to allocate an 234 // object of the given size. Young generations might 235 // wish to exclude very large objects, for example, since, if allocated 236 // often, they would greatly increase the frequency of young-gen 237 // collection. 238 virtual bool should_allocate(size_t word_size, bool is_tlab) { 239 bool result = false; 240 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize); 241 if (!is_tlab || supports_tlab_allocation()) { 242 result = (word_size > 0) && (word_size < overflow_limit); 243 } 244 return result; 245 } 246 247 // Allocate and returns a block of the requested size, or returns "NULL". 248 // Assumes the caller has done any necessary locking. 249 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0; 250 251 // Like "allocate", but performs any necessary locking internally. 252 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0; 253 254 // Some generation may offer a region for shared, contiguous allocation, 255 // via inlined code (by exporting the address of the top and end fields 256 // defining the extent of the contiguous allocation region.) 257 258 // This function returns "true" iff the heap supports this kind of 259 // allocation. (More precisely, this means the style of allocation that 260 // increments *top_addr()" with a CAS.) (Default is "no".) 261 // A generation that supports this allocation style must use lock-free 262 // allocation for *all* allocation, since there are times when lock free 263 // allocation will be concurrent with plain "allocate" calls. 264 virtual bool supports_inline_contig_alloc() const { return false; } 265 266 // These functions return the addresses of the fields that define the 267 // boundaries of the contiguous allocation area. (These fields should be 268 // physically near to one another.) 269 virtual HeapWord* volatile* top_addr() const { return NULL; } 270 virtual HeapWord** end_addr() const { return NULL; } 271 272 // Thread-local allocation buffers 273 virtual bool supports_tlab_allocation() const { return false; } 274 virtual size_t tlab_capacity() const { 275 guarantee(false, "Generation doesn't support thread local allocation buffers"); 276 return 0; 277 } 278 virtual size_t tlab_used() const { 279 guarantee(false, "Generation doesn't support thread local allocation buffers"); 280 return 0; 281 } 282 virtual size_t unsafe_max_tlab_alloc() const { 283 guarantee(false, "Generation doesn't support thread local allocation buffers"); 284 return 0; 285 } 286 287 // "obj" is the address of an object in a younger generation. Allocate space 288 // for "obj" in the current (or some higher) generation, and copy "obj" into 289 // the newly allocated space, if possible, returning the result (or NULL if 290 // the allocation failed). 291 // 292 // The "obj_size" argument is just obj->size(), passed along so the caller can 293 // avoid repeating the virtual call to retrieve it. 294 virtual oop promote(oop obj, size_t obj_size); 295 296 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote 297 // object "obj", whose original mark word was "m", and whose size is 298 // "word_sz". If possible, allocate space for "obj", copy obj into it 299 // (taking care to copy "m" into the mark word when done, since the mark 300 // word of "obj" may have been overwritten with a forwarding pointer, and 301 // also taking care to copy the klass pointer *last*. Returns the new 302 // object if successful, or else NULL. 303 virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz); 304 305 // Informs the current generation that all par_promote_alloc's in the 306 // collection have been completed; any supporting data structures can be 307 // reset. Default is to do nothing. 308 virtual void par_promote_alloc_done(int thread_num) {} 309 310 // Informs the current generation that all oop_since_save_marks_iterates 311 // performed by "thread_num" in the current collection, if any, have been 312 // completed; any supporting data structures can be reset. Default is to 313 // do nothing. 314 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {} 315 316 // Returns "true" iff collect() should subsequently be called on this 317 // this generation. See comment below. 318 // This is a generic implementation which can be overridden. 319 // 320 // Note: in the current (1.4) implementation, when genCollectedHeap's 321 // incremental_collection_will_fail flag is set, all allocations are 322 // slow path (the only fast-path place to allocate is DefNew, which 323 // will be full if the flag is set). 324 // Thus, older generations which collect younger generations should 325 // test this flag and collect if it is set. 326 virtual bool should_collect(bool full, 327 size_t word_size, 328 bool is_tlab) { 329 return (full || should_allocate(word_size, is_tlab)); 330 } 331 332 // Returns true if the collection is likely to be safely 333 // completed. Even if this method returns true, a collection 334 // may not be guaranteed to succeed, and the system should be 335 // able to safely unwind and recover from that failure, albeit 336 // at some additional cost. 337 virtual bool collection_attempt_is_safe() { 338 guarantee(false, "Are you sure you want to call this method?"); 339 return true; 340 } 341 342 // Perform a garbage collection. 343 // If full is true attempt a full garbage collection of this generation. 344 // Otherwise, attempting to (at least) free enough space to support an 345 // allocation of the given "word_size". 346 virtual void collect(bool full, 347 bool clear_all_soft_refs, 348 size_t word_size, 349 bool is_tlab) = 0; 350 351 // Perform a heap collection, attempting to create (at least) enough 352 // space to support an allocation of the given "word_size". If 353 // successful, perform the allocation and return the resulting 354 // "oop" (initializing the allocated block). If the allocation is 355 // still unsuccessful, return "NULL". 356 virtual HeapWord* expand_and_allocate(size_t word_size, 357 bool is_tlab, 358 bool parallel = false) = 0; 359 360 // Some generations may require some cleanup or preparation actions before 361 // allowing a collection. The default is to do nothing. 362 virtual void gc_prologue(bool full) {} 363 364 // Some generations may require some cleanup actions after a collection. 365 // The default is to do nothing. 366 virtual void gc_epilogue(bool full) {} 367 368 // Save the high water marks for the used space in a generation. 369 virtual void record_spaces_top() {} 370 371 // Some generations may need to be "fixed-up" after some allocation 372 // activity to make them parsable again. The default is to do nothing. 373 virtual void ensure_parsability() {} 374 375 // Time (in ms) when we were last collected or now if a collection is 376 // in progress. 377 virtual jlong time_of_last_gc(jlong now) { 378 // Both _time_of_last_gc and now are set using a time source 379 // that guarantees monotonically non-decreasing values provided 380 // the underlying platform provides such a source. So we still 381 // have to guard against non-monotonicity. 382 NOT_PRODUCT( 383 if (now < _time_of_last_gc) { 384 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now); 385 } 386 ) 387 return _time_of_last_gc; 388 } 389 390 virtual void update_time_of_last_gc(jlong now) { 391 _time_of_last_gc = now; 392 } 393 394 // Generations may keep statistics about collection. This method 395 // updates those statistics. current_generation is the generation 396 // that was most recently collected. This allows the generation to 397 // decide what statistics are valid to collect. For example, the 398 // generation can decide to gather the amount of promoted data if 399 // the collection of the young generation has completed. 400 GCStats* gc_stats() const { return _gc_stats; } 401 virtual void update_gc_stats(Generation* current_generation, bool full) {} 402 403 #if INCLUDE_SERIALGC 404 // Mark sweep support phase2 405 virtual void prepare_for_compaction(CompactPoint* cp); 406 // Mark sweep support phase3 407 virtual void adjust_pointers(); 408 // Mark sweep support phase4 409 virtual void compact(); 410 virtual void post_compact() { ShouldNotReachHere(); } 411 #endif 412 413 // Support for CMS's rescan. In this general form we return a pointer 414 // to an abstract object that can be used, based on specific previously 415 // decided protocols, to exchange information between generations, 416 // information that may be useful for speeding up certain types of 417 // garbage collectors. A NULL value indicates to the client that 418 // no data recording is expected by the provider. The data-recorder is 419 // expected to be GC worker thread-local, with the worker index 420 // indicated by "thr_num". 421 virtual void* get_data_recorder(int thr_num) { return NULL; } 422 virtual void sample_eden_chunk() {} 423 424 // Some generations may require some cleanup actions before allowing 425 // a verification. 426 virtual void prepare_for_verify() {} 427 428 // Accessing "marks". 429 430 // This function gives a generation a chance to note a point between 431 // collections. For example, a contiguous generation might note the 432 // beginning allocation point post-collection, which might allow some later 433 // operations to be optimized. 434 virtual void save_marks() {} 435 436 // This function allows generations to initialize any "saved marks". That 437 // is, should only be called when the generation is empty. 438 virtual void reset_saved_marks() {} 439 440 // This function is "true" iff any no allocations have occurred in the 441 // generation since the last call to "save_marks". 442 virtual bool no_allocs_since_save_marks() = 0; 443 444 // The "requestor" generation is performing some garbage collection 445 // action for which it would be useful to have scratch space. If 446 // the target is not the requestor, no gc actions will be required 447 // of the target. The requestor promises to allocate no more than 448 // "max_alloc_words" in the target generation (via promotion say, 449 // if the requestor is a young generation and the target is older). 450 // If the target generation can provide any scratch space, it adds 451 // it to "list", leaving "list" pointing to the head of the 452 // augmented list. The default is to offer no space. 453 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor, 454 size_t max_alloc_words) {} 455 456 // Give each generation an opportunity to do clean up for any 457 // contributed scratch. 458 virtual void reset_scratch() {} 459 460 // When an older generation has been collected, and perhaps resized, 461 // this method will be invoked on all younger generations (from older to 462 // younger), allowing them to resize themselves as appropriate. 463 virtual void compute_new_size() = 0; 464 465 // Printing 466 virtual const char* name() const = 0; 467 virtual const char* short_name() const = 0; 468 469 // Reference Processing accessor 470 ReferenceProcessor* const ref_processor() { return _ref_processor; } 471 472 // Iteration. 473 474 // Iterate over all the ref-containing fields of all objects in the 475 // generation, calling "cl.do_oop" on each. 476 virtual void oop_iterate(OopIterateClosure* cl); 477 478 // Iterate over all objects in the generation, calling "cl.do_object" on 479 // each. 480 virtual void object_iterate(ObjectClosure* cl); 481 482 // Iterate over all safe objects in the generation, calling "cl.do_object" on 483 // each. An object is safe if its references point to other objects in 484 // the heap. This defaults to object_iterate() unless overridden. 485 virtual void safe_object_iterate(ObjectClosure* cl); 486 487 // Apply "cl->do_oop" to (the address of) all and only all the ref fields 488 // in the current generation that contain pointers to objects in younger 489 // generations. Objects allocated since the last "save_marks" call are 490 // excluded. 491 virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0; 492 493 // Inform a generation that it longer contains references to objects 494 // in any younger generation. [e.g. Because younger gens are empty, 495 // clear the card table.] 496 virtual void clear_remembered_set() { } 497 498 // Inform a generation that some of its objects have moved. [e.g. The 499 // generation's spaces were compacted, invalidating the card table.] 500 virtual void invalidate_remembered_set() { } 501 502 // Block abstraction. 503 504 // Returns the address of the start of the "block" that contains the 505 // address "addr". We say "blocks" instead of "object" since some heaps 506 // may not pack objects densely; a chunk may either be an object or a 507 // non-object. 508 virtual HeapWord* block_start(const void* addr) const; 509 510 // Requires "addr" to be the start of a chunk, and returns its size. 511 // "addr + size" is required to be the start of a new chunk, or the end 512 // of the active area of the heap. 513 virtual size_t block_size(const HeapWord* addr) const ; 514 515 // Requires "addr" to be the start of a block, and returns "TRUE" iff 516 // the block is an object. 517 virtual bool block_is_obj(const HeapWord* addr) const; 518 519 void print_heap_change(size_t prev_used) const; 520 521 virtual void print() const; 522 virtual void print_on(outputStream* st) const; 523 524 virtual void verify() = 0; 525 526 struct StatRecord { 527 int invocations; 528 elapsedTimer accumulated_time; 529 StatRecord() : 530 invocations(0), 531 accumulated_time(elapsedTimer()) {} 532 }; 533 private: 534 StatRecord _stat_record; 535 public: 536 StatRecord* stat_record() { return &_stat_record; } 537 538 virtual void print_summary_info_on(outputStream* st); 539 540 // Performance Counter support 541 virtual void update_counters() = 0; 542 virtual CollectorCounters* counters() { return _gc_counters; } 543 544 GCMemoryManager* gc_manager() const { 545 assert(_gc_manager != NULL, "not initialized yet"); 546 return _gc_manager; 547 } 548 549 void set_gc_manager(GCMemoryManager* gc_manager) { 550 _gc_manager = gc_manager; 551 } 552 553 }; 554 555 #endif // SHARE_GC_SHARED_GENERATION_HPP