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