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