1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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).
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  20  * or visit www.oracle.com if you need additional information or have any
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  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 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  protected:
  90   // Minimum and maximum addresses for memory reserved (not necessarily
  91   // committed) for generation.
  92   // Used by card marking code. Must not overlap with address ranges of
  93   // other generations.
  94   MemRegion _reserved;
  95 
  96   // Memory area reserved for generation
  97   VirtualSpace _virtual_space;
  98 
  99   // ("Weak") Reference processing support
 100   ReferenceProcessor* _ref_processor;
 101 
 102   // Performance Counters
 103   CollectorCounters* _gc_counters;
 104 
 105   // Statistics for garbage collection
 106   GCStats* _gc_stats;
 107 
 108   // Initialize the generation.
 109   Generation(ReservedSpace rs, size_t initial_byte_size);
 110 
 111   // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
 112   // "sp" that point into younger generations.
 113   // The iteration is only over objects allocated at the start of the
 114   // iterations; objects allocated as a result of applying the closure are
 115   // not included.
 116   void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads);
 117 
 118  public:
 119   // The set of possible generation kinds.
 120   enum Name {
 121     DefNew,
 122     ParNew,
 123     MarkSweepCompact,
 124     ConcurrentMarkSweep,
 125     Other
 126   };
 127 
 128   enum SomePublicConstants {
 129     // Generations are GenGrain-aligned and have size that are multiples of
 130     // GenGrain.
 131     // Note: on ARM we add 1 bit for card_table_base to be properly aligned
 132     // (we expect its low byte to be zero - see implementation of post_barrier)
 133     LogOfGenGrain = 16 ARM32_ONLY(+1),
 134     GenGrain = 1 << LogOfGenGrain
 135   };
 136 
 137   // allocate and initialize ("weak") refs processing support
 138   virtual void ref_processor_init();
 139   void set_ref_processor(ReferenceProcessor* rp) {
 140     assert(_ref_processor == NULL, "clobbering existing _ref_processor");
 141     _ref_processor = rp;
 142   }
 143 
 144   virtual Generation::Name kind() { return Generation::Other; }
 145 
 146   // This properly belongs in the collector, but for now this
 147   // will do.
 148   virtual bool refs_discovery_is_atomic() const { return true;  }
 149   virtual bool refs_discovery_is_mt()     const { return false; }
 150 
 151   // Space inquiries (results in bytes)
 152   size_t initial_size();
 153   virtual size_t capacity() const = 0;  // The maximum number of object bytes the
 154                                         // generation can currently hold.
 155   virtual size_t used() const = 0;      // The number of used bytes in the gen.
 156   virtual size_t free() const = 0;      // The number of free bytes in the gen.
 157 
 158   // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
 159   // Returns the total number of bytes  available in a generation
 160   // for the allocation of objects.
 161   virtual size_t max_capacity() const;
 162 
 163   // If this is a young generation, the maximum number of bytes that can be
 164   // allocated in this generation before a GC is triggered.
 165   virtual size_t capacity_before_gc() const { return 0; }
 166 
 167   // The largest number of contiguous free bytes in the generation,
 168   // including expansion  (Assumes called at a safepoint.)
 169   virtual size_t contiguous_available() const = 0;
 170   // The largest number of contiguous free bytes in this or any higher generation.
 171   virtual size_t max_contiguous_available() const;
 172 
 173   // Returns true if promotions of the specified amount are
 174   // likely to succeed without a promotion failure.
 175   // Promotion of the full amount is not guaranteed but
 176   // might be attempted in the worst case.
 177   virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
 178 
 179   // For a non-young generation, this interface can be used to inform a
 180   // generation that a promotion attempt into that generation failed.
 181   // Typically used to enable diagnostic output for post-mortem analysis,
 182   // but other uses of the interface are not ruled out.
 183   virtual void promotion_failure_occurred() { /* does nothing */ }
 184 
 185   // Return an estimate of the maximum allocation that could be performed
 186   // in the generation without triggering any collection or expansion
 187   // activity.  It is "unsafe" because no locks are taken; the result
 188   // should be treated as an approximation, not a guarantee, for use in
 189   // heuristic resizing decisions.
 190   virtual size_t unsafe_max_alloc_nogc() const = 0;
 191 
 192   // Returns true if this generation cannot be expanded further
 193   // without a GC. Override as appropriate.
 194   virtual bool is_maximal_no_gc() const {
 195     return _virtual_space.uncommitted_size() == 0;
 196   }
 197 
 198   MemRegion reserved() const { return _reserved; }
 199 
 200   // Returns a region guaranteed to contain all the objects in the
 201   // generation.
 202   virtual MemRegion used_region() const { return _reserved; }
 203 
 204   MemRegion prev_used_region() const { return _prev_used_region; }
 205   virtual void  save_used_region()   { _prev_used_region = used_region(); }
 206 
 207   // Returns "TRUE" iff "p" points into the committed areas in the generation.
 208   // For some kinds of generations, this may be an expensive operation.
 209   // To avoid performance problems stemming from its inadvertent use in
 210   // product jvm's, we restrict its use to assertion checking or
 211   // verification only.
 212   virtual bool is_in(const void* p) const;
 213 
 214   /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
 215   bool is_in_reserved(const void* p) const {
 216     return _reserved.contains(p);
 217   }
 218 
 219   // If some space in the generation contains the given "addr", return a
 220   // pointer to that space, else return "NULL".
 221   virtual Space* space_containing(const void* addr) const;
 222 
 223   // Iteration - do not use for time critical operations
 224   virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
 225 
 226   // Returns the first space, if any, in the generation that can participate
 227   // in compaction, or else "NULL".
 228   virtual CompactibleSpace* first_compaction_space() const = 0;
 229 
 230   // Returns "true" iff this generation should be used to allocate an
 231   // object of the given size.  Young generations might
 232   // wish to exclude very large objects, for example, since, if allocated
 233   // often, they would greatly increase the frequency of young-gen
 234   // collection.
 235   virtual bool should_allocate(size_t word_size, bool is_tlab) {
 236     bool result = false;
 237     size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
 238     if (!is_tlab || supports_tlab_allocation()) {
 239       result = (word_size > 0) && (word_size < overflow_limit);
 240     }
 241     return result;
 242   }
 243 
 244   // Allocate and returns a block of the requested size, or returns "NULL".
 245   // Assumes the caller has done any necessary locking.
 246   virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
 247 
 248   // Like "allocate", but performs any necessary locking internally.
 249   virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
 250 
 251   // Some generation may offer a region for shared, contiguous allocation,
 252   // via inlined code (by exporting the address of the top and end fields
 253   // defining the extent of the contiguous allocation region.)
 254 
 255   // This function returns "true" iff the heap supports this kind of
 256   // allocation.  (More precisely, this means the style of allocation that
 257   // increments *top_addr()" with a CAS.) (Default is "no".)
 258   // A generation that supports this allocation style must use lock-free
 259   // allocation for *all* allocation, since there are times when lock free
 260   // allocation will be concurrent with plain "allocate" calls.
 261   virtual bool supports_inline_contig_alloc() const { return false; }
 262 
 263   // These functions return the addresses of the fields that define the
 264   // boundaries of the contiguous allocation area.  (These fields should be
 265   // physically near to one another.)
 266   virtual HeapWord** top_addr() const { return NULL; }
 267   virtual HeapWord** end_addr() const { return NULL; }
 268 
 269   // Thread-local allocation buffers
 270   virtual bool supports_tlab_allocation() const { return false; }
 271   virtual size_t tlab_capacity() const {
 272     guarantee(false, "Generation doesn't support thread local allocation buffers");
 273     return 0;
 274   }
 275   virtual size_t tlab_used() const {
 276     guarantee(false, "Generation doesn't support thread local allocation buffers");
 277     return 0;
 278   }
 279   virtual size_t unsafe_max_tlab_alloc() const {
 280     guarantee(false, "Generation doesn't support thread local allocation buffers");
 281     return 0;
 282   }
 283 
 284   // "obj" is the address of an object in a younger generation.  Allocate space
 285   // for "obj" in the current (or some higher) generation, and copy "obj" into
 286   // the newly allocated space, if possible, returning the result (or NULL if
 287   // the allocation failed).
 288   //
 289   // The "obj_size" argument is just obj->size(), passed along so the caller can
 290   // avoid repeating the virtual call to retrieve it.
 291   virtual oop promote(oop obj, size_t obj_size);
 292 
 293   // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
 294   // object "obj", whose original mark word was "m", and whose size is
 295   // "word_sz".  If possible, allocate space for "obj", copy obj into it
 296   // (taking care to copy "m" into the mark word when done, since the mark
 297   // word of "obj" may have been overwritten with a forwarding pointer, and
 298   // also taking care to copy the klass pointer *last*.  Returns the new
 299   // object if successful, or else NULL.
 300   virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz);
 301 
 302   // Informs the current generation that all par_promote_alloc's in the
 303   // collection have been completed; any supporting data structures can be
 304   // reset.  Default is to do nothing.
 305   virtual void par_promote_alloc_done(int thread_num) {}
 306 
 307   // Informs the current generation that all oop_since_save_marks_iterates
 308   // performed by "thread_num" in the current collection, if any, have been
 309   // completed; any supporting data structures can be reset.  Default is to
 310   // do nothing.
 311   virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
 312 
 313   // Returns "true" iff collect() should subsequently be called on this
 314   // this generation. See comment below.
 315   // This is a generic implementation which can be overridden.
 316   //
 317   // Note: in the current (1.4) implementation, when genCollectedHeap's
 318   // incremental_collection_will_fail flag is set, all allocations are
 319   // slow path (the only fast-path place to allocate is DefNew, which
 320   // will be full if the flag is set).
 321   // Thus, older generations which collect younger generations should
 322   // test this flag and collect if it is set.
 323   virtual bool should_collect(bool   full,
 324                               size_t word_size,
 325                               bool   is_tlab) {
 326     return (full || should_allocate(word_size, is_tlab));
 327   }
 328 
 329   // Returns true if the collection is likely to be safely
 330   // completed. Even if this method returns true, a collection
 331   // may not be guaranteed to succeed, and the system should be
 332   // able to safely unwind and recover from that failure, albeit
 333   // at some additional cost.
 334   virtual bool collection_attempt_is_safe() {
 335     guarantee(false, "Are you sure you want to call this method?");
 336     return true;
 337   }
 338 
 339   // Perform a garbage collection.
 340   // If full is true attempt a full garbage collection of this generation.
 341   // Otherwise, attempting to (at least) free enough space to support an
 342   // allocation of the given "word_size".
 343   virtual void collect(bool   full,
 344                        bool   clear_all_soft_refs,
 345                        size_t word_size,
 346                        bool   is_tlab) = 0;
 347 
 348   // Perform a heap collection, attempting to create (at least) enough
 349   // space to support an allocation of the given "word_size".  If
 350   // successful, perform the allocation and return the resulting
 351   // "oop" (initializing the allocated block). If the allocation is
 352   // still unsuccessful, return "NULL".
 353   virtual HeapWord* expand_and_allocate(size_t word_size,
 354                                         bool is_tlab,
 355                                         bool parallel = false) = 0;
 356 
 357   // Some generations may require some cleanup or preparation actions before
 358   // allowing a collection.  The default is to do nothing.
 359   virtual void gc_prologue(bool full) {}
 360 
 361   // Some generations may require some cleanup actions after a collection.
 362   // The default is to do nothing.
 363   virtual void gc_epilogue(bool full) {}
 364 
 365   // Save the high water marks for the used space in a generation.
 366   virtual void record_spaces_top() {}
 367 
 368   // Some generations may need to be "fixed-up" after some allocation
 369   // activity to make them parsable again. The default is to do nothing.
 370   virtual void ensure_parsability() {}
 371 
 372   // Time (in ms) when we were last collected or now if a collection is
 373   // in progress.
 374   virtual jlong time_of_last_gc(jlong now) {
 375     // Both _time_of_last_gc and now are set using a time source
 376     // that guarantees monotonically non-decreasing values provided
 377     // the underlying platform provides such a source. So we still
 378     // have to guard against non-monotonicity.
 379     NOT_PRODUCT(
 380       if (now < _time_of_last_gc) {
 381         log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now);
 382       }
 383     )
 384     return _time_of_last_gc;
 385   }
 386 
 387   virtual void update_time_of_last_gc(jlong now)  {
 388     _time_of_last_gc = now;
 389   }
 390 
 391   // Generations may keep statistics about collection. This method
 392   // updates those statistics. current_generation is the generation
 393   // that was most recently collected. This allows the generation to
 394   // decide what statistics are valid to collect. For example, the
 395   // generation can decide to gather the amount of promoted data if
 396   // the collection of the young generation has completed.
 397   GCStats* gc_stats() const { return _gc_stats; }
 398   virtual void update_gc_stats(Generation* current_generation, bool full) {}
 399 
 400   // Mark sweep support phase2
 401   virtual void prepare_for_compaction(CompactPoint* cp);
 402   // Mark sweep support phase3
 403   virtual void adjust_pointers();
 404   // Mark sweep support phase4
 405   virtual void compact();
 406   virtual void post_compact() { ShouldNotReachHere(); }
 407 
 408   // Support for CMS's rescan. In this general form we return a pointer
 409   // to an abstract object that can be used, based on specific previously
 410   // decided protocols, to exchange information between generations,
 411   // information that may be useful for speeding up certain types of
 412   // garbage collectors. A NULL value indicates to the client that
 413   // no data recording is expected by the provider. The data-recorder is
 414   // expected to be GC worker thread-local, with the worker index
 415   // indicated by "thr_num".
 416   virtual void* get_data_recorder(int thr_num) { return NULL; }
 417   virtual void sample_eden_chunk() {}
 418 
 419   // Some generations may require some cleanup actions before allowing
 420   // a verification.
 421   virtual void prepare_for_verify() {}
 422 
 423   // Accessing "marks".
 424 
 425   // This function gives a generation a chance to note a point between
 426   // collections.  For example, a contiguous generation might note the
 427   // beginning allocation point post-collection, which might allow some later
 428   // operations to be optimized.
 429   virtual void save_marks() {}
 430 
 431   // This function allows generations to initialize any "saved marks".  That
 432   // is, should only be called when the generation is empty.
 433   virtual void reset_saved_marks() {}
 434 
 435   // This function is "true" iff any no allocations have occurred in the
 436   // generation since the last call to "save_marks".
 437   virtual bool no_allocs_since_save_marks() = 0;
 438 
 439   // Apply "cl->apply" to (the addresses of) all reference fields in objects
 440   // allocated in the current generation since the last call to "save_marks".
 441   // If more objects are allocated in this generation as a result of applying
 442   // the closure, iterates over reference fields in those objects as well.
 443   // Calls "save_marks" at the end of the iteration.
 444   // General signature...
 445   virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0;
 446   // ...and specializations for de-virtualization.  (The general
 447   // implementation of the _nv versions call the virtual version.
 448   // Note that the _nv suffix is not really semantically necessary,
 449   // but it avoids some not-so-useful warnings on Solaris.)
 450 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)             \
 451   virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {    \
 452     oop_since_save_marks_iterate_v((OopsInGenClosure*)cl);                      \
 453   }
 454   SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL)
 455 
 456 #undef Generation_SINCE_SAVE_MARKS_DECL
 457 
 458   // The "requestor" generation is performing some garbage collection
 459   // action for which it would be useful to have scratch space.  If
 460   // the target is not the requestor, no gc actions will be required
 461   // of the target.  The requestor promises to allocate no more than
 462   // "max_alloc_words" in the target generation (via promotion say,
 463   // if the requestor is a young generation and the target is older).
 464   // If the target generation can provide any scratch space, it adds
 465   // it to "list", leaving "list" pointing to the head of the
 466   // augmented list.  The default is to offer no space.
 467   virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
 468                                   size_t max_alloc_words) {}
 469 
 470   // Give each generation an opportunity to do clean up for any
 471   // contributed scratch.
 472   virtual void reset_scratch() {}
 473 
 474   // When an older generation has been collected, and perhaps resized,
 475   // this method will be invoked on all younger generations (from older to
 476   // younger), allowing them to resize themselves as appropriate.
 477   virtual void compute_new_size() = 0;
 478 
 479   // Printing
 480   virtual const char* name() const = 0;
 481   virtual const char* short_name() const = 0;
 482 
 483   // Reference Processing accessor
 484   ReferenceProcessor* const ref_processor() { return _ref_processor; }
 485 
 486   // Iteration.
 487 
 488   // Iterate over all the ref-containing fields of all objects in the
 489   // generation, calling "cl.do_oop" on each.
 490   virtual void oop_iterate(ExtendedOopClosure* cl);
 491 
 492   // Iterate over all objects in the generation, calling "cl.do_object" on
 493   // each.
 494   virtual void object_iterate(ObjectClosure* cl);
 495 
 496   // Iterate over all safe objects in the generation, calling "cl.do_object" on
 497   // each.  An object is safe if its references point to other objects in
 498   // the heap.  This defaults to object_iterate() unless overridden.
 499   virtual void safe_object_iterate(ObjectClosure* cl);
 500 
 501   // Apply "cl->do_oop" to (the address of) all and only all the ref fields
 502   // in the current generation that contain pointers to objects in younger
 503   // generations. Objects allocated since the last "save_marks" call are
 504   // excluded.
 505   virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;
 506 
 507   // Inform a generation that it longer contains references to objects
 508   // in any younger generation.    [e.g. Because younger gens are empty,
 509   // clear the card table.]
 510   virtual void clear_remembered_set() { }
 511 
 512   // Inform a generation that some of its objects have moved.  [e.g. The
 513   // generation's spaces were compacted, invalidating the card table.]
 514   virtual void invalidate_remembered_set() { }
 515 
 516   // Block abstraction.
 517 
 518   // Returns the address of the start of the "block" that contains the
 519   // address "addr".  We say "blocks" instead of "object" since some heaps
 520   // may not pack objects densely; a chunk may either be an object or a
 521   // non-object.
 522   virtual HeapWord* block_start(const void* addr) const;
 523 
 524   // Requires "addr" to be the start of a chunk, and returns its size.
 525   // "addr + size" is required to be the start of a new chunk, or the end
 526   // of the active area of the heap.
 527   virtual size_t block_size(const HeapWord* addr) const ;
 528 
 529   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 530   // the block is an object.
 531   virtual bool block_is_obj(const HeapWord* addr) const;
 532 
 533   void print_heap_change(size_t prev_used) const;
 534 
 535   virtual void print() const;
 536   virtual void print_on(outputStream* st) const;
 537 
 538   virtual void verify() = 0;
 539 
 540   struct StatRecord {
 541     int invocations;
 542     elapsedTimer accumulated_time;
 543     StatRecord() :
 544       invocations(0),
 545       accumulated_time(elapsedTimer()) {}
 546   };
 547 private:
 548   StatRecord _stat_record;
 549 public:
 550   StatRecord* stat_record() { return &_stat_record; }
 551 
 552   virtual void print_summary_info();
 553   virtual void print_summary_info_on(outputStream* st);
 554 
 555   // Performance Counter support
 556   virtual void update_counters() = 0;
 557   virtual CollectorCounters* counters() { return _gc_counters; }
 558 };
 559 
 560 #endif // SHARE_VM_GC_SHARED_GENERATION_HPP