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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  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 // - CardGeneration                 - abstract class adding offset array behavior
  45 //   - TenuredGeneration             - tenured (old object) space (markSweepCompact)
  46 //
  47 // The system configuration currently allowed is:
  48 //
  49 //   DefNewGeneration + TenuredGeneration
  50 //
  51 
  52 class DefNewGeneration;
  53 class GCMemoryManager;
  54 class GenerationSpec;
  55 class CompactibleSpace;
  56 class ContiguousSpace;
  57 class CompactPoint;
  58 class OopsInGenClosure;
  59 class OopClosure;
  60 class ScanClosure;
  61 class FastScanClosure;
  62 class GenCollectedHeap;
  63 class GCStats;
  64 
  65 // A "ScratchBlock" represents a block of memory in one generation usable by
  66 // another.  It represents "num_words" free words, starting at and including
  67 // the address of "this".
  68 struct ScratchBlock {
  69   ScratchBlock* next;
  70   size_t num_words;
  71   HeapWord scratch_space[1];  // Actually, of size "num_words-2" (assuming
  72                               // first two fields are word-sized.)
  73 };
  74 
  75 class Generation: public CHeapObj<mtGC> {
  76   friend class VMStructs;
  77  private:
  78   MemRegion _prev_used_region; // for collectors that want to "remember" a value for
  79                                // used region at some specific point during collection.
  80 
  81   GCMemoryManager* _gc_manager;
  82 
  83  protected:
  84   // Minimum and maximum addresses for memory reserved (not necessarily
  85   // committed) for generation.
  86   // Used by card marking code. Must not overlap with address ranges of
  87   // other generations.
  88   MemRegion _reserved;
  89 
  90   // Memory area reserved for generation
  91   VirtualSpace _virtual_space;
  92 
  93   // ("Weak") Reference processing support
  94   SpanSubjectToDiscoveryClosure _span_based_discoverer;
  95   ReferenceProcessor* _ref_processor;
  96 
  97   // Performance Counters
  98   CollectorCounters* _gc_counters;
  99 
 100   // Statistics for garbage collection
 101   GCStats* _gc_stats;
 102 
 103   // Initialize the generation.
 104   Generation(ReservedSpace rs, size_t initial_byte_size);
 105 
 106   // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
 107   // "sp" that point into younger generations.
 108   // The iteration is only over objects allocated at the start of the
 109   // iterations; objects allocated as a result of applying the closure are
 110   // not included.
 111   void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads);
 112 
 113  public:
 114   // The set of possible generation kinds.
 115   enum Name {
 116     DefNew,
 117     MarkSweepCompact,
 118     Other
 119   };
 120 
 121   enum SomePublicConstants {
 122     // Generations are GenGrain-aligned and have size that are multiples of
 123     // GenGrain.
 124     // Note: on ARM we add 1 bit for card_table_base to be properly aligned
 125     // (we expect its low byte to be zero - see implementation of post_barrier)
 126     LogOfGenGrain = 16 ARM32_ONLY(+1),
 127     GenGrain = 1 << LogOfGenGrain
 128   };
 129 
 130   // allocate and initialize ("weak") refs processing support
 131   virtual void ref_processor_init();
 132   void set_ref_processor(ReferenceProcessor* rp) {
 133     assert(_ref_processor == NULL, "clobbering existing _ref_processor");
 134     _ref_processor = rp;
 135   }
 136 
 137   virtual Generation::Name kind() { return Generation::Other; }
 138 
 139   // This properly belongs in the collector, but for now this
 140   // will do.
 141   virtual bool refs_discovery_is_atomic() const { return true;  }
 142   virtual bool refs_discovery_is_mt()     const { return false; }
 143 
 144   // Space inquiries (results in bytes)
 145   size_t initial_size();
 146   virtual size_t capacity() const = 0;  // The maximum number of object bytes the
 147                                         // generation can currently hold.
 148   virtual size_t used() const = 0;      // The number of used bytes in the gen.
 149   virtual size_t free() const = 0;      // The number of free bytes in the gen.
 150 
 151   // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
 152   // Returns the total number of bytes  available in a generation
 153   // for the allocation of objects.
 154   virtual size_t max_capacity() const;
 155 
 156   // If this is a young generation, the maximum number of bytes that can be
 157   // allocated in this generation before a GC is triggered.
 158   virtual size_t capacity_before_gc() const { return 0; }
 159 
 160   // The largest number of contiguous free bytes in the generation,
 161   // including expansion  (Assumes called at a safepoint.)
 162   virtual size_t contiguous_available() const = 0;
 163   // The largest number of contiguous free bytes in this or any higher generation.
 164   virtual size_t max_contiguous_available() const;
 165 
 166   // Returns true if promotions of the specified amount are
 167   // likely to succeed without a promotion failure.
 168   // Promotion of the full amount is not guaranteed but
 169   // might be attempted in the worst case.
 170   virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
 171 
 172   // For a non-young generation, this interface can be used to inform a
 173   // generation that a promotion attempt into that generation failed.
 174   // Typically used to enable diagnostic output for post-mortem analysis,
 175   // but other uses of the interface are not ruled out.
 176   virtual void promotion_failure_occurred() { /* does nothing */ }
 177 
 178   // Return an estimate of the maximum allocation that could be performed
 179   // in the generation without triggering any collection or expansion
 180   // activity.  It is "unsafe" because no locks are taken; the result
 181   // should be treated as an approximation, not a guarantee, for use in
 182   // heuristic resizing decisions.
 183   virtual size_t unsafe_max_alloc_nogc() const = 0;
 184 
 185   // Returns true if this generation cannot be expanded further
 186   // without a GC. Override as appropriate.
 187   virtual bool is_maximal_no_gc() const {
 188     return _virtual_space.uncommitted_size() == 0;
 189   }
 190 
 191   MemRegion reserved() const { return _reserved; }
 192 
 193   // Returns a region guaranteed to contain all the objects in the
 194   // generation.
 195   virtual MemRegion used_region() const { return _reserved; }
 196 
 197   MemRegion prev_used_region() const { return _prev_used_region; }
 198   virtual void  save_used_region()   { _prev_used_region = used_region(); }
 199 
 200   // Returns "TRUE" iff "p" points into the committed areas in the generation.
 201   // For some kinds of generations, this may be an expensive operation.
 202   // To avoid performance problems stemming from its inadvertent use in
 203   // product jvm's, we restrict its use to assertion checking or
 204   // verification only.
 205   virtual bool is_in(const void* p) const;
 206 
 207   /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
 208   bool is_in_reserved(const void* p) const {
 209     return _reserved.contains(p);
 210   }
 211 
 212   // If some space in the generation contains the given "addr", return a
 213   // pointer to that space, else return "NULL".
 214   virtual Space* space_containing(const void* addr) const;
 215 
 216   // Iteration - do not use for time critical operations
 217   virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
 218 
 219   // Returns the first space, if any, in the generation that can participate
 220   // in compaction, or else "NULL".
 221   virtual CompactibleSpace* first_compaction_space() const = 0;
 222 
 223   // Returns "true" iff this generation should be used to allocate an
 224   // object of the given size.  Young generations might
 225   // wish to exclude very large objects, for example, since, if allocated
 226   // often, they would greatly increase the frequency of young-gen
 227   // collection.
 228   virtual bool should_allocate(size_t word_size, bool is_tlab) {
 229     bool result = false;
 230     size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
 231     if (!is_tlab || supports_tlab_allocation()) {
 232       result = (word_size > 0) && (word_size < overflow_limit);
 233     }
 234     return result;
 235   }
 236 
 237   // Allocate and returns a block of the requested size, or returns "NULL".
 238   // Assumes the caller has done any necessary locking.
 239   virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
 240 
 241   // Like "allocate", but performs any necessary locking internally.
 242   virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
 243 
 244   // Some generation may offer a region for shared, contiguous allocation,
 245   // via inlined code (by exporting the address of the top and end fields
 246   // defining the extent of the contiguous allocation region.)
 247 
 248   // This function returns "true" iff the heap supports this kind of
 249   // allocation.  (More precisely, this means the style of allocation that
 250   // increments *top_addr()" with a CAS.) (Default is "no".)
 251   // A generation that supports this allocation style must use lock-free
 252   // allocation for *all* allocation, since there are times when lock free
 253   // allocation will be concurrent with plain "allocate" calls.
 254   virtual bool supports_inline_contig_alloc() const { return false; }
 255 
 256   // These functions return the addresses of the fields that define the
 257   // boundaries of the contiguous allocation area.  (These fields should be
 258   // physically near to one another.)
 259   virtual HeapWord* volatile* top_addr() const { return NULL; }
 260   virtual HeapWord** end_addr() const { return NULL; }
 261 
 262   // Thread-local allocation buffers
 263   virtual bool supports_tlab_allocation() const { return false; }
 264   virtual size_t tlab_capacity() const {
 265     guarantee(false, "Generation doesn't support thread local allocation buffers");
 266     return 0;
 267   }
 268   virtual size_t tlab_used() const {
 269     guarantee(false, "Generation doesn't support thread local allocation buffers");
 270     return 0;
 271   }
 272   virtual size_t unsafe_max_tlab_alloc() const {
 273     guarantee(false, "Generation doesn't support thread local allocation buffers");
 274     return 0;
 275   }
 276 
 277   // "obj" is the address of an object in a younger generation.  Allocate space
 278   // for "obj" in the current (or some higher) generation, and copy "obj" into
 279   // the newly allocated space, if possible, returning the result (or NULL if
 280   // the allocation failed).
 281   //
 282   // The "obj_size" argument is just obj->size(), passed along so the caller can
 283   // avoid repeating the virtual call to retrieve it.
 284   virtual oop promote(oop obj, size_t obj_size);
 285 
 286   // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
 287   // object "obj", whose original mark word was "m", and whose size is
 288   // "word_sz".  If possible, allocate space for "obj", copy obj into it
 289   // (taking care to copy "m" into the mark word when done, since the mark
 290   // word of "obj" may have been overwritten with a forwarding pointer, and
 291   // also taking care to copy the klass pointer *last*.  Returns the new
 292   // object if successful, or else NULL.
 293   virtual oop par_promote(int thread_num, oop obj, markWord m, size_t word_sz);
 294 
 295   // Informs the current generation that all par_promote_alloc's in the
 296   // collection have been completed; any supporting data structures can be
 297   // reset.  Default is to do nothing.
 298   virtual void par_promote_alloc_done(int thread_num) {}
 299 
 300   // Informs the current generation that all oop_since_save_marks_iterates
 301   // performed by "thread_num" in the current collection, if any, have been
 302   // completed; any supporting data structures can be reset.  Default is to
 303   // do nothing.
 304   virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
 305 
 306   // Returns "true" iff collect() should subsequently be called on this
 307   // this generation. See comment below.
 308   // This is a generic implementation which can be overridden.
 309   //
 310   // Note: in the current (1.4) implementation, when genCollectedHeap's
 311   // incremental_collection_will_fail flag is set, all allocations are
 312   // slow path (the only fast-path place to allocate is DefNew, which
 313   // will be full if the flag is set).
 314   // Thus, older generations which collect younger generations should
 315   // test this flag and collect if it is set.
 316   virtual bool should_collect(bool   full,
 317                               size_t word_size,
 318                               bool   is_tlab) {
 319     return (full || should_allocate(word_size, is_tlab));
 320   }
 321 
 322   // Returns true if the collection is likely to be safely
 323   // completed. Even if this method returns true, a collection
 324   // may not be guaranteed to succeed, and the system should be
 325   // able to safely unwind and recover from that failure, albeit
 326   // at some additional cost.
 327   virtual bool collection_attempt_is_safe() {
 328     guarantee(false, "Are you sure you want to call this method?");
 329     return true;
 330   }
 331 
 332   // Perform a garbage collection.
 333   // If full is true attempt a full garbage collection of this generation.
 334   // Otherwise, attempting to (at least) free enough space to support an
 335   // allocation of the given "word_size".
 336   virtual void collect(bool   full,
 337                        bool   clear_all_soft_refs,
 338                        size_t word_size,
 339                        bool   is_tlab) = 0;
 340 
 341   // Perform a heap collection, attempting to create (at least) enough
 342   // space to support an allocation of the given "word_size".  If
 343   // successful, perform the allocation and return the resulting
 344   // "oop" (initializing the allocated block). If the allocation is
 345   // still unsuccessful, return "NULL".
 346   virtual HeapWord* expand_and_allocate(size_t word_size,
 347                                         bool is_tlab,
 348                                         bool parallel = false) = 0;
 349 
 350   // Some generations may require some cleanup or preparation actions before
 351   // allowing a collection.  The default is to do nothing.
 352   virtual void gc_prologue(bool full) {}
 353 
 354   // Some generations may require some cleanup actions after a collection.
 355   // The default is to do nothing.
 356   virtual void gc_epilogue(bool full) {}
 357 
 358   // Save the high water marks for the used space in a generation.
 359   virtual void record_spaces_top() {}
 360 
 361   // Some generations may need to be "fixed-up" after some allocation
 362   // activity to make them parsable again. The default is to do nothing.
 363   virtual void ensure_parsability() {}
 364 
 365   // Generations may keep statistics about collection. This method
 366   // updates those statistics. current_generation is the generation
 367   // that was most recently collected. This allows the generation to
 368   // decide what statistics are valid to collect. For example, the
 369   // generation can decide to gather the amount of promoted data if
 370   // the collection of the young generation has completed.
 371   GCStats* gc_stats() const { return _gc_stats; }
 372   virtual void update_gc_stats(Generation* current_generation, bool full) {}
 373 
 374 #if INCLUDE_SERIALGC
 375   // Mark sweep support phase2
 376   virtual void prepare_for_compaction(CompactPoint* cp);
 377   // Mark sweep support phase3
 378   virtual void adjust_pointers();
 379   // Mark sweep support phase4
 380   virtual void compact();
 381   virtual void post_compact() { ShouldNotReachHere(); }
 382 #endif
 383 
 384   // Support for CMS's rescan. In this general form we return a pointer
 385   // to an abstract object that can be used, based on specific previously
 386   // decided protocols, to exchange information between generations,
 387   // information that may be useful for speeding up certain types of
 388   // garbage collectors. A NULL value indicates to the client that
 389   // no data recording is expected by the provider. The data-recorder is
 390   // expected to be GC worker thread-local, with the worker index
 391   // indicated by "thr_num".
 392   virtual void* get_data_recorder(int thr_num) { return NULL; }
 393   virtual void sample_eden_chunk() {}
 394 
 395   // Some generations may require some cleanup actions before allowing
 396   // a verification.
 397   virtual void prepare_for_verify() {}
 398 
 399   // Accessing "marks".
 400 
 401   // This function gives a generation a chance to note a point between
 402   // collections.  For example, a contiguous generation might note the
 403   // beginning allocation point post-collection, which might allow some later
 404   // operations to be optimized.
 405   virtual void save_marks() {}
 406 
 407   // This function allows generations to initialize any "saved marks".  That
 408   // is, should only be called when the generation is empty.
 409   virtual void reset_saved_marks() {}
 410 
 411   // This function is "true" iff any no allocations have occurred in the
 412   // generation since the last call to "save_marks".
 413   virtual bool no_allocs_since_save_marks() = 0;
 414 
 415   // The "requestor" generation is performing some garbage collection
 416   // action for which it would be useful to have scratch space.  If
 417   // the target is not the requestor, no gc actions will be required
 418   // of the target.  The requestor promises to allocate no more than
 419   // "max_alloc_words" in the target generation (via promotion say,
 420   // if the requestor is a young generation and the target is older).
 421   // If the target generation can provide any scratch space, it adds
 422   // it to "list", leaving "list" pointing to the head of the
 423   // augmented list.  The default is to offer no space.
 424   virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
 425                                   size_t max_alloc_words) {}
 426 
 427   // Give each generation an opportunity to do clean up for any
 428   // contributed scratch.
 429   virtual void reset_scratch() {}
 430 
 431   // When an older generation has been collected, and perhaps resized,
 432   // this method will be invoked on all younger generations (from older to
 433   // younger), allowing them to resize themselves as appropriate.
 434   virtual void compute_new_size() = 0;
 435 
 436   // Printing
 437   virtual const char* name() const = 0;
 438   virtual const char* short_name() const = 0;
 439 
 440   // Reference Processing accessor
 441   ReferenceProcessor* const ref_processor() { return _ref_processor; }
 442 
 443   // Iteration.
 444 
 445   // Iterate over all the ref-containing fields of all objects in the
 446   // generation, calling "cl.do_oop" on each.
 447   virtual void oop_iterate(OopIterateClosure* cl);
 448 
 449   // Iterate over all objects in the generation, calling "cl.do_object" on
 450   // each.
 451   virtual void object_iterate(ObjectClosure* cl);
 452 
 453   // Apply "cl->do_oop" to (the address of) all and only all the ref fields
 454   // in the current generation that contain pointers to objects in younger
 455   // generations. Objects allocated since the last "save_marks" call are
 456   // excluded.
 457   virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;
 458 
 459   // Inform a generation that it longer contains references to objects
 460   // in any younger generation.    [e.g. Because younger gens are empty,
 461   // clear the card table.]
 462   virtual void clear_remembered_set() { }
 463 
 464   // Inform a generation that some of its objects have moved.  [e.g. The
 465   // generation's spaces were compacted, invalidating the card table.]
 466   virtual void invalidate_remembered_set() { }
 467 
 468   // Block abstraction.
 469 
 470   // Returns the address of the start of the "block" that contains the
 471   // address "addr".  We say "blocks" instead of "object" since some heaps
 472   // may not pack objects densely; a chunk may either be an object or a
 473   // non-object.
 474   virtual HeapWord* block_start(const void* addr) const;
 475 
 476   // Requires "addr" to be the start of a chunk, and returns its size.
 477   // "addr + size" is required to be the start of a new chunk, or the end
 478   // of the active area of the heap.
 479   virtual size_t block_size(const HeapWord* addr) const ;
 480 
 481   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 482   // the block is an object.
 483   virtual bool block_is_obj(const HeapWord* addr) const;
 484 
 485   void print_heap_change(size_t prev_used) const;
 486 
 487   virtual void print() const;
 488   virtual void print_on(outputStream* st) const;
 489 
 490   virtual void verify() = 0;
 491 
 492   struct StatRecord {
 493     int invocations;
 494     elapsedTimer accumulated_time;
 495     StatRecord() :
 496       invocations(0),
 497       accumulated_time(elapsedTimer()) {}
 498   };
 499 private:
 500   StatRecord _stat_record;
 501 public:
 502   StatRecord* stat_record() { return &_stat_record; }
 503 
 504   virtual void print_summary_info_on(outputStream* st);
 505 
 506   // Performance Counter support
 507   virtual void update_counters() = 0;
 508   virtual CollectorCounters* counters() { return _gc_counters; }
 509 
 510   GCMemoryManager* gc_manager() const {
 511     assert(_gc_manager != NULL, "not initialized yet");
 512     return _gc_manager;
 513   }
 514 
 515   void set_gc_manager(GCMemoryManager* gc_manager) {
 516     _gc_manager = gc_manager;
 517   }
 518 
 519 };
 520 
 521 #endif // SHARE_GC_SHARED_GENERATION_HPP