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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  20  * or visit www.oracle.com if you need additional information or have any
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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 //   - ParNewGeneration            - a DefNewGeneration that is collected by
  45 //                                   several threads
  46 // - CardGeneration                 - abstract class adding offset array behavior
  47 //   - TenuredGeneration             - tenured (old object) space (markSweepCompact)
  48 //   - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation
  49 //                                       (Detlefs-Printezis refinement of
  50 //                                       Boehm-Demers-Schenker)
  51 //
  52 // The system configurations currently allowed are:
  53 //
  54 //   DefNewGeneration + TenuredGeneration
  55 //
  56 //   ParNewGeneration + ConcurrentMarkSweepGeneration
  57 //
  58 
  59 class DefNewGeneration;
  60 class GCMemoryManager;
  61 class GenerationSpec;
  62 class CompactibleSpace;
  63 class ContiguousSpace;
  64 class CompactPoint;
  65 class OopsInGenClosure;
  66 class OopClosure;
  67 class ScanClosure;
  68 class FastScanClosure;
  69 class GenCollectedHeap;
  70 class GCStats;
  71 
  72 // A "ScratchBlock" represents a block of memory in one generation usable by
  73 // another.  It represents "num_words" free words, starting at and including
  74 // the address of "this".
  75 struct ScratchBlock {
  76   ScratchBlock* next;
  77   size_t num_words;
  78   HeapWord scratch_space[1];  // Actually, of size "num_words-2" (assuming
  79                               // first two fields are word-sized.)
  80 };
  81 
  82 class Generation: public CHeapObj<mtGC> {
  83   friend class VMStructs;
  84  private:
  85   jlong _time_of_last_gc; // time when last gc on this generation happened (ms)
  86   MemRegion _prev_used_region; // for collectors that want to "remember" a value for
  87                                // used region at some specific point during collection.
  88 
  89   GCMemoryManager* _gc_manager;
  90 
  91  protected:
  92   // Minimum and maximum addresses for memory reserved (not necessarily
  93   // committed) for generation.
  94   // Used by card marking code. Must not overlap with address ranges of
  95   // other generations.
  96   MemRegion _reserved;
  97 
  98   // Memory area reserved for generation
  99   VirtualSpace _virtual_space;
 100 
 101   // ("Weak") Reference processing support
 102   SpanSubjectToDiscoveryClosure _span_based_discoverer;
 103   ReferenceProcessor* _ref_processor;
 104 
 105   // Performance Counters
 106   CollectorCounters* _gc_counters;
 107 
 108   // Statistics for garbage collection
 109   GCStats* _gc_stats;
 110 
 111   // Initialize the generation.
 112   Generation(ReservedSpace rs, size_t initial_byte_size);
 113 
 114   // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
 115   // "sp" that point into younger generations.
 116   // The iteration is only over objects allocated at the start of the
 117   // iterations; objects allocated as a result of applying the closure are
 118   // not included.
 119   void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads);
 120 
 121  public:
 122   // The set of possible generation kinds.
 123   enum Name {
 124     DefNew,
 125     ParNew,
 126     MarkSweepCompact,
 127     ConcurrentMarkSweep,
 128     Other
 129   };
 130 
 131   enum SomePublicConstants {
 132     // Generations are GenGrain-aligned and have size that are multiples of
 133     // GenGrain.
 134     // Note: on ARM we add 1 bit for card_table_base to be properly aligned
 135     // (we expect its low byte to be zero - see implementation of post_barrier)
 136     LogOfGenGrain = 16 ARM32_ONLY(+1),
 137     GenGrain = 1 << LogOfGenGrain
 138   };
 139 
 140   // allocate and initialize ("weak") refs processing support
 141   virtual void ref_processor_init();
 142   void set_ref_processor(ReferenceProcessor* rp) {
 143     assert(_ref_processor == NULL, "clobbering existing _ref_processor");
 144     _ref_processor = rp;
 145   }
 146 
 147   virtual Generation::Name kind() { return Generation::Other; }
 148 
 149   // This properly belongs in the collector, but for now this
 150   // will do.
 151   virtual bool refs_discovery_is_atomic() const { return true;  }
 152   virtual bool refs_discovery_is_mt()     const { return false; }
 153 
 154   // Space inquiries (results in bytes)
 155   size_t initial_size();
 156   virtual size_t capacity() const = 0;  // The maximum number of object bytes the
 157                                         // generation can currently hold.
 158   virtual size_t used() const = 0;      // The number of used bytes in the gen.
 159   virtual size_t used_stable() const;   // The number of used bytes for memory monitoring tools.
 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, markWord 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 #if INCLUDE_SERIALGC
 405   // Mark sweep support phase2
 406   virtual void prepare_for_compaction(CompactPoint* cp);
 407   // Mark sweep support phase3
 408   virtual void adjust_pointers();
 409   // Mark sweep support phase4
 410   virtual void compact();
 411   virtual void post_compact() { ShouldNotReachHere(); }
 412 #endif
 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   // The "requestor" generation is performing some garbage collection
 446   // action for which it would be useful to have scratch space.  If
 447   // the target is not the requestor, no gc actions will be required
 448   // of the target.  The requestor promises to allocate no more than
 449   // "max_alloc_words" in the target generation (via promotion say,
 450   // if the requestor is a young generation and the target is older).
 451   // If the target generation can provide any scratch space, it adds
 452   // it to "list", leaving "list" pointing to the head of the
 453   // augmented list.  The default is to offer no space.
 454   virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
 455                                   size_t max_alloc_words) {}
 456 
 457   // Give each generation an opportunity to do clean up for any
 458   // contributed scratch.
 459   virtual void reset_scratch() {}
 460 
 461   // When an older generation has been collected, and perhaps resized,
 462   // this method will be invoked on all younger generations (from older to
 463   // younger), allowing them to resize themselves as appropriate.
 464   virtual void compute_new_size() = 0;
 465 
 466   // Printing
 467   virtual const char* name() const = 0;
 468   virtual const char* short_name() const = 0;
 469 
 470   // Reference Processing accessor
 471   ReferenceProcessor* const ref_processor() { return _ref_processor; }
 472 
 473   // Iteration.
 474 
 475   // Iterate over all the ref-containing fields of all objects in the
 476   // generation, calling "cl.do_oop" on each.
 477   virtual void oop_iterate(OopIterateClosure* cl);
 478 
 479   // Iterate over all objects in the generation, calling "cl.do_object" on
 480   // each.
 481   virtual void object_iterate(ObjectClosure* cl);
 482 
 483   // Iterate over all safe objects in the generation, calling "cl.do_object" on
 484   // each.  An object is safe if its references point to other objects in
 485   // the heap.  This defaults to object_iterate() unless overridden.
 486   virtual void safe_object_iterate(ObjectClosure* cl);
 487 
 488   // Apply "cl->do_oop" to (the address of) all and only all the ref fields
 489   // in the current generation that contain pointers to objects in younger
 490   // generations. Objects allocated since the last "save_marks" call are
 491   // excluded.
 492   virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;
 493 
 494   // Inform a generation that it longer contains references to objects
 495   // in any younger generation.    [e.g. Because younger gens are empty,
 496   // clear the card table.]
 497   virtual void clear_remembered_set() { }
 498 
 499   // Inform a generation that some of its objects have moved.  [e.g. The
 500   // generation's spaces were compacted, invalidating the card table.]
 501   virtual void invalidate_remembered_set() { }
 502 
 503   // Block abstraction.
 504 
 505   // Returns the address of the start of the "block" that contains the
 506   // address "addr".  We say "blocks" instead of "object" since some heaps
 507   // may not pack objects densely; a chunk may either be an object or a
 508   // non-object.
 509   virtual HeapWord* block_start(const void* addr) const;
 510 
 511   // Requires "addr" to be the start of a chunk, and returns its size.
 512   // "addr + size" is required to be the start of a new chunk, or the end
 513   // of the active area of the heap.
 514   virtual size_t block_size(const HeapWord* addr) const ;
 515 
 516   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 517   // the block is an object.
 518   virtual bool block_is_obj(const HeapWord* addr) const;
 519 
 520   void print_heap_change(size_t prev_used) const;
 521 
 522   virtual void print() const;
 523   virtual void print_on(outputStream* st) const;
 524 
 525   virtual void verify() = 0;
 526 
 527   struct StatRecord {
 528     int invocations;
 529     elapsedTimer accumulated_time;
 530     StatRecord() :
 531       invocations(0),
 532       accumulated_time(elapsedTimer()) {}
 533   };
 534 private:
 535   StatRecord _stat_record;
 536 public:
 537   StatRecord* stat_record() { return &_stat_record; }
 538 
 539   virtual void print_summary_info_on(outputStream* st);
 540 
 541   // Performance Counter support
 542   virtual void update_counters() = 0;
 543   virtual CollectorCounters* counters() { return _gc_counters; }
 544 
 545   GCMemoryManager* gc_manager() const {
 546     assert(_gc_manager != NULL, "not initialized yet");
 547     return _gc_manager;
 548   }
 549 
 550   void set_gc_manager(GCMemoryManager* gc_manager) {
 551     _gc_manager = gc_manager;
 552   }
 553 
 554 };
 555 
 556 #endif // SHARE_GC_SHARED_GENERATION_HPP