1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  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_VM_GC_SHARED_SPACE_HPP
  26 #define SHARE_VM_GC_SHARED_SPACE_HPP
  27 
  28 #include "gc/shared/blockOffsetTable.hpp"
  29 #include "gc/shared/cardTableModRefBS.hpp"
  30 #include "gc/shared/workgroup.hpp"
  31 #include "memory/allocation.hpp"
  32 #include "memory/iterator.hpp"
  33 #include "memory/memRegion.hpp"
  34 #include "oops/markOop.hpp"
  35 #include "runtime/mutexLocker.hpp"
  36 #include "utilities/macros.hpp"
  37 
  38 // A space is an abstraction for the "storage units" backing
  39 // up the generation abstraction. It includes specific
  40 // implementations for keeping track of free and used space,
  41 // for iterating over objects and free blocks, etc.
  42 
  43 // Forward decls.
  44 class Space;
  45 class BlockOffsetArray;
  46 class BlockOffsetArrayContigSpace;
  47 class Generation;
  48 class CompactibleSpace;
  49 class BlockOffsetTable;
  50 class CardTableRS;
  51 class DirtyCardToOopClosure;
  52 
  53 // A Space describes a heap area. Class Space is an abstract
  54 // base class.
  55 //
  56 // Space supports allocation, size computation and GC support is provided.
  57 //
  58 // Invariant: bottom() and end() are on page_size boundaries and
  59 // bottom() <= top() <= end()
  60 // top() is inclusive and end() is exclusive.
  61 
  62 class Space: public CHeapObj<mtGC> {
  63   friend class VMStructs;
  64  protected:
  65   HeapWord* _bottom;
  66   HeapWord* _end;
  67 
  68   // Used in support of save_marks()
  69   HeapWord* _saved_mark_word;
  70 
  71   // A sequential tasks done structure. This supports
  72   // parallel GC, where we have threads dynamically
  73   // claiming sub-tasks from a larger parallel task.
  74   SequentialSubTasksDone _par_seq_tasks;
  75 
  76   Space():
  77     _bottom(NULL), _end(NULL) { }
  78 
  79  public:
  80   // Accessors
  81   HeapWord* bottom() const         { return _bottom; }
  82   HeapWord* end() const            { return _end;    }
  83   virtual void set_bottom(HeapWord* value) { _bottom = value; }
  84   virtual void set_end(HeapWord* value)    { _end = value; }
  85 
  86   virtual HeapWord* saved_mark_word() const  { return _saved_mark_word; }
  87 
  88   void set_saved_mark_word(HeapWord* p) { _saved_mark_word = p; }
  89 
  90   // Returns true if this object has been allocated since a
  91   // generation's "save_marks" call.
  92   virtual bool obj_allocated_since_save_marks(const oop obj) const {
  93     return (HeapWord*)obj >= saved_mark_word();
  94   }
  95 
  96   virtual MemRegionClosure* preconsumptionDirtyCardClosure() const {
  97     return NULL;
  98   }
  99 
 100   // Returns a subregion of the space containing only the allocated objects in
 101   // the space.
 102   virtual MemRegion used_region() const = 0;
 103 
 104   // Returns a region that is guaranteed to contain (at least) all objects
 105   // allocated at the time of the last call to "save_marks".  If the space
 106   // initializes its DirtyCardToOopClosure's specifying the "contig" option
 107   // (that is, if the space is contiguous), then this region must contain only
 108   // such objects: the memregion will be from the bottom of the region to the
 109   // saved mark.  Otherwise, the "obj_allocated_since_save_marks" method of
 110   // the space must distinguish between objects in the region allocated before
 111   // and after the call to save marks.
 112   MemRegion used_region_at_save_marks() const {
 113     return MemRegion(bottom(), saved_mark_word());
 114   }
 115 
 116   // Initialization.
 117   // "initialize" should be called once on a space, before it is used for
 118   // any purpose.  The "mr" arguments gives the bounds of the space, and
 119   // the "clear_space" argument should be true unless the memory in "mr" is
 120   // known to be zeroed.
 121   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 122 
 123   // The "clear" method must be called on a region that may have
 124   // had allocation performed in it, but is now to be considered empty.
 125   virtual void clear(bool mangle_space);
 126 
 127   // For detecting GC bugs.  Should only be called at GC boundaries, since
 128   // some unused space may be used as scratch space during GC's.
 129   // We also call this when expanding a space to satisfy an allocation
 130   // request. See bug #4668531
 131   virtual void mangle_unused_area() = 0;
 132   virtual void mangle_unused_area_complete() = 0;
 133 
 134   // Testers
 135   bool is_empty() const              { return used() == 0; }
 136   bool not_empty() const             { return used() > 0; }
 137 
 138   // Returns true iff the given the space contains the
 139   // given address as part of an allocated object. For
 140   // certain kinds of spaces, this might be a potentially
 141   // expensive operation. To prevent performance problems
 142   // on account of its inadvertent use in product jvm's,
 143   // we restrict its use to assertion checks only.
 144   bool is_in(const void* p) const {
 145     return used_region().contains(p);
 146   }
 147 
 148   // Returns true iff the given reserved memory of the space contains the
 149   // given address.
 150   bool is_in_reserved(const void* p) const { return _bottom <= p && p < _end; }
 151 
 152   // Returns true iff the given block is not allocated.
 153   virtual bool is_free_block(const HeapWord* p) const = 0;
 154 
 155   // Test whether p is double-aligned
 156   static bool is_aligned(void* p) {
 157     return is_ptr_aligned(p, sizeof(double));
 158   }
 159 
 160   // Size computations.  Sizes are in bytes.
 161   size_t capacity()     const { return byte_size(bottom(), end()); }
 162   virtual size_t used() const = 0;
 163   virtual size_t free() const = 0;
 164 
 165   // Iterate over all the ref-containing fields of all objects in the
 166   // space, calling "cl.do_oop" on each.  Fields in objects allocated by
 167   // applications of the closure are not included in the iteration.
 168   virtual void oop_iterate(ExtendedOopClosure* cl);
 169 
 170   // Iterate over all objects in the space, calling "cl.do_object" on
 171   // each.  Objects allocated by applications of the closure are not
 172   // included in the iteration.
 173   virtual void object_iterate(ObjectClosure* blk) = 0;
 174   // Similar to object_iterate() except only iterates over
 175   // objects whose internal references point to objects in the space.
 176   virtual void safe_object_iterate(ObjectClosure* blk) = 0;
 177 
 178   // Create and return a new dirty card to oop closure. Can be
 179   // overridden to return the appropriate type of closure
 180   // depending on the type of space in which the closure will
 181   // operate. ResourceArea allocated.
 182   virtual DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
 183                                              CardTableModRefBS::PrecisionStyle precision,
 184                                              HeapWord* boundary,
 185                                              bool parallel);
 186 
 187   // If "p" is in the space, returns the address of the start of the
 188   // "block" that contains "p".  We say "block" instead of "object" since
 189   // some heaps may not pack objects densely; a chunk may either be an
 190   // object or a non-object.  If "p" is not in the space, return NULL.
 191   virtual HeapWord* block_start_const(const void* p) const = 0;
 192 
 193   // The non-const version may have benevolent side effects on the data
 194   // structure supporting these calls, possibly speeding up future calls.
 195   // The default implementation, however, is simply to call the const
 196   // version.
 197   virtual HeapWord* block_start(const void* p);
 198 
 199   // Requires "addr" to be the start of a chunk, and returns its size.
 200   // "addr + size" is required to be the start of a new chunk, or the end
 201   // of the active area of the heap.
 202   virtual size_t block_size(const HeapWord* addr) const = 0;
 203 
 204   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 205   // the block is an object.
 206   virtual bool block_is_obj(const HeapWord* addr) const = 0;
 207 
 208   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 209   // the block is an object and the object is alive.
 210   virtual bool obj_is_alive(const HeapWord* addr) const;
 211 
 212   // Allocation (return NULL if full).  Assumes the caller has established
 213   // mutually exclusive access to the space.
 214   virtual HeapWord* allocate(size_t word_size) = 0;
 215 
 216   // Allocation (return NULL if full).  Enforces mutual exclusion internally.
 217   virtual HeapWord* par_allocate(size_t word_size) = 0;
 218 
 219   // Mark-sweep-compact support: all spaces can update pointers to objects
 220   // moving as a part of compaction.
 221   virtual void adjust_pointers() = 0;
 222 
 223   virtual void print() const;
 224   virtual void print_on(outputStream* st) const;
 225   virtual void print_short() const;
 226   virtual void print_short_on(outputStream* st) const;
 227 
 228 
 229   // Accessor for parallel sequential tasks.
 230   SequentialSubTasksDone* par_seq_tasks() { return &_par_seq_tasks; }
 231 
 232   // IF "this" is a ContiguousSpace, return it, else return NULL.
 233   virtual ContiguousSpace* toContiguousSpace() {
 234     return NULL;
 235   }
 236 
 237   // Debugging
 238   virtual void verify() const = 0;
 239 };
 240 
 241 // A MemRegionClosure (ResourceObj) whose "do_MemRegion" function applies an
 242 // OopClosure to (the addresses of) all the ref-containing fields that could
 243 // be modified by virtue of the given MemRegion being dirty. (Note that
 244 // because of the imprecise nature of the write barrier, this may iterate
 245 // over oops beyond the region.)
 246 // This base type for dirty card to oop closures handles memory regions
 247 // in non-contiguous spaces with no boundaries, and should be sub-classed
 248 // to support other space types. See ContiguousDCTOC for a sub-class
 249 // that works with ContiguousSpaces.
 250 
 251 class DirtyCardToOopClosure: public MemRegionClosureRO {
 252 protected:
 253   ExtendedOopClosure* _cl;
 254   Space* _sp;
 255   CardTableModRefBS::PrecisionStyle _precision;
 256   HeapWord* _boundary;          // If non-NULL, process only non-NULL oops
 257                                 // pointing below boundary.
 258   HeapWord* _min_done;          // ObjHeadPreciseArray precision requires
 259                                 // a downwards traversal; this is the
 260                                 // lowest location already done (or,
 261                                 // alternatively, the lowest address that
 262                                 // shouldn't be done again.  NULL means infinity.)
 263   NOT_PRODUCT(HeapWord* _last_bottom;)
 264   NOT_PRODUCT(HeapWord* _last_explicit_min_done;)
 265 
 266   // Get the actual top of the area on which the closure will
 267   // operate, given where the top is assumed to be (the end of the
 268   // memory region passed to do_MemRegion) and where the object
 269   // at the top is assumed to start. For example, an object may
 270   // start at the top but actually extend past the assumed top,
 271   // in which case the top becomes the end of the object.
 272   virtual HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
 273 
 274   // Walk the given memory region from bottom to (actual) top
 275   // looking for objects and applying the oop closure (_cl) to
 276   // them. The base implementation of this treats the area as
 277   // blocks, where a block may or may not be an object. Sub-
 278   // classes should override this to provide more accurate
 279   // or possibly more efficient walking.
 280   virtual void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);
 281 
 282 public:
 283   DirtyCardToOopClosure(Space* sp, ExtendedOopClosure* cl,
 284                         CardTableModRefBS::PrecisionStyle precision,
 285                         HeapWord* boundary) :
 286     _sp(sp), _cl(cl), _precision(precision), _boundary(boundary),
 287     _min_done(NULL) {
 288     NOT_PRODUCT(_last_bottom = NULL);
 289     NOT_PRODUCT(_last_explicit_min_done = NULL);
 290   }
 291 
 292   void do_MemRegion(MemRegion mr);
 293 
 294   void set_min_done(HeapWord* min_done) {
 295     _min_done = min_done;
 296     NOT_PRODUCT(_last_explicit_min_done = _min_done);
 297   }
 298 #ifndef PRODUCT
 299   void set_last_bottom(HeapWord* last_bottom) {
 300     _last_bottom = last_bottom;
 301   }
 302 #endif
 303 };
 304 
 305 // A structure to represent a point at which objects are being copied
 306 // during compaction.
 307 class CompactPoint : public StackObj {
 308 public:
 309   Generation* gen;
 310   CompactibleSpace* space;
 311   HeapWord* threshold;
 312 
 313   CompactPoint(Generation* g = NULL) :
 314     gen(g), space(NULL), threshold(0) {}
 315 };
 316 
 317 // A space that supports compaction operations.  This is usually, but not
 318 // necessarily, a space that is normally contiguous.  But, for example, a
 319 // free-list-based space whose normal collection is a mark-sweep without
 320 // compaction could still support compaction in full GC's.
 321 //
 322 // The compaction operations are implemented by the
 323 // scan_and_{adjust_pointers,compact,forward} function templates.
 324 // The following are, non-virtual, auxiliary functions used by these function templates:
 325 // - scan_limit()
 326 // - scanned_block_is_obj()
 327 // - scanned_block_size()
 328 // - adjust_obj_size()
 329 // - obj_size()
 330 // These functions are to be used exclusively by the scan_and_* function templates,
 331 // and must be defined for all (non-abstract) subclasses of CompactibleSpace.
 332 //
 333 // NOTE: Any subclasses to CompactibleSpace wanting to change/define the behavior
 334 // in any of the auxiliary functions must also override the corresponding
 335 // prepare_for_compaction/adjust_pointers/compact functions using them.
 336 // If not, such changes will not be used or have no effect on the compaction operations.
 337 //
 338 // This translates to the following dependencies:
 339 // Overrides/definitions of
 340 //  - scan_limit
 341 //  - scanned_block_is_obj
 342 //  - scanned_block_size
 343 // require override/definition of prepare_for_compaction().
 344 // Similar dependencies exist between
 345 //  - adjust_obj_size  and adjust_pointers()
 346 //  - obj_size         and compact().
 347 //
 348 // Additionally, this also means that changes to block_size() or block_is_obj() that
 349 // should be effective during the compaction operations must provide a corresponding
 350 // definition of scanned_block_size/scanned_block_is_obj respectively.
 351 class CompactibleSpace: public Space {
 352   friend class VMStructs;
 353   friend class CompactibleFreeListSpace;
 354 private:
 355   HeapWord* _compaction_top;
 356   CompactibleSpace* _next_compaction_space;
 357 
 358   // Auxiliary functions for scan_and_{forward,adjust_pointers,compact} support.
 359   inline size_t adjust_obj_size(size_t size) const {
 360     return size;
 361   }
 362 
 363   inline size_t obj_size(const HeapWord* addr) const;
 364 
 365   template <class SpaceType>
 366   static inline void verify_up_to_first_dead(SpaceType* space) NOT_DEBUG_RETURN;
 367 
 368   template <class SpaceType>
 369   static inline void clear_empty_region(SpaceType* space);
 370 
 371 public:
 372   CompactibleSpace() :
 373    _compaction_top(NULL), _next_compaction_space(NULL) {}
 374 
 375   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 376   virtual void clear(bool mangle_space);
 377 
 378   // Used temporarily during a compaction phase to hold the value
 379   // top should have when compaction is complete.
 380   HeapWord* compaction_top() const { return _compaction_top;    }
 381 
 382   void set_compaction_top(HeapWord* value) {
 383     assert(value == NULL || (value >= bottom() && value <= end()),
 384       "should point inside space");
 385     _compaction_top = value;
 386   }
 387 
 388   // Perform operations on the space needed after a compaction
 389   // has been performed.
 390   virtual void reset_after_compaction() = 0;
 391 
 392   // Returns the next space (in the current generation) to be compacted in
 393   // the global compaction order.  Also is used to select the next
 394   // space into which to compact.
 395 
 396   virtual CompactibleSpace* next_compaction_space() const {
 397     return _next_compaction_space;
 398   }
 399 
 400   void set_next_compaction_space(CompactibleSpace* csp) {
 401     _next_compaction_space = csp;
 402   }
 403 
 404   // MarkSweep support phase2
 405 
 406   // Start the process of compaction of the current space: compute
 407   // post-compaction addresses, and insert forwarding pointers.  The fields
 408   // "cp->gen" and "cp->compaction_space" are the generation and space into
 409   // which we are currently compacting.  This call updates "cp" as necessary,
 410   // and leaves the "compaction_top" of the final value of
 411   // "cp->compaction_space" up-to-date.  Offset tables may be updated in
 412   // this phase as if the final copy had occurred; if so, "cp->threshold"
 413   // indicates when the next such action should be taken.
 414   virtual void prepare_for_compaction(CompactPoint* cp) = 0;
 415   // MarkSweep support phase3
 416   virtual void adjust_pointers();
 417   // MarkSweep support phase4
 418   virtual void compact();
 419 
 420   // The maximum percentage of objects that can be dead in the compacted
 421   // live part of a compacted space ("deadwood" support.)
 422   virtual size_t allowed_dead_ratio() const { return 0; };
 423 
 424   // Some contiguous spaces may maintain some data structures that should
 425   // be updated whenever an allocation crosses a boundary.  This function
 426   // returns the first such boundary.
 427   // (The default implementation returns the end of the space, so the
 428   // boundary is never crossed.)
 429   virtual HeapWord* initialize_threshold() { return end(); }
 430 
 431   // "q" is an object of the given "size" that should be forwarded;
 432   // "cp" names the generation ("gen") and containing "this" (which must
 433   // also equal "cp->space").  "compact_top" is where in "this" the
 434   // next object should be forwarded to.  If there is room in "this" for
 435   // the object, insert an appropriate forwarding pointer in "q".
 436   // If not, go to the next compaction space (there must
 437   // be one, since compaction must succeed -- we go to the first space of
 438   // the previous generation if necessary, updating "cp"), reset compact_top
 439   // and then forward.  In either case, returns the new value of "compact_top".
 440   // If the forwarding crosses "cp->threshold", invokes the "cross_threshold"
 441   // function of the then-current compaction space, and updates "cp->threshold
 442   // accordingly".
 443   virtual HeapWord* forward(oop q, size_t size, CompactPoint* cp,
 444                     HeapWord* compact_top);
 445 
 446   // Return a size with adjustments as required of the space.
 447   virtual size_t adjust_object_size_v(size_t size) const { return size; }
 448 
 449 protected:
 450   // Used during compaction.
 451   HeapWord* _first_dead;
 452   HeapWord* _end_of_live;
 453 
 454   // Minimum size of a free block.
 455   virtual size_t minimum_free_block_size() const { return 0; }
 456 
 457   // This the function is invoked when an allocation of an object covering
 458   // "start" to "end occurs crosses the threshold; returns the next
 459   // threshold.  (The default implementation does nothing.)
 460   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* the_end) {
 461     return end();
 462   }
 463 
 464   // Below are template functions for scan_and_* algorithms (avoiding virtual calls).
 465   // The space argument should be a subclass of CompactibleSpace, implementing
 466   // scan_limit(), scanned_block_is_obj(), and scanned_block_size(),
 467   // and possibly also overriding obj_size(), and adjust_obj_size().
 468   // These functions should avoid virtual calls whenever possible.
 469 
 470   // Frequently calls adjust_obj_size().
 471   template <class SpaceType>
 472   static inline void scan_and_adjust_pointers(SpaceType* space);
 473 
 474   // Frequently calls obj_size().
 475   template <class SpaceType>
 476   static inline void scan_and_compact(SpaceType* space);
 477 
 478   // Frequently calls scanned_block_is_obj() and scanned_block_size().
 479   // Requires the scan_limit() function.
 480   template <class SpaceType>
 481   static inline void scan_and_forward(SpaceType* space, CompactPoint* cp);
 482 };
 483 
 484 class GenSpaceMangler;
 485 
 486 // A space in which the free area is contiguous.  It therefore supports
 487 // faster allocation, and compaction.
 488 class ContiguousSpace: public CompactibleSpace {
 489   friend class VMStructs;
 490   // Allow scan_and_forward function to call (private) overrides for auxiliary functions on this class
 491   template <typename SpaceType>
 492   friend void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp);
 493 
 494  private:
 495   // Auxiliary functions for scan_and_forward support.
 496   // See comments for CompactibleSpace for more information.
 497   inline HeapWord* scan_limit() const {
 498     return top();
 499   }
 500 
 501   inline bool scanned_block_is_obj(const HeapWord* addr) const {
 502     return true; // Always true, since scan_limit is top
 503   }
 504 
 505   inline size_t scanned_block_size(const HeapWord* addr) const;
 506 
 507  protected:
 508   HeapWord* _top;
 509   HeapWord* _concurrent_iteration_safe_limit;
 510   // A helper for mangling the unused area of the space in debug builds.
 511   GenSpaceMangler* _mangler;
 512 
 513   GenSpaceMangler* mangler() { return _mangler; }
 514 
 515   // Allocation helpers (return NULL if full).
 516   inline HeapWord* allocate_impl(size_t word_size);
 517   inline HeapWord* par_allocate_impl(size_t word_size);
 518 
 519  public:
 520   ContiguousSpace();
 521   ~ContiguousSpace();
 522 
 523   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 524   virtual void clear(bool mangle_space);
 525 
 526   // Accessors
 527   HeapWord* top() const            { return _top;    }
 528   void set_top(HeapWord* value)    { _top = value; }
 529 
 530   void set_saved_mark()            { _saved_mark_word = top();    }
 531   void reset_saved_mark()          { _saved_mark_word = bottom(); }
 532 
 533   bool saved_mark_at_top() const { return saved_mark_word() == top(); }
 534 
 535   // In debug mode mangle (write it with a particular bit
 536   // pattern) the unused part of a space.
 537 
 538   // Used to save the an address in a space for later use during mangling.
 539   void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
 540   // Used to save the space's current top for later use during mangling.
 541   void set_top_for_allocations() PRODUCT_RETURN;
 542 
 543   // Mangle regions in the space from the current top up to the
 544   // previously mangled part of the space.
 545   void mangle_unused_area() PRODUCT_RETURN;
 546   // Mangle [top, end)
 547   void mangle_unused_area_complete() PRODUCT_RETURN;
 548 
 549   // Do some sparse checking on the area that should have been mangled.
 550   void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
 551   // Check the complete area that should have been mangled.
 552   // This code may be NULL depending on the macro DEBUG_MANGLING.
 553   void check_mangled_unused_area_complete() PRODUCT_RETURN;
 554 
 555   // Size computations: sizes in bytes.
 556   size_t capacity() const        { return byte_size(bottom(), end()); }
 557   size_t used() const            { return byte_size(bottom(), top()); }
 558   size_t free() const            { return byte_size(top(),    end()); }
 559 
 560   virtual bool is_free_block(const HeapWord* p) const;
 561 
 562   // In a contiguous space we have a more obvious bound on what parts
 563   // contain objects.
 564   MemRegion used_region() const { return MemRegion(bottom(), top()); }
 565 
 566   // Allocation (return NULL if full)
 567   virtual HeapWord* allocate(size_t word_size);
 568   virtual HeapWord* par_allocate(size_t word_size);
 569   HeapWord* allocate_aligned(size_t word_size);
 570 
 571   // Iteration
 572   void oop_iterate(ExtendedOopClosure* cl);
 573   void object_iterate(ObjectClosure* blk);
 574   // For contiguous spaces this method will iterate safely over objects
 575   // in the space (i.e., between bottom and top) when at a safepoint.
 576   void safe_object_iterate(ObjectClosure* blk);
 577 
 578   // Iterate over as many initialized objects in the space as possible,
 579   // calling "cl.do_object_careful" on each. Return NULL if all objects
 580   // in the space (at the start of the iteration) were iterated over.
 581   // Return an address indicating the extent of the iteration in the
 582   // event that the iteration had to return because of finding an
 583   // uninitialized object in the space, or if the closure "cl"
 584   // signaled early termination.
 585   HeapWord* object_iterate_careful(ObjectClosureCareful* cl);
 586   HeapWord* concurrent_iteration_safe_limit() {
 587     assert(_concurrent_iteration_safe_limit <= top(),
 588            "_concurrent_iteration_safe_limit update missed");
 589     return _concurrent_iteration_safe_limit;
 590   }
 591   // changes the safe limit, all objects from bottom() to the new
 592   // limit should be properly initialized
 593   void set_concurrent_iteration_safe_limit(HeapWord* new_limit) {
 594     assert(new_limit <= top(), "uninitialized objects in the safe range");
 595     _concurrent_iteration_safe_limit = new_limit;
 596   }
 597 
 598 
 599 #if INCLUDE_ALL_GCS
 600   // In support of parallel oop_iterate.
 601   #define ContigSpace_PAR_OOP_ITERATE_DECL(OopClosureType, nv_suffix)  \
 602     void par_oop_iterate(MemRegion mr, OopClosureType* blk);
 603 
 604     ALL_PAR_OOP_ITERATE_CLOSURES(ContigSpace_PAR_OOP_ITERATE_DECL)
 605   #undef ContigSpace_PAR_OOP_ITERATE_DECL
 606 #endif // INCLUDE_ALL_GCS
 607 
 608   // Compaction support
 609   virtual void reset_after_compaction() {
 610     assert(compaction_top() >= bottom() && compaction_top() <= end(), "should point inside space");
 611     set_top(compaction_top());
 612     // set new iteration safe limit
 613     set_concurrent_iteration_safe_limit(compaction_top());
 614   }
 615 
 616   // Override.
 617   DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
 618                                      CardTableModRefBS::PrecisionStyle precision,
 619                                      HeapWord* boundary,
 620                                      bool parallel);
 621 
 622   // Apply "blk->do_oop" to the addresses of all reference fields in objects
 623   // starting with the _saved_mark_word, which was noted during a generation's
 624   // save_marks and is required to denote the head of an object.
 625   // Fields in objects allocated by applications of the closure
 626   // *are* included in the iteration.
 627   // Updates _saved_mark_word to point to just after the last object
 628   // iterated over.
 629 #define ContigSpace_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \
 630   void oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk);
 631 
 632   ALL_SINCE_SAVE_MARKS_CLOSURES(ContigSpace_OOP_SINCE_SAVE_MARKS_DECL)
 633 #undef ContigSpace_OOP_SINCE_SAVE_MARKS_DECL
 634 
 635   // Same as object_iterate, but starting from "mark", which is required
 636   // to denote the start of an object.  Objects allocated by
 637   // applications of the closure *are* included in the iteration.
 638   virtual void object_iterate_from(HeapWord* mark, ObjectClosure* blk);
 639 
 640   // Very inefficient implementation.
 641   virtual HeapWord* block_start_const(const void* p) const;
 642   size_t block_size(const HeapWord* p) const;
 643   // If a block is in the allocated area, it is an object.
 644   bool block_is_obj(const HeapWord* p) const { return p < top(); }
 645 
 646   // Addresses for inlined allocation
 647   HeapWord** top_addr() { return &_top; }
 648   HeapWord** end_addr() { return &_end; }
 649 
 650   // Overrides for more efficient compaction support.
 651   void prepare_for_compaction(CompactPoint* cp);
 652 
 653   virtual void print_on(outputStream* st) const;
 654 
 655   // Checked dynamic downcasts.
 656   virtual ContiguousSpace* toContiguousSpace() {
 657     return this;
 658   }
 659 
 660   // Debugging
 661   virtual void verify() const;
 662 
 663   // Used to increase collection frequency.  "factor" of 0 means entire
 664   // space.
 665   void allocate_temporary_filler(int factor);
 666 };
 667 
 668 
 669 // A dirty card to oop closure that does filtering.
 670 // It knows how to filter out objects that are outside of the _boundary.
 671 class FilteringDCTOC : public DirtyCardToOopClosure {
 672 protected:
 673   // Override.
 674   void walk_mem_region(MemRegion mr,
 675                        HeapWord* bottom, HeapWord* top);
 676 
 677   // Walk the given memory region, from bottom to top, applying
 678   // the given oop closure to (possibly) all objects found. The
 679   // given oop closure may or may not be the same as the oop
 680   // closure with which this closure was created, as it may
 681   // be a filtering closure which makes use of the _boundary.
 682   // We offer two signatures, so the FilteringClosure static type is
 683   // apparent.
 684   virtual void walk_mem_region_with_cl(MemRegion mr,
 685                                        HeapWord* bottom, HeapWord* top,
 686                                        ExtendedOopClosure* cl) = 0;
 687   virtual void walk_mem_region_with_cl(MemRegion mr,
 688                                        HeapWord* bottom, HeapWord* top,
 689                                        FilteringClosure* cl) = 0;
 690 
 691 public:
 692   FilteringDCTOC(Space* sp, ExtendedOopClosure* cl,
 693                   CardTableModRefBS::PrecisionStyle precision,
 694                   HeapWord* boundary) :
 695     DirtyCardToOopClosure(sp, cl, precision, boundary) {}
 696 };
 697 
 698 // A dirty card to oop closure for contiguous spaces
 699 // (ContiguousSpace and sub-classes).
 700 // It is a FilteringClosure, as defined above, and it knows:
 701 //
 702 // 1. That the actual top of any area in a memory region
 703 //    contained by the space is bounded by the end of the contiguous
 704 //    region of the space.
 705 // 2. That the space is really made up of objects and not just
 706 //    blocks.
 707 
 708 class ContiguousSpaceDCTOC : public FilteringDCTOC {
 709 protected:
 710   // Overrides.
 711   HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
 712 
 713   virtual void walk_mem_region_with_cl(MemRegion mr,
 714                                        HeapWord* bottom, HeapWord* top,
 715                                        ExtendedOopClosure* cl);
 716   virtual void walk_mem_region_with_cl(MemRegion mr,
 717                                        HeapWord* bottom, HeapWord* top,
 718                                        FilteringClosure* cl);
 719 
 720 public:
 721   ContiguousSpaceDCTOC(ContiguousSpace* sp, ExtendedOopClosure* cl,
 722                        CardTableModRefBS::PrecisionStyle precision,
 723                        HeapWord* boundary) :
 724     FilteringDCTOC(sp, cl, precision, boundary)
 725   {}
 726 };
 727 
 728 // A ContigSpace that Supports an efficient "block_start" operation via
 729 // a BlockOffsetArray (whose BlockOffsetSharedArray may be shared with
 730 // other spaces.)  This is the abstract base class for old generation
 731 // (tenured) spaces.
 732 
 733 class OffsetTableContigSpace: public ContiguousSpace {
 734   friend class VMStructs;
 735  protected:
 736   BlockOffsetArrayContigSpace _offsets;
 737   Mutex _par_alloc_lock;
 738 
 739  public:
 740   // Constructor
 741   OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
 742                          MemRegion mr);
 743 
 744   void set_bottom(HeapWord* value);
 745   void set_end(HeapWord* value);
 746 
 747   void clear(bool mangle_space);
 748 
 749   inline HeapWord* block_start_const(const void* p) const;
 750 
 751   // Add offset table update.
 752   virtual inline HeapWord* allocate(size_t word_size);
 753   inline HeapWord* par_allocate(size_t word_size);
 754 
 755   // MarkSweep support phase3
 756   virtual HeapWord* initialize_threshold();
 757   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);
 758 
 759   virtual void print_on(outputStream* st) const;
 760 
 761   // Debugging
 762   void verify() const;
 763 };
 764 
 765 
 766 // Class TenuredSpace is used by TenuredGeneration
 767 
 768 class TenuredSpace: public OffsetTableContigSpace {
 769   friend class VMStructs;
 770  protected:
 771   // Mark sweep support
 772   size_t allowed_dead_ratio() const;
 773  public:
 774   // Constructor
 775   TenuredSpace(BlockOffsetSharedArray* sharedOffsetArray,
 776                MemRegion mr) :
 777     OffsetTableContigSpace(sharedOffsetArray, mr) {}
 778 };
 779 #endif // SHARE_VM_GC_SHARED_SPACE_HPP