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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  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_MEMORY_SPACE_HPP
  26 #define SHARE_VM_MEMORY_SPACE_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "memory/blockOffsetTable.hpp"
  30 #include "memory/cardTableModRefBS.hpp"
  31 #include "memory/iterator.hpp"
  32 #include "memory/memRegion.hpp"
  33 #include "memory/watermark.hpp"
  34 #include "oops/markOop.hpp"
  35 #include "runtime/mutexLocker.hpp"
  36 #include "utilities/macros.hpp"
  37 #include "utilities/workgroup.hpp"
  38 
  39 // A space is an abstraction for the "storage units" backing
  40 // up the generation abstraction. It includes specific
  41 // implementations for keeping track of free and used space,
  42 // for iterating over objects and free blocks, etc.
  43 
  44 // Forward decls.
  45 class Space;
  46 class BlockOffsetArray;
  47 class BlockOffsetArrayContigSpace;
  48 class Generation;
  49 class CompactibleSpace;
  50 class BlockOffsetTable;
  51 class GenRemSet;
  52 class CardTableRS;
  53 class DirtyCardToOopClosure;
  54 
  55 // A Space describes a heap area. Class Space is an abstract
  56 // base class.
  57 //
  58 // Space supports allocation, size computation and GC support is provided.
  59 //
  60 // Invariant: bottom() and end() are on page_size boundaries and
  61 // bottom() <= top() <= end()
  62 // top() is inclusive and end() is exclusive.
  63 
  64 class Space: public CHeapObj<mtGC> {
  65   friend class VMStructs;
  66  protected:
  67   HeapWord* _bottom;
  68   HeapWord* _end;
  69 
  70   // Used in support of save_marks()
  71   HeapWord* _saved_mark_word;
  72 
  73   // A sequential tasks done structure. This supports
  74   // parallel GC, where we have threads dynamically
  75   // claiming sub-tasks from a larger parallel task.
  76   SequentialSubTasksDone _par_seq_tasks;
  77 
  78   Space():
  79     _bottom(NULL), _end(NULL) { }
  80 
  81  public:
  82   // Accessors
  83   HeapWord* bottom() const         { return _bottom; }
  84   HeapWord* end() const            { return _end;    }
  85   virtual void set_bottom(HeapWord* value) { _bottom = value; }
  86   virtual void set_end(HeapWord* value)    { _end = value; }
  87 
  88   virtual HeapWord* saved_mark_word() const  { return _saved_mark_word; }
  89 
  90   void set_saved_mark_word(HeapWord* p) { _saved_mark_word = p; }
  91 
  92   // Returns true if this object has been allocated since a
  93   // generation's "save_marks" call.
  94   virtual bool obj_allocated_since_save_marks(const oop obj) const {
  95     return (HeapWord*)obj >= saved_mark_word();
  96   }
  97 
  98   virtual MemRegionClosure* preconsumptionDirtyCardClosure() const {
  99     return NULL;
 100   }
 101 
 102   // Returns a subregion of the space containing only the allocated objects in
 103   // the space.
 104   virtual MemRegion used_region() const = 0;
 105 
 106   // Returns a region that is guaranteed to contain (at least) all objects
 107   // allocated at the time of the last call to "save_marks".  If the space
 108   // initializes its DirtyCardToOopClosure's specifying the "contig" option
 109   // (that is, if the space is contiguous), then this region must contain only
 110   // such objects: the memregion will be from the bottom of the region to the
 111   // saved mark.  Otherwise, the "obj_allocated_since_save_marks" method of
 112   // the space must distinguish between objects in the region allocated before
 113   // and after the call to save marks.
 114   MemRegion used_region_at_save_marks() const {
 115     return MemRegion(bottom(), saved_mark_word());
 116   }
 117 
 118   // Initialization.
 119   // "initialize" should be called once on a space, before it is used for
 120   // any purpose.  The "mr" arguments gives the bounds of the space, and
 121   // the "clear_space" argument should be true unless the memory in "mr" is
 122   // known to be zeroed.
 123   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 124 
 125   // The "clear" method must be called on a region that may have
 126   // had allocation performed in it, but is now to be considered empty.
 127   virtual void clear(bool mangle_space);
 128 
 129   // For detecting GC bugs.  Should only be called at GC boundaries, since
 130   // some unused space may be used as scratch space during GC's.
 131   // We also call this when expanding a space to satisfy an allocation
 132   // request. See bug #4668531
 133   virtual void mangle_unused_area() = 0;
 134   virtual void mangle_unused_area_complete() = 0;
 135 
 136   // Testers
 137   bool is_empty() const              { return used() == 0; }
 138   bool not_empty() const             { return used() > 0; }
 139 
 140   // Returns true iff the given the space contains the
 141   // given address as part of an allocated object. For
 142   // certain kinds of spaces, this might be a potentially
 143   // expensive operation. To prevent performance problems
 144   // on account of its inadvertent use in product jvm's,
 145   // we restrict its use to assertion checks only.
 146   bool is_in(const void* p) const {
 147     return used_region().contains(p);
 148   }
 149 
 150   // Returns true iff the given reserved memory of the space contains the
 151   // given address.
 152   bool is_in_reserved(const void* p) const { return _bottom <= p && p < _end; }
 153 
 154   // Returns true iff the given block is not allocated.
 155   virtual bool is_free_block(const HeapWord* p) const = 0;
 156 
 157   // Test whether p is double-aligned
 158   static bool is_aligned(void* p) {
 159     return ((intptr_t)p & (sizeof(double)-1)) == 0;
 160   }
 161 
 162   // Size computations.  Sizes are in bytes.
 163   size_t capacity()     const { return byte_size(bottom(), end()); }
 164   virtual size_t used() const = 0;
 165   virtual size_t free() const = 0;
 166 
 167   // Iterate over all the ref-containing fields of all objects in the
 168   // space, calling "cl.do_oop" on each.  Fields in objects allocated by
 169   // applications of the closure are not included in the iteration.
 170   virtual void oop_iterate(ExtendedOopClosure* cl);
 171 
 172   // Iterate over all objects in the space, calling "cl.do_object" on
 173   // each.  Objects allocated by applications of the closure are not
 174   // included in the iteration.
 175   virtual void object_iterate(ObjectClosure* blk) = 0;
 176   // Similar to object_iterate() except only iterates over
 177   // objects whose internal references point to objects in the space.
 178   virtual void safe_object_iterate(ObjectClosure* blk) = 0;
 179 
 180   // Create and return a new dirty card to oop closure. Can be
 181   // overridden to return the appropriate type of closure
 182   // depending on the type of space in which the closure will
 183   // operate. ResourceArea allocated.
 184   virtual DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
 185                                              CardTableModRefBS::PrecisionStyle precision,
 186                                              HeapWord* boundary = NULL);
 187 
 188   // If "p" is in the space, returns the address of the start of the
 189   // "block" that contains "p".  We say "block" instead of "object" since
 190   // some heaps may not pack objects densely; a chunk may either be an
 191   // object or a non-object.  If "p" is not in the space, return NULL.
 192   virtual HeapWord* block_start_const(const void* p) const = 0;
 193 
 194   // The non-const version may have benevolent side effects on the data
 195   // structure supporting these calls, possibly speeding up future calls.
 196   // The default implementation, however, is simply to call the const
 197   // version.
 198   virtual HeapWord* block_start(const void* p);
 199 
 200   // Requires "addr" to be the start of a chunk, and returns its size.
 201   // "addr + size" is required to be the start of a new chunk, or the end
 202   // of the active area of the heap.
 203   virtual size_t block_size(const HeapWord* addr) const = 0;
 204 
 205   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 206   // the block is an object.
 207   virtual bool block_is_obj(const HeapWord* addr) const = 0;
 208 
 209   // Requires "addr" to be the start of a block, and returns "TRUE" iff
 210   // the block is an object and the object is alive.
 211   virtual bool obj_is_alive(const HeapWord* addr) const;
 212 
 213   // Allocation (return NULL if full).  Assumes the caller has established
 214   // mutually exclusive access to the space.
 215   virtual HeapWord* allocate(size_t word_size) = 0;
 216 
 217   // Allocation (return NULL if full).  Enforces mutual exclusion internally.
 218   virtual HeapWord* par_allocate(size_t word_size) = 0;
 219 
 220   // Mark-sweep-compact support: all spaces can update pointers to objects
 221   // moving as a part of compaction.
 222   virtual void adjust_pointers() = 0;
 223 
 224   // PrintHeapAtGC support
 225   virtual void print() const;
 226   virtual void print_on(outputStream* st) const;
 227   virtual void print_short() const;
 228   virtual void print_short_on(outputStream* st) const;
 229 
 230 
 231   // Accessor for parallel sequential tasks.
 232   SequentialSubTasksDone* par_seq_tasks() { return &_par_seq_tasks; }
 233 
 234   // IF "this" is a ContiguousSpace, return it, else return NULL.
 235   virtual ContiguousSpace* toContiguousSpace() {
 236     return NULL;
 237   }
 238 
 239   // Debugging
 240   virtual void verify() const = 0;
 241 };
 242 
 243 // A MemRegionClosure (ResourceObj) whose "do_MemRegion" function applies an
 244 // OopClosure to (the addresses of) all the ref-containing fields that could
 245 // be modified by virtue of the given MemRegion being dirty. (Note that
 246 // because of the imprecise nature of the write barrier, this may iterate
 247 // over oops beyond the region.)
 248 // This base type for dirty card to oop closures handles memory regions
 249 // in non-contiguous spaces with no boundaries, and should be sub-classed
 250 // to support other space types. See ContiguousDCTOC for a sub-class
 251 // that works with ContiguousSpaces.
 252 
 253 class DirtyCardToOopClosure: public MemRegionClosureRO {
 254 protected:
 255   ExtendedOopClosure* _cl;
 256   Space* _sp;
 257   CardTableModRefBS::PrecisionStyle _precision;
 258   HeapWord* _boundary;          // If non-NULL, process only non-NULL oops
 259                                 // pointing below boundary.
 260   HeapWord* _min_done;          // ObjHeadPreciseArray precision requires
 261                                 // a downwards traversal; this is the
 262                                 // lowest location already done (or,
 263                                 // alternatively, the lowest address that
 264                                 // shouldn't be done again.  NULL means infinity.)
 265   NOT_PRODUCT(HeapWord* _last_bottom;)
 266   NOT_PRODUCT(HeapWord* _last_explicit_min_done;)
 267 
 268   // Get the actual top of the area on which the closure will
 269   // operate, given where the top is assumed to be (the end of the
 270   // memory region passed to do_MemRegion) and where the object
 271   // at the top is assumed to start. For example, an object may
 272   // start at the top but actually extend past the assumed top,
 273   // in which case the top becomes the end of the object.
 274   virtual HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
 275 
 276   // Walk the given memory region from bottom to (actual) top
 277   // looking for objects and applying the oop closure (_cl) to
 278   // them. The base implementation of this treats the area as
 279   // blocks, where a block may or may not be an object. Sub-
 280   // classes should override this to provide more accurate
 281   // or possibly more efficient walking.
 282   virtual void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);
 283 
 284 public:
 285   DirtyCardToOopClosure(Space* sp, ExtendedOopClosure* cl,
 286                         CardTableModRefBS::PrecisionStyle precision,
 287                         HeapWord* boundary) :
 288     _sp(sp), _cl(cl), _precision(precision), _boundary(boundary),
 289     _min_done(NULL) {
 290     NOT_PRODUCT(_last_bottom = NULL);
 291     NOT_PRODUCT(_last_explicit_min_done = NULL);
 292   }
 293 
 294   void do_MemRegion(MemRegion mr);
 295 
 296   void set_min_done(HeapWord* min_done) {
 297     _min_done = min_done;
 298     NOT_PRODUCT(_last_explicit_min_done = _min_done);
 299   }
 300 #ifndef PRODUCT
 301   void set_last_bottom(HeapWord* last_bottom) {
 302     _last_bottom = last_bottom;
 303   }
 304 #endif
 305 };
 306 
 307 // A structure to represent a point at which objects are being copied
 308 // during compaction.
 309 class CompactPoint : public StackObj {
 310 public:
 311   Generation* gen;
 312   CompactibleSpace* space;
 313   HeapWord* threshold;
 314 
 315   CompactPoint(Generation* g = NULL) :
 316     gen(g), space(NULL), threshold(0) {}
 317 };
 318 
 319 // A space that supports compaction operations.  This is usually, but not
 320 // necessarily, a space that is normally contiguous.  But, for example, a
 321 // free-list-based space whose normal collection is a mark-sweep without
 322 // compaction could still support compaction in full GC's.
 323 //
 324 // The compaction operations are implemented by the
 325 // scan_and_{adjust_pointers,compact,forward} function templates.
 326 // The following are, non-virtual, auxiliary functions used by these function templates:
 327 // - scan_limit()
 328 // - scanned_block_is_obj()
 329 // - scanned_block_size()
 330 // - adjust_obj_size()
 331 // - obj_size()
 332 // These functions are to be used exclusively by the scan_and_* function templates,
 333 // and must be defined for all (non-abstract) subclasses of CompactibleSpace.
 334 //
 335 // NOTE: Any subclasses to CompactibleSpace wanting to change/define the behavior
 336 // in any of the auxiliary functions must also override the corresponding
 337 // prepare_for_compaction/adjust_pointers/compact functions using them.
 338 // If not, such changes will not be used or have no effect on the compaction operations.
 339 //
 340 // This translates to the following dependencies:
 341 // Overrides/definitions of
 342 //  - scan_limit
 343 //  - scanned_block_is_obj
 344 //  - scanned_block_size
 345 // require override/definition of prepare_for_compaction().
 346 // Similar dependencies exist between
 347 //  - adjust_obj_size  and adjust_pointers()
 348 //  - obj_size         and compact().
 349 //
 350 // Additionally, this also means that changes to block_size() or block_is_obj() that
 351 // should be effective during the compaction operations must provide a corresponding
 352 // definition of scanned_block_size/scanned_block_is_obj respectively.
 353 class CompactibleSpace: public Space {
 354   friend class VMStructs;
 355   friend class CompactibleFreeListSpace;
 356 private:
 357   HeapWord* _compaction_top;
 358   CompactibleSpace* _next_compaction_space;
 359 
 360   // Auxiliary functions for scan_and_{forward,adjust_pointers,compact} support.
 361   inline size_t adjust_obj_size(size_t size) const {
 362     return size;
 363   }
 364 
 365   inline size_t obj_size(const HeapWord* addr) const {
 366     return oop(addr)->size();
 367   }
 368 
 369 public:
 370   CompactibleSpace() :
 371    _compaction_top(NULL), _next_compaction_space(NULL) {}
 372 
 373   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 374   virtual void clear(bool mangle_space);
 375 
 376   // Used temporarily during a compaction phase to hold the value
 377   // top should have when compaction is complete.
 378   HeapWord* compaction_top() const { return _compaction_top;    }
 379 
 380   void set_compaction_top(HeapWord* value) {
 381     assert(value == NULL || (value >= bottom() && value <= end()),
 382       "should point inside space");
 383     _compaction_top = value;
 384   }
 385 
 386   // Perform operations on the space needed after a compaction
 387   // has been performed.
 388   virtual void reset_after_compaction() = 0;
 389 
 390   // Returns the next space (in the current generation) to be compacted in
 391   // the global compaction order.  Also is used to select the next
 392   // space into which to compact.
 393 
 394   virtual CompactibleSpace* next_compaction_space() const {
 395     return _next_compaction_space;
 396   }
 397 
 398   void set_next_compaction_space(CompactibleSpace* csp) {
 399     _next_compaction_space = csp;
 400   }
 401 
 402   // MarkSweep support phase2
 403 
 404   // Start the process of compaction of the current space: compute
 405   // post-compaction addresses, and insert forwarding pointers.  The fields
 406   // "cp->gen" and "cp->compaction_space" are the generation and space into
 407   // which we are currently compacting.  This call updates "cp" as necessary,
 408   // and leaves the "compaction_top" of the final value of
 409   // "cp->compaction_space" up-to-date.  Offset tables may be updated in
 410   // this phase as if the final copy had occurred; if so, "cp->threshold"
 411   // indicates when the next such action should be taken.
 412   virtual void prepare_for_compaction(CompactPoint* cp) = 0;
 413   // MarkSweep support phase3
 414   virtual void adjust_pointers();
 415   // MarkSweep support phase4
 416   virtual void compact();
 417 
 418   // The maximum percentage of objects that can be dead in the compacted
 419   // live part of a compacted space ("deadwood" support.)
 420   virtual size_t allowed_dead_ratio() const { return 0; };
 421 
 422   // Some contiguous spaces may maintain some data structures that should
 423   // be updated whenever an allocation crosses a boundary.  This function
 424   // returns the first such boundary.
 425   // (The default implementation returns the end of the space, so the
 426   // boundary is never crossed.)
 427   virtual HeapWord* initialize_threshold() { return end(); }
 428 
 429   // "q" is an object of the given "size" that should be forwarded;
 430   // "cp" names the generation ("gen") and containing "this" (which must
 431   // also equal "cp->space").  "compact_top" is where in "this" the
 432   // next object should be forwarded to.  If there is room in "this" for
 433   // the object, insert an appropriate forwarding pointer in "q".
 434   // If not, go to the next compaction space (there must
 435   // be one, since compaction must succeed -- we go to the first space of
 436   // the previous generation if necessary, updating "cp"), reset compact_top
 437   // and then forward.  In either case, returns the new value of "compact_top".
 438   // If the forwarding crosses "cp->threshold", invokes the "cross_threshold"
 439   // function of the then-current compaction space, and updates "cp->threshold
 440   // accordingly".
 441   virtual HeapWord* forward(oop q, size_t size, CompactPoint* cp,
 442                     HeapWord* compact_top);
 443 
 444   // Return a size with adjustments as required of the space.
 445   virtual size_t adjust_object_size_v(size_t size) const { return size; }
 446 
 447 protected:
 448   // Used during compaction.
 449   HeapWord* _first_dead;
 450   HeapWord* _end_of_live;
 451 
 452   // Minimum size of a free block.
 453   virtual size_t minimum_free_block_size() const { return 0; }
 454 
 455   // This the function is invoked when an allocation of an object covering
 456   // "start" to "end occurs crosses the threshold; returns the next
 457   // threshold.  (The default implementation does nothing.)
 458   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* the_end) {
 459     return end();
 460   }
 461 
 462   // Requires "allowed_deadspace_words > 0", that "q" is the start of a
 463   // free block of the given "word_len", and that "q", were it an object,
 464   // would not move if forwarded.  If the size allows, fill the free
 465   // block with an object, to prevent excessive compaction.  Returns "true"
 466   // iff the free region was made deadspace, and modifies
 467   // "allowed_deadspace_words" to reflect the number of available deadspace
 468   // words remaining after this operation.
 469   bool insert_deadspace(size_t& allowed_deadspace_words, HeapWord* q,
 470                         size_t word_len);
 471 
 472   // Below are template functions for scan_and_* algorithms (avoiding virtual calls).
 473   // The space argument should be a subclass of CompactibleSpace, implementing
 474   // scan_limit(), scanned_block_is_obj(), and scanned_block_size(),
 475   // and possibly also overriding obj_size(), and adjust_obj_size().
 476   // These functions should avoid virtual calls whenever possible.
 477 
 478   // Frequently calls adjust_obj_size().
 479   template <class SpaceType>
 480   static inline void scan_and_adjust_pointers(SpaceType* space);
 481 
 482   // Frequently calls obj_size().
 483   template <class SpaceType>
 484   static inline void scan_and_compact(SpaceType* space);
 485 
 486   // Frequently calls scanned_block_is_obj() and scanned_block_size().
 487   // Requires the scan_limit() function.
 488   template <class SpaceType>
 489   static inline void scan_and_forward(SpaceType* space, CompactPoint* cp);
 490 };
 491 
 492 class GenSpaceMangler;
 493 
 494 // A space in which the free area is contiguous.  It therefore supports
 495 // faster allocation, and compaction.
 496 class ContiguousSpace: public CompactibleSpace {
 497   friend class VMStructs;
 498   // Allow scan_and_forward function to call (private) overrides for auxiliary functions on this class
 499   template <typename SpaceType>
 500   friend void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp);
 501 
 502  private:
 503   // Auxiliary functions for scan_and_forward support.
 504   // See comments for CompactibleSpace for more information.
 505   inline HeapWord* scan_limit() const {
 506     return top();
 507   }
 508 
 509   inline bool scanned_block_is_obj(const HeapWord* addr) const {
 510     return true; // Always true, since scan_limit is top
 511   }
 512 
 513   inline size_t scanned_block_size(const HeapWord* addr) const {
 514     return oop(addr)->size();
 515   }
 516 
 517  protected:
 518   HeapWord* _top;
 519   HeapWord* _concurrent_iteration_safe_limit;
 520   // A helper for mangling the unused area of the space in debug builds.
 521   GenSpaceMangler* _mangler;
 522 
 523   GenSpaceMangler* mangler() { return _mangler; }
 524 
 525   // Allocation helpers (return NULL if full).
 526   inline HeapWord* allocate_impl(size_t word_size);
 527   inline HeapWord* par_allocate_impl(size_t word_size);
 528 
 529  public:
 530   ContiguousSpace();
 531   ~ContiguousSpace();
 532 
 533   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
 534   virtual void clear(bool mangle_space);
 535 
 536   // Accessors
 537   HeapWord* top() const            { return _top;    }
 538   void set_top(HeapWord* value)    { _top = value; }
 539 
 540   void set_saved_mark()            { _saved_mark_word = top();    }
 541   void reset_saved_mark()          { _saved_mark_word = bottom(); }
 542 
 543   WaterMark bottom_mark()     { return WaterMark(this, bottom()); }
 544   WaterMark top_mark()        { return WaterMark(this, top()); }
 545   WaterMark saved_mark()      { return WaterMark(this, saved_mark_word()); }
 546   bool saved_mark_at_top() const { return saved_mark_word() == top(); }
 547 
 548   // In debug mode mangle (write it with a particular bit
 549   // pattern) the unused part of a space.
 550 
 551   // Used to save the an address in a space for later use during mangling.
 552   void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
 553   // Used to save the space's current top for later use during mangling.
 554   void set_top_for_allocations() PRODUCT_RETURN;
 555 
 556   // Mangle regions in the space from the current top up to the
 557   // previously mangled part of the space.
 558   void mangle_unused_area() PRODUCT_RETURN;
 559   // Mangle [top, end)
 560   void mangle_unused_area_complete() PRODUCT_RETURN;
 561 
 562   // Do some sparse checking on the area that should have been mangled.
 563   void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
 564   // Check the complete area that should have been mangled.
 565   // This code may be NULL depending on the macro DEBUG_MANGLING.
 566   void check_mangled_unused_area_complete() PRODUCT_RETURN;
 567 
 568   // Size computations: sizes in bytes.
 569   size_t capacity() const        { return byte_size(bottom(), end()); }
 570   size_t used() const            { return byte_size(bottom(), top()); }
 571   size_t free() const            { return byte_size(top(),    end()); }
 572 
 573   virtual bool is_free_block(const HeapWord* p) const;
 574 
 575   // In a contiguous space we have a more obvious bound on what parts
 576   // contain objects.
 577   MemRegion used_region() const { return MemRegion(bottom(), top()); }
 578 
 579   // Allocation (return NULL if full)
 580   virtual HeapWord* allocate(size_t word_size);
 581   virtual HeapWord* par_allocate(size_t word_size);
 582   HeapWord* allocate_aligned(size_t word_size);
 583 
 584   // Iteration
 585   void oop_iterate(ExtendedOopClosure* cl);
 586   void object_iterate(ObjectClosure* blk);
 587   // For contiguous spaces this method will iterate safely over objects
 588   // in the space (i.e., between bottom and top) when at a safepoint.
 589   void safe_object_iterate(ObjectClosure* blk);
 590 
 591   // Iterate over as many initialized objects in the space as possible,
 592   // calling "cl.do_object_careful" on each. Return NULL if all objects
 593   // in the space (at the start of the iteration) were iterated over.
 594   // Return an address indicating the extent of the iteration in the
 595   // event that the iteration had to return because of finding an
 596   // uninitialized object in the space, or if the closure "cl"
 597   // signaled early termination.
 598   HeapWord* object_iterate_careful(ObjectClosureCareful* cl);
 599   HeapWord* concurrent_iteration_safe_limit() {
 600     assert(_concurrent_iteration_safe_limit <= top(),
 601            "_concurrent_iteration_safe_limit update missed");
 602     return _concurrent_iteration_safe_limit;
 603   }
 604   // changes the safe limit, all objects from bottom() to the new
 605   // limit should be properly initialized
 606   void set_concurrent_iteration_safe_limit(HeapWord* new_limit) {
 607     assert(new_limit <= top(), "uninitialized objects in the safe range");
 608     _concurrent_iteration_safe_limit = new_limit;
 609   }
 610 
 611 
 612 #if INCLUDE_ALL_GCS
 613   // In support of parallel oop_iterate.
 614   #define ContigSpace_PAR_OOP_ITERATE_DECL(OopClosureType, nv_suffix)  \
 615     void par_oop_iterate(MemRegion mr, OopClosureType* blk);
 616 
 617     ALL_PAR_OOP_ITERATE_CLOSURES(ContigSpace_PAR_OOP_ITERATE_DECL)
 618   #undef ContigSpace_PAR_OOP_ITERATE_DECL
 619 #endif // INCLUDE_ALL_GCS
 620 
 621   // Compaction support
 622   virtual void reset_after_compaction() {
 623     assert(compaction_top() >= bottom() && compaction_top() <= end(), "should point inside space");
 624     set_top(compaction_top());
 625     // set new iteration safe limit
 626     set_concurrent_iteration_safe_limit(compaction_top());
 627   }
 628 
 629   // Override.
 630   DirtyCardToOopClosure* new_dcto_cl(ExtendedOopClosure* cl,
 631                                      CardTableModRefBS::PrecisionStyle precision,
 632                                      HeapWord* boundary = NULL);
 633 
 634   // Apply "blk->do_oop" to the addresses of all reference fields in objects
 635   // starting with the _saved_mark_word, which was noted during a generation's
 636   // save_marks and is required to denote the head of an object.
 637   // Fields in objects allocated by applications of the closure
 638   // *are* included in the iteration.
 639   // Updates _saved_mark_word to point to just after the last object
 640   // iterated over.
 641 #define ContigSpace_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \
 642   void oop_since_save_marks_iterate##nv_suffix(OopClosureType* blk);
 643 
 644   ALL_SINCE_SAVE_MARKS_CLOSURES(ContigSpace_OOP_SINCE_SAVE_MARKS_DECL)
 645 #undef ContigSpace_OOP_SINCE_SAVE_MARKS_DECL
 646 
 647   // Same as object_iterate, but starting from "mark", which is required
 648   // to denote the start of an object.  Objects allocated by
 649   // applications of the closure *are* included in the iteration.
 650   virtual void object_iterate_from(WaterMark mark, ObjectClosure* blk);
 651 
 652   // Very inefficient implementation.
 653   virtual HeapWord* block_start_const(const void* p) const;
 654   size_t block_size(const HeapWord* p) const;
 655   // If a block is in the allocated area, it is an object.
 656   bool block_is_obj(const HeapWord* p) const { return p < top(); }
 657 
 658   // Addresses for inlined allocation
 659   HeapWord** top_addr() { return &_top; }
 660   HeapWord** end_addr() { return &_end; }
 661 
 662   // Overrides for more efficient compaction support.
 663   void prepare_for_compaction(CompactPoint* cp);
 664 
 665   // PrintHeapAtGC support.
 666   virtual void print_on(outputStream* st) const;
 667 
 668   // Checked dynamic downcasts.
 669   virtual ContiguousSpace* toContiguousSpace() {
 670     return this;
 671   }
 672 
 673   // Debugging
 674   virtual void verify() const;
 675 
 676   // Used to increase collection frequency.  "factor" of 0 means entire
 677   // space.
 678   void allocate_temporary_filler(int factor);
 679 };
 680 
 681 
 682 // A dirty card to oop closure that does filtering.
 683 // It knows how to filter out objects that are outside of the _boundary.
 684 class Filtering_DCTOC : public DirtyCardToOopClosure {
 685 protected:
 686   // Override.
 687   void walk_mem_region(MemRegion mr,
 688                        HeapWord* bottom, HeapWord* top);
 689 
 690   // Walk the given memory region, from bottom to top, applying
 691   // the given oop closure to (possibly) all objects found. The
 692   // given oop closure may or may not be the same as the oop
 693   // closure with which this closure was created, as it may
 694   // be a filtering closure which makes use of the _boundary.
 695   // We offer two signatures, so the FilteringClosure static type is
 696   // apparent.
 697   virtual void walk_mem_region_with_cl(MemRegion mr,
 698                                        HeapWord* bottom, HeapWord* top,
 699                                        ExtendedOopClosure* cl) = 0;
 700   virtual void walk_mem_region_with_cl(MemRegion mr,
 701                                        HeapWord* bottom, HeapWord* top,
 702                                        FilteringClosure* cl) = 0;
 703 
 704 public:
 705   Filtering_DCTOC(Space* sp, ExtendedOopClosure* cl,
 706                   CardTableModRefBS::PrecisionStyle precision,
 707                   HeapWord* boundary) :
 708     DirtyCardToOopClosure(sp, cl, precision, boundary) {}
 709 };
 710 
 711 // A dirty card to oop closure for contiguous spaces
 712 // (ContiguousSpace and sub-classes).
 713 // It is a FilteringClosure, as defined above, and it knows:
 714 //
 715 // 1. That the actual top of any area in a memory region
 716 //    contained by the space is bounded by the end of the contiguous
 717 //    region of the space.
 718 // 2. That the space is really made up of objects and not just
 719 //    blocks.
 720 
 721 class ContiguousSpaceDCTOC : public Filtering_DCTOC {
 722 protected:
 723   // Overrides.
 724   HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
 725 
 726   virtual void walk_mem_region_with_cl(MemRegion mr,
 727                                        HeapWord* bottom, HeapWord* top,
 728                                        ExtendedOopClosure* cl);
 729   virtual void walk_mem_region_with_cl(MemRegion mr,
 730                                        HeapWord* bottom, HeapWord* top,
 731                                        FilteringClosure* cl);
 732 
 733 public:
 734   ContiguousSpaceDCTOC(ContiguousSpace* sp, ExtendedOopClosure* cl,
 735                        CardTableModRefBS::PrecisionStyle precision,
 736                        HeapWord* boundary) :
 737     Filtering_DCTOC(sp, cl, precision, boundary)
 738   {}
 739 };
 740 
 741 // A ContigSpace that Supports an efficient "block_start" operation via
 742 // a BlockOffsetArray (whose BlockOffsetSharedArray may be shared with
 743 // other spaces.)  This is the abstract base class for old generation
 744 // (tenured) spaces.
 745 
 746 class OffsetTableContigSpace: public ContiguousSpace {
 747   friend class VMStructs;
 748  protected:
 749   BlockOffsetArrayContigSpace _offsets;
 750   Mutex _par_alloc_lock;
 751 
 752  public:
 753   // Constructor
 754   OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
 755                          MemRegion mr);
 756 
 757   void set_bottom(HeapWord* value);
 758   void set_end(HeapWord* value);
 759 
 760   void clear(bool mangle_space);
 761 
 762   inline HeapWord* block_start_const(const void* p) const;
 763 
 764   // Add offset table update.
 765   virtual inline HeapWord* allocate(size_t word_size);
 766   inline HeapWord* par_allocate(size_t word_size);
 767 
 768   // MarkSweep support phase3
 769   virtual HeapWord* initialize_threshold();
 770   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);
 771 
 772   virtual void print_on(outputStream* st) const;
 773 
 774   // Debugging
 775   void verify() const;
 776 };
 777 
 778 
 779 // Class TenuredSpace is used by TenuredGeneration
 780 
 781 class TenuredSpace: public OffsetTableContigSpace {
 782   friend class VMStructs;
 783  protected:
 784   // Mark sweep support
 785   size_t allowed_dead_ratio() const;
 786  public:
 787   // Constructor
 788   TenuredSpace(BlockOffsetSharedArray* sharedOffsetArray,
 789                MemRegion mr) :
 790     OffsetTableContigSpace(sharedOffsetArray, mr) {}
 791 };
 792 #endif // SHARE_VM_MEMORY_SPACE_HPP