1 /*
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 24 
 25 #ifndef SHARE_GC_SHARED_SPACE_HPP
 26 #define SHARE_GC_SHARED_SPACE_HPP
 27 
 28 #include "gc/shared/blockOffsetTable.hpp"
 29 #include "gc/shared/cardTable.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/markWord.hpp"
 35 #include "runtime/mutexLocker.hpp"
 36 #include "utilities/align.hpp"
 37 #include "utilities/macros.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 CardTableRS;
 52 class DirtyCardToOopClosure;
 53 class SlidingForwarding;
 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   Space():
 74     _bottom(NULL), _end(NULL) { }
 75 
 76  public:
 77   // Accessors
 78   HeapWord* bottom() const         { return _bottom; }
 79   HeapWord* end() const            { return _end;    }
 80   virtual void set_bottom(HeapWord* value) { _bottom = value; }
 81   virtual void set_end(HeapWord* value)    { _end = value; }
 82 
 83   virtual HeapWord* saved_mark_word() const  { return _saved_mark_word; }
 84 
 85   void set_saved_mark_word(HeapWord* p) { _saved_mark_word = p; }
 86 
 87   // Returns true if this object has been allocated since a
 88   // generation's "save_marks" call.
 89   virtual bool obj_allocated_since_save_marks(const oop obj) const {
 90     return cast_from_oop<HeapWord*>(obj) >= saved_mark_word();
 91   }
 92 
 93   // Returns a subregion of the space containing only the allocated objects in
 94   // the space.
 95   virtual MemRegion used_region() const = 0;
 96 
 97   // Returns a region that is guaranteed to contain (at least) all objects
 98   // allocated at the time of the last call to "save_marks".  If the space
 99   // initializes its DirtyCardToOopClosure's specifying the "contig" option
100   // (that is, if the space is contiguous), then this region must contain only
101   // such objects: the memregion will be from the bottom of the region to the
102   // saved mark.  Otherwise, the "obj_allocated_since_save_marks" method of
103   // the space must distinguish between objects in the region allocated before
104   // and after the call to save marks.
105   MemRegion used_region_at_save_marks() const {
106     return MemRegion(bottom(), saved_mark_word());
107   }
108 
109   // Initialization.
110   // "initialize" should be called once on a space, before it is used for
111   // any purpose.  The "mr" arguments gives the bounds of the space, and
112   // the "clear_space" argument should be true unless the memory in "mr" is
113   // known to be zeroed.
114   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
115 
116   // The "clear" method must be called on a region that may have
117   // had allocation performed in it, but is now to be considered empty.
118   virtual void clear(bool mangle_space);
119 
120   // For detecting GC bugs.  Should only be called at GC boundaries, since
121   // some unused space may be used as scratch space during GC's.
122   // We also call this when expanding a space to satisfy an allocation
123   // request. See bug #4668531
124   virtual void mangle_unused_area() = 0;
125   virtual void mangle_unused_area_complete() = 0;
126 
127   // Testers
128   bool is_empty() const              { return used() == 0; }
129   bool not_empty() const             { return used() > 0; }
130 
131   // Returns true iff the given the space contains the
132   // given address as part of an allocated object. For
133   // certain kinds of spaces, this might be a potentially
134   // expensive operation. To prevent performance problems
135   // on account of its inadvertent use in product jvm's,
136   // we restrict its use to assertion checks only.
137   bool is_in(const void* p) const {
138     return used_region().contains(p);
139   }
140   bool is_in(oop obj) const {
141     return is_in((void*)obj);
142   }
143 
144   // Returns true iff the given reserved memory of the space contains the
145   // given address.
146   bool is_in_reserved(const void* p) const { return _bottom <= p && p < _end; }
147 
148   // Returns true iff the given block is not allocated.
149   virtual bool is_free_block(const HeapWord* p) const = 0;
150 
151   // Test whether p is double-aligned
152   static bool is_aligned(void* p) {
153     return ::is_aligned(p, sizeof(double));
154   }
155 
156   // Size computations.  Sizes are in bytes.
157   size_t capacity()     const { return byte_size(bottom(), end()); }
158   virtual size_t used() const = 0;
159   virtual size_t free() const = 0;
160 
161   // Iterate over all the ref-containing fields of all objects in the
162   // space, calling "cl.do_oop" on each.  Fields in objects allocated by
163   // applications of the closure are not included in the iteration.
164   virtual void oop_iterate(OopIterateClosure* cl);
165 
166   // Iterate over all objects in the space, calling "cl.do_object" on
167   // each.  Objects allocated by applications of the closure are not
168   // included in the iteration.
169   virtual void object_iterate(ObjectClosure* blk) = 0;
170 
171   // Create and return a new dirty card to oop closure. Can be
172   // overridden to return the appropriate type of closure
173   // depending on the type of space in which the closure will
174   // operate. ResourceArea allocated.
175   virtual DirtyCardToOopClosure* new_dcto_cl(OopIterateClosure* cl,
176                                              CardTable::PrecisionStyle precision,
177                                              HeapWord* boundary);
178 
179   // If "p" is in the space, returns the address of the start of the
180   // "block" that contains "p".  We say "block" instead of "object" since
181   // some heaps may not pack objects densely; a chunk may either be an
182   // object or a non-object.  If "p" is not in the space, return NULL.
183   virtual HeapWord* block_start_const(const void* p) const = 0;
184 
185   // The non-const version may have benevolent side effects on the data
186   // structure supporting these calls, possibly speeding up future calls.
187   // The default implementation, however, is simply to call the const
188   // version.
189   virtual HeapWord* block_start(const void* p);
190 
191   // Requires "addr" to be the start of a chunk, and returns its size.
192   // "addr + size" is required to be the start of a new chunk, or the end
193   // of the active area of the heap.
194   virtual size_t block_size(const HeapWord* addr) const = 0;
195 
196   // Requires "addr" to be the start of a block, and returns "TRUE" iff
197   // the block is an object.
198   virtual bool block_is_obj(const HeapWord* addr) const = 0;
199 
200   // Requires "addr" to be the start of a block, and returns "TRUE" iff
201   // the block is an object and the object is alive.
202   virtual bool obj_is_alive(const HeapWord* addr) const;
203 
204   // Allocation (return NULL if full).  Assumes the caller has established
205   // mutually exclusive access to the space.
206   virtual HeapWord* allocate(size_t word_size) = 0;
207 
208   // Allocation (return NULL if full).  Enforces mutual exclusion internally.
209   virtual HeapWord* par_allocate(size_t word_size) = 0;
210 
211 #if INCLUDE_SERIALGC
212   // Mark-sweep-compact support: all spaces can update pointers to objects
213   // moving as a part of compaction.
214   virtual void adjust_pointers() = 0;
215 #endif
216 
217   virtual void print() const;
218   virtual void print_on(outputStream* st) const;
219   virtual void print_short() const;
220   virtual void print_short_on(outputStream* st) const;
221 
222 
223   // IF "this" is a ContiguousSpace, return it, else return NULL.
224   virtual ContiguousSpace* toContiguousSpace() {
225     return NULL;
226   }
227 
228   // Debugging
229   virtual void verify() const = 0;
230 };
231 
232 // A MemRegionClosure (ResourceObj) whose "do_MemRegion" function applies an
233 // OopClosure to (the addresses of) all the ref-containing fields that could
234 // be modified by virtue of the given MemRegion being dirty. (Note that
235 // because of the imprecise nature of the write barrier, this may iterate
236 // over oops beyond the region.)
237 // This base type for dirty card to oop closures handles memory regions
238 // in non-contiguous spaces with no boundaries, and should be sub-classed
239 // to support other space types. See ContiguousDCTOC for a sub-class
240 // that works with ContiguousSpaces.
241 
242 class DirtyCardToOopClosure: public MemRegionClosureRO {
243 protected:
244   OopIterateClosure* _cl;
245   Space* _sp;
246   CardTable::PrecisionStyle _precision;
247   HeapWord* _boundary;          // If non-NULL, process only non-NULL oops
248                                 // pointing below boundary.
249   HeapWord* _min_done;          // ObjHeadPreciseArray precision requires
250                                 // a downwards traversal; this is the
251                                 // lowest location already done (or,
252                                 // alternatively, the lowest address that
253                                 // shouldn't be done again.  NULL means infinity.)
254   NOT_PRODUCT(HeapWord* _last_bottom;)
255   NOT_PRODUCT(HeapWord* _last_explicit_min_done;)
256 
257   // Get the actual top of the area on which the closure will
258   // operate, given where the top is assumed to be (the end of the
259   // memory region passed to do_MemRegion) and where the object
260   // at the top is assumed to start. For example, an object may
261   // start at the top but actually extend past the assumed top,
262   // in which case the top becomes the end of the object.
263   virtual HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
264 
265   // Walk the given memory region from bottom to (actual) top
266   // looking for objects and applying the oop closure (_cl) to
267   // them. The base implementation of this treats the area as
268   // blocks, where a block may or may not be an object. Sub-
269   // classes should override this to provide more accurate
270   // or possibly more efficient walking.
271   virtual void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);
272 
273 public:
274   DirtyCardToOopClosure(Space* sp, OopIterateClosure* cl,
275                         CardTable::PrecisionStyle precision,
276                         HeapWord* boundary) :
277     _cl(cl), _sp(sp), _precision(precision), _boundary(boundary),
278     _min_done(NULL) {
279     NOT_PRODUCT(_last_bottom = NULL);
280     NOT_PRODUCT(_last_explicit_min_done = NULL);
281   }
282 
283   void do_MemRegion(MemRegion mr);
284 
285   void set_min_done(HeapWord* min_done) {
286     _min_done = min_done;
287     NOT_PRODUCT(_last_explicit_min_done = _min_done);
288   }
289 #ifndef PRODUCT
290   void set_last_bottom(HeapWord* last_bottom) {
291     _last_bottom = last_bottom;
292   }
293 #endif
294 };
295 
296 // A structure to represent a point at which objects are being copied
297 // during compaction.
298 class CompactPoint : public StackObj {
299 public:
300   Generation* gen;
301   CompactibleSpace* space;
302   HeapWord* threshold;
303 
304   CompactPoint(Generation* g = NULL) :
305     gen(g), space(NULL), threshold(0) {}
306 };
307 
308 // A space that supports compaction operations.  This is usually, but not
309 // necessarily, a space that is normally contiguous.  But, for example, a
310 // free-list-based space whose normal collection is a mark-sweep without
311 // compaction could still support compaction in full GC's.
312 //
313 // The compaction operations are implemented by the
314 // scan_and_{adjust_pointers,compact,forward} function templates.
315 // The following are, non-virtual, auxiliary functions used by these function templates:
316 // - scan_limit()
317 // - scanned_block_is_obj()
318 // - scanned_block_size()
319 // - adjust_obj_size()
320 // - obj_size()
321 // These functions are to be used exclusively by the scan_and_* function templates,
322 // and must be defined for all (non-abstract) subclasses of CompactibleSpace.
323 //
324 // NOTE: Any subclasses to CompactibleSpace wanting to change/define the behavior
325 // in any of the auxiliary functions must also override the corresponding
326 // prepare_for_compaction/adjust_pointers/compact functions using them.
327 // If not, such changes will not be used or have no effect on the compaction operations.
328 //
329 // This translates to the following dependencies:
330 // Overrides/definitions of
331 //  - scan_limit
332 //  - scanned_block_is_obj
333 //  - scanned_block_size
334 // require override/definition of prepare_for_compaction().
335 // Similar dependencies exist between
336 //  - adjust_obj_size  and adjust_pointers()
337 //  - obj_size         and compact().
338 //
339 // Additionally, this also means that changes to block_size() or block_is_obj() that
340 // should be effective during the compaction operations must provide a corresponding
341 // definition of scanned_block_size/scanned_block_is_obj respectively.
342 class CompactibleSpace: public Space {
343   friend class VMStructs;
344 private:
345   HeapWord* _compaction_top;
346   CompactibleSpace* _next_compaction_space;
347 
348   // Auxiliary functions for scan_and_{forward,adjust_pointers,compact} support.
349   inline size_t adjust_obj_size(size_t size) const {
350     return size;
351   }
352 
353   inline size_t obj_size(const HeapWord* addr) const;
354 
355   template <class SpaceType>
356   static inline void verify_up_to_first_dead(SpaceType* space) NOT_DEBUG_RETURN;
357 
358   template <class SpaceType>
359   static inline void clear_empty_region(SpaceType* space);
360 
361 public:
362   CompactibleSpace() :
363    _compaction_top(NULL), _next_compaction_space(NULL) {}
364 
365   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
366   virtual void clear(bool mangle_space);
367 
368   // Used temporarily during a compaction phase to hold the value
369   // top should have when compaction is complete.
370   HeapWord* compaction_top() const { return _compaction_top;    }
371 
372   void set_compaction_top(HeapWord* value) {
373     assert(value == NULL || (value >= bottom() && value <= end()),
374       "should point inside space");
375     _compaction_top = value;
376   }
377 
378   // Perform operations on the space needed after a compaction
379   // has been performed.
380   virtual void reset_after_compaction() = 0;
381 
382   // Returns the next space (in the current generation) to be compacted in
383   // the global compaction order.  Also is used to select the next
384   // space into which to compact.
385 
386   virtual CompactibleSpace* next_compaction_space() const {
387     return _next_compaction_space;
388   }
389 
390   void set_next_compaction_space(CompactibleSpace* csp) {
391     _next_compaction_space = csp;
392   }
393 
394 #if INCLUDE_SERIALGC
395   // MarkSweep support phase2
396 
397   // Start the process of compaction of the current space: compute
398   // post-compaction addresses, and insert forwarding pointers.  The fields
399   // "cp->gen" and "cp->compaction_space" are the generation and space into
400   // which we are currently compacting.  This call updates "cp" as necessary,
401   // and leaves the "compaction_top" of the final value of
402   // "cp->compaction_space" up-to-date.  Offset tables may be updated in
403   // this phase as if the final copy had occurred; if so, "cp->threshold"
404   // indicates when the next such action should be taken.
405   virtual void prepare_for_compaction(CompactPoint* cp) = 0;
406   // MarkSweep support phase3
407   virtual void adjust_pointers();
408   // MarkSweep support phase4
409   virtual void compact();
410 #endif // INCLUDE_SERIALGC
411 
412   // The maximum percentage of objects that can be dead in the compacted
413   // live part of a compacted space ("deadwood" support.)
414   virtual size_t allowed_dead_ratio() const { return 0; };
415 
416   // Some contiguous spaces may maintain some data structures that should
417   // be updated whenever an allocation crosses a boundary.  This function
418   // returns the first such boundary.
419   // (The default implementation returns the end of the space, so the
420   // boundary is never crossed.)
421   virtual HeapWord* initialize_threshold() { return end(); }
422 
423   // "q" is an object of the given "size" that should be forwarded;
424   // "cp" names the generation ("gen") and containing "this" (which must
425   // also equal "cp->space").  "compact_top" is where in "this" the
426   // next object should be forwarded to.  If there is room in "this" for
427   // the object, insert an appropriate forwarding pointer in "q".
428   // If not, go to the next compaction space (there must
429   // be one, since compaction must succeed -- we go to the first space of
430   // the previous generation if necessary, updating "cp"), reset compact_top
431   // and then forward.  In either case, returns the new value of "compact_top".
432   // If the forwarding crosses "cp->threshold", invokes the "cross_threshold"
433   // function of the then-current compaction space, and updates "cp->threshold
434   // accordingly".
435   virtual HeapWord* forward(oop q, size_t size, CompactPoint* cp,
436                     HeapWord* compact_top, SlidingForwarding* const forwarding);
437 
438   // Return a size with adjustments as required of the space.
439   virtual size_t adjust_object_size_v(size_t size) const { return size; }
440 
441   void set_first_dead(HeapWord* value) { _first_dead = value; }
442   void set_end_of_live(HeapWord* value) { _end_of_live = value; }
443 
444 protected:
445   // Used during compaction.
446   HeapWord* _first_dead;
447   HeapWord* _end_of_live;
448 
449   // This the function is invoked when an allocation of an object covering
450   // "start" to "end occurs crosses the threshold; returns the next
451   // threshold.  (The default implementation does nothing.)
452   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* the_end) {
453     return end();
454   }
455 
456   // Below are template functions for scan_and_* algorithms (avoiding virtual calls).
457   // The space argument should be a subclass of CompactibleSpace, implementing
458   // scan_limit(), scanned_block_is_obj(), and scanned_block_size(),
459   // and possibly also overriding obj_size(), and adjust_obj_size().
460   // These functions should avoid virtual calls whenever possible.
461 
462 #if INCLUDE_SERIALGC
463   // Frequently calls adjust_obj_size().
464   template <class SpaceType>
465   static inline void scan_and_adjust_pointers(SpaceType* space);
466 #endif
467 
468   // Frequently calls obj_size().
469   template <class SpaceType>
470   static inline void scan_and_compact(SpaceType* space);
471 
472   // Frequently calls scanned_block_is_obj() and scanned_block_size().
473   // Requires the scan_limit() function.
474   template <class SpaceType>
475   static inline void scan_and_forward(SpaceType* space, CompactPoint* cp);
476 };
477 
478 class GenSpaceMangler;
479 
480 // A space in which the free area is contiguous.  It therefore supports
481 // faster allocation, and compaction.
482 class ContiguousSpace: public CompactibleSpace {
483   friend class VMStructs;
484   // Allow scan_and_forward function to call (private) overrides for auxiliary functions on this class
485   template <typename SpaceType>
486   friend void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp);
487 
488  private:
489   // Auxiliary functions for scan_and_forward support.
490   // See comments for CompactibleSpace for more information.
491   inline HeapWord* scan_limit() const {
492     return top();
493   }
494 
495   inline bool scanned_block_is_obj(const HeapWord* addr) const {
496     return true; // Always true, since scan_limit is top
497   }
498 
499   inline size_t scanned_block_size(const HeapWord* addr) const;
500 
501  protected:
502   HeapWord* _top;
503   // A helper for mangling the unused area of the space in debug builds.
504   GenSpaceMangler* _mangler;
505 
506   GenSpaceMangler* mangler() { return _mangler; }
507 
508   // Allocation helpers (return NULL if full).
509   inline HeapWord* allocate_impl(size_t word_size);
510   inline HeapWord* par_allocate_impl(size_t word_size);
511 
512  public:
513   ContiguousSpace();
514   ~ContiguousSpace();
515 
516   virtual void initialize(MemRegion mr, bool clear_space, bool mangle_space);
517   virtual void clear(bool mangle_space);
518 
519   // Accessors
520   HeapWord* top() const            { return _top;    }
521   void set_top(HeapWord* value)    { _top = value; }
522 
523   void set_saved_mark()            { _saved_mark_word = top();    }
524   void reset_saved_mark()          { _saved_mark_word = bottom(); }
525 
526   bool saved_mark_at_top() const { return saved_mark_word() == top(); }
527 
528   // In debug mode mangle (write it with a particular bit
529   // pattern) the unused part of a space.
530 
531   // Used to save the an address in a space for later use during mangling.
532   void set_top_for_allocations(HeapWord* v) PRODUCT_RETURN;
533   // Used to save the space's current top for later use during mangling.
534   void set_top_for_allocations() PRODUCT_RETURN;
535 
536   // Mangle regions in the space from the current top up to the
537   // previously mangled part of the space.
538   void mangle_unused_area() PRODUCT_RETURN;
539   // Mangle [top, end)
540   void mangle_unused_area_complete() PRODUCT_RETURN;
541 
542   // Do some sparse checking on the area that should have been mangled.
543   void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
544   // Check the complete area that should have been mangled.
545   // This code may be NULL depending on the macro DEBUG_MANGLING.
546   void check_mangled_unused_area_complete() PRODUCT_RETURN;
547 
548   // Size computations: sizes in bytes.
549   size_t capacity() const        { return byte_size(bottom(), end()); }
550   size_t used() const            { return byte_size(bottom(), top()); }
551   size_t free() const            { return byte_size(top(),    end()); }
552 
553   virtual bool is_free_block(const HeapWord* p) const;
554 
555   // In a contiguous space we have a more obvious bound on what parts
556   // contain objects.
557   MemRegion used_region() const { return MemRegion(bottom(), top()); }
558 
559   // Allocation (return NULL if full)
560   virtual HeapWord* allocate(size_t word_size);
561   virtual HeapWord* par_allocate(size_t word_size);
562 
563   // Iteration
564   void oop_iterate(OopIterateClosure* cl);
565   void object_iterate(ObjectClosure* blk);
566 
567   // Compaction support
568   virtual void reset_after_compaction() {
569     assert(compaction_top() >= bottom() && compaction_top() <= end(), "should point inside space");
570     set_top(compaction_top());
571   }
572 
573   // Override.
574   DirtyCardToOopClosure* new_dcto_cl(OopIterateClosure* cl,
575                                      CardTable::PrecisionStyle precision,
576                                      HeapWord* boundary);
577 
578   // Apply "blk->do_oop" to the addresses of all reference fields in objects
579   // starting with the _saved_mark_word, which was noted during a generation's
580   // save_marks and is required to denote the head of an object.
581   // Fields in objects allocated by applications of the closure
582   // *are* included in the iteration.
583   // Updates _saved_mark_word to point to just after the last object
584   // iterated over.
585   template <typename OopClosureType>
586   void oop_since_save_marks_iterate(OopClosureType* blk);
587 
588   // Same as object_iterate, but starting from "mark", which is required
589   // to denote the start of an object.  Objects allocated by
590   // applications of the closure *are* included in the iteration.
591   virtual void object_iterate_from(HeapWord* mark, ObjectClosure* blk);
592 
593   // Very inefficient implementation.
594   virtual HeapWord* block_start_const(const void* p) const;
595   size_t block_size(const HeapWord* p) const;
596   // If a block is in the allocated area, it is an object.
597   bool block_is_obj(const HeapWord* p) const { return p < top(); }
598 
599   // Addresses for inlined allocation
600   HeapWord** top_addr() { return &_top; }
601   HeapWord** end_addr() { return &_end; }
602 
603 #if INCLUDE_SERIALGC
604   // Overrides for more efficient compaction support.
605   void prepare_for_compaction(CompactPoint* cp);
606 #endif
607 
608   virtual void print_on(outputStream* st) const;
609 
610   // Checked dynamic downcasts.
611   virtual ContiguousSpace* toContiguousSpace() {
612     return this;
613   }
614 
615   // Debugging
616   virtual void verify() const;
617 
618   // Used to increase collection frequency.  "factor" of 0 means entire
619   // space.
620   void allocate_temporary_filler(int factor);
621 };
622 
623 
624 // A dirty card to oop closure that does filtering.
625 // It knows how to filter out objects that are outside of the _boundary.
626 class FilteringDCTOC : public DirtyCardToOopClosure {
627 protected:
628   // Override.
629   void walk_mem_region(MemRegion mr,
630                        HeapWord* bottom, HeapWord* top);
631 
632   // Walk the given memory region, from bottom to top, applying
633   // the given oop closure to (possibly) all objects found. The
634   // given oop closure may or may not be the same as the oop
635   // closure with which this closure was created, as it may
636   // be a filtering closure which makes use of the _boundary.
637   // We offer two signatures, so the FilteringClosure static type is
638   // apparent.
639   virtual void walk_mem_region_with_cl(MemRegion mr,
640                                        HeapWord* bottom, HeapWord* top,
641                                        OopIterateClosure* cl) = 0;
642   virtual void walk_mem_region_with_cl(MemRegion mr,
643                                        HeapWord* bottom, HeapWord* top,
644                                        FilteringClosure* cl) = 0;
645 
646 public:
647   FilteringDCTOC(Space* sp, OopIterateClosure* cl,
648                   CardTable::PrecisionStyle precision,
649                   HeapWord* boundary) :
650     DirtyCardToOopClosure(sp, cl, precision, boundary) {}
651 };
652 
653 // A dirty card to oop closure for contiguous spaces
654 // (ContiguousSpace and sub-classes).
655 // It is a FilteringClosure, as defined above, and it knows:
656 //
657 // 1. That the actual top of any area in a memory region
658 //    contained by the space is bounded by the end of the contiguous
659 //    region of the space.
660 // 2. That the space is really made up of objects and not just
661 //    blocks.
662 
663 class ContiguousSpaceDCTOC : public FilteringDCTOC {
664 protected:
665   // Overrides.
666   HeapWord* get_actual_top(HeapWord* top, HeapWord* top_obj);
667 
668   virtual void walk_mem_region_with_cl(MemRegion mr,
669                                        HeapWord* bottom, HeapWord* top,
670                                        OopIterateClosure* cl);
671   virtual void walk_mem_region_with_cl(MemRegion mr,
672                                        HeapWord* bottom, HeapWord* top,
673                                        FilteringClosure* cl);
674 
675 public:
676   ContiguousSpaceDCTOC(ContiguousSpace* sp, OopIterateClosure* cl,
677                        CardTable::PrecisionStyle precision,
678                        HeapWord* boundary) :
679     FilteringDCTOC(sp, cl, precision, boundary)
680   {}
681 };
682 
683 // A ContigSpace that Supports an efficient "block_start" operation via
684 // a BlockOffsetArray (whose BlockOffsetSharedArray may be shared with
685 // other spaces.)  This is the abstract base class for old generation
686 // (tenured) spaces.
687 
688 class OffsetTableContigSpace: public ContiguousSpace {
689   friend class VMStructs;
690  protected:
691   BlockOffsetArrayContigSpace _offsets;
692   Mutex _par_alloc_lock;
693 
694  public:
695   // Constructor
696   OffsetTableContigSpace(BlockOffsetSharedArray* sharedOffsetArray,
697                          MemRegion mr);
698 
699   void set_bottom(HeapWord* value);
700   void set_end(HeapWord* value);
701 
702   void clear(bool mangle_space);
703 
704   inline HeapWord* block_start_const(const void* p) const;
705 
706   // Add offset table update.
707   virtual inline HeapWord* allocate(size_t word_size);
708   inline HeapWord* par_allocate(size_t word_size);
709 
710   // MarkSweep support phase3
711   virtual HeapWord* initialize_threshold();
712   virtual HeapWord* cross_threshold(HeapWord* start, HeapWord* end);
713 
714   virtual void print_on(outputStream* st) const;
715 
716   // Debugging
717   void verify() const;
718 };
719 
720 
721 // Class TenuredSpace is used by TenuredGeneration
722 
723 class TenuredSpace: public OffsetTableContigSpace {
724   friend class VMStructs;
725  protected:
726   // Mark sweep support
727   size_t allowed_dead_ratio() const;
728  public:
729   // Constructor
730   TenuredSpace(BlockOffsetSharedArray* sharedOffsetArray,
731                MemRegion mr) :
732     OffsetTableContigSpace(sharedOffsetArray, mr) {}
733 };
734 #endif // SHARE_GC_SHARED_SPACE_HPP