hotspot/src/share/vm/memory/cardTableModRefBS.hpp - platform/libcore - Git at Google

 /*
  * Copyright 2000-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */

 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
 // enumerate ref fields that have been modified (since the last
 // enumeration.)

 // As it currently stands, this barrier is *imprecise*: when a ref field in
 // an object "o" is modified, the card table entry for the card containing
 // the head of "o" is dirtied, not necessarily the card containing the
 // modified field itself.  For object arrays, however, the barrier *is*
 // precise; only the card containing the modified element is dirtied.
 // Any MemRegionClosures used to scan dirty cards should take these
 // considerations into account.

 class Generation;
 class OopsInGenClosure;
 class DirtyCardToOopClosure;

 class CardTableModRefBS: public ModRefBarrierSet {
   // Some classes get to look at some private stuff.
   friend class BytecodeInterpreter;
   friend class VMStructs;
   friend class CardTableRS;
   friend class CheckForUnmarkedOops; // Needs access to raw card bytes.
 #ifndef PRODUCT
   // For debugging.
   friend class GuaranteeNotModClosure;
 #endif
  protected:

   enum CardValues {
     clean_card                  = -1,
     dirty_card                  =  0,
     precleaned_card             =  1,
     claimed_card                =  3,
     last_card                   =  4,
     CT_MR_BS_last_reserved      = 10
   };

   // dirty and precleaned are equivalent wrt younger_refs_iter.
   static bool card_is_dirty_wrt_gen_iter(jbyte cv) {
     return cv == dirty_card || cv == precleaned_card;
   }

   // Returns "true" iff the value "cv" will cause the card containing it
   // to be scanned in the current traversal.  May be overridden by
   // subtypes.
   virtual bool card_will_be_scanned(jbyte cv) {
     return CardTableModRefBS::card_is_dirty_wrt_gen_iter(cv);
   }

   // Returns "true" iff the value "cv" may have represented a dirty card at
   // some point.
   virtual bool card_may_have_been_dirty(jbyte cv) {
     return card_is_dirty_wrt_gen_iter(cv);
   }

   // The declaration order of these const fields is important; see the
   // constructor before changing.
   const MemRegion _whole_heap;       // the region covered by the card table
   const size_t    _guard_index;      // index of very last element in the card
                                      // table; it is set to a guard value
                                      // (last_card) and should never be modified
   const size_t    _last_valid_index; // index of the last valid element
   const size_t    _page_size;        // page size used when mapping _byte_map
   const size_t    _byte_map_size;    // in bytes
   jbyte*          _byte_map;         // the card marking array

   int _cur_covered_regions;
   // The covered regions should be in address order.
   MemRegion* _covered;
   // The committed regions correspond one-to-one to the covered regions.
   // They represent the card-table memory that has been committed to service
   // the corresponding covered region.  It may be that committed region for
   // one covered region corresponds to a larger region because of page-size
   // roundings.  Thus, a committed region for one covered region may
   // actually extend onto the card-table space for the next covered region.
   MemRegion* _committed;

   // The last card is a guard card, and we commit the page for it so
   // we can use the card for verification purposes. We make sure we never
   // uncommit the MemRegion for that page.
   MemRegion _guard_region;

  protected:
   // Initialization utilities; covered_words is the size of the covered region
   // in, um, words.
   inline size_t cards_required(size_t covered_words);
   inline size_t compute_byte_map_size();

   // Finds and return the index of the region, if any, to which the given
   // region would be contiguous.  If none exists, assign a new region and
   // returns its index.  Requires that no more than the maximum number of
   // covered regions defined in the constructor are ever in use.
   int find_covering_region_by_base(HeapWord* base);

   // Same as above, but finds the region containing the given address
   // instead of starting at a given base address.
   int find_covering_region_containing(HeapWord* addr);

   // Resize one of the regions covered by the remembered set.
   void resize_covered_region(MemRegion new_region);

   // Returns the leftmost end of a committed region corresponding to a
   // covered region before covered region "ind", or else "NULL" if "ind" is
   // the first covered region.
   HeapWord* largest_prev_committed_end(int ind) const;

   // Returns the part of the region mr that doesn't intersect with
   // any committed region other than self.  Used to prevent uncommitting
   // regions that are also committed by other regions.  Also protects
   // against uncommitting the guard region.
   MemRegion committed_unique_to_self(int self, MemRegion mr) const;

   // Mapping from address to card marking array entry
   jbyte* byte_for(const void* p) const {
     assert(_whole_heap.contains(p),
            "out of bounds access to card marking array");
     jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
     assert(result >= _byte_map && result < _byte_map + _byte_map_size,
            "out of bounds accessor for card marking array");
     return result;
   }

   // The card table byte one after the card marking array
   // entry for argument address. Typically used for higher bounds
   // for loops iterating through the card table.
   jbyte* byte_after(const void* p) const {
     return byte_for(p) + 1;
   }

   // Iterate over the portion of the card-table which covers the given
   // region mr in the given space and apply cl to any dirty sub-regions
   // of mr. cl and dcto_cl must either be the same closure or cl must
   // wrap dcto_cl. Both are required - neither may be NULL. Also, dcto_cl
   // may be modified. Note that this function will operate in a parallel
   // mode if worker threads are available.
   void non_clean_card_iterate(Space* sp, MemRegion mr,
                               DirtyCardToOopClosure* dcto_cl,
                               MemRegionClosure* cl,
                               bool clear);

   // Utility function used to implement the other versions below.
   void non_clean_card_iterate_work(MemRegion mr, MemRegionClosure* cl,
                                    bool clear);

   void par_non_clean_card_iterate_work(Space* sp, MemRegion mr,
                                        DirtyCardToOopClosure* dcto_cl,
                                        MemRegionClosure* cl,
                                        bool clear,
                                        int n_threads);

   // Dirty the bytes corresponding to "mr" (not all of which must be
   // covered.)
   void dirty_MemRegion(MemRegion mr);

   // Clear (to clean_card) the bytes entirely contained within "mr" (not
   // all of which must be covered.)
   void clear_MemRegion(MemRegion mr);

   // *** Support for parallel card scanning.

   enum SomeConstantsForParallelism {
     StridesPerThread    = 2,
     CardsPerStrideChunk = 256
   };

   // This is an array, one element per covered region of the card table.
   // Each entry is itself an array, with one element per chunk in the
   // covered region.  Each entry of these arrays is the lowest non-clean
   // card of the corresponding chunk containing part of an object from the
   // previous chunk, or else NULL.
   typedef jbyte*  CardPtr;
   typedef CardPtr* CardArr;
   CardArr* _lowest_non_clean;
   size_t*  _lowest_non_clean_chunk_size;
   uintptr_t* _lowest_non_clean_base_chunk_index;
   int* _last_LNC_resizing_collection;

   // Initializes "lowest_non_clean" to point to the array for the region
   // covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk
   // index of the corresponding to the first element of that array.
   // Ensures that these arrays are of sufficient size, allocating if necessary.
   // May be called by several threads concurrently.
   void get_LNC_array_for_space(Space* sp,
                                jbyte**& lowest_non_clean,
                                uintptr_t& lowest_non_clean_base_chunk_index,
                                size_t& lowest_non_clean_chunk_size);

   // Returns the number of chunks necessary to cover "mr".
   size_t chunks_to_cover(MemRegion mr) {
     return (size_t)(addr_to_chunk_index(mr.last()) -
                     addr_to_chunk_index(mr.start()) + 1);
   }

   // Returns the index of the chunk in a stride which
   // covers the given address.
   uintptr_t addr_to_chunk_index(const void* addr) {
     uintptr_t card = (uintptr_t) byte_for(addr);
     return card / CardsPerStrideChunk;
   }

   // Apply cl, which must either itself apply dcto_cl or be dcto_cl,
   // to the cards in the stride (of n_strides) within the given space.
   void process_stride(Space* sp,
                       MemRegion used,
                       jint stride, int n_strides,
                       DirtyCardToOopClosure* dcto_cl,
                       MemRegionClosure* cl,
                       bool clear,
                       jbyte** lowest_non_clean,
                       uintptr_t lowest_non_clean_base_chunk_index,
                       size_t lowest_non_clean_chunk_size);

   // Makes sure that chunk boundaries are handled appropriately, by
   // adjusting the min_done of dcto_cl, and by using a special card-table
   // value to indicate how min_done should be set.
   void process_chunk_boundaries(Space* sp,
                                 DirtyCardToOopClosure* dcto_cl,
                                 MemRegion chunk_mr,
                                 MemRegion used,
                                 jbyte** lowest_non_clean,
                                 uintptr_t lowest_non_clean_base_chunk_index,
                                 size_t    lowest_non_clean_chunk_size);

 public:
   // Constants
   enum SomePublicConstants {
     card_shift                  = 9,
     card_size                   = 1 << card_shift,
     card_size_in_words          = card_size / sizeof(HeapWord)
   };

   static int clean_card_val()      { return clean_card; }
   static int dirty_card_val()      { return dirty_card; }
   static int claimed_card_val()    { return claimed_card; }
   static int precleaned_card_val() { return precleaned_card; }

   // For RTTI simulation.
   bool is_a(BarrierSet::Name bsn) {
     return bsn == BarrierSet::CardTableModRef || ModRefBarrierSet::is_a(bsn);
   }

   CardTableModRefBS(MemRegion whole_heap, int max_covered_regions);

   // *** Barrier set functions.

   bool has_write_ref_pre_barrier() { return false; }

   inline bool write_ref_needs_barrier(void* field, oop new_val) {
     // Note that this assumes the perm gen is the highest generation
     // in the address space
     return new_val != NULL && !new_val->is_perm();
   }

   // Record a reference update. Note that these versions are precise!
   // The scanning code has to handle the fact that the write barrier may be
   // either precise or imprecise. We make non-virtual inline variants of
   // these functions here for performance.
 protected:
   void write_ref_field_work(oop obj, size_t offset, oop newVal);
   void write_ref_field_work(void* field, oop newVal);
 public:

   bool has_write_ref_array_opt() { return true; }
   bool has_write_region_opt() { return true; }

   inline void inline_write_region(MemRegion mr) {
     dirty_MemRegion(mr);
   }
 protected:
   void write_region_work(MemRegion mr) {
     inline_write_region(mr);
   }
 public:

   inline void inline_write_ref_array(MemRegion mr) {
     dirty_MemRegion(mr);
   }
 protected:
   void write_ref_array_work(MemRegion mr) {
     inline_write_ref_array(mr);
   }
 public:

   bool is_aligned(HeapWord* addr) {
     return is_card_aligned(addr);
   }

   // *** Card-table-barrier-specific things.

   inline void inline_write_ref_field_pre(void* field, oop newVal) {}

   inline void inline_write_ref_field(void* field, oop newVal) {
     jbyte* byte = byte_for(field);
     *byte = dirty_card;
   }

   // These are used by G1, when it uses the card table as a temporary data
   // structure for card claiming.
   bool is_card_dirty(size_t card_index) {
     return _byte_map[card_index] == dirty_card_val();
   }

   void mark_card_dirty(size_t card_index) {
     _byte_map[card_index] = dirty_card_val();
   }

   bool is_card_claimed(size_t card_index) {
     return _byte_map[card_index] == claimed_card_val();
   }

   bool claim_card(size_t card_index);

   bool is_card_clean(size_t card_index) {
     return _byte_map[card_index] == clean_card_val();
   }

   // Card marking array base (adjusted for heap low boundary)
   // This would be the 0th element of _byte_map, if the heap started at 0x0.
   // But since the heap starts at some higher address, this points to somewhere
   // before the beginning of the actual _byte_map.
   jbyte* byte_map_base;

   // Return true if "p" is at the start of a card.
   bool is_card_aligned(HeapWord* p) {
     jbyte* pcard = byte_for(p);
     return (addr_for(pcard) == p);
   }

   // The kinds of precision a CardTableModRefBS may offer.
   enum PrecisionStyle {
     Precise,
     ObjHeadPreciseArray
   };

   // Tells what style of precision this card table offers.
   PrecisionStyle precision() {
     return ObjHeadPreciseArray; // Only one supported for now.
   }

   // ModRefBS functions.
   virtual void invalidate(MemRegion mr, bool whole_heap = false);
   void clear(MemRegion mr);
   void dirty(MemRegion mr);
   void mod_oop_in_space_iterate(Space* sp, OopClosure* cl,
                                 bool clear = false,
                                 bool before_save_marks = false);

   // *** Card-table-RemSet-specific things.

   // Invoke "cl.do_MemRegion" on a set of MemRegions that collectively
   // includes all the modified cards (expressing each card as a
   // MemRegion).  Thus, several modified cards may be lumped into one
   // region.  The regions are non-overlapping, and are visited in
   // *decreasing* address order.  (This order aids with imprecise card
   // marking, where a dirty card may cause scanning, and summarization
   // marking, of objects that extend onto subsequent cards.)
   // If "clear" is true, the card is (conceptually) marked unmodified before
   // applying the closure.
   void mod_card_iterate(MemRegionClosure* cl, bool clear = false) {
     non_clean_card_iterate_work(_whole_heap, cl, clear);
   }

   // Like the "mod_cards_iterate" above, except only invokes the closure
   // for cards within the MemRegion "mr" (which is required to be
   // card-aligned and sized.)
   void mod_card_iterate(MemRegion mr, MemRegionClosure* cl,
                         bool clear = false) {
     non_clean_card_iterate_work(mr, cl, clear);
   }

   static uintx ct_max_alignment_constraint();

   // Apply closure "cl" to the dirty cards containing some part of
   // MemRegion "mr".
   void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);

   // Return the MemRegion corresponding to the first maximal run
   // of dirty cards lying completely within MemRegion mr.
   // If reset is "true", then sets those card table entries to the given
   // value.
   MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
                                          int reset_val);

   // Set all the dirty cards in the given region to precleaned state.
   void preclean_dirty_cards(MemRegion mr);

   // Provide read-only access to the card table array.
   const jbyte* byte_for_const(const void* p) const {
     return byte_for(p);
   }
   const jbyte* byte_after_const(const void* p) const {
     return byte_after(p);
   }

   // Mapping from card marking array entry to address of first word
   HeapWord* addr_for(const jbyte* p) const {
     assert(p >= _byte_map && p < _byte_map + _byte_map_size,
            "out of bounds access to card marking array");
     size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
     HeapWord* result = (HeapWord*) (delta << card_shift);
     assert(_whole_heap.contains(result),
            "out of bounds accessor from card marking array");
     return result;
   }

   // Mapping from address to card marking array index.
   size_t index_for(void* p) {
     assert(_whole_heap.contains(p),
            "out of bounds access to card marking array");
     return byte_for(p) - _byte_map;
   }

   void verify();
   void verify_guard();

   void verify_clean_region(MemRegion mr) PRODUCT_RETURN;

   static size_t par_chunk_heapword_alignment() {
     return CardsPerStrideChunk * card_size_in_words;
   }

 };

 class CardTableRS;

 // A specialization for the CardTableRS gen rem set.
 class CardTableModRefBSForCTRS: public CardTableModRefBS {
   CardTableRS* _rs;
 protected:
   bool card_will_be_scanned(jbyte cv);
   bool card_may_have_been_dirty(jbyte cv);
 public:
   CardTableModRefBSForCTRS(MemRegion whole_heap,
                            int max_covered_regions) :
     CardTableModRefBS(whole_heap, max_covered_regions) {}

   void set_CTRS(CardTableRS* rs) { _rs = rs; }
 };
	/*
	* Copyright 2000-2008 Sun Microsystems, Inc. All Rights Reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
	* CA 95054 USA or visit www.sun.com if you need additional information or
	* have any questions.
	*
	*/

	// This kind of "BarrierSet" allows a "CollectedHeap" to detect and
	// enumerate ref fields that have been modified (since the last
	// enumeration.)

	// As it currently stands, this barrier is imprecise: when a ref field in
	// an object "o" is modified, the card table entry for the card containing
	// the head of "o" is dirtied, not necessarily the card containing the
	// modified field itself. For object arrays, however, the barrier is
	// precise; only the card containing the modified element is dirtied.
	// Any MemRegionClosures used to scan dirty cards should take these
	// considerations into account.

	class Generation;
	class OopsInGenClosure;
	class DirtyCardToOopClosure;

	class CardTableModRefBS: public ModRefBarrierSet {
	// Some classes get to look at some private stuff.
	friend class BytecodeInterpreter;
	friend class VMStructs;
	friend class CardTableRS;
	friend class CheckForUnmarkedOops; // Needs access to raw card bytes.
	#ifndef PRODUCT
	// For debugging.
	friend class GuaranteeNotModClosure;
	#endif
	protected:

	enum CardValues {
	clean_card = -1,
	dirty_card = 0,
	precleaned_card = 1,
	claimed_card = 3,
	last_card = 4,
	CT_MR_BS_last_reserved = 10
	};

	// dirty and precleaned are equivalent wrt younger_refs_iter.
	static bool card_is_dirty_wrt_gen_iter(jbyte cv) {
	return cv == dirty_card \|\| cv == precleaned_card;
	}

	// Returns "true" iff the value "cv" will cause the card containing it
	// to be scanned in the current traversal. May be overridden by
	// subtypes.
	virtual bool card_will_be_scanned(jbyte cv) {
	return CardTableModRefBS::card_is_dirty_wrt_gen_iter(cv);
	}

	// Returns "true" iff the value "cv" may have represented a dirty card at
	// some point.
	virtual bool card_may_have_been_dirty(jbyte cv) {
	return card_is_dirty_wrt_gen_iter(cv);
	}

	// The declaration order of these const fields is important; see the
	// constructor before changing.
	const MemRegion _whole_heap; // the region covered by the card table
	const size_t _guard_index; // index of very last element in the card
	// table; it is set to a guard value
	// (last_card) and should never be modified
	const size_t _last_valid_index; // index of the last valid element
	const size_t _page_size; // page size used when mapping _byte_map
	const size_t _byte_map_size; // in bytes
	jbyte* _byte_map; // the card marking array

	int _cur_covered_regions;
	// The covered regions should be in address order.
	MemRegion* _covered;
	// The committed regions correspond one-to-one to the covered regions.
	// They represent the card-table memory that has been committed to service
	// the corresponding covered region. It may be that committed region for
	// one covered region corresponds to a larger region because of page-size
	// roundings. Thus, a committed region for one covered region may
	// actually extend onto the card-table space for the next covered region.
	MemRegion* _committed;

	// The last card is a guard card, and we commit the page for it so
	// we can use the card for verification purposes. We make sure we never
	// uncommit the MemRegion for that page.
	MemRegion _guard_region;

	protected:
	// Initialization utilities; covered_words is the size of the covered region
	// in, um, words.
	inline size_t cards_required(size_t covered_words);
	inline size_t compute_byte_map_size();

	// Finds and return the index of the region, if any, to which the given
	// region would be contiguous. If none exists, assign a new region and
	// returns its index. Requires that no more than the maximum number of
	// covered regions defined in the constructor are ever in use.
	int find_covering_region_by_base(HeapWord* base);

	// Same as above, but finds the region containing the given address
	// instead of starting at a given base address.
	int find_covering_region_containing(HeapWord* addr);

	// Resize one of the regions covered by the remembered set.
	void resize_covered_region(MemRegion new_region);

	// Returns the leftmost end of a committed region corresponding to a
	// covered region before covered region "ind", or else "NULL" if "ind" is
	// the first covered region.
	HeapWord* largest_prev_committed_end(int ind) const;

	// Returns the part of the region mr that doesn't intersect with
	// any committed region other than self. Used to prevent uncommitting
	// regions that are also committed by other regions. Also protects
	// against uncommitting the guard region.
	MemRegion committed_unique_to_self(int self, MemRegion mr) const;

	// Mapping from address to card marking array entry
	jbyte* byte_for(const void* p) const {
	assert(_whole_heap.contains(p),
	"out of bounds access to card marking array");
	jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
	assert(result >= _byte_map && result < _byte_map + _byte_map_size,
	"out of bounds accessor for card marking array");
	return result;
	}

	// The card table byte one after the card marking array
	// entry for argument address. Typically used for higher bounds
	// for loops iterating through the card table.
	jbyte* byte_after(const void* p) const {
	return byte_for(p) + 1;
	}

	// Iterate over the portion of the card-table which covers the given
	// region mr in the given space and apply cl to any dirty sub-regions
	// of mr. cl and dcto_cl must either be the same closure or cl must
	// wrap dcto_cl. Both are required - neither may be NULL. Also, dcto_cl
	// may be modified. Note that this function will operate in a parallel
	// mode if worker threads are available.
	void non_clean_card_iterate(Space* sp, MemRegion mr,
	DirtyCardToOopClosure* dcto_cl,
	MemRegionClosure* cl,
	bool clear);

	// Utility function used to implement the other versions below.
	void non_clean_card_iterate_work(MemRegion mr, MemRegionClosure* cl,
	bool clear);

	void par_non_clean_card_iterate_work(Space* sp, MemRegion mr,
	DirtyCardToOopClosure* dcto_cl,
	MemRegionClosure* cl,
	bool clear,
	int n_threads);

	// Dirty the bytes corresponding to "mr" (not all of which must be
	// covered.)
	void dirty_MemRegion(MemRegion mr);

	// Clear (to clean_card) the bytes entirely contained within "mr" (not
	// all of which must be covered.)
	void clear_MemRegion(MemRegion mr);

	// *** Support for parallel card scanning.

	enum SomeConstantsForParallelism {
	StridesPerThread = 2,
	CardsPerStrideChunk = 256
	};

	// This is an array, one element per covered region of the card table.
	// Each entry is itself an array, with one element per chunk in the
	// covered region. Each entry of these arrays is the lowest non-clean
	// card of the corresponding chunk containing part of an object from the
	// previous chunk, or else NULL.
	typedef jbyte* CardPtr;
	typedef CardPtr* CardArr;
	CardArr* _lowest_non_clean;
	size_t* _lowest_non_clean_chunk_size;
	uintptr_t* _lowest_non_clean_base_chunk_index;
	int* _last_LNC_resizing_collection;

	// Initializes "lowest_non_clean" to point to the array for the region
	// covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk
	// index of the corresponding to the first element of that array.
	// Ensures that these arrays are of sufficient size, allocating if necessary.
	// May be called by several threads concurrently.
	void get_LNC_array_for_space(Space* sp,
	jbyte**& lowest_non_clean,
	uintptr_t& lowest_non_clean_base_chunk_index,
	size_t& lowest_non_clean_chunk_size);

	// Returns the number of chunks necessary to cover "mr".
	size_t chunks_to_cover(MemRegion mr) {
	return (size_t)(addr_to_chunk_index(mr.last()) -
	addr_to_chunk_index(mr.start()) + 1);
	}

	// Returns the index of the chunk in a stride which
	// covers the given address.
	uintptr_t addr_to_chunk_index(const void* addr) {
	uintptr_t card = (uintptr_t) byte_for(addr);
	return card / CardsPerStrideChunk;
	}

	// Apply cl, which must either itself apply dcto_cl or be dcto_cl,
	// to the cards in the stride (of n_strides) within the given space.
	void process_stride(Space* sp,
	MemRegion used,
	jint stride, int n_strides,
	DirtyCardToOopClosure* dcto_cl,
	MemRegionClosure* cl,
	bool clear,
	jbyte** lowest_non_clean,
	uintptr_t lowest_non_clean_base_chunk_index,
	size_t lowest_non_clean_chunk_size);

	// Makes sure that chunk boundaries are handled appropriately, by
	// adjusting the min_done of dcto_cl, and by using a special card-table
	// value to indicate how min_done should be set.
	void process_chunk_boundaries(Space* sp,
	DirtyCardToOopClosure* dcto_cl,
	MemRegion chunk_mr,
	MemRegion used,
	jbyte** lowest_non_clean,
	uintptr_t lowest_non_clean_base_chunk_index,
	size_t lowest_non_clean_chunk_size);

	public:
	// Constants
	enum SomePublicConstants {
	card_shift = 9,
	card_size = 1 << card_shift,
	card_size_in_words = card_size / sizeof(HeapWord)
	};

	static int clean_card_val() { return clean_card; }
	static int dirty_card_val() { return dirty_card; }
	static int claimed_card_val() { return claimed_card; }
	static int precleaned_card_val() { return precleaned_card; }

	// For RTTI simulation.
	bool is_a(BarrierSet::Name bsn) {
	return bsn == BarrierSet::CardTableModRef \|\| ModRefBarrierSet::is_a(bsn);
	}

	CardTableModRefBS(MemRegion whole_heap, int max_covered_regions);

	// *** Barrier set functions.

	bool has_write_ref_pre_barrier() { return false; }

	inline bool write_ref_needs_barrier(void* field, oop new_val) {
	// Note that this assumes the perm gen is the highest generation
	// in the address space
	return new_val != NULL && !new_val->is_perm();
	}

	// Record a reference update. Note that these versions are precise!
	// The scanning code has to handle the fact that the write barrier may be
	// either precise or imprecise. We make non-virtual inline variants of
	// these functions here for performance.
	protected:
	void write_ref_field_work(oop obj, size_t offset, oop newVal);
	void write_ref_field_work(void* field, oop newVal);
	public:

	bool has_write_ref_array_opt() { return true; }
	bool has_write_region_opt() { return true; }

	inline void inline_write_region(MemRegion mr) {
	dirty_MemRegion(mr);
	}
	protected:
	void write_region_work(MemRegion mr) {
	inline_write_region(mr);
	}
	public:

	inline void inline_write_ref_array(MemRegion mr) {
	dirty_MemRegion(mr);
	}
	protected:
	void write_ref_array_work(MemRegion mr) {
	inline_write_ref_array(mr);
	}
	public:

	bool is_aligned(HeapWord* addr) {
	return is_card_aligned(addr);
	}

	// *** Card-table-barrier-specific things.

	inline void inline_write_ref_field_pre(void* field, oop newVal) {}

	inline void inline_write_ref_field(void* field, oop newVal) {
	jbyte* byte = byte_for(field);
	*byte = dirty_card;
	}

	// These are used by G1, when it uses the card table as a temporary data
	// structure for card claiming.
	bool is_card_dirty(size_t card_index) {
	return _byte_map[card_index] == dirty_card_val();
	}

	void mark_card_dirty(size_t card_index) {
	_byte_map[card_index] = dirty_card_val();
	}

	bool is_card_claimed(size_t card_index) {
	return _byte_map[card_index] == claimed_card_val();
	}

	bool claim_card(size_t card_index);

	bool is_card_clean(size_t card_index) {
	return _byte_map[card_index] == clean_card_val();
	}

	// Card marking array base (adjusted for heap low boundary)
	// This would be the 0th element of _byte_map, if the heap started at 0x0.
	// But since the heap starts at some higher address, this points to somewhere
	// before the beginning of the actual _byte_map.
	jbyte* byte_map_base;

	// Return true if "p" is at the start of a card.
	bool is_card_aligned(HeapWord* p) {
	jbyte* pcard = byte_for(p);
	return (addr_for(pcard) == p);
	}

	// The kinds of precision a CardTableModRefBS may offer.
	enum PrecisionStyle {
	Precise,
	ObjHeadPreciseArray
	};

	// Tells what style of precision this card table offers.
	PrecisionStyle precision() {
	return ObjHeadPreciseArray; // Only one supported for now.
	}

	// ModRefBS functions.
	virtual void invalidate(MemRegion mr, bool whole_heap = false);
	void clear(MemRegion mr);
	void dirty(MemRegion mr);
	void mod_oop_in_space_iterate(Space* sp, OopClosure* cl,
	bool clear = false,
	bool before_save_marks = false);

	// *** Card-table-RemSet-specific things.

	// Invoke "cl.do_MemRegion" on a set of MemRegions that collectively
	// includes all the modified cards (expressing each card as a
	// MemRegion). Thus, several modified cards may be lumped into one
	// region. The regions are non-overlapping, and are visited in
	// decreasing address order. (This order aids with imprecise card
	// marking, where a dirty card may cause scanning, and summarization
	// marking, of objects that extend onto subsequent cards.)
	// If "clear" is true, the card is (conceptually) marked unmodified before
	// applying the closure.
	void mod_card_iterate(MemRegionClosure* cl, bool clear = false) {
	non_clean_card_iterate_work(_whole_heap, cl, clear);
	}

	// Like the "mod_cards_iterate" above, except only invokes the closure
	// for cards within the MemRegion "mr" (which is required to be
	// card-aligned and sized.)
	void mod_card_iterate(MemRegion mr, MemRegionClosure* cl,
	bool clear = false) {
	non_clean_card_iterate_work(mr, cl, clear);
	}

	static uintx ct_max_alignment_constraint();

	// Apply closure "cl" to the dirty cards containing some part of
	// MemRegion "mr".
	void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);

	// Return the MemRegion corresponding to the first maximal run
	// of dirty cards lying completely within MemRegion mr.
	// If reset is "true", then sets those card table entries to the given
	// value.
	MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
	int reset_val);

	// Set all the dirty cards in the given region to precleaned state.
	void preclean_dirty_cards(MemRegion mr);

	// Provide read-only access to the card table array.
	const jbyte* byte_for_const(const void* p) const {
	return byte_for(p);
	}
	const jbyte* byte_after_const(const void* p) const {
	return byte_after(p);
	}

	// Mapping from card marking array entry to address of first word
	HeapWord* addr_for(const jbyte* p) const {
	assert(p >= _byte_map && p < _byte_map + _byte_map_size,
	"out of bounds access to card marking array");
	size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
	HeapWord* result = (HeapWord*) (delta << card_shift);
	assert(_whole_heap.contains(result),
	"out of bounds accessor from card marking array");
	return result;
	}

	// Mapping from address to card marking array index.
	size_t index_for(void* p) {
	assert(_whole_heap.contains(p),
	"out of bounds access to card marking array");
	return byte_for(p) - _byte_map;
	}

	void verify();
	void verify_guard();

	void verify_clean_region(MemRegion mr) PRODUCT_RETURN;

	static size_t par_chunk_heapword_alignment() {
	return CardsPerStrideChunk * card_size_in_words;
	}

	};

	class CardTableRS;

	// A specialization for the CardTableRS gen rem set.
	class CardTableModRefBSForCTRS: public CardTableModRefBS {
	CardTableRS* _rs;
	protected:
	bool card_will_be_scanned(jbyte cv);
	bool card_may_have_been_dirty(jbyte cv);
	public:
	CardTableModRefBSForCTRS(MemRegion whole_heap,
	int max_covered_regions) :
	CardTableModRefBS(whole_heap, max_covered_regions) {}

	void set_CTRS(CardTableRS* rs) { _rs = rs; }
	};