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 /*

  * Copyright 2000-2009 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

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  */

 // 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,

     // The mask contains zeros in places for all other values.

     clean_card_mask             = clean_card - 31,

     dirty_card                  =  0,

     precleaned_card             =  1,

     claimed_card                =  2,

     deferred_card               =  4,

     last_card                   =  8,

     CT_MR_BS_last_reserved      = 16

   };

   // 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 clean_card_mask_val() { return clean_card_mask; }

   static int dirty_card_val()      { return dirty_card; }

   static int claimed_card_val()    { return claimed_card; }

   static int precleaned_card_val() { return precleaned_card; }

   static int deferred_card_val()   { return deferred_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);

   virtual 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.

   template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}

   template <class T> inline void inline_write_ref_field(T* field, oop newVal) {

     jbyte* byte = byte_for((void*)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) {

     jbyte val = _byte_map[card_index];

     return (val & (clean_card_mask_val() | claimed_card_val())) == 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();

   }

   bool is_card_deferred(size_t card_index) {

     jbyte val = _byte_map[card_index];

     return (val & (clean_card_mask_val() | deferred_card_val())) == deferred_card_val();

   }

   bool mark_card_deferred(size_t card_index);

   // 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;

   }

   const jbyte* byte_for_index(const size_t card_index) const {

     return _byte_map + card_index;

   }

   void verify();

   void verify_guard();

   void verify_clean_region(MemRegion mr) PRODUCT_RETURN;

   void verify_dirty_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; }

 };