1 /*

     2  * Copyright 2000-2006 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    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).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    20  * CA 95054 USA or visit www.sun.com if you need additional information or

    21  * have any questions.

    22  *

    23  */

    24 

    25 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and

    26 // enumerate ref fields that have been modified (since the last

    27 // enumeration.)

    28 

    29 // As it currently stands, this barrier is *imprecise*: when a ref field in

    30 // an object "o" is modified, the card table entry for the card containing

    31 // the head of "o" is dirtied, not necessarily the card containing the

    32 // modified field itself.  For object arrays, however, the barrier *is*

    33 // precise; only the card containing the modified element is dirtied.

    34 // Any MemRegionClosures used to scan dirty cards should take these

    35 // considerations into account.

    36 

    37 class Generation;

    38 class OopsInGenClosure;

    39 class DirtyCardToOopClosure;

    40 

    41 class CardTableModRefBS: public ModRefBarrierSet {

    42   // Some classes get to look at some private stuff.

    43   friend class BytecodeInterpreter;

    44   friend class VMStructs;

    45   friend class CardTableRS;

    46   friend class CheckForUnmarkedOops; // Needs access to raw card bytes.

    47 #ifndef PRODUCT

    48   // For debugging.

    49   friend class GuaranteeNotModClosure;

    50 #endif

    51  protected:

    52 

    53   enum CardValues {

    54     clean_card                  = -1,

    55     dirty_card                  =  0,

    56     precleaned_card             =  1,

    57     last_card                   =  4,

    58     CT_MR_BS_last_reserved      = 10

    59   };

    60 

    61   // dirty and precleaned are equivalent wrt younger_refs_iter.

    62   static bool card_is_dirty_wrt_gen_iter(jbyte cv) {

    63     return cv == dirty_card || cv == precleaned_card;

    64   }

    65 

    66   // Returns "true" iff the value "cv" will cause the card containing it

    67   // to be scanned in the current traversal.  May be overridden by

    68   // subtypes.

    69   virtual bool card_will_be_scanned(jbyte cv) {

    70     return CardTableModRefBS::card_is_dirty_wrt_gen_iter(cv);

    71   }

    72 

    73   // Returns "true" iff the value "cv" may have represented a dirty card at

    74   // some point.

    75   virtual bool card_may_have_been_dirty(jbyte cv) {

    76     return card_is_dirty_wrt_gen_iter(cv);

    77   }

    78 

    79   // The declaration order of these const fields is important; see the

    80   // constructor before changing.

    81   const MemRegion _whole_heap;       // the region covered by the card table

    82   const size_t    _guard_index;      // index of very last element in the card

    83                                      // table; it is set to a guard value

    84                                      // (last_card) and should never be modified

    85   const size_t    _last_valid_index; // index of the last valid element

    86   const size_t    _page_size;        // page size used when mapping _byte_map

    87   const size_t    _byte_map_size;    // in bytes

    88   jbyte*          _byte_map;         // the card marking array

    89 

    90   int _cur_covered_regions;

    91   // The covered regions should be in address order.

    92   MemRegion* _covered;

    93   // The committed regions correspond one-to-one to the covered regions.

    94   // They represent the card-table memory that has been committed to service

    95   // the corresponding covered region.  It may be that committed region for

    96   // one covered region corresponds to a larger region because of page-size

    97   // roundings.  Thus, a committed region for one covered region may

    98   // actually extend onto the card-table space for the next covered region.

    99   MemRegion* _committed;

   100 

   101   // The last card is a guard card, and we commit the page for it so

   102   // we can use the card for verification purposes. We make sure we never

   103   // uncommit the MemRegion for that page.

   104   MemRegion _guard_region;

   105 

   106  protected:

   107   // Initialization utilities; covered_words is the size of the covered region

   108   // in, um, words.

   109   inline size_t cards_required(size_t covered_words);

   110   inline size_t compute_byte_map_size();

   111 

   112   // Finds and return the index of the region, if any, to which the given

   113   // region would be contiguous.  If none exists, assign a new region and

   114   // returns its index.  Requires that no more than the maximum number of

   115   // covered regions defined in the constructor are ever in use.

   116   int find_covering_region_by_base(HeapWord* base);

   117 

   118   // Same as above, but finds the region containing the given address

   119   // instead of starting at a given base address.

   120   int find_covering_region_containing(HeapWord* addr);

   121 

   122   // Resize one of the regions covered by the remembered set.

   123   void resize_covered_region(MemRegion new_region);

   124 

   125   // Returns the leftmost end of a committed region corresponding to a

   126   // covered region before covered region "ind", or else "NULL" if "ind" is

   127   // the first covered region.

   128   HeapWord* largest_prev_committed_end(int ind) const;

   129 

   130   // Returns the part of the region mr that doesn't intersect with

   131   // any committed region other than self.  Used to prevent uncommitting

   132   // regions that are also committed by other regions.  Also protects

   133   // against uncommitting the guard region.

   134   MemRegion committed_unique_to_self(int self, MemRegion mr) const;

   135 

   136   // Mapping from address to card marking array entry

   137   jbyte* byte_for(const void* p) const {

   138     assert(_whole_heap.contains(p),

   139            "out of bounds access to card marking array");

   140     jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];

   141     assert(result >= _byte_map && result < _byte_map + _byte_map_size,

   142            "out of bounds accessor for card marking array");

   143     return result;

   144   }

   145 

   146   // The card table byte one after the card marking array

   147   // entry for argument address. Typically used for higher bounds

   148   // for loops iterating through the card table.

   149   jbyte* byte_after(const void* p) const {

   150     return byte_for(p) + 1;

   151   }

   152 

   153   // Mapping from card marking array entry to address of first word

   154   HeapWord* addr_for(const jbyte* p) const {

   155     assert(p >= _byte_map && p < _byte_map + _byte_map_size,

   156            "out of bounds access to card marking array");

   157     size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));

   158     HeapWord* result = (HeapWord*) (delta << card_shift);

   159     assert(_whole_heap.contains(result),

   160            "out of bounds accessor from card marking array");

   161     return result;

   162   }

   163 

   164   // Iterate over the portion of the card-table which covers the given

   165   // region mr in the given space and apply cl to any dirty sub-regions

   166   // of mr. cl and dcto_cl must either be the same closure or cl must

   167   // wrap dcto_cl. Both are required - neither may be NULL. Also, dcto_cl

   168   // may be modified. Note that this function will operate in a parallel

   169   // mode if worker threads are available.

   170   void non_clean_card_iterate(Space* sp, MemRegion mr,

   171                               DirtyCardToOopClosure* dcto_cl,

   172                               MemRegionClosure* cl,

   173                               bool clear);

   174 

   175   // Utility function used to implement the other versions below.

   176   void non_clean_card_iterate_work(MemRegion mr, MemRegionClosure* cl,

   177                                    bool clear);

   178 

   179   void par_non_clean_card_iterate_work(Space* sp, MemRegion mr,

   180                                        DirtyCardToOopClosure* dcto_cl,

   181                                        MemRegionClosure* cl,

   182                                        bool clear,

   183                                        int n_threads);

   184 

   185   // Dirty the bytes corresponding to "mr" (not all of which must be

   186   // covered.)

   187   void dirty_MemRegion(MemRegion mr);

   188 

   189   // Clear (to clean_card) the bytes entirely contained within "mr" (not

   190   // all of which must be covered.)

   191   void clear_MemRegion(MemRegion mr);

   192 

   193   // *** Support for parallel card scanning.

   194 

   195   enum SomeConstantsForParallelism {

   196     StridesPerThread    = 2,

   197     CardsPerStrideChunk = 256

   198   };

   199 

   200   // This is an array, one element per covered region of the card table.

   201   // Each entry is itself an array, with one element per chunk in the

   202   // covered region.  Each entry of these arrays is the lowest non-clean

   203   // card of the corresponding chunk containing part of an object from the

   204   // previous chunk, or else NULL.

   205   typedef jbyte*  CardPtr;

   206   typedef CardPtr* CardArr;

   207   CardArr* _lowest_non_clean;

   208   size_t*  _lowest_non_clean_chunk_size;

   209   uintptr_t* _lowest_non_clean_base_chunk_index;

   210   int* _last_LNC_resizing_collection;

   211 

   212   // Initializes "lowest_non_clean" to point to the array for the region

   213   // covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk

   214   // index of the corresponding to the first element of that array.

   215   // Ensures that these arrays are of sufficient size, allocating if necessary.

   216   // May be called by several threads concurrently.

   217   void get_LNC_array_for_space(Space* sp,

   218                                jbyte**& lowest_non_clean,

   219                                uintptr_t& lowest_non_clean_base_chunk_index,

   220                                size_t& lowest_non_clean_chunk_size);

   221 

   222   // Returns the number of chunks necessary to cover "mr".

   223   size_t chunks_to_cover(MemRegion mr) {

   224     return (size_t)(addr_to_chunk_index(mr.last()) -

   225                     addr_to_chunk_index(mr.start()) + 1);

   226   }

   227 

   228   // Returns the index of the chunk in a stride which

   229   // covers the given address.

   230   uintptr_t addr_to_chunk_index(const void* addr) {

   231     uintptr_t card = (uintptr_t) byte_for(addr);

   232     return card / CardsPerStrideChunk;

   233   }

   234 

   235   // Apply cl, which must either itself apply dcto_cl or be dcto_cl,

   236   // to the cards in the stride (of n_strides) within the given space.

   237   void process_stride(Space* sp,

   238                       MemRegion used,

   239                       jint stride, int n_strides,

   240                       DirtyCardToOopClosure* dcto_cl,

   241                       MemRegionClosure* cl,

   242                       bool clear,

   243                       jbyte** lowest_non_clean,

   244                       uintptr_t lowest_non_clean_base_chunk_index,

   245                       size_t lowest_non_clean_chunk_size);

   246 

   247   // Makes sure that chunk boundaries are handled appropriately, by

   248   // adjusting the min_done of dcto_cl, and by using a special card-table

   249   // value to indicate how min_done should be set.

   250   void process_chunk_boundaries(Space* sp,

   251                                 DirtyCardToOopClosure* dcto_cl,

   252                                 MemRegion chunk_mr,

   253                                 MemRegion used,

   254                                 jbyte** lowest_non_clean,

   255                                 uintptr_t lowest_non_clean_base_chunk_index,

   256                                 size_t    lowest_non_clean_chunk_size);

   257 

   258 public:

   259   // Constants

   260   enum SomePublicConstants {

   261     card_shift                  = 9,

   262     card_size                   = 1 << card_shift,

   263     card_size_in_words          = card_size / sizeof(HeapWord)

   264   };

   265 

   266   // For RTTI simulation.

   267   BarrierSet::Name kind() { return BarrierSet::CardTableModRef; }

   268   bool is_a(BarrierSet::Name bsn) {

   269     return bsn == BarrierSet::CardTableModRef || bsn == BarrierSet::ModRef;

   270   }

   271 

   272   CardTableModRefBS(MemRegion whole_heap, int max_covered_regions);

   273 

   274   // *** Barrier set functions.

   275 

   276   inline bool write_ref_needs_barrier(oop* field, oop new_val) {

   277     // Note that this assumes the perm gen is the highest generation

   278     // in the address space

   279     return new_val != NULL && !new_val->is_perm();

   280   }

   281 

   282   // Record a reference update. Note that these versions are precise!

   283   // The scanning code has to handle the fact that the write barrier may be

   284   // either precise or imprecise. We make non-virtual inline variants of

   285   // these functions here for performance.

   286 protected:

   287   void write_ref_field_work(oop obj, size_t offset, oop newVal);

   288   void write_ref_field_work(oop* field, oop newVal);

   289 public:

   290 

   291   bool has_write_ref_array_opt() { return true; }

   292   bool has_write_region_opt() { return true; }

   293 

   294   inline void inline_write_region(MemRegion mr) {

   295     dirty_MemRegion(mr);

   296   }

   297 protected:

   298   void write_region_work(MemRegion mr) {

   299     inline_write_region(mr);

   300   }

   301 public:

   302 

   303   inline void inline_write_ref_array(MemRegion mr) {

   304     dirty_MemRegion(mr);

   305   }

   306 protected:

   307   void write_ref_array_work(MemRegion mr) {

   308     inline_write_ref_array(mr);

   309   }

   310 public:

   311 

   312   bool is_aligned(HeapWord* addr) {

   313     return is_card_aligned(addr);

   314   }

   315 

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

   317 

   318   inline void inline_write_ref_field(oop* field, oop newVal) {

   319     jbyte* byte = byte_for(field);

   320     *byte = dirty_card;

   321   }

   322 

   323   // Card marking array base (adjusted for heap low boundary)

   324   // This would be the 0th element of _byte_map, if the heap started at 0x0.

   325   // But since the heap starts at some higher address, this points to somewhere

   326   // before the beginning of the actual _byte_map.

   327   jbyte* byte_map_base;

   328 

   329   // Return true if "p" is at the start of a card.

   330   bool is_card_aligned(HeapWord* p) {

   331     jbyte* pcard = byte_for(p);

   332     return (addr_for(pcard) == p);

   333   }

   334 

   335   // The kinds of precision a CardTableModRefBS may offer.

   336   enum PrecisionStyle {

   337     Precise,

   338     ObjHeadPreciseArray

   339   };

   340 

   341   // Tells what style of precision this card table offers.

   342   PrecisionStyle precision() {

   343     return ObjHeadPreciseArray; // Only one supported for now.

   344   }

   345 

   346   // ModRefBS functions.

   347   void invalidate(MemRegion mr);

   348   void clear(MemRegion mr);

   349   void mod_oop_in_space_iterate(Space* sp, OopClosure* cl,

   350                                 bool clear = false,

   351                                 bool before_save_marks = false);

   352 

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

   354 

   355   // Invoke "cl.do_MemRegion" on a set of MemRegions that collectively

   356   // includes all the modified cards (expressing each card as a

   357   // MemRegion).  Thus, several modified cards may be lumped into one

   358   // region.  The regions are non-overlapping, and are visited in

   359   // *decreasing* address order.  (This order aids with imprecise card

   360   // marking, where a dirty card may cause scanning, and summarization

   361   // marking, of objects that extend onto subsequent cards.)

   362   // If "clear" is true, the card is (conceptually) marked unmodified before

   363   // applying the closure.

   364   void mod_card_iterate(MemRegionClosure* cl, bool clear = false) {

   365     non_clean_card_iterate_work(_whole_heap, cl, clear);

   366   }

   367 

   368   // Like the "mod_cards_iterate" above, except only invokes the closure

   369   // for cards within the MemRegion "mr" (which is required to be

   370   // card-aligned and sized.)

   371   void mod_card_iterate(MemRegion mr, MemRegionClosure* cl,

   372                         bool clear = false) {

   373     non_clean_card_iterate_work(mr, cl, clear);

   374   }

   375 

   376   static uintx ct_max_alignment_constraint();

   377 

   378   // Apply closure cl to the dirty cards lying completely

   379   // within MemRegion mr, setting the cards to precleaned.

   380   void      dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);

   381 

   382   // Return the MemRegion corresponding to the first maximal run

   383   // of dirty cards lying completely within MemRegion mr, after

   384   // marking those cards precleaned.

   385   MemRegion dirty_card_range_after_preclean(MemRegion mr);

   386 

   387   // Set all the dirty cards in the given region to precleaned state.

   388   void preclean_dirty_cards(MemRegion mr);

   389 

   390   // Mapping from address to card marking array index.

   391   int index_for(void* p) {

   392     assert(_whole_heap.contains(p),

   393            "out of bounds access to card marking array");

   394     return byte_for(p) - _byte_map;

   395   }

   396 

   397   void verify();

   398   void verify_guard();

   399 

   400   void verify_clean_region(MemRegion mr) PRODUCT_RETURN;

   401 

   402   static size_t par_chunk_heapword_alignment() {

   403     return CardsPerStrideChunk * card_size_in_words;

   404   }

   405 };

   406 

   407 class CardTableRS;

   408 

   409 // A specialization for the CardTableRS gen rem set.

   410 class CardTableModRefBSForCTRS: public CardTableModRefBS {

   411   CardTableRS* _rs;

   412 protected:

   413   bool card_will_be_scanned(jbyte cv);

   414   bool card_may_have_been_dirty(jbyte cv);

   415 public:

   416   CardTableModRefBSForCTRS(MemRegion whole_heap,

   417                            int max_covered_regions) :

   418     CardTableModRefBS(whole_heap, max_covered_regions) {}

   419 

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

   421 };