1 /*
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 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).
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 24 
 25 #ifndef SHARE_GC_SHARED_CARDTABLEBARRIERSET_HPP
 26 #define SHARE_GC_SHARED_CARDTABLEBARRIERSET_HPP
 27 
 28 #include "gc/shared/cardTable.hpp"
 29 #include "gc/shared/modRefBarrierSet.hpp"
 30 #include "utilities/align.hpp"
 31 
 32 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
 33 // enumerate ref fields that have been modified (since the last
 34 // enumeration.)
 35 
 36 // As it currently stands, this barrier is *imprecise*: when a ref field in
 37 // an object "o" is modified, the card table entry for the card containing
 38 // the head of "o" is dirtied, not necessarily the card containing the
 39 // modified field itself.  For object arrays, however, the barrier *is*
 40 // precise; only the card containing the modified element is dirtied.
 41 // Closures used to scan dirty cards should take these
 42 // considerations into account.
 43 
 44 class CardTableBarrierSet: public ModRefBarrierSet {
 45   // Some classes get to look at some private stuff.
 46   friend class VMStructs;
 47 
 48 public:
 49 
 50   typedef CardTable::CardValue CardValue;
 51 protected:
 52   // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2
 53   // or INCLUDE_JVMCI is being used
 54   bool       _defer_initial_card_mark;
 55   CardTable* _card_table;
 56 
 57   CardTableBarrierSet(BarrierSetAssembler* barrier_set_assembler,
 58                       BarrierSetC1* barrier_set_c1,
 59                       BarrierSetC2* barrier_set_c2,
 60                       CardTable* card_table,
 61                       const BarrierSet::FakeRtti& fake_rtti);
 62 
 63  public:
 64   CardTableBarrierSet(CardTable* card_table);
 65   ~CardTableBarrierSet();
 66 
 67   CardTable* card_table() const { return _card_table; }
 68 
 69   virtual void initialize();
 70 
 71   void write_region(MemRegion mr) {
 72     invalidate(mr);
 73   }
 74 
 75   void write_ref_array_work(MemRegion mr);
 76 
 77  public:
 78   // Record a reference update. Note that these versions are precise!
 79   // The scanning code has to handle the fact that the write barrier may be
 80   // either precise or imprecise. We make non-virtual inline variants of
 81   // these functions here for performance.
 82   template <DecoratorSet decorators, typename T>
 83   void write_ref_field_post(T* field, oop newVal);
 84 
 85   virtual void invalidate(MemRegion mr);
 86 
 87   // ReduceInitialCardMarks
 88   void initialize_deferred_card_mark_barriers();
 89 
 90   // If the CollectedHeap was asked to defer a store barrier above,
 91   // this informs it to flush such a deferred store barrier to the
 92   // remembered set.
 93   void flush_deferred_card_mark_barrier(JavaThread* thread);
 94 



 95   // If a compiler is eliding store barriers for TLAB-allocated objects,
 96   // we will be informed of a slow-path allocation by a call
 97   // to on_slowpath_allocation_exit() below. Such a call precedes the
 98   // initialization of the object itself, and no post-store-barriers will
 99   // be issued. Some heap types require that the barrier strictly follows
100   // the initializing stores. (This is currently implemented by deferring the
101   // barrier until the next slow-path allocation or gc-related safepoint.)
102   // This interface answers whether a particular barrier type needs the card
103   // mark to be thus strictly sequenced after the stores.
104   virtual bool card_mark_must_follow_store() const;
105 
106   virtual void on_slowpath_allocation_exit(JavaThread* thread, oop new_obj);
107   virtual void on_thread_detach(Thread* thread);
108 
109   virtual void make_parsable(JavaThread* thread) { flush_deferred_card_mark_barrier(thread); }
110 
111   virtual void print_on(outputStream* st) const;
112 
113   template <DecoratorSet decorators, typename BarrierSetT = CardTableBarrierSet>
114   class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {};
115 };
116 
117 template<>
118 struct BarrierSet::GetName<CardTableBarrierSet> {
119   static const BarrierSet::Name value = BarrierSet::CardTableBarrierSet;
120 };
121 
122 template<>
123 struct BarrierSet::GetType<BarrierSet::CardTableBarrierSet> {
124   typedef ::CardTableBarrierSet type;
125 };
126 
127 #endif // SHARE_GC_SHARED_CARDTABLEBARRIERSET_HPP
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