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24 
25 #ifndef SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
26 #define SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
27 
28 #include "oops/generateOopMap.hpp"
29 #include "runtime/mutex.hpp"
30 
31 // A Cache for storing (method, bci) -> oopMap.
32 // The memory management system uses the cache when locating object
33 // references in an interpreted frame.
34 //
35 // OopMapCache's are allocated lazily per InstanceKlass.
36 
37 // The oopMap (InterpreterOopMap) is stored as a bit mask. If the
38 // bit_mask can fit into two words it is stored in
39 // the _bit_mask array, otherwise it is allocated on the heap.
40 // For OopMapCacheEntry the bit_mask is allocated in the C heap
41 // because these entries persist between garbage collections.
42 // For InterpreterOopMap the bit_mask is allocated in
43 // a resource area for better performance.  InterpreterOopMap
44 // should only be created and deleted during same garbage collection.
45 //
46 // If ENABBLE_ZAP_DEAD_LOCALS is defined, two bits are used
47 // per entry instead of one. In all cases,
48 // the first bit is set to indicate oops as opposed to other
49 // values. If the second bit is available,
50 // it is set for dead values. We get the following encoding:
51 //
52 // 00 live value
53 // 01 live oop
54 // 10 dead value
55 // 11 <unused>                                   (we cannot distinguish between dead oops or values with the current oop map generator)
56 
57 
58 class OffsetClosure  {
59  public:
60   virtual void offset_do(int offset) = 0;
61 };
62 
63 
64 class InterpreterOopMap: ResourceObj {
65   friend class OopMapCache;
66 
67  public:
68   enum {
69     N                = 4,                // the number of words reserved
70                                          // for inlined mask storage
71     small_mask_limit = N * BitsPerWord,  // the maximum number of bits
72                                          // available for small masks,
73                                          // small_mask_limit can be set to 0
74                                          // for testing bit_mask allocation
75 
76     bits_per_entry   = 2,
77     dead_bit_number  = 1,
78     oop_bit_number   = 0
79   };
80 
81  private:
82   Method*        _method;         // the method for which the mask is valid
83   unsigned short _bci;            // the bci    for which the mask is valid
84   int            _mask_size;      // the mask size in bits
85   int            _expression_stack_size; // the size of the expression stack in slots
86 
87  protected:
88   intptr_t       _bit_mask[N];    // the bit mask if
89                                   // mask_size <= small_mask_limit,
90                                   // ptr to bit mask otherwise
91                                   // "protected" so that sub classes can
92                                   // access it without using trickery in
93                                   // methd bit_mask().
94 #ifdef ASSERT
95   bool _resource_allocate_bit_mask;
96 #endif
97 
98   // access methods
method() const99   Method*        method() const                  { return _method; }
set_method(Method * v)100   void           set_method(Method* v)           { _method = v; }
bci() const101   int            bci() const                     { return _bci; }
set_bci(int v)102   void           set_bci(int v)                  { _bci = v; }
mask_size() const103   int            mask_size() const               { return _mask_size; }
set_mask_size(int v)104   void           set_mask_size(int v)            { _mask_size = v; }
105   // Test bit mask size and return either the in-line bit mask or allocated
106   // bit mask.
bit_mask() const107   uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
108 
109   // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT
mask_word_size() const110   size_t mask_word_size() const {
111     return (mask_size() + BitsPerWord - 1) / BitsPerWord;
112   }
113 
entry_at(int offset) const114   uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
115 
set_expression_stack_size(int sz)116   void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }
117 
118   // Lookup
match(const methodHandle & method,int bci) const119   bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }
120   bool is_empty() const;
121 
122   // Initialization
123   void initialize();
124 
125  public:
126   InterpreterOopMap();
127   ~InterpreterOopMap();
128 
129   // Copy the OopMapCacheEntry in parameter "from" into this
130   // InterpreterOopMap.  If the _bit_mask[0] in "from" points to
131   // allocated space (i.e., the bit mask was to large to hold
132   // in-line), allocate the space from a Resource area.
133   void resource_copy(OopMapCacheEntry* from);
134 
135   void iterate_oop(OffsetClosure* oop_closure) const;
136   void print() const;
137 
number_of_entries() const138   int number_of_entries() const                  { return mask_size() / bits_per_entry; }
is_dead(int offset) const139   bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
is_oop(int offset) const140   bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
141 
expression_stack_size() const142   int expression_stack_size() const              { return _expression_stack_size; }
143 
144 };
145 
146 class OopMapCache : public CHeapObj<mtClass> {
147  static OopMapCacheEntry* volatile _old_entries;
148  private:
149   enum { _size        = 32,     // Use fixed size for now
150          _probe_depth = 3       // probe depth in case of collisions
151   };
152 
153   OopMapCacheEntry* volatile * _array;
154 
155   unsigned int hash_value_for(const methodHandle& method, int bci) const;
156   OopMapCacheEntry* entry_at(int i) const;
157   bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);
158 
159   static void enqueue_for_cleanup(OopMapCacheEntry* entry);
160 
161   void flush();
162 
163  public:
164   OopMapCache();
165   ~OopMapCache();                                // free up memory
166 
167   // flush cache entry is occupied by an obsolete method
168   void flush_obsolete_entries();
169 
170   // Returns the oopMap for (method, bci) in parameter "entry".
171   // Returns false if an oop map was not found.
172   void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry);
173 
174   // Compute an oop map without updating the cache or grabbing any locks (for debugging)
175   static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);
176   static void cleanup_old_entries();
177 };
178 
179 #endif // SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
180