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24 
25 #ifndef SHARE_INTERPRETER_OOPMAPCACHE_HPP
26 #define SHARE_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 class OopMapCacheEntry;
64 
65 class InterpreterOopMap: ResourceObj {
66   friend class OopMapCache;
67 
68  public:
69   enum {
70     N                = 4,                // the number of words reserved
71                                          // for inlined mask storage
72     small_mask_limit = N * BitsPerWord,  // the maximum number of bits
73                                          // available for small masks,
74                                          // small_mask_limit can be set to 0
75                                          // for testing bit_mask allocation
76 
77     bits_per_entry   = 2,
78     dead_bit_number  = 1,
79     oop_bit_number   = 0
80   };
81 
82  private:
83   Method*        _method;         // the method for which the mask is valid
84   unsigned short _bci;            // the bci    for which the mask is valid
85   int            _mask_size;      // the mask size in bits
86   int            _expression_stack_size; // the size of the expression stack in slots
87 
88  protected:
89   intptr_t       _bit_mask[N];    // the bit mask if
90                                   // mask_size <= small_mask_limit,
91                                   // ptr to bit mask otherwise
92                                   // "protected" so that sub classes can
93                                   // access it without using trickery in
94                                   // methd bit_mask().
95 #ifdef ASSERT
96   bool _resource_allocate_bit_mask;
97 #endif
98 
99   // access methods
method() const100   Method*        method() const                  { return _method; }
set_method(Method * v)101   void           set_method(Method* v)           { _method = v; }
bci() const102   int            bci() const                     { return _bci; }
set_bci(int v)103   void           set_bci(int v)                  { _bci = v; }
mask_size() const104   int            mask_size() const               { return _mask_size; }
set_mask_size(int v)105   void           set_mask_size(int v)            { _mask_size = v; }
106   // Test bit mask size and return either the in-line bit mask or allocated
107   // bit mask.
bit_mask() const108   uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
109 
110   // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT
mask_word_size() const111   size_t mask_word_size() const {
112     return (mask_size() + BitsPerWord - 1) / BitsPerWord;
113   }
114 
entry_at(int offset) const115   uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
116 
set_expression_stack_size(int sz)117   void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }
118 
119   // Lookup
match(const methodHandle & method,int bci) const120   bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }
121   bool is_empty() const;
122 
123   // Initialization
124   void initialize();
125 
126  public:
127   InterpreterOopMap();
128   ~InterpreterOopMap();
129 
130   // Copy the OopMapCacheEntry in parameter "from" into this
131   // InterpreterOopMap.  If the _bit_mask[0] in "from" points to
132   // allocated space (i.e., the bit mask was to large to hold
133   // in-line), allocate the space from a Resource area.
134   void resource_copy(OopMapCacheEntry* from);
135 
136   void iterate_oop(OffsetClosure* oop_closure) const;
137   void print() const;
138 
number_of_entries() const139   int number_of_entries() const                  { return mask_size() / bits_per_entry; }
is_dead(int offset) const140   bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
is_oop(int offset) const141   bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
142 
expression_stack_size() const143   int expression_stack_size() const              { return _expression_stack_size; }
144 
145 };
146 
147 class OopMapCache : public CHeapObj<mtClass> {
148  static OopMapCacheEntry* volatile _old_entries;
149  private:
150   enum { _size        = 32,     // Use fixed size for now
151          _probe_depth = 3       // probe depth in case of collisions
152   };
153 
154   OopMapCacheEntry* volatile * _array;
155 
156   unsigned int hash_value_for(const methodHandle& method, int bci) const;
157   OopMapCacheEntry* entry_at(int i) const;
158   bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);
159 
160   static void enqueue_for_cleanup(OopMapCacheEntry* entry);
161 
162   void flush();
163 
164  public:
165   OopMapCache();
166   ~OopMapCache();                                // free up memory
167 
168   // flush cache entry is occupied by an obsolete method
169   void flush_obsolete_entries();
170 
171   // Returns the oopMap for (method, bci) in parameter "entry".
172   // Returns false if an oop map was not found.
173   void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry);
174 
175   // Compute an oop map without updating the cache or grabbing any locks (for debugging)
176   static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);
177   static void cleanup_old_entries();
178 };
179 
180 #endif // SHARE_INTERPRETER_OOPMAPCACHE_HPP
181