1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  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.
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  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  *
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 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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   int            _num_oops;
 96 #ifdef ASSERT
 97   bool _resource_allocate_bit_mask;
 98 #endif
 99 
100   // access methods
101   Method*        method() const                  { return _method; }
102   void           set_method(Method* v)           { _method = v; }
103   int            bci() const                     { return _bci; }
104   void           set_bci(int v)                  { _bci = v; }
105   int            mask_size() const               { return _mask_size; }
106   void           set_mask_size(int v)            { _mask_size = v; }
107   // Test bit mask size and return either the in-line bit mask or allocated
108   // bit mask.
109   uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
110 
111   // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT
112   size_t mask_word_size() const {
113     return (mask_size() + BitsPerWord - 1) / BitsPerWord;
114   }
115 
116   uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
117 
118   void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }
119 
120   // Lookup
121   bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }
122   bool is_empty() const;
123 
124   // Initialization
125   void initialize();
126 
127  public:
128   InterpreterOopMap();
129   ~InterpreterOopMap();
130 
131   // Copy the OopMapCacheEntry in parameter "from" into this
132   // InterpreterOopMap.  If the _bit_mask[0] in "from" points to
133   // allocated space (i.e., the bit mask was to large to hold
134   // in-line), allocate the space from a Resource area.
135   void resource_copy(OopMapCacheEntry* from);
136 
137   void iterate_oop(OffsetClosure* oop_closure) const;
138   void print() const;
139 
140   int number_of_entries() const                  { return mask_size() / bits_per_entry; }
141   bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
142   bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
143   int  num_oops() const                          { return _num_oops; }
144 
145   int expression_stack_size() const              { return _expression_stack_size; }
146 
147 };
148 
149 class OopMapCache : public CHeapObj<mtClass> {
150  static OopMapCacheEntry* volatile _old_entries;
151  private:
152   enum { _size        = 32,     // Use fixed size for now
153          _probe_depth = 3       // probe depth in case of collisions
154   };
155 
156   OopMapCacheEntry* volatile * _array;
157 
158   unsigned int hash_value_for(const methodHandle& method, int bci) const;
159   OopMapCacheEntry* entry_at(int i) const;
160   bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);
161 
162   static void enqueue_for_cleanup(OopMapCacheEntry* entry);
163 
164   void flush();
165 
166  public:
167   OopMapCache();
168   ~OopMapCache();                                // free up memory
169 
170   // flush cache entry is occupied by an obsolete method
171   void flush_obsolete_entries();
172 
173   // Returns the oopMap for (method, bci) in parameter "entry".
174   // Returns false if an oop map was not found.
175   void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry);
176 
177   // Compute an oop map without updating the cache or grabbing any locks (for debugging)
178   static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);
179   static void cleanup_old_entries();
180 };
181 
182 #endif // SHARE_INTERPRETER_OOPMAPCACHE_HPP