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 /*

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

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

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  * published by the Free Software Foundation.

  *

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

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

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

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

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

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  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 #ifndef SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP

 #define SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP

 #include "oops/generateOopMap.hpp"

 #include "runtime/mutex.hpp"

 // A Cache for storing (method, bci) -> oopMap.

 // The memory management system uses the cache when locating object

 // references in an interpreted frame.

 //

 // OopMapCache's are allocated lazily per InstanceKlass.

 // The oopMap (InterpreterOopMap) is stored as a bit mask. If the

 // bit_mask can fit into two words it is stored in

 // the _bit_mask array, otherwise it is allocated on the heap.

 // For OopMapCacheEntry the bit_mask is allocated in the C heap

 // because these entries persist between garbage collections.

 // For InterpreterOopMap the bit_mask is allocated in

 // a resource area for better performance.  InterpreterOopMap

 // should only be created and deleted during same garbage collection.

 //

 // If ENABBLE_ZAP_DEAD_LOCALS is defined, two bits are used

 // per entry instead of one. In all cases,

 // the first bit is set to indicate oops as opposed to other

 // values. If the second bit is available,

 // it is set for dead values. We get the following encoding:

 //

 // 00 live value

 // 01 live oop

 // 10 dead value

 // 11 <unused>                                   (we cannot distinguish between dead oops or values with the current oop map generator)

 class OffsetClosure  {

  public:

   virtual void offset_do(int offset) = 0;

 };

 class InterpreterOopMap: ResourceObj {

   friend class OopMapCache;

  public:

   enum {

     N                = 4,                // the number of words reserved

                                          // for inlined mask storage

     small_mask_limit = N * BitsPerWord,  // the maximum number of bits

                                          // available for small masks,

                                          // small_mask_limit can be set to 0

                                          // for testing bit_mask allocation

     bits_per_entry   = 2,

     dead_bit_number  = 1,

     oop_bit_number   = 0

   };

  private:

   Method*        _method;         // the method for which the mask is valid

   unsigned short _bci;            // the bci    for which the mask is valid

   int            _mask_size;      // the mask size in bits

   int            _expression_stack_size; // the size of the expression stack in slots

  protected:

   intptr_t       _bit_mask[N];    // the bit mask if

                                   // mask_size <= small_mask_limit,

                                   // ptr to bit mask otherwise

                                   // "protected" so that sub classes can

                                   // access it without using trickery in

                                   // methd bit_mask().

 #ifdef ASSERT

   bool _resource_allocate_bit_mask;

 #endif

   // access methods

   Method*        method() const                  { return _method; }

   void           set_method(Method* v)           { _method = v; }

   int            bci() const                     { return _bci; }

   void           set_bci(int v)                  { _bci = v; }

   int            mask_size() const               { return _mask_size; }

   void           set_mask_size(int v)            { _mask_size = v; }

   // Test bit mask size and return either the in-line bit mask or allocated

   // bit mask.

   uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }

   // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT

   size_t mask_word_size() const {

     return (mask_size() + BitsPerWord - 1) / BitsPerWord;

   }

   uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }

   void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }

   // Lookup

   bool match(methodHandle method, int bci) const { return _method == method() && _bci == bci; }

   bool is_empty() const;

   // Initialization

   void initialize();

  public:

   InterpreterOopMap();

   ~InterpreterOopMap();

   // Copy the OopMapCacheEntry in parameter "from" into this

   // InterpreterOopMap.  If the _bit_mask[0] in "from" points to

   // allocated space (i.e., the bit mask was to large to hold

   // in-line), allocate the space from a Resource area.

   void resource_copy(OopMapCacheEntry* from);

   void iterate_oop(OffsetClosure* oop_closure) const;

   void print() const;

   int number_of_entries() const                  { return mask_size() / bits_per_entry; }

   bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }

   bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }

   int expression_stack_size() const              { return _expression_stack_size; }

 #ifdef ENABLE_ZAP_DEAD_LOCALS

   void iterate_all(OffsetClosure* oop_closure, OffsetClosure* value_closure, OffsetClosure* dead_closure);

 #endif

 };

 class OopMapCache : public CHeapObj<mtClass> {

  private:

   enum { _size        = 32,     // Use fixed size for now

          _probe_depth = 3       // probe depth in case of collisions

   };

   OopMapCacheEntry* _array;

   unsigned int hash_value_for(methodHandle method, int bci) const;

   OopMapCacheEntry* entry_at(int i) const;

   mutable Mutex _mut;

   void flush();

  public:

   OopMapCache();

   ~OopMapCache();                                // free up memory

   // flush cache entry is occupied by an obsolete method

   void flush_obsolete_entries();

   // Returns the oopMap for (method, bci) in parameter "entry".

   // Returns false if an oop map was not found.

   void lookup(methodHandle method, int bci, InterpreterOopMap* entry) const;

   // Compute an oop map without updating the cache or grabbing any locks (for debugging)

   static void compute_one_oop_map(methodHandle method, int bci, InterpreterOopMap* entry);

   // Returns total no. of bytes allocated as part of OopMapCache's

   static long memory_usage()                     PRODUCT_RETURN0;

 };

 #endif // SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP