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 * 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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#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.

//

// 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                = 2,                // 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

#ifdef ENABLE_ZAP_DEAD_LOCALS

    bits_per_entry   = 2,

    dead_bit_number  = 1,

#else

    bits_per_entry   = 1,

#endif

    oop_bit_number   = 0

  };

 private:

  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

  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; }

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

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

  // bit mask.

  uintptr_t*  bit_mask()                         { 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() {

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

  }

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

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

#ifdef ENABLE_ZAP_DEAD_LOCALS

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

#endif

  // Lookup

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

  bool is_empty();

  // 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);

  void print();

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

  int expression_stack_size()                    { 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);

  OopMapCacheEntry* entry_at(int i) const;

  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);

  // 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