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 /*

  * Copyright (c) 1998, 2010, Oracle and/or its affiliates. All rights reserved.

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

  *

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

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * 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.

  *

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

  * or visit www.oracle.com if you need additional information or have any

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  */

 #ifndef SHARE_VM_CODE_OOPRECORDER_HPP

 #define SHARE_VM_CODE_OOPRECORDER_HPP

 #include "runtime/handles.hpp"

 #include "utilities/growableArray.hpp"

 // Recording and retrieval of oop relocations in compiled code.

 class CodeBlob;

 class OopRecorder : public ResourceObj {

  public:

   // A two-way mapping from positive indexes to oop handles.

   // The zero index is reserved for a constant (sharable) null.

   // Indexes may not be negative.

   // Use the given arena to manage storage, if not NULL.

   // By default, uses the current ResourceArea.

   OopRecorder(Arena* arena = NULL);

   // Generate a new index on which CodeBlob::oop_addr_at will work.

   // allocate_index and find_index never return the same index,

   // and allocate_index never returns the same index twice.

   // In fact, two successive calls to allocate_index return successive ints.

   int allocate_index(jobject h) {

     return add_handle(h, false);

   }

   // For a given jobject, this will return the same index repeatedly.

   // The index can later be given to oop_at to retrieve the oop.

   // However, the oop must not be changed via CodeBlob::oop_addr_at.

   int find_index(jobject h) {

     int index = maybe_find_index(h);

     if (index < 0) {  // previously unallocated

       index = add_handle(h, true);

     }

     return index;

   }

   // variant of find_index which does not allocate if not found (yields -1)

   int maybe_find_index(jobject h);

   // returns the size of the generated oop table, for sizing the CodeBlob.

   // must be called after all oops are allocated!

   int oop_size();

   // Retrieve the oop handle at a given index.

   jobject handle_at(int index);

   int element_count() {

     // there is always a NULL virtually present as first object

     return _handles->length() + first_index;

   }

   // copy the generated oop table to nmethod

   void copy_to(nmethod* nm);  // => nm->copy_oops(_handles)

   bool is_unused() { return _handles == NULL && !_complete; }

 #ifdef ASSERT

   bool is_complete() { return _complete; }

 #endif

  private:

   // leaky hash table of handle => index, to help detect duplicate insertion

   class IndexCache: public ResourceObj {

     // This class is only used by the OopRecorder class.

     friend class OopRecorder;

     enum {

       _log_cache_size = 9,

       _cache_size = (1<<_log_cache_size),

       // Index entries are ints.  The LSBit is a collision indicator.

       _collision_bit_shift = 0,

       _collision_bit = 1,

       _index_shift = _collision_bit_shift+1

     };

     int _cache[_cache_size];

     static juint cache_index(jobject handle) {

       juint ci = (int) (intptr_t) handle;

       ci ^= ci >> (BitsPerByte*2);

       ci += ci >> (BitsPerByte*1);

       return ci & (_cache_size-1);

     }

     int* cache_location(jobject handle) {

       return &_cache[ cache_index(handle) ];

     }

     static bool cache_location_collision(int* cloc) {

       return ((*cloc) & _collision_bit) != 0;

     }

     static int cache_location_index(int* cloc) {

       return (*cloc) >> _index_shift;

     }

     static void set_cache_location_index(int* cloc, int index) {

       int cval0 = (*cloc);

       int cval1 = (index << _index_shift);

       if (cval0 != 0 && cval1 != cval0)  cval1 += _collision_bit;

       (*cloc) = cval1;

     }

     IndexCache();

   };

   // Helper function; returns false for NULL or Universe::non_oop_word().

   inline bool is_real_jobject(jobject h);

   void maybe_initialize();

   int add_handle(jobject h, bool make_findable);

   enum { null_index = 0, first_index = 1, index_cache_threshold = 20 };

   GrowableArray<jobject>*   _handles;  // ordered list (first is always NULL)

   GrowableArray<int>*       _no_finds; // all unfindable indexes; usually empty

   IndexCache*               _indexes;  // map: jobject -> its probable index

   Arena*                    _arena;

   bool                      _complete;

 #ifdef ASSERT

   static int _find_index_calls, _hit_indexes, _missed_indexes;

 #endif

 };

 #endif // SHARE_VM_CODE_OOPRECORDER_HPP