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 /*

  * Copyright (c) 2012, 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

  * questions.

  *

  */

 #ifndef SHARE_VM_MEMORY_METACHUNK_HPP

 #define SHARE_VM_MEMORY_METACHUNK_HPP

 //  Metachunk - Quantum of allocation from a Virtualspace

 //    Metachunks are reused (when freed are put on a global freelist) and

 //    have no permanent association to a SpaceManager.

 //            +--------------+ <- end

 //            |              |          --+       ---+

 //            |              |            | free     |

 //            |              |            |          |

 //            |              |            |          | capacity

 //            |              |            |          |

 //            |              | <- top   --+          |

 //            |              |           ---+        |

 //            |              |              | used   |

 //            |              |              |        |

 //            |              |              |        |

 //            +--------------+ <- bottom ---+     ---+

 class Metachunk VALUE_OBJ_CLASS_SPEC {

   // link to support lists of chunks

   Metachunk* _next;

   Metachunk* _prev;

   MetaWord* _bottom;

   MetaWord* _end;

   MetaWord* _top;

   size_t _word_size;

   // Used in a guarantee() so included in the Product builds

   // even through it is only for debugging.

   bool _is_free;

   // Metachunks are allocated out of a MetadataVirtualSpace and

   // and use some of its space to describe itself (plus alignment

   // considerations).  Metadata is allocated in the rest of the chunk.

   // This size is the overhead of maintaining the Metachunk within

   // the space.

   static size_t _overhead;

   void set_bottom(MetaWord* v) { _bottom = v; }

   void set_end(MetaWord* v) { _end = v; }

   void set_top(MetaWord* v) { _top = v; }

   void set_word_size(size_t v) { _word_size = v; }

  public:

 #ifdef ASSERT

   Metachunk() : _bottom(NULL), _end(NULL), _top(NULL), _is_free(false),

     _next(NULL), _prev(NULL) {}

 #else

   Metachunk() : _bottom(NULL), _end(NULL), _top(NULL),

     _next(NULL), _prev(NULL) {}

 #endif

   // Used to add a Metachunk to a list of Metachunks

   void set_next(Metachunk* v) { _next = v; assert(v != this, "Boom");}

   void set_prev(Metachunk* v) { _prev = v; assert(v != this, "Boom");}

   MetaWord* allocate(size_t word_size);

   static Metachunk* initialize(MetaWord* ptr, size_t word_size);

   // Accessors

   Metachunk* next() const { return _next; }

   Metachunk* prev() const { return _prev; }

   MetaWord* bottom() const { return _bottom; }

   MetaWord* end() const { return _end; }

   MetaWord* top() const { return _top; }

   size_t word_size() const { return _word_size; }

   size_t size() const volatile { return _word_size; }

   void set_size(size_t v) { _word_size = v; }

   bool is_free() { return _is_free; }

   void set_is_free(bool v) { _is_free = v; }

   static size_t overhead() { return _overhead; }

   void clear_next()              { set_next(NULL); }

   void link_prev(Metachunk* ptr) { set_prev(ptr); }

   uintptr_t* end()              { return ((uintptr_t*) this) + size(); }

   bool cantCoalesce() const     { return false; }

   void link_next(Metachunk* ptr) { set_next(ptr); }

   void link_after(Metachunk* ptr){

     link_next(ptr);

     if (ptr != NULL) ptr->link_prev(this);

   }

   // Reset top to bottom so chunk can be reused.

   void reset_empty() { _top = (_bottom + _overhead); _next = NULL; _prev = NULL; }

   bool is_empty() { return _top == (_bottom + _overhead); }

   // used (has been allocated)

   // free (available for future allocations)

   // capacity (total size of chunk)

   size_t used_word_size() const;

   size_t free_word_size() const;

   size_t capacity_word_size()const;

   // Debug support

 #ifdef ASSERT

   void* prev_addr() const { return (void*)&_prev; }

   void* next_addr() const { return (void*)&_next; }

   void* size_addr() const { return (void*)&_word_size; }

 #endif

   bool verify_chunk_in_free_list(Metachunk* tc) const { return true; }

   bool verify_par_locked() { return true; }

   void assert_is_mangled() const {/* Don't check "\*/}

   NOT_PRODUCT(void mangle();)

   void print_on(outputStream* st) const;

   void verify();

 };

 #endif  // SHARE_VM_MEMORY_METACHUNK_HPP