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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_METABLOCK_HPP

 #define SHARE_VM_MEMORY_METABLOCK_HPP

 // Metablock are the unit of allocation from a Chunk.  It is initialized

 // with the size of the requested allocation.  That size is overwritten

 // once the allocation returns.

 //

 // A Metablock may be reused by its SpaceManager but are never moved between

 // SpaceManagers.  There is no explicit link to the Metachunk

 // from which it was allocated.  Metablock may be deallocated and

 // put on a freelist but the space is never freed, rather

 // the Metachunk it is a part of will be deallocated when it's

 // associated class loader is collected.

 class Metablock VALUE_OBJ_CLASS_SPEC {

   friend class VMStructs;

  private:

   // Used to align the allocation (see below).

   union block_t {

     void* _data[3];

     struct header_t {

       size_t _word_size;

       Metablock* _next;

       Metablock* _prev;

     } _header;

   } _block;

   static size_t _min_block_byte_size;

   static size_t _overhead;

   typedef union block_t Block;

   typedef struct header_t Header;

   const Block* block() const { return &_block; }

   const Block::header_t* header() const { return &(block()->_header); }

  public:

   static Metablock* initialize(MetaWord* p, size_t word_size);

   // This places the body of the block at a 2 word boundary

   // because every block starts on a 2 word boundary.  Work out

   // how to make the body on a 2 word boundary if the block

   // starts on a arbitrary boundary.  JJJ

   size_t word_size() const  { return header()->_word_size; }

   void set_word_size(size_t v) { _block._header._word_size = v; }

   size_t size() const volatile { return _block._header._word_size; }

   void set_size(size_t v) { _block._header._word_size = v; }

   Metablock* next() const { return header()->_next; }

   void set_next(Metablock* v) { _block._header._next = v; }

   Metablock* prev() const { return header()->_prev; }

   void set_prev(Metablock* v) { _block._header._prev = v; }

   static size_t min_block_byte_size() { return _min_block_byte_size; }

   static size_t overhead() { return _overhead; }

   bool is_free()                 { return header()->_word_size != 0; }

   void clear_next()              { set_next(NULL); }

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

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

   bool cantCoalesce() const     { return false; }

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

   void link_after(Metablock* ptr){

     link_next(ptr);

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

   }

   // Should not be needed in a free list of Metablocks

   void markNotFree()            { ShouldNotReachHere(); }

   // Debug support

 #ifdef ASSERT

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

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

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

 #endif

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

   bool verify_par_locked() { return true; }

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

 };

 #endif // SHARE_VM_MEMORY_METABLOCK_HPP