1 /*

     2  * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.

     8  *

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

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

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

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

    13  * accompanied this code).

    14  *

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

    16  * 2 along with this work; if not, write to the Free Software Foundation,

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

    18  *

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

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

    21  * questions.

    22  *

    23  */

    24 #ifndef SHARE_VM_MEMORY_METABLOCK_HPP

    25 #define SHARE_VM_MEMORY_METABLOCK_HPP

    26 

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

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

    29 // once the allocation returns.

    30 //

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

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

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

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

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

    36 // associated class loader is collected.

    37 

    38 class Metablock VALUE_OBJ_CLASS_SPEC {

    39   friend class VMStructs;

    40  private:

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

    42   union block_t {

    43     void* _data[3];

    44     struct header_t {

    45       size_t _word_size;

    46       Metablock* _next;

    47       Metablock* _prev;

    48     } _header;

    49   } _block;

    50   static size_t _min_block_byte_size;

    51   static size_t _overhead;

    52 

    53   typedef union block_t Block;

    54   typedef struct header_t Header;

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

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

    57  public:

    58 

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

    60 

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

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

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

    64   // starts on a arbitrary boundary.  JJJ

    65 

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

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

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

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

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

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

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

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

    74 

    75   static size_t min_block_byte_size() { return _min_block_byte_size; }

    76   static size_t overhead() { return _overhead; }

    77 

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

    79   void clear_next()              { set_next(NULL); }

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

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

    82   bool cantCoalesce() const     { return false; }

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

    84   void link_after(Metablock* ptr){

    85     link_next(ptr);

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

    87   }

    88 

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

    90   void markNotFree()            { ShouldNotReachHere(); }

    91 

    92   // Debug support

    93 #ifdef ASSERT

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

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

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

    97 #endif

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

    99   bool verify_par_locked() { return true; }

   100 

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

   102 };

   103 #endif // SHARE_VM_MEMORY_METABLOCK_HPP