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