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_METACHUNK_HPP

    25 #define SHARE_VM_MEMORY_METACHUNK_HPP

    26 

    27 //  Metachunk - Quantum of allocation from a Virtualspace

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

    29 //    have no permanent association to a SpaceManager.

    30 

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

    32 //            |              |          --+       ---+

    33 //            |              |            | free     |

    34 //            |              |            |          |

    35 //            |              |            |          | capacity

    36 //            |              |            |          |

    37 //            |              | <- top   --+          |

    38 //            |              |           ---+        |

    39 //            |              |              | used   |

    40 //            |              |              |        |

    41 //            |              |              |        |

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

    43 

    44 class Metachunk VALUE_OBJ_CLASS_SPEC {

    45   // link to support lists of chunks

    46   Metachunk* _next;

    47   Metachunk* _prev;

    48 

    49   MetaWord* _bottom;

    50   MetaWord* _end;

    51   MetaWord* _top;

    52   size_t _word_size;

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

    54   // even through it is only for debugging.

    55   bool _is_free;

    56 

    57   // Metachunks are allocated out of a MetadataVirtualSpace and

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

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

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

    61   // the space.

    62   static size_t _overhead;

    63 

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

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

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

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

    68  public:

    69 #ifdef ASSERT

    70   Metachunk() : _bottom(NULL), _end(NULL), _top(NULL), _is_free(false) {}

    71 #else

    72   Metachunk() : _bottom(NULL), _end(NULL), _top(NULL) {}

    73 #endif

    74 

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

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

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

    78 

    79   MetaWord* allocate(size_t word_size);

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

    81 

    82   // Accessors

    83   Metachunk* next() const { return _next; }

    84   Metachunk* prev() const { return _prev; }

    85   MetaWord* bottom() const { return _bottom; }

    86   MetaWord* end() const { return _end; }

    87   MetaWord* top() const { return _top; }

    88   size_t word_size() const { return _word_size; }

    89   size_t size() const volatile { return _word_size; }

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

    91   bool is_free() { return _is_free; }

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

    93   static size_t overhead() { return _overhead; }

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

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

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

    97   bool cantCoalesce() const     { return false; }

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

    99   void link_after(Metachunk* ptr){

   100     link_next(ptr);

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

   102   }

   103 

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

   105   void reset_empty() { _top = (_bottom + _overhead); }

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

   107 

   108   // used (has been allocated)

   109   // free (available for future allocations)

   110   // capacity (total size of chunk)

   111   size_t used_word_size();

   112   size_t free_word_size();

   113   size_t capacity_word_size();

   114 

   115   // Debug support

   116 #ifdef ASSERT

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

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

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

   120 #endif

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

   122   bool verify_par_locked() { return true; }

   123 

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

   125 

   126 #ifdef ASSERT

   127   void mangle();

   128 #endif // ASSERT

   129 

   130   void print_on(outputStream* st) const;

   131   void verify();

   132 };

   133 #endif  // SHARE_VM_MEMORY_METACHUNK_HPP