1 /*

     2  * Copyright 2003 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    20  * CA 95054 USA or visit www.sun.com if you need additional information or

    21  * have any questions.

    22  *

    23  */

    24 

    25 

    26 // Contains two virtual spaces that each can individually span

    27 // most of the reserved region but committed parts of which

    28 // cannot overlap.

    29 //

    30 //      +-------+ <--- high_boundary for H

    31 //      |       |

    32 //      |   H   |

    33 //      |       |

    34 //      |       |

    35 //      |       |

    36 //      --------- <--- low for H

    37 //      |       |

    38 //      ========= <--- low_boundary for H, high_boundary for L

    39 //      |       |

    40 //      |       |

    41 //      |       |

    42 //      --------- <--- high for L

    43 //      |       |

    44 //      |   L   |

    45 //      |       |

    46 //      |       |

    47 //      |       |

    48 //      +-------+ <--- low_boundary for L

    49 //

    50 // Each virtual space in the AdjoiningVirtualSpaces grows and shrink

    51 // within its reserved region (between the low_boundary and the

    52 // boundary) independently.  If L want to grow above its high_boundary,

    53 // then the high_boundary of L and the low_boundary of H must be

    54 // moved up consistently.  AdjoiningVirtualSpaces provide the

    55 // interfaces for moving the this boundary.

    56 

    57 class AdjoiningVirtualSpaces {

    58   // space at the high end and the low end, respectively

    59   PSVirtualSpace*    _high;

    60   PSVirtualSpace*    _low;

    61 

    62   // The reserved space spanned by the two spaces.

    63   ReservedSpace      _reserved_space;

    64 

    65   // The minimum byte size for the low space.  It will not

    66   // be shrunk below this value.

    67   size_t _min_low_byte_size;

    68   // Same for the high space

    69   size_t _min_high_byte_size;

    70 

    71   const size_t _alignment;

    72 

    73  public:

    74   // Allocates two virtual spaces that will be located at the

    75   // high and low ends.  Does no initialization.

    76   AdjoiningVirtualSpaces(ReservedSpace rs,

    77                          size_t min_low_byte_size,

    78                          size_t min_high_byte_size,

    79                          size_t alignment);

    80 

    81   // accessors

    82   PSVirtualSpace* high() { return _high; }

    83   PSVirtualSpace* low()  { return _low; }

    84   ReservedSpace reserved_space() { return _reserved_space; }

    85   size_t min_low_byte_size() { return _min_low_byte_size; }

    86   size_t min_high_byte_size() { return _min_high_byte_size; }

    87   size_t alignment() const { return _alignment; }

    88 

    89   // move boundary between the two spaces up

    90   bool adjust_boundary_up(size_t size_in_bytes);

    91   // and down

    92   bool adjust_boundary_down(size_t size_in_bytes);

    93 

    94   // Maximum byte size for the high space.

    95   size_t high_byte_size_limit() {

    96     return _reserved_space.size() - _min_low_byte_size;

    97   }

    98   // Maximum byte size for the low space.

    99   size_t low_byte_size_limit() {

   100     return _reserved_space.size() - _min_high_byte_size;

   101   }

   102 

   103   // Sets the boundaries for the virtual spaces and commits and

   104   // initial size;

   105   void initialize(size_t max_low_byte_size,

   106                   size_t init_low_byte_size,

   107                   size_t init_high_byte_size);

   108 };