1 | /* -*- C++ -*- */ |
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2 | |
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3 | #ifndef _COALESCEHEAP_H_ |
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4 | #define _COALESCEHEAP_H_ |
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5 | |
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6 | /* |
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7 | |
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8 | Heap Layers: An Extensible Memory Allocation Infrastructure |
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9 | |
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10 | Copyright (C) 2000-2003 by Emery Berger |
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11 | http://www.cs.umass.edu/~emery |
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12 | emery@cs.umass.edu |
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13 | |
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14 | This program is free software; you can redistribute it and/or modify |
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15 | it under the terms of the GNU General Public License as published by |
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16 | the Free Software Foundation; either version 2 of the License, or |
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17 | (at your option) any later version. |
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18 | |
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19 | This program is distributed in the hope that it will be useful, |
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20 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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21 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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22 | GNU General Public License for more details. |
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23 | |
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24 | You should have received a copy of the GNU General Public License |
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25 | along with this program; if not, write to the Free Software |
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26 | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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27 | |
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28 | */ |
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29 | |
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30 | #include <assert.h> |
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31 | |
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32 | #include "heaplayers.h" |
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33 | |
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34 | /** |
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35 | * @class CoalesceHeap |
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36 | * @brief Applies splitting and coalescing. |
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37 | * @see CoalesceableHeap |
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38 | * @see RequireCoalesceable |
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39 | */ |
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40 | |
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41 | namespace HL { |
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42 | |
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43 | template <class super> |
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44 | class CoalesceHeap : public super { |
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45 | public: |
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46 | |
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47 | inline void * malloc (const size_t sz) |
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48 | { |
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49 | void * ptr = super::malloc (sz); |
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50 | if (ptr != NULL) { |
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51 | super::markInUse (ptr); |
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52 | void * splitPiece = split (ptr, sz); |
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53 | if (splitPiece != NULL) { |
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54 | super::markFree (splitPiece); |
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55 | super::free (splitPiece); |
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56 | } |
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57 | } |
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58 | return ptr; |
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59 | } |
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60 | |
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61 | |
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62 | inline void free (void * ptr) |
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63 | { |
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64 | // Try to coalesce this object with its predecessor & successor. |
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65 | if ((super::getNext(super::getPrev(ptr)) != ptr) || (super::getPrev(super::getNext(ptr)) != ptr)) { |
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66 | // We're done with this object. |
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67 | super::free (ptr); |
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68 | return; |
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69 | } |
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70 | assert (super::getPrev(super::getNext(ptr)) == ptr); |
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71 | // Try to coalesce with the previous object.. |
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72 | void * prev = super::getPrev(ptr); |
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73 | void * next = super::getNext (ptr); |
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74 | assert (prev != ptr); |
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75 | |
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76 | if (super::isPrevFree(ptr)) { |
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77 | assert (super::isFree(prev)); |
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78 | super::remove (prev); |
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79 | coalesce (prev, ptr); |
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80 | ptr = prev; |
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81 | } |
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82 | if (super::isFree(next)) { |
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83 | super::remove (next); |
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84 | coalesce (ptr, next); |
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85 | } |
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86 | |
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87 | super::markFree (ptr); |
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88 | |
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89 | // We're done with this object. |
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90 | super::free (ptr); |
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91 | } |
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92 | |
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93 | private: |
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94 | |
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95 | |
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96 | // Combine the first object with the second. |
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97 | inline static void coalesce (void * first, const void * second) { |
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98 | // A few sanity checks first. |
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99 | assert (super::getNext(first) == second); |
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100 | assert (super::getPrev(second) == first); |
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101 | // Now coalesce. |
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102 | size_t newSize = ((size_t) second - (size_t) first) + super::getSize(second); |
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103 | super::setSize (first, newSize); |
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104 | setPrevSize (super::getNext(first), newSize); |
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105 | } |
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106 | |
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107 | // Split an object if it is big enough. |
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108 | inline static void * split (void * obj, const size_t requestedSize) { |
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109 | assert (super::getSize(obj) >= requestedSize); |
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110 | // We split aggressively (for now; this could be a parameter). |
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111 | const size_t actualSize = super::getSize(obj); |
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112 | if (actualSize - requestedSize >= sizeof(typename super::Header) + sizeof(double)) { |
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113 | // Split the object. |
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114 | super::setSize(obj, requestedSize); |
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115 | void * splitPiece = (char *) obj + requestedSize + sizeof(typename super::Header); |
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116 | super::makeObject ((void *) super::getHeader(splitPiece), |
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117 | requestedSize, |
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118 | actualSize - requestedSize - sizeof(typename super::Header)); |
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119 | assert (!super::isFree(splitPiece)); |
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120 | // Now that we have a new successor (splitPiece), we need to |
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121 | // mark obj as in use. |
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122 | (super::getHeader(splitPiece))->markPrevInUse(); |
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123 | assert (super::getSize(splitPiece) >= sizeof(double)); |
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124 | assert (super::getSize(obj) >= requestedSize); |
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125 | return splitPiece; |
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126 | } else { |
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127 | return NULL; |
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128 | } |
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129 | } |
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130 | |
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131 | }; |
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132 | |
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133 | }; |
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134 | |
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135 | |
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136 | #endif |
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