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6885
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1 /*
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2 * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24 #ifndef SHARE_VM_MEMORY_METABLOCK_HPP
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25 #define SHARE_VM_MEMORY_METABLOCK_HPP
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26
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27 // Metablock are the unit of allocation from a Chunk. It is initialized
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28 // with the size of the requested allocation. That size is overwritten
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29 // once the allocation returns.
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30 //
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31 // A Metablock may be reused by its SpaceManager but are never moved between
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32 // SpaceManagers. There is no explicit link to the Metachunk
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33 // from which it was allocated. Metablock may be deallocated and
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34 // put on a freelist but the space is never freed, rather
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35 // the Metachunk it is a part of will be deallocated when it's
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36 // associated class loader is collected.
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37
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38 class Metablock VALUE_OBJ_CLASS_SPEC {
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39 friend class VMStructs;
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40 private:
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41 // Used to align the allocation (see below).
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42 union block_t {
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43 void* _data[3];
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44 struct header_t {
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45 size_t _word_size;
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46 Metablock* _next;
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47 Metablock* _prev;
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48 } _header;
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49 } _block;
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50 static size_t _min_block_byte_size;
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51 static size_t _overhead;
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52
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53 typedef union block_t Block;
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54 typedef struct header_t Header;
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55 const Block* block() const { return &_block; }
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56 const Block::header_t* header() const { return &(block()->_header); }
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57 public:
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58
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59 static Metablock* initialize(MetaWord* p, size_t word_size);
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60
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61 // This places the body of the block at a 2 word boundary
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62 // because every block starts on a 2 word boundary. Work out
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63 // how to make the body on a 2 word boundary if the block
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64 // starts on a arbitrary boundary. JJJ
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65
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66 size_t word_size() const { return header()->_word_size; }
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67 void set_word_size(size_t v) { _block._header._word_size = v; }
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68 size_t size() const volatile { return _block._header._word_size; }
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69 void set_size(size_t v) { _block._header._word_size = v; }
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70 Metablock* next() const { return header()->_next; }
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71 void set_next(Metablock* v) { _block._header._next = v; }
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72 Metablock* prev() const { return header()->_prev; }
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73 void set_prev(Metablock* v) { _block._header._prev = v; }
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74
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75 static size_t min_block_byte_size() { return _min_block_byte_size; }
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76 static size_t overhead() { return _overhead; }
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77
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78 bool is_free() { return header()->_word_size != 0; }
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79 void clear_next() { set_next(NULL); }
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80 void link_prev(Metablock* ptr) { set_prev(ptr); }
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81 uintptr_t* end() { return ((uintptr_t*) this) + size(); }
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82 bool cantCoalesce() const { return false; }
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83 void link_next(Metablock* ptr) { set_next(ptr); }
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84 void link_after(Metablock* ptr){
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85 link_next(ptr);
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86 if (ptr != NULL) ptr->link_prev(this);
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87 }
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88
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89 // Should not be needed in a free list of Metablocks
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90 void markNotFree() { ShouldNotReachHere(); }
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91
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92 // Debug support
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93 #ifdef ASSERT
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94 void* prev_addr() const { return (void*)&_block._header._prev; }
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95 void* next_addr() const { return (void*)&_block._header._next; }
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96 void* size_addr() const { return (void*)&_block._header._word_size; }
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97 #endif
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98 bool verify_chunk_in_free_list(Metablock* tc) const { return true; }
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99 bool verify_par_locked() { return true; }
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100
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101 void assert_is_mangled() const {/* Don't check "\*/}
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102 };
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103 #endif // SHARE_VM_MEMORY_METABLOCK_HPP
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