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