1 /* 2 * Copyright (c) 2001, 2015, 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 25 #ifndef SHARE_VM_GC_CMS_FREECHUNK_HPP 26 #define SHARE_VM_GC_CMS_FREECHUNK_HPP 27 28 #include "memory/memRegion.hpp" 29 #include "oops/markOop.hpp" 30 #include "runtime/mutex.hpp" 31 #include "runtime/orderAccess.hpp" 32 #include "utilities/debug.hpp" 33 #include "utilities/globalDefinitions.hpp" 34 #include "utilities/ostream.hpp" 35 36 // 37 // Free block maintenance for Concurrent Mark Sweep Generation 38 // 39 // The main data structure for free blocks are 40 // . an indexed array of small free blocks, and 41 // . a dictionary of large free blocks 42 // 43 44 // No virtuals in FreeChunk (don't want any vtables). 45 46 // A FreeChunk is merely a chunk that can be in a doubly linked list 47 // and has a size field. NOTE: FreeChunks are distinguished from allocated 48 // objects in two ways (by the sweeper), depending on whether the VM is 32 or 49 // 64 bits. 50 // In 32 bits or 64 bits without CompressedOops, the second word (prev) has the 51 // LSB set to indicate a free chunk; allocated objects' klass() pointers 52 // don't have their LSB set. The corresponding bit in the CMSBitMap is 53 // set when the chunk is allocated. There are also blocks that "look free" 54 // but are not part of the free list and should not be coalesced into larger 55 // free blocks. These free blocks have their two LSB's set. 56 57 class FreeChunk { 58 friend class VMStructs; 59 // For 64 bit compressed oops, the markOop encodes both the size and the 60 // indication that this is a FreeChunk and not an object. 61 volatile size_t _size; 62 FreeChunk* _prev; 63 FreeChunk* _next; 64 65 markOop mark() const volatile { return (markOop)_size; } 66 void set_mark(markOop m) { _size = (size_t)m; } 67 68 public: 69 NOT_PRODUCT(static const size_t header_size();) 70 71 // Returns "true" if the address indicates that the block represents 72 // a free chunk. 73 static bool indicatesFreeChunk(const HeapWord* addr) { 74 // Force volatile read from addr because value might change between 75 // calls. We really want the read of _mark and _prev from this pointer 76 // to be volatile but making the fields volatile causes all sorts of 77 // compilation errors. 78 return ((volatile FreeChunk*)addr)->is_free(); 79 } 80 81 bool is_free() const volatile { 82 LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else) 83 return (((intptr_t)_prev) & 0x1) == 0x1; 84 } 85 bool cantCoalesce() const { 86 assert(is_free(), "can't get coalesce bit on not free"); 87 return (((intptr_t)_prev) & 0x2) == 0x2; 88 } 89 void dontCoalesce() { 90 // the block should be free 91 assert(is_free(), "Should look like a free block"); 92 _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2); 93 } 94 FreeChunk* prev() const { 95 return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); 96 } 97 98 debug_only(void* prev_addr() const { return (void*)&_prev; }) 99 debug_only(void* next_addr() const { return (void*)&_next; }) 100 debug_only(void* size_addr() const { return (void*)&_size; }) 101 102 size_t size() const volatile { 103 LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else ) 104 return _size; 105 } 106 void set_size(size_t sz) { 107 LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else ) 108 _size = sz; 109 } 110 111 FreeChunk* next() const { return _next; } 112 113 void link_after(FreeChunk* ptr) { 114 link_next(ptr); 115 if (ptr != NULL) ptr->link_prev(this); 116 } 117 void link_next(FreeChunk* ptr) { _next = ptr; } 118 void link_prev(FreeChunk* ptr) { 119 LP64_ONLY(if (UseCompressedOops) _prev = ptr; else) 120 _prev = (FreeChunk*)((intptr_t)ptr | 0x1); 121 } 122 void clear_next() { _next = NULL; } 123 void markNotFree() { 124 // Set _prev (klass) to null before (if) clearing the mark word below 125 _prev = NULL; 126 #ifdef _LP64 127 if (UseCompressedOops) { 128 OrderAccess::storestore(); 129 set_mark(markOopDesc::prototype()); 130 } 131 #endif 132 assert(!is_free(), "Error"); 133 } 134 135 // Return the address past the end of this chunk 136 uintptr_t* end() const { return ((uintptr_t*) this) + size(); } 137 138 // debugging 139 void verify() const PRODUCT_RETURN; 140 void verifyList() const PRODUCT_RETURN; 141 void mangleAllocated(size_t size) PRODUCT_RETURN; 142 void mangleFreed(size_t size) PRODUCT_RETURN; 143 144 void print_on(outputStream* st); 145 }; 146 147 extern size_t MinChunkSize; 148 149 150 #endif // SHARE_VM_GC_CMS_FREECHUNK_HPP