Mercurial > hg > graal-compiler
annotate src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp @ 1716:be3f9c242c9d
6948538: CMS: BOT walkers can fall into object allocation and initialization cracks
Summary: GC workers now recognize an intermediate transient state of blocks which are allocated but have not yet completed initialization. blk_start() calls do not attempt to determine the size of a block in the transient state, rather waiting for the block to become initialized so that it is safe to query its size. Audited and ensured the order of initialization of object fields (klass, free bit and size) to respect block state transition protocol. Also included some new assertion checking code enabled in debug mode.
Reviewed-by: chrisphi, johnc, poonam
| author | ysr |
|---|---|
| date | Mon, 16 Aug 2010 15:58:42 -0700 |
| parents | e9ff18c4ace7 |
| children | f95d63e2154a |
| rev | line source |
|---|---|
| 187 | 1 /* |
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2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved. |
| 187 | 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 * | |
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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. |
| 187 | 22 * |
| 23 */ | |
| 24 | |
| 25 // | |
| 26 // Free block maintenance for Concurrent Mark Sweep Generation | |
| 27 // | |
| 28 // The main data structure for free blocks are | |
| 29 // . an indexed array of small free blocks, and | |
| 30 // . a dictionary of large free blocks | |
| 31 // | |
| 32 | |
| 33 // No virtuals in FreeChunk (don't want any vtables). | |
| 34 | |
| 35 // A FreeChunk is merely a chunk that can be in a doubly linked list | |
| 36 // and has a size field. NOTE: FreeChunks are distinguished from allocated | |
| 37 // objects in two ways (by the sweeper), depending on whether the VM is 32 or | |
| 38 // 64 bits. | |
| 39 // In 32 bits or 64 bits without CompressedOops, the second word (prev) has the | |
| 40 // LSB set to indicate a free chunk; allocated objects' klass() pointers | |
| 41 // don't have their LSB set. The corresponding bit in the CMSBitMap is | |
| 42 // set when the chunk is allocated. There are also blocks that "look free" | |
| 43 // but are not part of the free list and should not be coalesced into larger | |
| 44 // free blocks. These free blocks have their two LSB's set. | |
| 45 | |
| 46 class FreeChunk VALUE_OBJ_CLASS_SPEC { | |
| 47 friend class VMStructs; | |
| 48 // For 64 bit compressed oops, the markOop encodes both the size and the | |
| 49 // indication that this is a FreeChunk and not an object. | |
| 50 volatile size_t _size; | |
| 51 FreeChunk* _prev; | |
| 52 FreeChunk* _next; | |
| 53 | |
| 54 markOop mark() const volatile { return (markOop)_size; } | |
| 55 void set_mark(markOop m) { _size = (size_t)m; } | |
| 56 | |
| 57 public: | |
| 58 NOT_PRODUCT(static const size_t header_size();) | |
| 59 | |
| 60 // Returns "true" if the address indicates that the block represents | |
| 61 // a free chunk. | |
| 62 static bool indicatesFreeChunk(const HeapWord* addr) { | |
| 63 // Force volatile read from addr because value might change between | |
| 64 // calls. We really want the read of _mark and _prev from this pointer | |
| 65 // to be volatile but making the fields volatile causes all sorts of | |
| 66 // compilation errors. | |
| 67 return ((volatile FreeChunk*)addr)->isFree(); | |
| 68 } | |
| 69 | |
| 70 bool isFree() const volatile { | |
| 71 LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else) | |
| 72 return (((intptr_t)_prev) & 0x1) == 0x1; | |
| 73 } | |
| 74 bool cantCoalesce() const { | |
| 75 assert(isFree(), "can't get coalesce bit on not free"); | |
| 76 return (((intptr_t)_prev) & 0x2) == 0x2; | |
| 77 } | |
| 78 void dontCoalesce() { | |
| 79 // the block should be free | |
| 80 assert(isFree(), "Should look like a free block"); | |
| 81 _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2); | |
| 82 } | |
| 83 FreeChunk* prev() const { | |
| 84 return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); | |
| 85 } | |
| 86 | |
| 87 debug_only(void* prev_addr() const { return (void*)&_prev; }) | |
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88 debug_only(void* next_addr() const { return (void*)&_next; }) |
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89 debug_only(void* size_addr() const { return (void*)&_size; }) |
| 187 | 90 |
| 91 size_t size() const volatile { | |
| 92 LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else ) | |
| 93 return _size; | |
| 94 } | |
| 95 void setSize(size_t sz) { | |
| 96 LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else ) | |
| 97 _size = sz; | |
| 98 } | |
| 99 | |
| 100 FreeChunk* next() const { return _next; } | |
| 101 | |
| 102 void linkAfter(FreeChunk* ptr) { | |
| 103 linkNext(ptr); | |
| 104 if (ptr != NULL) ptr->linkPrev(this); | |
| 105 } | |
| 106 void linkAfterNonNull(FreeChunk* ptr) { | |
| 107 assert(ptr != NULL, "precondition violation"); | |
| 108 linkNext(ptr); | |
| 109 ptr->linkPrev(this); | |
| 110 } | |
| 111 void linkNext(FreeChunk* ptr) { _next = ptr; } | |
| 112 void linkPrev(FreeChunk* ptr) { | |
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113 LP64_ONLY(if (UseCompressedOops) _prev = ptr; else) |
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114 _prev = (FreeChunk*)((intptr_t)ptr | 0x1); |
| 187 | 115 } |
| 116 void clearPrev() { _prev = NULL; } | |
| 117 void clearNext() { _next = NULL; } | |
| 118 void markNotFree() { | |
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119 // Set _prev (klass) to null before (if) clearing the mark word below |
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120 _prev = NULL; |
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121 #ifdef _LP64 |
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122 if (UseCompressedOops) { |
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123 OrderAccess::storestore(); |
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124 set_mark(markOopDesc::prototype()); |
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125 } |
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126 #endif |
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127 assert(!isFree(), "Error"); |
| 187 | 128 } |
| 129 | |
| 130 // Return the address past the end of this chunk | |
| 131 HeapWord* end() const { return ((HeapWord*) this) + size(); } | |
| 132 | |
| 133 // debugging | |
| 134 void verify() const PRODUCT_RETURN; | |
| 135 void verifyList() const PRODUCT_RETURN; | |
| 136 void mangleAllocated(size_t size) PRODUCT_RETURN; | |
| 137 void mangleFreed(size_t size) PRODUCT_RETURN; | |
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138 |
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139 void print_on(outputStream* st); |
| 187 | 140 }; |
| 141 | |
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142 extern size_t MinChunkSize; |
| 187 | 143 |