1 /*
2 * Copyright (c) 2001, 2010, 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.
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23 */
24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP
27
28 #include "memory/allocation.hpp"
29 #include "memory/memRegion.hpp"
30 #include "oops/markOop.hpp"
31 #include "runtime/mutex.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 VALUE_OBJ_CLASS_SPEC {
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)->isFree();
79 }
80
81 bool isFree() 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(isFree(), "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(isFree(), "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 setSize(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 linkAfter(FreeChunk* ptr) {
114 linkNext(ptr);
115 if (ptr != NULL) ptr->linkPrev(this);
116 }
117 void linkAfterNonNull(FreeChunk* ptr) {
118 assert(ptr != NULL, "precondition violation");
119 linkNext(ptr);
120 ptr->linkPrev(this);
121 }
122 void linkNext(FreeChunk* ptr) { _next = ptr; }
123 void linkPrev(FreeChunk* ptr) {
124 LP64_ONLY(if (UseCompressedOops) _prev = ptr; else)
125 _prev = (FreeChunk*)((intptr_t)ptr | 0x1);
126 }
127 void clearPrev() { _prev = NULL; }
128 void clearNext() { _next = NULL; }
129 void markNotFree() {
130 // Set _prev (klass) to null before (if) clearing the mark word below
131 _prev = NULL;
132 #ifdef _LP64
133 if (UseCompressedOops) {
134 OrderAccess::storestore();
135 set_mark(markOopDesc::prototype());
136 }
137 #endif
138 assert(!isFree(), "Error");
139 }
140
141 // Return the address past the end of this chunk
142 HeapWord* end() const { return ((HeapWord*) this) + size(); }
143
144 // debugging
145 void verify() const PRODUCT_RETURN;
146 void verifyList() const PRODUCT_RETURN;
147 void mangleAllocated(size_t size) PRODUCT_RETURN;
148 void mangleFreed(size_t size) PRODUCT_RETURN;
149
150 void print_on(outputStream* st);
151 };
152
153 extern size_t MinChunkSize;
154
155
156 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP