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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
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). The second word (prev) has the
38 // LSB set to indicate a free chunk; allocated objects' klass() pointers
39 // don't have their LSB set. The corresponding bit in the CMSBitMap is
40 // set when the chunk is allocated. There are also blocks that "look free"
41 // but are not part of the free list and should not be coalesced into larger
42 // free blocks. These free blocks have their two LSB's set.
43
44 class FreeChunk VALUE_OBJ_CLASS_SPEC {
45 friend class VMStructs;
46 FreeChunk* _next;
47 FreeChunk* _prev;
48 size_t _size;
49
50 public:
51 NOT_PRODUCT(static const size_t header_size();)
52 // Returns "true" if the "wrd", which is required to be the second word
53 // of a block, indicates that the block represents a free chunk.
54 static bool secondWordIndicatesFreeChunk(intptr_t wrd) {
55 return (wrd & 0x1) == 0x1;
56 }
57 bool isFree() const {
58 return secondWordIndicatesFreeChunk((intptr_t)_prev);
59 }
60 bool cantCoalesce() const { return (((intptr_t)_prev) & 0x3) == 0x3; }
61 FreeChunk* next() const { return _next; }
62 FreeChunk* prev() const { return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); }
63 debug_only(void* prev_addr() const { return (void*)&_prev; })
64
65 void linkAfter(FreeChunk* ptr) {
66 linkNext(ptr);
67 if (ptr != NULL) ptr->linkPrev(this);
68 }
69 void linkAfterNonNull(FreeChunk* ptr) {
70 assert(ptr != NULL, "precondition violation");
71 linkNext(ptr);
72 ptr->linkPrev(this);
73 }
74 void linkNext(FreeChunk* ptr) { _next = ptr; }
75 void linkPrev(FreeChunk* ptr) { _prev = (FreeChunk*)((intptr_t)ptr | 0x1); }
76 void clearPrev() { _prev = NULL; }
77 void clearNext() { _next = NULL; }
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 void markFree() { _prev = (FreeChunk*)((intptr_t)_prev | 0x1); }
84 void markNotFree() { _prev = NULL; }
85
86 size_t size() const { return _size; }
87 void setSize(size_t size) { _size = size; }
88
89 // For volatile reads:
90 size_t* size_addr() { return &_size; }
91
92 // Return the address past the end of this chunk
93 HeapWord* end() const { return ((HeapWord*) this) + _size; }
94
95 // debugging
96 void verify() const PRODUCT_RETURN;
97 void verifyList() const PRODUCT_RETURN;
98 void mangleAllocated(size_t size) PRODUCT_RETURN;
99 void mangleFreed(size_t size) PRODUCT_RETURN;
100 };
101
102 // Alignment helpers etc.
103 #define numQuanta(x,y) ((x+y-1)/y)
104 enum AlignmentConstants {
105 MinChunkSize = numQuanta(sizeof(FreeChunk), MinObjAlignmentInBytes) * MinObjAlignment
106 };
107
108 // A FreeBlockDictionary is an abstract superclass that will allow
109 // a number of alternative implementations in the future.
110 class FreeBlockDictionary: public CHeapObj {
111 public:
112 enum Dither {
113 atLeast,
114 exactly,
115 roughly
116 };
117 enum DictionaryChoice {
118 dictionaryBinaryTree = 0,
119 dictionarySplayTree = 1,
120 dictionarySkipList = 2
121 };
122
123 private:
124 NOT_PRODUCT(Mutex* _lock;)
125
126 public:
127 virtual void removeChunk(FreeChunk* fc) = 0;
|
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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
24
25
26 // A FreeBlockDictionary is an abstract superclass that will allow
27 // a number of alternative implementations in the future.
28 class FreeBlockDictionary: public CHeapObj {
29 public:
30 enum Dither {
31 atLeast,
32 exactly,
33 roughly
34 };
35 enum DictionaryChoice {
36 dictionaryBinaryTree = 0,
37 dictionarySplayTree = 1,
38 dictionarySkipList = 2
39 };
40
41 private:
42 NOT_PRODUCT(Mutex* _lock;)
43
44 public:
45 virtual void removeChunk(FreeChunk* fc) = 0;
|