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comparison src/share/vm/gc_implementation/concurrentMarkSweep/freeBlockDictionary.hpp @ 187:790e66e5fbac

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6687581: Make CMS work with compressed oops Summary: Make FreeChunk read markword instead of LSB in _klass pointer to indicate that it's a FreeChunk for compressed oops. Reviewed-by: ysr, jmasa
author coleenp
date Mon, 09 Jun 2008 11:51:19 -0400
parents a61af66fc99e
children d1605aabd0a1 12eea04c8b06
comparison
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185:8759d37f2524 187:790e66e5fbac
20 * CA 95054 USA or visit www.sun.com if you need additional information or 20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions. 21 * have any questions.
22 * 22 *
23 */ 23 */
24 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 25
108 // A FreeBlockDictionary is an abstract superclass that will allow 26 // A FreeBlockDictionary is an abstract superclass that will allow
109 // a number of alternative implementations in the future. 27 // a number of alternative implementations in the future.
110 class FreeBlockDictionary: public CHeapObj { 28 class FreeBlockDictionary: public CHeapObj {
111 public: 29 public: