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 // |
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26 // Free block maintenance for Concurrent Mark Sweep Generation |
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27 // |
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28 // The main data structure for free blocks are |
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29 // . an indexed array of small free blocks, and |
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30 // . a dictionary of large free blocks |
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31 // |
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32 |
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33 // No virtuals in FreeChunk (don't want any vtables). |
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34 |
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35 // A FreeChunk is merely a chunk that can be in a doubly linked list |
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36 // and has a size field. NOTE: FreeChunks are distinguished from allocated |
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37 // objects in two ways (by the sweeper). The second word (prev) has the |
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38 // LSB set to indicate a free chunk; allocated objects' klass() pointers |
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39 // don't have their LSB set. The corresponding bit in the CMSBitMap is |
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40 // set when the chunk is allocated. There are also blocks that "look free" |
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41 // but are not part of the free list and should not be coalesced into larger |
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42 // free blocks. These free blocks have their two LSB's set. |
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43 |
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44 class FreeChunk VALUE_OBJ_CLASS_SPEC { |
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45 friend class VMStructs; |
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46 FreeChunk* _next; |
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47 FreeChunk* _prev; |
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48 size_t _size; |
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49 |
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50 public: |
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51 NOT_PRODUCT(static const size_t header_size();) |
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52 // Returns "true" if the "wrd", which is required to be the second word |
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53 // of a block, indicates that the block represents a free chunk. |
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54 static bool secondWordIndicatesFreeChunk(intptr_t wrd) { |
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55 return (wrd & 0x1) == 0x1; |
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56 } |
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57 bool isFree() const { |
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58 return secondWordIndicatesFreeChunk((intptr_t)_prev); |
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59 } |
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60 bool cantCoalesce() const { return (((intptr_t)_prev) & 0x3) == 0x3; } |
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61 FreeChunk* next() const { return _next; } |
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62 FreeChunk* prev() const { return (FreeChunk*)(((intptr_t)_prev) & ~(0x3)); } |
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63 debug_only(void* prev_addr() const { return (void*)&_prev; }) |
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64 |
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65 void linkAfter(FreeChunk* ptr) { |
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66 linkNext(ptr); |
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67 if (ptr != NULL) ptr->linkPrev(this); |
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68 } |
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69 void linkAfterNonNull(FreeChunk* ptr) { |
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70 assert(ptr != NULL, "precondition violation"); |
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71 linkNext(ptr); |
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72 ptr->linkPrev(this); |
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73 } |
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74 void linkNext(FreeChunk* ptr) { _next = ptr; } |
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75 void linkPrev(FreeChunk* ptr) { _prev = (FreeChunk*)((intptr_t)ptr | 0x1); } |
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76 void clearPrev() { _prev = NULL; } |
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77 void clearNext() { _next = NULL; } |
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78 void dontCoalesce() { |
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79 // the block should be free |
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80 assert(isFree(), "Should look like a free block"); |
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81 _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2); |
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82 } |
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83 void markFree() { _prev = (FreeChunk*)((intptr_t)_prev | 0x1); } |
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84 void markNotFree() { _prev = NULL; } |
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85 |
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86 size_t size() const { return _size; } |
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87 void setSize(size_t size) { _size = size; } |
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88 |
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89 // For volatile reads: |
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90 size_t* size_addr() { return &_size; } |
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91 |
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92 // Return the address past the end of this chunk |
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93 HeapWord* end() const { return ((HeapWord*) this) + _size; } |
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94 |
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95 // debugging |
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96 void verify() const PRODUCT_RETURN; |
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97 void verifyList() const PRODUCT_RETURN; |
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98 void mangleAllocated(size_t size) PRODUCT_RETURN; |
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99 void mangleFreed(size_t size) PRODUCT_RETURN; |
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100 }; |
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101 |
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102 // Alignment helpers etc. |
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103 #define numQuanta(x,y) ((x+y-1)/y) |
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104 enum AlignmentConstants { |
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105 MinChunkSize = numQuanta(sizeof(FreeChunk), MinObjAlignmentInBytes) * MinObjAlignment |
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106 }; |
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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: |