oopRecorder.hpp revision 1483:1a5913bf5e19 
1/*
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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
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23 */
24
25// Recording and retrieval of oop relocations in compiled code.
26
27class CodeBlob;
28
29class OopRecorder : public ResourceObj {
30 public:
31  // A two-way mapping from positive indexes to oop handles.
32  // The zero index is reserved for a constant (sharable) null.
33  // Indexes may not be negative.
34
35  // Use the given arena to manage storage, if not NULL.
36  // By default, uses the current ResourceArea.
37  OopRecorder(Arena* arena = NULL);
38
39  // Generate a new index on which CodeBlob::oop_addr_at will work.
40  // allocate_index and find_index never return the same index,
41  // and allocate_index never returns the same index twice.
42  // In fact, two successive calls to allocate_index return successive ints.
43  int allocate_index(jobject h) {
44    return add_handle(h, false);
45  }
46
47  // For a given jobject, this will return the same index repeatedly.
48  // The index can later be given to oop_at to retrieve the oop.
49  // However, the oop must not be changed via CodeBlob::oop_addr_at.
50  int find_index(jobject h) {
51    int index = maybe_find_index(h);
52    if (index < 0) {  // previously unallocated
53      index = add_handle(h, true);
54    }
55    return index;
56  }
57
58  // variant of find_index which does not allocate if not found (yields -1)
59  int maybe_find_index(jobject h);
60
61  // returns the size of the generated oop table, for sizing the CodeBlob.
62  // must be called after all oops are allocated!
63  int oop_size();
64
65  // Retrieve the oop handle at a given index.
66  jobject handle_at(int index);
67
68  int element_count() {
69    // there is always a NULL virtually present as first object
70    return _handles->length() + first_index;
71  }
72
73  // copy the generated oop table to nmethod
74  void copy_to(nmethod* nm);  // => nm->copy_oops(_handles)
75
76  bool is_unused() { return _handles == NULL && !_complete; }
77#ifdef ASSERT
78  bool is_complete() { return _complete; }
79#endif
80
81 private:
82  // leaky hash table of handle => index, to help detect duplicate insertion
83  class IndexCache: public ResourceObj {
84    // This class is only used by the OopRecorder class.
85    friend class OopRecorder;
86    enum {
87      _log_cache_size = 9,
88      _cache_size = (1<<_log_cache_size),
89      // Index entries are ints.  The LSBit is a collision indicator.
90      _collision_bit_shift = 0,
91      _collision_bit = 1,
92      _index_shift = _collision_bit_shift+1
93    };
94    int _cache[_cache_size];
95    static juint cache_index(jobject handle) {
96      juint ci = (int) (intptr_t) handle;
97      ci ^= ci >> (BitsPerByte*2);
98      ci += ci >> (BitsPerByte*1);
99      return ci & (_cache_size-1);
100    }
101    int* cache_location(jobject handle) {
102      return &_cache[ cache_index(handle) ];
103    }
104    static bool cache_location_collision(int* cloc) {
105      return ((*cloc) & _collision_bit) != 0;
106    }
107    static int cache_location_index(int* cloc) {
108      return (*cloc) >> _index_shift;
109    }
110    static void set_cache_location_index(int* cloc, int index) {
111      int cval0 = (*cloc);
112      int cval1 = (index << _index_shift);
113      if (cval0 != 0 && cval1 != cval0)  cval1 += _collision_bit;
114      (*cloc) = cval1;
115    }
116    IndexCache();
117  };
118
119  // Helper function; returns false for NULL or Universe::non_oop_word().
120  inline bool is_real_jobject(jobject h);
121
122  void maybe_initialize();
123  int add_handle(jobject h, bool make_findable);
124
125  enum { null_index = 0, first_index = 1, index_cache_threshold = 20 };
126
127  GrowableArray<jobject>*   _handles;  // ordered list (first is always NULL)
128  GrowableArray<int>*       _no_finds; // all unfindable indexes; usually empty
129  IndexCache*               _indexes;  // map: jobject -> its probable index
130  Arena*                    _arena;
131  bool                      _complete;
132
133#ifdef ASSERT
134  static int _find_index_calls, _hit_indexes, _missed_indexes;
135#endif
136};
137