1/*
2 * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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23 */
24
25#ifndef SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
26#define SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
27
28#include "oops/generateOopMap.hpp"
29#include "runtime/mutex.hpp"
30
31// A Cache for storing (method, bci) -> oopMap.
32// The memory management system uses the cache when locating object
33// references in an interpreted frame.
34//
35// OopMapCache's are allocated lazily per InstanceKlass.
36
37// The oopMap (InterpreterOopMap) is stored as a bit mask. If the
38// bit_mask can fit into two words it is stored in
39// the _bit_mask array, otherwise it is allocated on the heap.
40// For OopMapCacheEntry the bit_mask is allocated in the C heap
41// because these entries persist between garbage collections.
42// For InterpreterOopMap the bit_mask is allocated in
43// a resource area for better performance.  InterpreterOopMap
44// should only be created and deleted during same garbage collection.
45//
46// If ENABBLE_ZAP_DEAD_LOCALS is defined, two bits are used
47// per entry instead of one. In all cases,
48// the first bit is set to indicate oops as opposed to other
49// values. If the second bit is available,
50// it is set for dead values. We get the following encoding:
51//
52// 00 live value
53// 01 live oop
54// 10 dead value
55// 11 <unused>                                   (we cannot distinguish between dead oops or values with the current oop map generator)
56
57
58class OffsetClosure  {
59 public:
60  virtual void offset_do(int offset) = 0;
61};
62
63
64class InterpreterOopMap: ResourceObj {
65  friend class OopMapCache;
66
67 public:
68  enum {
69    N                = 4,                // the number of words reserved
70                                         // for inlined mask storage
71    small_mask_limit = N * BitsPerWord,  // the maximum number of bits
72                                         // available for small masks,
73                                         // small_mask_limit can be set to 0
74                                         // for testing bit_mask allocation
75
76    bits_per_entry   = 2,
77    dead_bit_number  = 1,
78    oop_bit_number   = 0
79  };
80
81 private:
82  Method*        _method;         // the method for which the mask is valid
83  unsigned short _bci;            // the bci    for which the mask is valid
84  int            _mask_size;      // the mask size in bits
85  int            _expression_stack_size; // the size of the expression stack in slots
86
87 protected:
88  intptr_t       _bit_mask[N];    // the bit mask if
89                                  // mask_size <= small_mask_limit,
90                                  // ptr to bit mask otherwise
91                                  // "protected" so that sub classes can
92                                  // access it without using trickery in
93                                  // methd bit_mask().
94#ifdef ASSERT
95  bool _resource_allocate_bit_mask;
96#endif
97
98  // access methods
99  Method*        method() const                  { return _method; }
100  void           set_method(Method* v)           { _method = v; }
101  int            bci() const                     { return _bci; }
102  void           set_bci(int v)                  { _bci = v; }
103  int            mask_size() const               { return _mask_size; }
104  void           set_mask_size(int v)            { _mask_size = v; }
105  // Test bit mask size and return either the in-line bit mask or allocated
106  // bit mask.
107  uintptr_t*  bit_mask() const                   { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
108
109  // return the word size of_bit_mask.  mask_size() <= 4 * MAX_USHORT
110  size_t mask_word_size() const {
111    return (mask_size() + BitsPerWord - 1) / BitsPerWord;
112  }
113
114  uintptr_t entry_at(int offset) const           { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
115
116  void set_expression_stack_size(int sz)         { _expression_stack_size = sz; }
117
118  // Lookup
119  bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }
120  bool is_empty() const;
121
122  // Initialization
123  void initialize();
124
125 public:
126  InterpreterOopMap();
127  ~InterpreterOopMap();
128
129  // Copy the OopMapCacheEntry in parameter "from" into this
130  // InterpreterOopMap.  If the _bit_mask[0] in "from" points to
131  // allocated space (i.e., the bit mask was to large to hold
132  // in-line), allocate the space from a Resource area.
133  void resource_copy(OopMapCacheEntry* from);
134
135  void iterate_oop(OffsetClosure* oop_closure) const;
136  void print() const;
137
138  int number_of_entries() const                  { return mask_size() / bits_per_entry; }
139  bool is_dead(int offset) const                 { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
140  bool is_oop (int offset) const                 { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
141
142  int expression_stack_size() const              { return _expression_stack_size; }
143
144};
145
146class OopMapCache : public CHeapObj<mtClass> {
147 private:
148  enum { _size        = 32,     // Use fixed size for now
149         _probe_depth = 3       // probe depth in case of collisions
150  };
151
152  OopMapCacheEntry* _array;
153
154  unsigned int hash_value_for(const methodHandle& method, int bci) const;
155  OopMapCacheEntry* entry_at(int i) const;
156
157  mutable Mutex _mut;
158
159  void flush();
160
161 public:
162  OopMapCache();
163  ~OopMapCache();                                // free up memory
164
165  // flush cache entry is occupied by an obsolete method
166  void flush_obsolete_entries();
167
168  // Returns the oopMap for (method, bci) in parameter "entry".
169  // Returns false if an oop map was not found.
170  void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry) const;
171
172  // Compute an oop map without updating the cache or grabbing any locks (for debugging)
173  static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);
174
175  // Returns total no. of bytes allocated as part of OopMapCache's
176  static long memory_usage()                     PRODUCT_RETURN0;
177};
178
179#endif // SHARE_VM_INTERPRETER_OOPMAPCACHE_HPP
180