1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25#ifndef SHARE_INTERPRETER_OOPMAPCACHE_HPP
26#define SHARE_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
63class OopMapCacheEntry;
64
65class InterpreterOopMap: ResourceObj {
66 friend class OopMapCache;
67
68 public:
69 enum {
70 N = 4, // the number of words reserved
71 // for inlined mask storage
72 small_mask_limit = N * BitsPerWord, // the maximum number of bits
73 // available for small masks,
74 // small_mask_limit can be set to 0
75 // for testing bit_mask allocation
76
77 bits_per_entry = 2,
78 dead_bit_number = 1,
79 oop_bit_number = 0
80 };
81
82 private:
83 Method* _method; // the method for which the mask is valid
84 unsigned short _bci; // the bci for which the mask is valid
85 int _mask_size; // the mask size in bits
86 int _expression_stack_size; // the size of the expression stack in slots
87
88 protected:
89 intptr_t _bit_mask[N]; // the bit mask if
90 // mask_size <= small_mask_limit,
91 // ptr to bit mask otherwise
92 // "protected" so that sub classes can
93 // access it without using trickery in
94 // methd bit_mask().
95#ifdef ASSERT
96 bool _resource_allocate_bit_mask;
97#endif
98
99 // access methods
100 Method* method() const { return _method; }
101 void set_method(Method* v) { _method = v; }
102 int bci() const { return _bci; }
103 void set_bci(int v) { _bci = v; }
104 int mask_size() const { return _mask_size; }
105 void set_mask_size(int v) { _mask_size = v; }
106 // Test bit mask size and return either the in-line bit mask or allocated
107 // bit mask.
108 uintptr_t* bit_mask() const { return (uintptr_t*)(mask_size() <= small_mask_limit ? (intptr_t)_bit_mask : _bit_mask[0]); }
109
110 // return the word size of_bit_mask. mask_size() <= 4 * MAX_USHORT
111 size_t mask_word_size() const {
112 return (mask_size() + BitsPerWord - 1) / BitsPerWord;
113 }
114
115 uintptr_t entry_at(int offset) const { int i = offset * bits_per_entry; return bit_mask()[i / BitsPerWord] >> (i % BitsPerWord); }
116
117 void set_expression_stack_size(int sz) { _expression_stack_size = sz; }
118
119 // Lookup
120 bool match(const methodHandle& method, int bci) const { return _method == method() && _bci == bci; }
121 bool is_empty() const;
122
123 // Initialization
124 void initialize();
125
126 public:
127 InterpreterOopMap();
128 ~InterpreterOopMap();
129
130 // Copy the OopMapCacheEntry in parameter "from" into this
131 // InterpreterOopMap. If the _bit_mask[0] in "from" points to
132 // allocated space (i.e., the bit mask was to large to hold
133 // in-line), allocate the space from a Resource area.
134 void resource_copy(OopMapCacheEntry* from);
135
136 void iterate_oop(OffsetClosure* oop_closure) const;
137 void print() const;
138
139 int number_of_entries() const { return mask_size() / bits_per_entry; }
140 bool is_dead(int offset) const { return (entry_at(offset) & (1 << dead_bit_number)) != 0; }
141 bool is_oop (int offset) const { return (entry_at(offset) & (1 << oop_bit_number )) != 0; }
142
143 int expression_stack_size() const { return _expression_stack_size; }
144
145};
146
147class OopMapCache : public CHeapObj<mtClass> {
148 static OopMapCacheEntry* volatile _old_entries;
149 private:
150 enum { _size = 32, // Use fixed size for now
151 _probe_depth = 3 // probe depth in case of collisions
152 };
153
154 OopMapCacheEntry* volatile * _array;
155
156 unsigned int hash_value_for(const methodHandle& method, int bci) const;
157 OopMapCacheEntry* entry_at(int i) const;
158 bool put_at(int i, OopMapCacheEntry* entry, OopMapCacheEntry* old);
159
160 static void enqueue_for_cleanup(OopMapCacheEntry* entry);
161
162 void flush();
163
164 public:
165 OopMapCache();
166 ~OopMapCache(); // free up memory
167
168 // flush cache entry is occupied by an obsolete method
169 void flush_obsolete_entries();
170
171 // Returns the oopMap for (method, bci) in parameter "entry".
172 // Returns false if an oop map was not found.
173 void lookup(const methodHandle& method, int bci, InterpreterOopMap* entry);
174
175 // Compute an oop map without updating the cache or grabbing any locks (for debugging)
176 static void compute_one_oop_map(const methodHandle& method, int bci, InterpreterOopMap* entry);
177 static void cleanup_old_entries();
178};
179
180#endif // SHARE_INTERPRETER_OOPMAPCACHE_HPP
181