1 /*
2 * Copyright (c) 1998, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 // Recording and retrieval of oop relocations in compiled code.
26
27 class CodeBlob;
28
29 class 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 };