1 /*
2 * Copyright (c) 1997, 2011, 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.
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23 */
24
25 #ifndef SHARE_VM_OOPS_ARRAYOOP_HPP
26 #define SHARE_VM_OOPS_ARRAYOOP_HPP
27
28 #include "memory/universe.inline.hpp"
29 #include "oops/oop.hpp"
30
31 // arrayOopDesc is the abstract baseclass for all arrays. It doesn't
32 // declare pure virtual to enforce this because that would allocate a vtbl
33 // in each instance, which we don't want.
34
35 // The layout of array Oops is:
36 //
37 // markOop
38 // klassOop // 32 bits if compressed but declared 64 in LP64.
39 // length // shares klass memory or allocated after declared fields.
40
41
42 class arrayOopDesc : public oopDesc {
43 friend class VMStructs;
44
45 // Interpreter/Compiler offsets
46
47 // Header size computation.
48 // The header is considered the oop part of this type plus the length.
49 // Returns the aligned header_size_in_bytes. This is not equivalent to
50 // sizeof(arrayOopDesc) which should not appear in the code.
51 static int header_size_in_bytes() {
52 size_t hs = align_size_up(length_offset_in_bytes() + sizeof(int),
53 HeapWordSize);
54 #ifdef ASSERT
55 // make sure it isn't called before UseCompressedOops is initialized.
56 static size_t arrayoopdesc_hs = 0;
57 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
58 assert(arrayoopdesc_hs == hs, "header size can't change");
59 #endif // ASSERT
60 return (int)hs;
61 }
62
63 public:
64 // The _length field is not declared in C++. It is allocated after the
65 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
66 // it occupies the second half of the _klass field in oopDesc.
67 static int length_offset_in_bytes() {
68 return UseCompressedOops ? klass_gap_offset_in_bytes() :
69 sizeof(arrayOopDesc);
70 }
71
72 // Returns the offset of the first element.
73 static int base_offset_in_bytes(BasicType type) {
74 return header_size(type) * HeapWordSize;
75 }
76
77 // Returns the address of the first element.
78 void* base(BasicType type) const {
79 return (void*) (((intptr_t) this) + base_offset_in_bytes(type));
80 }
81
82 // Tells whether index is within bounds.
83 bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
84
85 // Accessors for instance variable which is not a C++ declared nonstatic
86 // field.
87 int length() const {
88 return *(int*)(((intptr_t)this) + length_offset_in_bytes());
89 }
90 void set_length(int length) {
91 *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length;
92 }
93
94 // Should only be called with constants as argument
95 // (will not constant fold otherwise)
96 // Returns the header size in words aligned to the requirements of the
97 // array object type.
98 static int header_size(BasicType type) {
99 size_t typesize_in_bytes = header_size_in_bytes();
100 return (int)(Universe::element_type_should_be_aligned(type)
101 ? align_object_offset(typesize_in_bytes/HeapWordSize)
102 : typesize_in_bytes/HeapWordSize);
103 }
104
105 // Return the maximum length of an array of BasicType. The length can passed
106 // to typeArrayOop::object_size(scale, length, header_size) without causing an
107 // overflow.
108 static int32_t max_array_length(BasicType type) {
109 assert(type >= 0 && type < T_CONFLICT, "wrong type");
110 assert(type2aelembytes(type) != 0, "wrong type");
111 const int bytes_per_element = type2aelembytes(type);
112 if (bytes_per_element < HeapWordSize) {
113 return max_jint;
114 }
115
116 const size_t max_words_per_size_t = SIZE_MAX / HeapWordSize;
117 const int32_t max_words = (int32_t)MIN2((size_t)max_jint, max_words_per_size_t);
118 const int32_t max_element_words = align_size_down(max_words - header_size(type), MinObjAlignment);
119 const int32_t words_per_element = bytes_per_element >> LogHeapWordSize;
120 return max_element_words / words_per_element;
121 }
122
123 // for unit testing
124 #ifndef PRODUCT
125 static bool check_overflow(BasicType type);
126 static int32_t old_max_array_length(BasicType type);
127 static bool test_max_array_length();
128 #endif
129 };
130
131 #endif // SHARE_VM_OOPS_ARRAYOOP_HPP