1 /*
2 * Copyright (c) 1997, 2016, 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.
8 *
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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).
14 *
15 * You should have received a copy of the GNU General Public License version
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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 // Klass* // 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 friend class arrayOopDescTest;
45
46 // Interpreter/Compiler offsets
47
48 // Header size computation.
49 // The header is considered the oop part of this type plus the length.
50 // Returns the aligned header_size_in_bytes. This is not equivalent to
51 // sizeof(arrayOopDesc) which should not appear in the code.
52 static int header_size_in_bytes() {
53 size_t hs = align_up(length_offset_in_bytes() + sizeof(int),
54 HeapWordSize);
55 #ifdef ASSERT
56 // make sure it isn't called before UseCompressedOops is initialized.
57 static size_t arrayoopdesc_hs = 0;
58 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
59 assert(arrayoopdesc_hs == hs, "header size can't change");
60 #endif // ASSERT
61 return (int)hs;
62 }
63
64 public:
65 // The _length field is not declared in C++. It is allocated after the
66 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
67 // it occupies the second half of the _klass field in oopDesc.
68 static int length_offset_in_bytes() {
69 return UseCompressedClassPointers ? klass_gap_offset_in_bytes() :
70 sizeof(arrayOopDesc);
71 }
72
73 // Returns the offset of the first element.
74 static int base_offset_in_bytes(BasicType type) {
75 return header_size(type) * HeapWordSize;
76 }
77
78 // Returns the address of the first element.
79 void* base(BasicType type) const {
80 return (void*) (((intptr_t) this) + base_offset_in_bytes(type));
81 }
82
83 // Tells whether index is within bounds.
84 bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
85
86 // Accessors for instance variable which is not a C++ declared nonstatic
87 // field.
88 int length() const {
89 return *(int*)(((intptr_t)this) + length_offset_in_bytes());
90 }
91 void set_length(int length) {
92 *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length;
93 }
94
95 // Should only be called with constants as argument
96 // (will not constant fold otherwise)
97 // Returns the header size in words aligned to the requirements of the
98 // array object type.
99 static int header_size(BasicType type) {
100 size_t typesize_in_bytes = header_size_in_bytes();
101 return (int)(Universe::element_type_should_be_aligned(type)
102 ? align_object_offset(typesize_in_bytes/HeapWordSize)
103 : typesize_in_bytes/HeapWordSize);
104 }
105
106 // Return the maximum length of an array of BasicType. The length can passed
107 // to typeArrayOop::object_size(scale, length, header_size) without causing an
108 // overflow. We also need to make sure that this will not overflow a size_t on
109 // 32 bit platforms when we convert it to a byte size.
110 static int32_t max_array_length(BasicType type) {
111 assert(type >= 0 && type < T_CONFLICT, "wrong type");
112 assert(type2aelembytes(type) != 0, "wrong type");
113
114 const size_t max_element_words_per_size_t =
115 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
116 const size_t max_elements_per_size_t =
117 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
118 if ((size_t)max_jint < max_elements_per_size_t) {
119 // It should be ok to return max_jint here, but parts of the code
120 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
121 // passing around the size (in words) of an object. So, we need to avoid
122 // overflowing an int when we add the header. See CRs 4718400 and 7110613.
123 return align_down(max_jint - header_size(type), MinObjAlignment);
124 }
125 return (int32_t)max_elements_per_size_t;
126 }
127
128 };
129
130 #endif // SHARE_VM_OOPS_ARRAYOOP_HPP