1 /*
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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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24
25 #ifndef SHARE_OOPS_ARRAYOOP_HPP
26 #define SHARE_OOPS_ARRAYOOP_HPP
27
28 #include "memory/universe.hpp"
29 #include "oops/oop.hpp"
30 #include "utilities/align.hpp"
31
32 // arrayOopDesc is the abstract baseclass for all arrays. It doesn't
33 // declare pure virtual to enforce this because that would allocate a vtbl
34 // in each instance, which we don't want.
35
36 // The layout of array Oops is:
37 //
38 // markOop
39 // Klass* // 32 bits if compressed but declared 64 in LP64.
40 // length // shares klass memory or allocated after declared fields.
41
42
43 class arrayOopDesc : public oopDesc {
44 friend class VMStructs;
45 friend class arrayOopDescTest;
46
47 // Interpreter/Compiler offsets
48 protected:
49 // Header size computation.
50 // The header is considered the oop part of this type plus the length.
51 // Returns the aligned header_size_in_bytes. This is not equivalent to
52 // sizeof(arrayOopDesc) which should not appear in the code.
53 static int header_size_in_bytes() {
54 size_t hs = align_up(length_offset_in_bytes() + sizeof(int),
55 HeapWordSize);
56 #ifdef ASSERT
57 // make sure it isn't called before UseCompressedOops is initialized.
58 static size_t arrayoopdesc_hs = 0;
59 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
60 assert(arrayoopdesc_hs == hs, "header size can't change");
61 #endif // ASSERT
62 return (int)hs;
63 }
64
65 // Check whether an element of a typeArrayOop with the given type must be
66 // aligned 0 mod 8. The typeArrayOop itself must be aligned at least this
67 // strongly.
68 static bool element_type_should_be_aligned(BasicType type) {
69 return type == T_DOUBLE || type == T_LONG || type == T_VALUETYPE;
70 }
71
72 public:
73 // The _length field is not declared in C++. It is allocated after the
74 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
75 // it occupies the second half of the _klass field in oopDesc.
76 static int length_offset_in_bytes() {
77 return UseCompressedClassPointers ? klass_gap_offset_in_bytes() :
78 sizeof(arrayOopDesc);
79 }
80
81 // Returns the offset of the first element.
82 static int base_offset_in_bytes(BasicType type) {
83 return header_size(type) * HeapWordSize;
84 }
85
86 // Returns the address of the first element. The elements in the array will not
87 // relocate from this address until a subsequent thread transition.
88 inline void* base(BasicType type) const;
89 inline void* base_raw(BasicType type) const; // GC barrier invariant
90
91 template <typename T>
92 static T* obj_offset_to_raw(arrayOop obj, size_t offset_in_bytes, T* raw) {
93 if (obj != NULL) {
94 assert(raw == NULL, "either raw or in-heap");
95 char* base = reinterpret_cast<char*>((void*) obj);
96 raw = reinterpret_cast<T*>(base + offset_in_bytes);
97 } else {
98 assert(raw != NULL, "either raw or in-heap");
99 }
100 return raw;
101 }
102
103 // Tells whether index is within bounds.
104 bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
105
106 // Accessors for instance variable which is not a C++ declared nonstatic
107 // field.
108 int length() const {
109 return *(int*)(((intptr_t)this) + length_offset_in_bytes());
110 }
111 void set_length(int length) {
112 set_length((HeapWord*)this, length);
113 }
114 static void set_length(HeapWord* mem, int length) {
115 *(int*)(((char*)mem) + length_offset_in_bytes()) = length;
116 }
117
118 // Should only be called with constants as argument
119 // (will not constant fold otherwise)
120 // Returns the header size in words aligned to the requirements of the
121 // array object type.
122 static int header_size(BasicType type) {
123 size_t typesize_in_bytes = header_size_in_bytes();
124 return (int)(element_type_should_be_aligned(type)
125 ? align_object_offset(typesize_in_bytes/HeapWordSize)
126 : typesize_in_bytes/HeapWordSize);
127 }
128
129 static int32_t max_array_length(int header_size, int elembytes) {
130 const size_t max_element_words_per_size_t =
131 align_down((SIZE_MAX/HeapWordSize - header_size), MinObjAlignment);
132 const size_t max_elements_per_size_t =
133 HeapWordSize * max_element_words_per_size_t / elembytes;
134 if ((size_t)max_jint < max_elements_per_size_t) {
135 // It should be ok to return max_jint here, but parts of the code
136 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
137 // passing around the size (in words) of an object. So, we need to avoid
138 // overflowing an int when we add the header. See CRs 4718400 and 7110613.
139 return align_down(max_jint - header_size, MinObjAlignment);
140 }
141 return (int32_t)max_elements_per_size_t;
142 }
143
144 // Return the maximum length of an array of BasicType. The length can passed
145 // to typeArrayOop::object_size(scale, length, header_size) without causing an
146 // overflow. We also need to make sure that this will not overflow a size_t on
147 // 32 bit platforms when we convert it to a byte size.
148 static int32_t max_array_length(BasicType type) {
149 assert(type >= 0 && type < T_CONFLICT, "wrong type");
150 assert(type2aelembytes(type) != 0, "wrong type");
151
152 const size_t max_element_words_per_size_t =
153 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
154 const size_t max_elements_per_size_t =
155 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
156 if ((size_t)max_jint < max_elements_per_size_t) {
157 // It should be ok to return max_jint here, but parts of the code
158 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
159 // passing around the size (in words) of an object. So, we need to avoid
160 // overflowing an int when we add the header. See CRs 4718400 and 7110613.
161 return align_down(max_jint - header_size(type), MinObjAlignment);
162 }
163 return (int32_t)max_elements_per_size_t;
164 }
165
166 };
167
168 #endif // SHARE_OOPS_ARRAYOOP_HPP