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24
25#ifndef SHARE_OOPS_ARRAYOOP_HPP
26#define SHARE_OOPS_ARRAYOOP_HPP
27
28#include "oops/oop.hpp"
29#include "utilities/align.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
42class 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 // Check whether an element of a typeArrayOop with the given type must be
65 // aligned 0 mod 8. The typeArrayOop itself must be aligned at least this
66 // strongly.
67 static bool element_type_should_be_aligned(BasicType type) {
68 return type == T_DOUBLE || type == T_LONG;
69 }
70
71 public:
72 // The _length field is not declared in C++. It is allocated after the
73 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
74 // it occupies the second half of the _klass field in oopDesc.
75 static int length_offset_in_bytes() {
76 return UseCompressedClassPointers ? klass_gap_offset_in_bytes() :
77 sizeof(arrayOopDesc);
78 }
79
80 // Returns the offset of the first element.
81 static int base_offset_in_bytes(BasicType type) {
82 return header_size(type) * HeapWordSize;
83 }
84
85 // Returns the address of the first element. The elements in the array will not
86 // relocate from this address until a subsequent thread transition.
87 inline void* base(BasicType type) const;
88 inline void* base_raw(BasicType type) const; // GC barrier invariant
89
90 template <typename T>
91 static T* obj_offset_to_raw(arrayOop obj, size_t offset_in_bytes, T* raw) {
92 if (obj != NULL) {
93 assert(raw == NULL, "either raw or in-heap");
94 char* base = reinterpret_cast<char*>((void*) obj);
95 raw = reinterpret_cast<T*>(base + offset_in_bytes);
96 } else {
97 assert(raw != NULL, "either raw or in-heap");
98 }
99 return raw;
100 }
101
102 // Tells whether index is within bounds.
103 bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
104
105 // Accessors for instance variable which is not a C++ declared nonstatic
106 // field.
107 int length() const {
108 return *(int*)(((intptr_t)this) + length_offset_in_bytes());
109 }
110 void set_length(int length) {
111 set_length((HeapWord*)this, length);
112 }
113 static void set_length(HeapWord* mem, int length) {
114 *(int*)(((char*)mem) + length_offset_in_bytes()) = length;
115 }
116
117 // Should only be called with constants as argument
118 // (will not constant fold otherwise)
119 // Returns the header size in words aligned to the requirements of the
120 // array object type.
121 static int header_size(BasicType type) {
122 size_t typesize_in_bytes = header_size_in_bytes();
123 return (int)(element_type_should_be_aligned(type)
124 ? align_object_offset(typesize_in_bytes/HeapWordSize)
125 : typesize_in_bytes/HeapWordSize);
126 }
127
128 // Return the maximum length of an array of BasicType. The length can passed
129 // to typeArrayOop::object_size(scale, length, header_size) without causing an
130 // overflow. We also need to make sure that this will not overflow a size_t on
131 // 32 bit platforms when we convert it to a byte size.
132 static int32_t max_array_length(BasicType type) {
133 assert(type >= 0 && type < T_CONFLICT, "wrong type");
134 assert(type2aelembytes(type) != 0, "wrong type");
135
136 const size_t max_element_words_per_size_t =
137 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
138 const size_t max_elements_per_size_t =
139 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
140 if ((size_t)max_jint < max_elements_per_size_t) {
141 // It should be ok to return max_jint here, but parts of the code
142 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
143 // passing around the size (in words) of an object. So, we need to avoid
144 // overflowing an int when we add the header. See CRs 4718400 and 7110613.
145 return align_down(max_jint - header_size(type), MinObjAlignment);
146 }
147 return (int32_t)max_elements_per_size_t;
148 }
149
150};
151
152#endif // SHARE_OOPS_ARRAYOOP_HPP
153