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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 //  markWord
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.
header_size_in_bytes()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   // Returns the address of the length "field".  See length_offset_in_bytes().
length_addr_impl(void * obj_ptr)65   static int* length_addr_impl(void* obj_ptr) {
66     char* ptr = static_cast<char*>(obj_ptr);
67     return reinterpret_cast<int*>(ptr + length_offset_in_bytes());
68   }
69 
70   // Check whether an element of a typeArrayOop with the given type must be
71   // aligned 0 mod 8.  The typeArrayOop itself must be aligned at least this
72   // strongly.
element_type_should_be_aligned(BasicType type)73   static bool element_type_should_be_aligned(BasicType type) {
74     return type == T_DOUBLE || type == T_LONG;
75   }
76 
77  public:
78   // The _length field is not declared in C++.  It is allocated after the
79   // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
80   // it occupies the second half of the _klass field in oopDesc.
length_offset_in_bytes()81   static int length_offset_in_bytes() {
82     return UseCompressedClassPointers ? klass_gap_offset_in_bytes() :
83                                sizeof(arrayOopDesc);
84   }
85 
86   // Returns the offset of the first element.
base_offset_in_bytes(BasicType type)87   static int base_offset_in_bytes(BasicType type) {
88     return header_size(type) * HeapWordSize;
89   }
90 
91   // Returns the address of the first element. The elements in the array will not
92   // relocate from this address until a subsequent thread transition.
base(BasicType type) const93   void* base(BasicType type) const {
94     return reinterpret_cast<void*>(cast_from_oop<intptr_t>(as_oop()) + base_offset_in_bytes(type));
95   }
96 
97   template <typename T>
obj_offset_to_raw(arrayOop obj,size_t offset_in_bytes,T * raw)98   static T* obj_offset_to_raw(arrayOop obj, size_t offset_in_bytes, T* raw) {
99     if (obj != NULL) {
100       assert(raw == NULL, "either raw or in-heap");
101       char* base = reinterpret_cast<char*>((void*) obj);
102       raw = reinterpret_cast<T*>(base + offset_in_bytes);
103     } else {
104       assert(raw != NULL, "either raw or in-heap");
105     }
106     return raw;
107   }
108 
109   // Tells whether index is within bounds.
is_within_bounds(int index) const110   bool is_within_bounds(int index) const        { return 0 <= index && index < length(); }
111 
112   // Accessors for array length.  There's not a member variable for
113   // it; see length_offset_in_bytes().
length() const114   int length() const { return *length_addr_impl(const_cast<arrayOopDesc*>(this)); }
set_length(int length)115   void set_length(int length) { *length_addr_impl(this) = length; }
116 
length_addr()117   int* length_addr() {
118     return length_addr_impl(this);
119   }
120 
set_length(HeapWord * mem,int length)121   static void set_length(HeapWord* mem, int length) {
122     *length_addr_impl(mem) = length;
123   }
124 
125   // Should only be called with constants as argument
126   // (will not constant fold otherwise)
127   // Returns the header size in words aligned to the requirements of the
128   // array object type.
header_size(BasicType type)129   static int header_size(BasicType type) {
130     size_t typesize_in_bytes = header_size_in_bytes();
131     return (int)(element_type_should_be_aligned(type)
132       ? align_object_offset(typesize_in_bytes/HeapWordSize)
133       : typesize_in_bytes/HeapWordSize);
134   }
135 
136   // Return the maximum length of an array of BasicType.  The length can passed
137   // to typeArrayOop::object_size(scale, length, header_size) without causing an
138   // overflow. We also need to make sure that this will not overflow a size_t on
139   // 32 bit platforms when we convert it to a byte size.
max_array_length(BasicType type)140   static int32_t max_array_length(BasicType type) {
141     assert(type >= 0 && type < T_CONFLICT, "wrong type");
142     assert(type2aelembytes(type) != 0, "wrong type");
143 
144     const size_t max_element_words_per_size_t =
145       align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment);
146     const size_t max_elements_per_size_t =
147       HeapWordSize * max_element_words_per_size_t / type2aelembytes(type);
148     if ((size_t)max_jint < max_elements_per_size_t) {
149       // It should be ok to return max_jint here, but parts of the code
150       // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
151       // passing around the size (in words) of an object. So, we need to avoid
152       // overflowing an int when we add the header. See CRs 4718400 and 7110613.
153       return align_down(max_jint - header_size(type), MinObjAlignment);
154     }
155     return (int32_t)max_elements_per_size_t;
156   }
157 
158 };
159 
160 #endif // SHARE_OOPS_ARRAYOOP_HPP
161