arrayOop.hpp revision 1879:f95d63e2154a 
1/*
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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
42class 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 int32_t max_words = align_size_down(max_jint, MinObjAlignment);
117    const int32_t max_element_words = max_words - header_size(type);
118    const int32_t words_per_element = bytes_per_element >> LogHeapWordSize;
119    return max_element_words / words_per_element;
120  }
121};
122
123#endif // SHARE_VM_OOPS_ARRAYOOP_HPP
124