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
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 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
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
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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.
 52   static int header_size_in_bytes() {
 53     size_t hs = length_offset_in_bytes() + sizeof(int);

 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   // Returns the address of the length "field".  See length_offset_in_bytes().
 64   static int* length_addr_impl(void* obj_ptr) {
 65     char* ptr = static_cast<char*>(obj_ptr);
 66     return reinterpret_cast<int*>(ptr + length_offset_in_bytes());
 67   }
 68 
 69   // Check whether an element of a typeArrayOop with the given type must be
 70   // aligned 0 mod 8.  The typeArrayOop itself must be aligned at least this
 71   // strongly.
 72   static bool element_type_should_be_aligned(BasicType type) {
 73 #ifdef _LP64
 74     if (type == T_OBJECT || type == T_ARRAY) {
 75       return !UseCompressedOops;
 76     }
 77 #endif
 78     return type == T_DOUBLE || type == T_LONG;
 79   }
 80 
 81  public:
 82   // The _length field is not declared in C++.  It is allocated after the
 83   // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
 84   // it occupies the second half of the _klass field in oopDesc.
 85   static int length_offset_in_bytes() {
 86     return sizeof(arrayOopDesc);

 87   }
 88 
 89   // Returns the offset of the first element.
 90   static int base_offset_in_bytes(BasicType type) {
 91     size_t typesize_in_bytes = header_size_in_bytes();
 92     return (int)(element_type_should_be_aligned(type)
 93                  ? align_up(typesize_in_bytes, BytesPerLong)
 94                  : typesize_in_bytes);
 95   }
 96 
 97   // Returns the address of the first element. The elements in the array will not
 98   // relocate from this address until a subsequent thread transition.
 99   void* base(BasicType type) const {
100     return reinterpret_cast<void*>(cast_from_oop<intptr_t>(as_oop()) + base_offset_in_bytes(type));
101   }
102 
103   template <typename T>
104   static T* obj_offset_to_raw(arrayOop obj, size_t offset_in_bytes, T* raw) {
105     if (obj != NULL) {
106       assert(raw == NULL, "either raw or in-heap");
107       char* base = reinterpret_cast<char*>((void*) obj);
108       raw = reinterpret_cast<T*>(base + offset_in_bytes);
109     } else {
110       assert(raw != NULL, "either raw or in-heap");
111     }
112     return raw;
113   }
114 
115   // Tells whether index is within bounds.
116   bool is_within_bounds(int index) const        { return 0 <= index && index < length(); }
117 
118   // Accessors for array length.  There's not a member variable for
119   // it; see length_offset_in_bytes().
120   int length() const { return *length_addr_impl(const_cast<arrayOopDesc*>(this)); }
121   void set_length(int length) { *length_addr_impl(this) = length; }
122 
123   int* length_addr() {
124     return length_addr_impl(this);
125   }
126 
127   static void set_length(HeapWord* mem, int length) {
128     *length_addr_impl(mem) = length;
129   }
130 











131   // Return the maximum length of an array of BasicType.  The length can passed
132   // to typeArrayOop::object_size(scale, length, header_size) without causing an
133   // overflow. We also need to make sure that this will not overflow a size_t on
134   // 32 bit platforms when we convert it to a byte size.
135   static int32_t max_array_length(BasicType type) {
136     assert(type >= 0 && type < T_CONFLICT, "wrong type");
137     assert(type2aelembytes(type) != 0, "wrong type");
138 
139     const size_t max_size_bytes = align_down(SIZE_MAX - base_offset_in_bytes(type), MinObjAlignmentInBytes);
140     const size_t max_elements_per_size_t = max_size_bytes / type2aelembytes(type);


141     if ((size_t)max_jint < max_elements_per_size_t) {
142       // It should be ok to return max_jint here, but parts of the code
143       // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for
144       // passing around the size (in words) of an object. So, we need to avoid
145       // overflowing an int when we add the header. See CRs 4718400 and 7110613.
146       int header_size_words = align_up(base_offset_in_bytes(type), HeapWordSize) / HeapWordSize;
147       return align_down(max_jint - header_size_words, MinObjAlignment);
148     }
149     return (int32_t)max_elements_per_size_t;
150   }
151 
152 };
153 
154 #endif // SHARE_OOPS_ARRAYOOP_HPP
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