1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  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  *
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 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
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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 protected:
 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   // Returns the address of the length "field".  See length_offset_in_bytes().
 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.
 73   static bool element_type_should_be_aligned(BasicType type) {
 74     return type == T_DOUBLE || type == T_LONG || type == T_INLINE_TYPE;
 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.
 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.
 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.
 93   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>
 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.
110   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().
114   int length() const { return *length_addr_impl(const_cast<arrayOopDesc*>(this)); }
115   void set_length(int length) { *length_addr_impl(this) = length; }
116 
117   int* length_addr() {
118     return length_addr_impl(this);
119   }
120 
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.
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.
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