arrayOop.hpp revision 1472:c18cbe5936b8
1/* 2 * Copyright (c) 1997, 2009, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 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. 22 * 23 */ 24 25// arrayOopDesc is the abstract baseclass for all arrays. It doesn't 26// declare pure virtual to enforce this because that would allocate a vtbl 27// in each instance, which we don't want. 28 29// The layout of array Oops is: 30// 31// markOop 32// klassOop // 32 bits if compressed but declared 64 in LP64. 33// length // shares klass memory or allocated after declared fields. 34 35 36class arrayOopDesc : public oopDesc { 37 friend class VMStructs; 38 39 // Interpreter/Compiler offsets 40 41 // Header size computation. 42 // The header is considered the oop part of this type plus the length. 43 // Returns the aligned header_size_in_bytes. This is not equivalent to 44 // sizeof(arrayOopDesc) which should not appear in the code. 45 static int header_size_in_bytes() { 46 size_t hs = align_size_up(length_offset_in_bytes() + sizeof(int), 47 HeapWordSize); 48#ifdef ASSERT 49 // make sure it isn't called before UseCompressedOops is initialized. 50 static size_t arrayoopdesc_hs = 0; 51 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs; 52 assert(arrayoopdesc_hs == hs, "header size can't change"); 53#endif // ASSERT 54 return (int)hs; 55 } 56 57 public: 58 // The _length field is not declared in C++. It is allocated after the 59 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise 60 // it occupies the second half of the _klass field in oopDesc. 61 static int length_offset_in_bytes() { 62 return UseCompressedOops ? klass_gap_offset_in_bytes() : 63 sizeof(arrayOopDesc); 64 } 65 66 // Returns the offset of the first element. 67 static int base_offset_in_bytes(BasicType type) { 68 return header_size(type) * HeapWordSize; 69 } 70 71 // Returns the address of the first element. 72 void* base(BasicType type) const { 73 return (void*) (((intptr_t) this) + base_offset_in_bytes(type)); 74 } 75 76 // Tells whether index is within bounds. 77 bool is_within_bounds(int index) const { return 0 <= index && index < length(); } 78 79 // Accessors for instance variable which is not a C++ declared nonstatic 80 // field. 81 int length() const { 82 return *(int*)(((intptr_t)this) + length_offset_in_bytes()); 83 } 84 void set_length(int length) { 85 *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length; 86 } 87 88 // Should only be called with constants as argument 89 // (will not constant fold otherwise) 90 // Returns the header size in words aligned to the requirements of the 91 // array object type. 92 static int header_size(BasicType type) { 93 size_t typesize_in_bytes = header_size_in_bytes(); 94 return (int)(Universe::element_type_should_be_aligned(type) 95 ? align_object_size(typesize_in_bytes/HeapWordSize) 96 : typesize_in_bytes/HeapWordSize); 97 } 98 99 // Return the maximum length of an array of BasicType. The length can passed 100 // to typeArrayOop::object_size(scale, length, header_size) without causing an 101 // overflow. 102 static int32_t max_array_length(BasicType type) { 103 assert(type >= 0 && type < T_CONFLICT, "wrong type"); 104 assert(type2aelembytes(type) != 0, "wrong type"); 105 const int bytes_per_element = type2aelembytes(type); 106 if (bytes_per_element < HeapWordSize) { 107 return max_jint; 108 } 109 110 const int32_t max_words = align_size_down(max_jint, MinObjAlignment); 111 const int32_t max_element_words = max_words - header_size(type); 112 const int32_t words_per_element = bytes_per_element >> LogHeapWordSize; 113 return max_element_words / words_per_element; 114 } 115}; 116