arrayOop.hpp revision 3602:da91efe96a93
1/* 2 * Copyright (c) 1997, 2012, 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#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// Klass* // 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 UseCompressedKlassPointers ? 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. We also need to make sure that this will not overflow a size_t on 108 // 32 bit platforms when we convert it to a byte size. 109 static int32_t max_array_length(BasicType type) { 110 assert(type >= 0 && type < T_CONFLICT, "wrong type"); 111 assert(type2aelembytes(type) != 0, "wrong type"); 112 113 const size_t max_element_words_per_size_t = 114 align_size_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment); 115 const size_t max_elements_per_size_t = 116 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type); 117 if ((size_t)max_jint < max_elements_per_size_t) { 118 // It should be ok to return max_jint here, but parts of the code 119 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for 120 // passing around the size (in words) of an object. So, we need to avoid 121 // overflowing an int when we add the header. See CRs 4718400 and 7110613. 122 return align_size_down(max_jint - header_size(type), MinObjAlignment); 123 } 124 return (int32_t)max_elements_per_size_t; 125 } 126 127// for unit testing 128#ifndef PRODUCT 129 static bool check_max_length_overflow(BasicType type); 130 static int32_t old_max_array_length(BasicType type); 131 static void test_max_array_length(); 132#endif 133}; 134 135#endif // SHARE_VM_OOPS_ARRAYOOP_HPP 136