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annotate src/share/vm/oops/arrayOop.hpp @ 113:ba764ed4b6f2

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6420645: Create a vm that uses compressed oops for up to 32gb heapsizes Summary: Compressed oops in instances, arrays, and headers. Code contributors are coleenp, phh, never, swamyv Reviewed-by: jmasa, kamg, acorn, tbell, kvn, rasbold
author coleenp
date Sun, 13 Apr 2008 17:43:42 -0400
parents d5fc211aea19
children 437d03ea40b1
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1 /*
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2 * Copyright 1997-2006 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 // arrayOopDesc is the abstract baseclass for all arrays. It doesn't
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26 // declare pure virtual to enforce this because that would allocate a vtbl
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27 // in each instance, which we don't want.
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28
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29 // The layout of array Oops is:
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30 //
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31 // markOop
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32 // klassOop // 32 bits if compressed but declared 64 in LP64.
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33 // length // shares klass memory or allocated after declared fields.
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34
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35
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36 class arrayOopDesc : public oopDesc {
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37 friend class VMStructs;
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38
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39 // Interpreter/Compiler offsets
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40
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41 // Header size computation.
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42 // The header is considered the oop part of this type plus the length.
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43 // Returns the aligned header_size_in_bytes. This is not equivalent to
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44 // sizeof(arrayOopDesc) which should not appear in the code, except here.
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45 static int header_size_in_bytes() {
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46 size_t hs = UseCompressedOops ?
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47 sizeof(arrayOopDesc) :
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48 align_size_up(sizeof(arrayOopDesc) + sizeof(int), HeapWordSize);
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49 #ifdef ASSERT
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50 // make sure it isn't called before UseCompressedOops is initialized.
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51 static size_t arrayoopdesc_hs = 0;
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52 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs;
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53 assert(arrayoopdesc_hs == hs, "header size can't change");
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54 #endif // ASSERT
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55 return (int)hs;
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56 }
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57
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58 public:
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59 // The _length field is not declared in C++. It is allocated after the
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60 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise
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61 // it occupies the second half of the _klass field in oopDesc.
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62 static int length_offset_in_bytes() {
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63 return UseCompressedOops ? klass_gap_offset_in_bytes() :
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64 sizeof(arrayOopDesc);
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65 }
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66
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67 // Returns the offset of the first element.
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68 static int base_offset_in_bytes(BasicType type) {
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69 return header_size(type) * HeapWordSize;
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70 }
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72 // Returns the address of the first element.
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73 void* base(BasicType type) const {
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74 return (void*) (((intptr_t) this) + base_offset_in_bytes(type));
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75 }
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77 // Tells whether index is within bounds.
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78 bool is_within_bounds(int index) const { return 0 <= index && index < length(); }
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79
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80 // Accessors for instance variable which is not a C++ declared nonstatic
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81 // field.
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82 int length() const {
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83 return *(int*)(((intptr_t)this) + length_offset_in_bytes());
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84 }
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85 void set_length(int length) {
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86 *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length;
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87 }
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88
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89 // Should only be called with constants as argument
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90 // (will not constant fold otherwise)
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91 // Returns the header size in words aligned to the requirements of the
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92 // array object type.
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93 static int header_size(BasicType type) {
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94 size_t typesize_in_bytes = header_size_in_bytes();
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95 return (int)(Universe::element_type_should_be_aligned(type)
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96 ? align_object_size(typesize_in_bytes/HeapWordSize)
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97 : typesize_in_bytes/HeapWordSize);
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98 }
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99
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100 // This method returns the maximum length that can passed into
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101 // typeArrayOop::object_size(scale, length, header_size) without causing an
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102 // overflow. We substract an extra 2*wordSize to guard against double word
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103 // alignments. It gets the scale from the type2aelembytes array.
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104 static int32_t max_array_length(BasicType type) {
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105 assert(type >= 0 && type < T_CONFLICT, "wrong type");
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106 assert(type2aelembytes(type) != 0, "wrong type");
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107 // We use max_jint, since object_size is internally represented by an 'int'
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108 // This gives us an upper bound of max_jint words for the size of the oop.
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109 int32_t max_words = (max_jint - header_size(type) - 2);
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110 int elembytes = type2aelembytes(type);
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111 jlong len = ((jlong)max_words * HeapWordSize) / elembytes;
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112 return (len > max_jint) ? max_jint : (int32_t)len;
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113 }
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115 };