1 /* 2 * Copyright (c) 2012, 2015, 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 package jdk.vm.ci.meta; 24 25 import java.lang.invoke.MethodHandle; 26 27 /** 28 * Reflection operations on values represented as {@linkplain JavaConstant constants}. All methods 29 * in this interface require the VM to access the actual object encapsulated in 30 * {@link JavaKind#Object object} constants. This access is not always possible, depending on kind 31 * of VM and the state that the VM is in. Therefore, all methods can return {@code null} at any 32 * time, to indicate that the result is not available at this point. The caller is responsible to 33 * check for {@code null} results and handle them properly, e.g., not perform an optimization. 34 */ 35 public interface ConstantReflectionProvider { 36 37 /** 38 * Compares two constants for equality. The equality relationship is symmetric. Returns 39 * {@link Boolean#TRUE true} if the two constants represent the same run time value, 40 * {@link Boolean#FALSE false} if they are different. Returns {@code null} if the constants 41 * cannot be compared at this point. 42 */ 43 Boolean constantEquals(Constant x, Constant y); 44 45 /** 46 * Returns the length of the array constant. Returns {@code null} if the constant is not an 47 * array, or if the array length is not available at this point. 48 */ 49 Integer readArrayLength(JavaConstant array); 50 51 /** 52 * Reads a value from the given array at the given index. Returns {@code null} if the constant 53 * is not an array, if the index is out of bounds, or if the value is not available at this 54 * point. 55 */ 56 JavaConstant readArrayElement(JavaConstant array, int index); 57 58 /** 59 * Reads a value from the given array at the given index if it is a stable array. Returns 60 * {@code null} if the constant is not a stable array, if it is a default value, if the index is 61 * out of bounds, or if the value is not available at this point. 62 */ 63 JavaConstant readConstantArrayElement(JavaConstant array, int index); 64 65 /** 66 * Reads a value from the given array at the given offset if it is a stable array. The offset 67 * will be decoded relative to the platform addressing into an index into the array. Returns 68 * {@code null} if the constant is not a stable array, if it is a default value, if the offset 69 * is out of bounds, or if the value is not available at this point. 70 */ 71 JavaConstant readConstantArrayElementForOffset(JavaConstant array, long offset); 72 73 /** 74 * Gets the constant value of this field. Note that a {@code static final} field may not be 75 * considered constant if its declaring class is not yet initialized or if it is a well known 76 * field that can be updated via other means (e.g., {@link System#setOut(java.io.PrintStream)}). 77 * 78 * @param receiver object from which this field's value is to be read. This value is ignored if 79 * this field is static. 80 * @return the constant value of this field or {@code null} if this field is not considered 81 * constant by the runtime 82 */ 83 JavaConstant readConstantFieldValue(JavaField field, JavaConstant receiver); 84 85 /** 86 * Gets the current value of this field for a given object, if available. 87 * 88 * There is no guarantee that the same value will be returned by this method for a field unless 89 * the field is considered to be {@linkplain #readConstantFieldValue(JavaField, JavaConstant) 90 * constant} by the runtime. 91 * 92 * @param receiver object from which this field's value is to be read. This value is ignored if 93 * this field is static. 94 * @return the value of this field or {@code null} if the value is not available (e.g., because 95 * the field holder is not yet initialized). 96 */ 97 JavaConstant readFieldValue(JavaField field, JavaConstant receiver); 98 99 /** 100 * Gets the current value of this field for a given object, if available. Like 101 * {@link #readFieldValue(JavaField, JavaConstant)} but treats array fields as stable. 102 * 103 * There is no guarantee that the same value will be returned by this method for a field unless 104 * the field is considered to be {@linkplain #readConstantFieldValue(JavaField, JavaConstant) 105 * constant} by the runtime. 106 * 107 * @param receiver object from which this field's value is to be read. This value is ignored if 108 * this field is static. 109 * @param isDefaultStable if {@code true}, default values are considered stable 110 * @return the value of this field or {@code null} if the value is not available (e.g., because 111 * the field holder is not yet initialized). 112 */ 113 JavaConstant readStableFieldValue(JavaField field, JavaConstant receiver, boolean isDefaultStable); 114 115 /** 116 * Converts the given {@link JavaKind#isPrimitive() primitive} constant to a boxed 117 * {@link JavaKind#Object object} constant, according to the Java boxing rules. Returns 118 * {@code null} if the source is is not a primitive constant, or the boxed value is not 119 * available at this point. 120 */ 121 JavaConstant boxPrimitive(JavaConstant source); 122 123 /** 124 * Converts the given {@link JavaKind#Object object} constant to a 125 * {@link JavaKind#isPrimitive() primitive} constant, according to the Java unboxing rules. 126 * Returns {@code null} if the source is is not an object constant that can be unboxed, or the 127 * unboxed value is not available at this point. 128 */ 129 JavaConstant unboxPrimitive(JavaConstant source); 130 131 /** 132 * Gets a string as a {@link JavaConstant}. 133 */ 134 JavaConstant forString(String value); 135 136 /** 137 * Returns the {@link ResolvedJavaType} for a {@link Class} object (or any other object regarded 138 * as a class by the VM) encapsulated in the given constant. Returns {@code null} if the 139 * constant does not encapsulate a class, or if the type is not available at this point. 140 */ 141 ResolvedJavaType asJavaType(Constant constant); 142 143 /** 144 * Check if the constant is embeddable in the code. 145 * 146 * @param constant the constant to test 147 */ 148 default boolean isEmbeddable(Constant constant) { 149 return true; 150 } 151 152 /** 153 * Gets access to the internals of {@link MethodHandle}. 154 */ 155 MethodHandleAccessProvider getMethodHandleAccess(); 156 157 /** 158 * Gets raw memory access. 159 */ 160 MemoryAccessProvider getMemoryAccessProvider(); 161 }