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(ResolvedJavaField 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
  90      * {@linkplain #readConstantFieldValue(ResolvedJavaField, JavaConstant) constant} by the
  91      * runtime.
  92      *
  93      * @param receiver object from which this field's value is to be read. This value is ignored if
  94      *            this field is static.
  95      * @return the value of this field or {@code null} if the value is not available (e.g., because
  96      *         the field holder is not yet initialized).
  97      */
  98     JavaConstant readFieldValue(ResolvedJavaField field, JavaConstant receiver);
  99 
 100     /**
 101      * Gets the current value of this field for a given object, if available. Like
 102      * {@link #readFieldValue(ResolvedJavaField, JavaConstant)} but treats array fields as stable.
 103      *
 104      * There is no guarantee that the same value will be returned by this method for a field unless
 105      * the field is considered to be
 106      * {@linkplain #readConstantFieldValue(ResolvedJavaField, JavaConstant) constant} by the
 107      * runtime.
 108      *
 109      * @param receiver object from which this field's value is to be read. This value is ignored if
 110      *            this field is static.
 111      * @param isDefaultStable if {@code true}, default values are considered stable
 112      * @return the value of this field or {@code null} if the value is not available (e.g., because
 113      *         the field holder is not yet initialized).
 114      */
 115     JavaConstant readStableFieldValue(ResolvedJavaField field, JavaConstant receiver, boolean isDefaultStable);
 116 
 117     /**
 118      * Converts the given {@link JavaKind#isPrimitive() primitive} constant to a boxed
 119      * {@link JavaKind#Object object} constant, according to the Java boxing rules. Returns
 120      * {@code null} if the source is is not a primitive constant, or the boxed value is not
 121      * available at this point.
 122      */
 123     JavaConstant boxPrimitive(JavaConstant source);
 124 
 125     /**
 126      * Converts the given {@link JavaKind#Object object} constant to a {@link JavaKind#isPrimitive()
 127      * primitive} constant, according to the Java unboxing rules. Returns {@code null} if the source
 128      * is is not an object constant that can be unboxed, or the unboxed value is not available at
 129      * this point.
 130      */
 131     JavaConstant unboxPrimitive(JavaConstant source);
 132 
 133     /**
 134      * Gets a string as a {@link JavaConstant}.
 135      */
 136     JavaConstant forString(String value);
 137 
 138     /**
 139      * Returns the {@link ResolvedJavaType} for a {@link Class} object (or any other object regarded
 140      * as a class by the VM) encapsulated in the given constant. Returns {@code null} if the
 141      * constant does not encapsulate a class, or if the type is not available at this point.
 142      */
 143     ResolvedJavaType asJavaType(Constant constant);
 144 
 145     /**
 146      * Check if the constant is embeddable in the code.
 147      *
 148      * @param constant the constant to test
 149      */
 150     default boolean isEmbeddable(Constant constant) {
 151         return true;
 152     }
 153 
 154     /**
 155      * Gets access to the internals of {@link MethodHandle}.
 156      */
 157     MethodHandleAccessProvider getMethodHandleAccess();
 158 
 159     /**
 160      * Gets raw memory access.
 161      */
 162     MemoryAccessProvider getMemoryAccessProvider();
 163 
 164     /**
 165      * Gets the runtime representation of the {@link Class} object of this type.
 166      */
 167     JavaConstant asJavaClass(ResolvedJavaType type);
 168 
 169     /**
 170      * Gets the runtime representation of the "hub" of this type--that is, the closest part of the
 171      * type representation which is typically stored in the object header.
 172      */
 173     Constant asObjectHub(ResolvedJavaType type);
 174 }