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
127 * {@link JavaKind#isPrimitive() primitive} constant, according to the Java unboxing rules.
128 * Returns {@code null} if the source is is not an object constant that can be unboxed, or the
129 * unboxed value is not available at 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 }