1 /*
2 * Copyright (c) 2025, 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package jdk.internal.value;
27
28 import java.lang.invoke.MethodHandle;
29 import java.lang.invoke.MethodHandles;
30 import java.lang.invoke.MethodType;
31 import java.lang.reflect.Field;
32 import java.lang.reflect.Modifier;
33 import java.util.ArrayList;
34 import java.util.List;
35
36 import jdk.internal.access.JavaLangInvokeAccess;
37 import jdk.internal.access.SharedSecrets;
38 import jdk.internal.misc.Unsafe;
39 import sun.invoke.util.Wrapper;
40
41 /**
42 * Iterates the layout elements of a value type.
43 * <p>
44 * In the long run, we should do this:
45 * Iterate the layout, create a mask masking bytes used by Object/abstract value
46 * class reference fields. Do a byte-wise compare and get the mask of value
47 * mismatch; if the mask's all clear, fine; if the mask has bits beyond our
48 * mask, fail; otherwise, compare reference fields indicated by the mismatch
49 * mask. There may be paddings to ignore, too, depends...
50 */
51 public final class LayoutIteration {
52 // Initializer in static initializers below, order dependent
53 public static final ClassValue<List<MethodHandle>> ELEMENTS;
54
55 /**
56 * {@return a list of method handles accessing the basic elements}
57 * Basic elements are 8 primitives and pointers (to identity or value objects).
58 * Primitives and pointers are distinguished by the MH return types.
59 * The MH types are {@code flatType -> fieldType}.
60 *
61 * @param flatType the class that has a flat layout
62 * @return the accessors
63 * @throws IllegalArgumentException if argument has no flat layout
64 */
65 public static List<MethodHandle> computeElementGetters(Class<?> flatType) {
66 if (!canHaveFlatLayout(flatType))
67 throw new IllegalArgumentException(flatType + " cannot be flat");
68 var sink = new Sink(flatType);
69 iterateFields(U.valueHeaderSize(flatType), flatType, sink);
70 return List.copyOf(sink.getters);
71 }
72
73 // Ensures the given class has a potential a flat layout
74 private static boolean canHaveFlatLayout(Class<?> flatType) {
75 return flatType.isValue() && Modifier.isFinal(flatType.getModifiers());
76 }
77
78 private static final class Sink {
79 final Class<?> receiverType;
80 final List<MethodHandle> getters = new ArrayList<>();
81
82 Sink(Class<?> receiverType) {
83 this.receiverType = receiverType;
84 }
85
86 void accept(long offsetNoHeader, Class<?> itemType) {
87 Wrapper w = itemType.isPrimitive() ? Wrapper.forPrimitiveType(itemType) : Wrapper.OBJECT;
88 var mh = MethodHandles.insertArguments(FIELD_GETTERS.get(w.ordinal()), 1, offsetNoHeader);
89 assert mh.type() == MethodType.methodType(w.primitiveType(), Object.class);
90 mh = JLIA.assertAsType(mh, MethodType.methodType(itemType, receiverType));
91 getters.add(mh);
92 }
93 }
94
95 // Sink is good for one to many mappings
96 private static void iterateFields(long enclosingOffset, Class<?> currentClass, Sink sink) {
97 assert canHaveFlatLayout(currentClass) : currentClass + " cannot be flat";
98 long memberOffsetDelta = enclosingOffset - U.valueHeaderSize(currentClass);
99 for (Field f : currentClass.getDeclaredFields()) {
100 if (Modifier.isStatic(f.getModifiers()))
101 continue;
102 var type = f.getType();
103 long memberOffset = U.objectFieldOffset(f) + memberOffsetDelta;
104 if (!U.isFlatField(f)) {
105 sink.accept(memberOffset, type);
106 } else {
107 iterateFields(memberOffset, type, sink);
108 }
109 }
110 }
111
112 private static boolean getBoolean(Object o, long offset) {
113 return U.getBoolean(o, offset);
114 }
115 private static byte getByte(Object o, long offset) {
116 return U.getByte(o, offset);
117 }
118 private static short getShort(Object o, long offset) {
119 return U.getShort(o, offset);
120 }
121 private static char getCharacter(Object o, long offset) {
122 return U.getChar(o, offset);
123 }
124 private static int getInteger(Object o, long offset) {
125 return U.getInt(o, offset);
126 }
127 private static long getLong(Object o, long offset) {
128 return U.getLong(o, offset);
129 }
130 private static float getFloat(Object o, long offset) {
131 return U.getFloat(o, offset);
132 }
133 private static double getDouble(Object o, long offset) {
134 return U.getDouble(o, offset);
135 }
136 public static Object getObject(Object o, long offset) {
137 return U.getReference(o, offset);
138 }
139
140 private static final Unsafe U = Unsafe.getUnsafe();
141 private static final JavaLangInvokeAccess JLIA = SharedSecrets.getJavaLangInvokeAccess();
142 private static final List<MethodHandle> FIELD_GETTERS;
143 static {
144 MethodHandle[] fieldGetters = new MethodHandle[9];
145 var lookup = MethodHandles.lookup();
146 var type = MethodType.methodType(void.class, Object.class, long.class);
147 try {
148 for (Wrapper w : Wrapper.values()) {
149 if (w != Wrapper.VOID) {
150 fieldGetters[w.ordinal()] = lookup.findStatic(LayoutIteration.class,
151 "get" + w.wrapperSimpleName(), type.changeReturnType(w.primitiveType()));
152 }
153 }
154 } catch (ReflectiveOperationException ex) {
155 throw new ExceptionInInitializerError(ex);
156 }
157 FIELD_GETTERS = List.of(fieldGetters);
158 ELEMENTS = new ClassValue<>() {
159 @Override
160 protected List<MethodHandle> computeValue(Class<?> type) {
161 return computeElementGetters(type);
162 }
163 };
164 }
165
166 private LayoutIteration() {}
167 }