Showing the changes to java/pkg/java/lang/invoke/ConstantCallSite.java (1 of 18352 files). Show all
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| 1 | +/* | |
| 2 | + * Copyright (c) 2010, 2011, 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 java.lang.invoke; | |
| 27 | + | |
| 28 | +/** | |
| 29 | + * A {@code ConstantCallSite} is a {@link CallSite} whose target is permanent, and can never be changed. | |
| 30 | + * An {@code invokedynamic} instruction linked to a {@code ConstantCallSite} is permanently | |
| 31 | + * bound to the call site's target. | |
| 32 | + * @author John Rose, JSR 292 EG | |
| 33 | + */ | |
| 34 | +public class ConstantCallSite extends CallSite { | |
| 35 | + private final boolean isFrozen; | |
| 36 | + | |
| 37 | + /** | |
| 38 | + * Creates a call site with a permanent target. | |
| 39 | + * @param target the target to be permanently associated with this call site | |
| 40 | + * @throws NullPointerException if the proposed target is null | |
| 41 | + */ | |
| 42 | + public ConstantCallSite(MethodHandle target) { | |
| 43 | + super(target); | |
| 44 | + isFrozen = true; | |
| 45 | + } | |
| 46 | + | |
| 47 | + /** | |
| 48 | + * Creates a call site with a permanent target, possibly bound to the call site itself. | |
| 49 | + * <p> | |
| 50 | + * During construction of the call site, the {@code createTargetHook} is invoked to | |
| 51 | + * produce the actual target, as if by a call of the form | |
| 52 | + * {@code (MethodHandle) createTargetHook.invoke(this)}. | |
| 53 | + * <p> | |
| 54 | + * Note that user code cannot perform such an action directly in a subclass constructor, | |
| 55 | + * since the target must be fixed before the {@code ConstantCallSite} constructor returns. | |
| 56 | + * <p> | |
| 57 | + * The hook is said to bind the call site to a target method handle, | |
| 58 | + * and a typical action would be {@code someTarget.bindTo(this)}. | |
| 59 | + * However, the hook is free to take any action whatever, | |
| 60 | + * including ignoring the call site and returning a constant target. | |
| 61 | + * <p> | |
| 62 | + * The result returned by the hook must be a method handle of exactly | |
| 63 | + * the same type as the call site. | |
| 64 | + * <p> | |
| 65 | + * While the hook is being called, the new {@code ConstantCallSite} | |
| 66 | + * object is in a partially constructed state. | |
| 67 | + * In this state, | |
| 68 | + * a call to {@code getTarget}, or any other attempt to use the target, | |
| 69 | + * will result in an {@code IllegalStateException}. | |
| 70 | + * It is legal at all times to obtain the call site's type using the {@code type} method. | |
| 71 | + * | |
| 72 | + * @param targetType the type of the method handle to be permanently associated with this call site | |
| 73 | + * @param createTargetHook a method handle to invoke (on the call site) to produce the call site's target | |
| 74 | + * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments, | |
| 75 | + * or if the target returned by the hook is not of the given {@code targetType} | |
| 76 | + * @throws NullPointerException if the hook returns a null value | |
| 77 | + * @throws ClassCastException if the hook returns something other than a {@code MethodHandle} | |
| 78 | + * @throws Throwable anything else thrown by the the hook function | |
| 79 | + */ | |
| 80 | + protected ConstantCallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable { | |
| 81 | + super(targetType, createTargetHook); | |
| 82 | + isFrozen = true; | |
| 83 | + } | |
| 84 | + | |
| 85 | + /** | |
| 86 | + * Returns the target method of the call site, which behaves | |
| 87 | + * like a {@code final} field of the {@code ConstantCallSite}. | |
| 88 | + * That is, the the target is always the original value passed | |
| 89 | + * to the constructor call which created this instance. | |
| 90 | + * | |
| 91 | + * @return the immutable linkage state of this call site, a constant method handle | |
| 92 | + * @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed | |
| 93 | + */ | |
| 94 | + @Override public final MethodHandle getTarget() { | |
| 95 | + if (!isFrozen) throw new IllegalStateException(); | |
| 96 | + return target; | |
| 97 | + } | |
| 98 | + | |
| 99 | + /** | |
| 100 | + * Always throws an {@link UnsupportedOperationException}. | |
| 101 | + * This kind of call site cannot change its target. | |
| 102 | + * @param ignore a new target proposed for the call site, which is ignored | |
| 103 | + * @throws UnsupportedOperationException because this kind of call site cannot change its target | |
| 104 | + */ | |
| 105 | + @Override public final void setTarget(MethodHandle ignore) { | |
| 106 | + throw new UnsupportedOperationException(); | |
| 107 | + } | |
| 108 | + | |
| 109 | + /** | |
| 110 | + * Returns this call site's permanent target. | |
| 111 | + * Since that target will never change, this is a correct implementation | |
| 112 | + * of {@link CallSite#dynamicInvoker CallSite.dynamicInvoker}. | |
| 113 | + * @return the immutable linkage state of this call site, a constant method handle | |
| 114 | + * @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed | |
| 115 | + */ | |
| 116 | + @Override | |
| 117 | + public final MethodHandle dynamicInvoker() { | |
| 118 | + return getTarget(); | |
| 119 | + } | |
| 120 | +} | |