1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/rt/emul/compact/src/main/java/java/lang/invoke/ConstantCallSite.java Sun Aug 17 20:09:05 2014 +0200
1.3 @@ -0,0 +1,120 @@
1.4 +/*
1.5 + * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation. Oracle designates this
1.11 + * particular file as subject to the "Classpath" exception as provided
1.12 + * by Oracle in the LICENSE file that accompanied this code.
1.13 + *
1.14 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 + * version 2 for more details (a copy is included in the LICENSE file that
1.18 + * accompanied this code).
1.19 + *
1.20 + * You should have received a copy of the GNU General Public License version
1.21 + * 2 along with this work; if not, write to the Free Software Foundation,
1.22 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 + *
1.24 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 + * or visit www.oracle.com if you need additional information or have any
1.26 + * questions.
1.27 + */
1.28 +
1.29 +package java.lang.invoke;
1.30 +
1.31 +/**
1.32 + * A {@code ConstantCallSite} is a {@link CallSite} whose target is permanent, and can never be changed.
1.33 + * An {@code invokedynamic} instruction linked to a {@code ConstantCallSite} is permanently
1.34 + * bound to the call site's target.
1.35 + * @author John Rose, JSR 292 EG
1.36 + */
1.37 +public class ConstantCallSite extends CallSite {
1.38 + private final boolean isFrozen;
1.39 +
1.40 + /**
1.41 + * Creates a call site with a permanent target.
1.42 + * @param target the target to be permanently associated with this call site
1.43 + * @throws NullPointerException if the proposed target is null
1.44 + */
1.45 + public ConstantCallSite(MethodHandle target) {
1.46 + super(target);
1.47 + isFrozen = true;
1.48 + }
1.49 +
1.50 + /**
1.51 + * Creates a call site with a permanent target, possibly bound to the call site itself.
1.52 + * <p>
1.53 + * During construction of the call site, the {@code createTargetHook} is invoked to
1.54 + * produce the actual target, as if by a call of the form
1.55 + * {@code (MethodHandle) createTargetHook.invoke(this)}.
1.56 + * <p>
1.57 + * Note that user code cannot perform such an action directly in a subclass constructor,
1.58 + * since the target must be fixed before the {@code ConstantCallSite} constructor returns.
1.59 + * <p>
1.60 + * The hook is said to bind the call site to a target method handle,
1.61 + * and a typical action would be {@code someTarget.bindTo(this)}.
1.62 + * However, the hook is free to take any action whatever,
1.63 + * including ignoring the call site and returning a constant target.
1.64 + * <p>
1.65 + * The result returned by the hook must be a method handle of exactly
1.66 + * the same type as the call site.
1.67 + * <p>
1.68 + * While the hook is being called, the new {@code ConstantCallSite}
1.69 + * object is in a partially constructed state.
1.70 + * In this state,
1.71 + * a call to {@code getTarget}, or any other attempt to use the target,
1.72 + * will result in an {@code IllegalStateException}.
1.73 + * It is legal at all times to obtain the call site's type using the {@code type} method.
1.74 + *
1.75 + * @param targetType the type of the method handle to be permanently associated with this call site
1.76 + * @param createTargetHook a method handle to invoke (on the call site) to produce the call site's target
1.77 + * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments,
1.78 + * or if the target returned by the hook is not of the given {@code targetType}
1.79 + * @throws NullPointerException if the hook returns a null value
1.80 + * @throws ClassCastException if the hook returns something other than a {@code MethodHandle}
1.81 + * @throws Throwable anything else thrown by the hook function
1.82 + */
1.83 + protected ConstantCallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable {
1.84 + super(targetType, createTargetHook);
1.85 + isFrozen = true;
1.86 + }
1.87 +
1.88 + /**
1.89 + * Returns the target method of the call site, which behaves
1.90 + * like a {@code final} field of the {@code ConstantCallSite}.
1.91 + * That is, the target is always the original value passed
1.92 + * to the constructor call which created this instance.
1.93 + *
1.94 + * @return the immutable linkage state of this call site, a constant method handle
1.95 + * @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed
1.96 + */
1.97 + @Override public final MethodHandle getTarget() {
1.98 + if (!isFrozen) throw new IllegalStateException();
1.99 + return target;
1.100 + }
1.101 +
1.102 + /**
1.103 + * Always throws an {@link UnsupportedOperationException}.
1.104 + * This kind of call site cannot change its target.
1.105 + * @param ignore a new target proposed for the call site, which is ignored
1.106 + * @throws UnsupportedOperationException because this kind of call site cannot change its target
1.107 + */
1.108 + @Override public final void setTarget(MethodHandle ignore) {
1.109 + throw new UnsupportedOperationException();
1.110 + }
1.111 +
1.112 + /**
1.113 + * Returns this call site's permanent target.
1.114 + * Since that target will never change, this is a correct implementation
1.115 + * of {@link CallSite#dynamicInvoker CallSite.dynamicInvoker}.
1.116 + * @return the immutable linkage state of this call site, a constant method handle
1.117 + * @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed
1.118 + */
1.119 + @Override
1.120 + public final MethodHandle dynamicInvoker() {
1.121 + return getTarget();
1.122 + }
1.123 +}