121 lines
5.5 KiB
Java
121 lines
5.5 KiB
Java
/*
|
|
* Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
|
|
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
|
|
*
|
|
* This code is free software; you can redistribute it and/or modify it
|
|
* under the terms of the GNU General Public License version 2 only, as
|
|
* published by the Free Software Foundation. Oracle designates this
|
|
* particular file as subject to the "Classpath" exception as provided
|
|
* by Oracle in the LICENSE file that accompanied this code.
|
|
*
|
|
* This code is distributed in the hope that it will be useful, but WITHOUT
|
|
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
|
|
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
|
|
* version 2 for more details (a copy is included in the LICENSE file that
|
|
* accompanied this code).
|
|
*
|
|
* You should have received a copy of the GNU General Public License version
|
|
* 2 along with this work; if not, write to the Free Software Foundation,
|
|
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
|
|
*
|
|
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
|
|
* or visit www.oracle.com if you need additional information or have any
|
|
* questions.
|
|
*/
|
|
|
|
package java.lang.invoke;
|
|
|
|
/**
|
|
* A {@code ConstantCallSite} is a {@link CallSite} whose target is permanent, and can never be changed.
|
|
* An {@code invokedynamic} instruction linked to a {@code ConstantCallSite} is permanently
|
|
* bound to the call site's target.
|
|
* @author John Rose, JSR 292 EG
|
|
*/
|
|
public class ConstantCallSite extends CallSite {
|
|
private final boolean isFrozen;
|
|
|
|
/**
|
|
* Creates a call site with a permanent target.
|
|
* @param target the target to be permanently associated with this call site
|
|
* @throws NullPointerException if the proposed target is null
|
|
*/
|
|
public ConstantCallSite(MethodHandle target) {
|
|
super(target);
|
|
isFrozen = true;
|
|
}
|
|
|
|
/**
|
|
* Creates a call site with a permanent target, possibly bound to the call site itself.
|
|
* <p>
|
|
* During construction of the call site, the {@code createTargetHook} is invoked to
|
|
* produce the actual target, as if by a call of the form
|
|
* {@code (MethodHandle) createTargetHook.invoke(this)}.
|
|
* <p>
|
|
* Note that user code cannot perform such an action directly in a subclass constructor,
|
|
* since the target must be fixed before the {@code ConstantCallSite} constructor returns.
|
|
* <p>
|
|
* The hook is said to bind the call site to a target method handle,
|
|
* and a typical action would be {@code someTarget.bindTo(this)}.
|
|
* However, the hook is free to take any action whatever,
|
|
* including ignoring the call site and returning a constant target.
|
|
* <p>
|
|
* The result returned by the hook must be a method handle of exactly
|
|
* the same type as the call site.
|
|
* <p>
|
|
* While the hook is being called, the new {@code ConstantCallSite}
|
|
* object is in a partially constructed state.
|
|
* In this state,
|
|
* a call to {@code getTarget}, or any other attempt to use the target,
|
|
* will result in an {@code IllegalStateException}.
|
|
* It is legal at all times to obtain the call site's type using the {@code type} method.
|
|
*
|
|
* @param targetType the type of the method handle to be permanently associated with this call site
|
|
* @param createTargetHook a method handle to invoke (on the call site) to produce the call site's target
|
|
* @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments,
|
|
* or if the target returned by the hook is not of the given {@code targetType}
|
|
* @throws NullPointerException if the hook returns a null value
|
|
* @throws ClassCastException if the hook returns something other than a {@code MethodHandle}
|
|
* @throws Throwable anything else thrown by the the hook function
|
|
*/
|
|
protected ConstantCallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable {
|
|
super(targetType, createTargetHook);
|
|
isFrozen = true;
|
|
}
|
|
|
|
/**
|
|
* Returns the target method of the call site, which behaves
|
|
* like a {@code final} field of the {@code ConstantCallSite}.
|
|
* That is, the the target is always the original value passed
|
|
* to the constructor call which created this instance.
|
|
*
|
|
* @return the immutable linkage state of this call site, a constant method handle
|
|
* @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed
|
|
*/
|
|
@Override public final MethodHandle getTarget() {
|
|
if (!isFrozen) throw new IllegalStateException();
|
|
return target;
|
|
}
|
|
|
|
/**
|
|
* Always throws an {@link UnsupportedOperationException}.
|
|
* This kind of call site cannot change its target.
|
|
* @param ignore a new target proposed for the call site, which is ignored
|
|
* @throws UnsupportedOperationException because this kind of call site cannot change its target
|
|
*/
|
|
@Override public final void setTarget(MethodHandle ignore) {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Returns this call site's permanent target.
|
|
* Since that target will never change, this is a correct implementation
|
|
* of {@link CallSite#dynamicInvoker CallSite.dynamicInvoker}.
|
|
* @return the immutable linkage state of this call site, a constant method handle
|
|
* @throws IllegalStateException if the {@code ConstantCallSite} constructor has not completed
|
|
*/
|
|
@Override
|
|
public final MethodHandle dynamicInvoker() {
|
|
return getTarget();
|
|
}
|
|
}
|