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/*
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* Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.lang.invoke;
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/**
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* A {@code VolatileCallSite} is a {@link CallSite} whose target acts like a volatile variable.
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* An {@code invokedynamic} instruction linked to a {@code VolatileCallSite} sees updates
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* to its call site target immediately, even if the update occurs in another thread.
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* There may be a performance penalty for such tight coupling between threads.
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* <p>
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* Unlike {@code MutableCallSite}, there is no
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* {@linkplain MutableCallSite#syncAll syncAll operation} on volatile
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* call sites, since every write to a volatile variable is implicitly
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* synchronized with reader threads.
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* <p>
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* In other respects, a {@code VolatileCallSite} is interchangeable
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* with {@code MutableCallSite}.
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* @see MutableCallSite
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* @author John Rose, JSR 292 EG
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*/
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public class VolatileCallSite extends CallSite {
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/**
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* Creates a call site with a volatile binding to its target.
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* The initial target is set to a method handle
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* of the given type which will throw an {@code IllegalStateException} if called.
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* @param type the method type that this call site will have
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* @throws NullPointerException if the proposed type is null
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*/
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public VolatileCallSite(MethodType type) {
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super(type);
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}
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/**
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* Creates a call site with a volatile binding to its target.
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* The target is set to the given value.
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* @param target the method handle that will be the initial target of the call site
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* @throws NullPointerException if the proposed target is null
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*/
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public VolatileCallSite(MethodHandle target) {
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super(target);
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}
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/**
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* Returns the target method of the call site, which behaves
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* like a {@code volatile} field of the {@code VolatileCallSite}.
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* <p>
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* The interactions of {@code getTarget} with memory are the same
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* as of a read from a {@code volatile} field.
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* <p>
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* In particular, the current thread is required to issue a fresh
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* read of the target from memory, and must not fail to see
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* a recent update to the target by another thread.
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*
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* @return the linkage state of this call site, a method handle which can change over time
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* @see #setTarget
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*/
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@Override public final MethodHandle getTarget() {
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return getTargetVolatile();
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}
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/**
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* Updates the target method of this call site, as a volatile variable.
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* The type of the new target must agree with the type of the old target.
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* <p>
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* The interactions with memory are the same as of a write to a volatile field.
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* In particular, any threads is guaranteed to see the updated target
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* the next time it calls {@code getTarget}.
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* @param newTarget the new target
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* @throws NullPointerException if the proposed new target is null
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* @throws WrongMethodTypeException if the proposed new target
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* has a method type that differs from the previous target
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* @see #getTarget
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*/
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@Override public void setTarget(MethodHandle newTarget) {
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checkTargetChange(getTargetVolatile(), newTarget);
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setTargetVolatile(newTarget);
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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public final MethodHandle dynamicInvoker() {
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return makeDynamicInvoker();
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}
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}
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