jaroslav@1646: /*
jaroslav@1646:  * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
jaroslav@1646:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1646:  *
jaroslav@1646:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1646:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1646:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1646:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1646:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1646:  *
jaroslav@1646:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1646:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1646:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1646:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1646:  * accompanied this code).
jaroslav@1646:  *
jaroslav@1646:  * You should have received a copy of the GNU General Public License version
jaroslav@1646:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1646:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1646:  *
jaroslav@1646:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1646:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1646:  * questions.
jaroslav@1646:  */
jaroslav@1646: 
jaroslav@1646: package java.lang.invoke;
jaroslav@1646: 
jaroslav@1646: /**
jaroslav@1646:  * A {@code VolatileCallSite} is a {@link CallSite} whose target acts like a volatile variable.
jaroslav@1646:  * An {@code invokedynamic} instruction linked to a {@code VolatileCallSite} sees updates
jaroslav@1646:  * to its call site target immediately, even if the update occurs in another thread.
jaroslav@1646:  * There may be a performance penalty for such tight coupling between threads.
jaroslav@1646:  * <p>
jaroslav@1646:  * Unlike {@code MutableCallSite}, there is no
jaroslav@1646:  * {@linkplain MutableCallSite#syncAll syncAll operation} on volatile
jaroslav@1646:  * call sites, since every write to a volatile variable is implicitly
jaroslav@1646:  * synchronized with reader threads.
jaroslav@1646:  * <p>
jaroslav@1646:  * In other respects, a {@code VolatileCallSite} is interchangeable
jaroslav@1646:  * with {@code MutableCallSite}.
jaroslav@1646:  * @see MutableCallSite
jaroslav@1646:  * @author John Rose, JSR 292 EG
jaroslav@1646:  */
jaroslav@1646: public class VolatileCallSite extends CallSite {
jaroslav@1646:     /**
jaroslav@1646:      * Creates a call site with a volatile binding to its target.
jaroslav@1646:      * The initial target is set to a method handle
jaroslav@1646:      * of the given type which will throw an {@code IllegalStateException} if called.
jaroslav@1646:      * @param type the method type that this call site will have
jaroslav@1646:      * @throws NullPointerException if the proposed type is null
jaroslav@1646:      */
jaroslav@1646:     public VolatileCallSite(MethodType type) {
jaroslav@1646:         super(type);
jaroslav@1646:     }
jaroslav@1646: 
jaroslav@1646:     /**
jaroslav@1646:      * Creates a call site with a volatile binding to its target.
jaroslav@1646:      * The target is set to the given value.
jaroslav@1646:      * @param target the method handle that will be the initial target of the call site
jaroslav@1646:      * @throws NullPointerException if the proposed target is null
jaroslav@1646:      */
jaroslav@1646:     public VolatileCallSite(MethodHandle target) {
jaroslav@1646:         super(target);
jaroslav@1646:     }
jaroslav@1646: 
jaroslav@1646:     /**
jaroslav@1646:      * Returns the target method of the call site, which behaves
jaroslav@1646:      * like a {@code volatile} field of the {@code VolatileCallSite}.
jaroslav@1646:      * <p>
jaroslav@1646:      * The interactions of {@code getTarget} with memory are the same
jaroslav@1646:      * as of a read from a {@code volatile} field.
jaroslav@1646:      * <p>
jaroslav@1646:      * In particular, the current thread is required to issue a fresh
jaroslav@1646:      * read of the target from memory, and must not fail to see
jaroslav@1646:      * a recent update to the target by another thread.
jaroslav@1646:      *
jaroslav@1646:      * @return the linkage state of this call site, a method handle which can change over time
jaroslav@1646:      * @see #setTarget
jaroslav@1646:      */
jaroslav@1646:     @Override public final MethodHandle getTarget() {
jaroslav@1646:         return getTargetVolatile();
jaroslav@1646:     }
jaroslav@1646: 
jaroslav@1646:     /**
jaroslav@1646:      * Updates the target method of this call site, as a volatile variable.
jaroslav@1646:      * The type of the new target must agree with the type of the old target.
jaroslav@1646:      * <p>
jaroslav@1646:      * The interactions with memory are the same as of a write to a volatile field.
jaroslav@1646:      * In particular, any threads is guaranteed to see the updated target
jaroslav@1646:      * the next time it calls {@code getTarget}.
jaroslav@1646:      * @param newTarget the new target
jaroslav@1646:      * @throws NullPointerException if the proposed new target is null
jaroslav@1646:      * @throws WrongMethodTypeException if the proposed new target
jaroslav@1646:      *         has a method type that differs from the previous target
jaroslav@1646:      * @see #getTarget
jaroslav@1646:      */
jaroslav@1646:     @Override public void setTarget(MethodHandle newTarget) {
jaroslav@1646:         checkTargetChange(getTargetVolatile(), newTarget);
jaroslav@1646:         setTargetVolatile(newTarget);
jaroslav@1646:     }
jaroslav@1646: 
jaroslav@1646:     /**
jaroslav@1646:      * {@inheritDoc}
jaroslav@1646:      */
jaroslav@1646:     @Override
jaroslav@1646:     public final MethodHandle dynamicInvoker() {
jaroslav@1646:         return makeDynamicInvoker();
jaroslav@1646:     }
jaroslav@1646: }