/*

 * 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 VolatileCallSite} is a {@link CallSite} whose target acts like a volatile variable.

 * An {@code invokedynamic} instruction linked to a {@code VolatileCallSite} sees updates

 * to its call site target immediately, even if the update occurs in another thread.

 * There may be a performance penalty for such tight coupling between threads.

 * <p>

 * Unlike {@code MutableCallSite}, there is no

 * {@linkplain MutableCallSite#syncAll syncAll operation} on volatile

 * call sites, since every write to a volatile variable is implicitly

 * synchronized with reader threads.

 * <p>

 * In other respects, a {@code VolatileCallSite} is interchangeable

 * with {@code MutableCallSite}.

 * @see MutableCallSite

 * @author John Rose, JSR 292 EG

 * @since 1.7

 */

public class VolatileCallSite extends CallSite {

    /**

     * Creates a call site with a volatile binding to its target.

     * The initial target is set to a method handle

     * of the given type which will throw an {@code IllegalStateException} if called.

     * @param type the method type that this call site will have

     * @throws NullPointerException if the proposed type is null

     */

    public VolatileCallSite(MethodType type) {

        super(type);

    }

    /**

     * Creates a call site with a volatile binding to its target.

     * The target is set to the given value.

     * @param target the method handle that will be the initial target of the call site

     * @throws NullPointerException if the proposed target is null

     */

    public VolatileCallSite(MethodHandle target) {

        super(target);

    }

    /**

     * Returns the target method of the call site, which behaves

     * like a {@code volatile} field of the {@code VolatileCallSite}.

     * <p>

     * The interactions of {@code getTarget} with memory are the same

     * as of a read from a {@code volatile} field.

     * <p>

     * In particular, the current thread is required to issue a fresh

     * read of the target from memory, and must not fail to see

     * a recent update to the target by another thread.

     *

     * @return the linkage state of this call site, a method handle which can change over time

     * @see #setTarget

     */

    @Override public final MethodHandle getTarget() {

        return getTargetVolatile();

    }

    /**

     * Updates the target method of this call site, as a volatile variable.

     * The type of the new target must agree with the type of the old target.

     * <p>

     * The interactions with memory are the same as of a write to a volatile field.

     * In particular, any threads is guaranteed to see the updated target

     * the next time it calls {@code getTarget}.

     * @param newTarget the new target

     * @throws NullPointerException if the proposed new target is null

     * @throws WrongMethodTypeException if the proposed new target

     *         has a method type that differs from the previous target

     * @see #getTarget

     */

    @Override public void setTarget(MethodHandle newTarget) {

        checkTargetChange(getTargetVolatile(), newTarget);

        setTargetVolatile(newTarget);

    }

    /**

     * {@inheritDoc}

     */

    @Override

    public final MethodHandle dynamicInvoker() {

        return makeDynamicInvoker();

    }

}