diff -r 000000000000 -r c880a8a8803b rt/emul/compact/src/main/java/java/lang/invoke/VolatileCallSite.java --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/rt/emul/compact/src/main/java/java/lang/invoke/VolatileCallSite.java Sat Aug 09 11:11:13 2014 +0200 @@ -0,0 +1,109 @@ +/* + * 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. + *

+ * 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. + *

+ * In other respects, a {@code VolatileCallSite} is interchangeable + * with {@code MutableCallSite}. + * @see MutableCallSite + * @author John Rose, JSR 292 EG + */ +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}. + *

+ * The interactions of {@code getTarget} with memory are the same + * as of a read from a {@code volatile} field. + *

+ * 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. + *

+ * 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(); + } +}