| /* |
| * Copyright (c) 2013, 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 jdk.internal.vm.annotation; |
| |
| import java.lang.annotation.ElementType; |
| import java.lang.annotation.Retention; |
| import java.lang.annotation.RetentionPolicy; |
| import java.lang.annotation.Target; |
| |
| /** |
| * <p>An annotation expressing that objects and/or their fields are |
| * expected to encounter memory contention, generally in the form of |
| * "false sharing". This annotation serves as a hint that such objects |
| * and fields should reside in locations isolated from those of other |
| * objects or fields. Susceptibility to memory contention is a |
| * property of the intended usages of objects and fields, not their |
| * types or qualifiers. The effects of this annotation will nearly |
| * always add significant space overhead to objects. The use of |
| * {@code @Contended} is warranted only when the performance impact of |
| * this time/space tradeoff is intrinsically worthwhile; for example, |
| * in concurrent contexts in which each instance of the annotated |
| * class is often accessed by a different thread. |
| * |
| * <p>A {@code @Contended} field annotation may optionally include a |
| * <i>contention group</i> tag. A contention group defines a set of one |
| * or more fields that collectively must be isolated from all other |
| * contention groups. The fields in the same contention group may not be |
| * pairwise isolated. With no contention group tag (or with the default |
| * empty tag: "") each {@code @Contended} field resides in its own |
| * <i>distinct</i> and <i>anonymous</i> contention group. |
| * |
| * <p>When the annotation is used at the class level, the effect is |
| * equivalent to grouping all the declared fields not already having the |
| * {@code @Contended} annotation into the same anonymous group. |
| * With the class level annotation, implementations may choose different |
| * isolation techniques, such as isolating the entire object, rather than |
| * isolating distinct fields. A contention group tag has no meaning |
| * in a class level {@code @Contended} annotation, and is ignored. |
| * |
| * <p>The class level {@code @Contended} annotation is not inherited and has |
| * no effect on the fields declared in any sub-classes. The effects of all |
| * {@code @Contended} annotations, however, remain in force for all |
| * subclass instances, providing isolation of all the defined contention |
| * groups. Contention group tags are not inherited, and the same tag used |
| * in a superclass and subclass, represent distinct contention groups. |
| * |
| * @since 1.8 |
| */ |
| @Retention(RetentionPolicy.RUNTIME) |
| @Target({ElementType.FIELD, ElementType.TYPE}) |
| public @interface Contended { |
| |
| /** |
| * The (optional) contention group tag. |
| * This tag is only meaningful for field level annotations. |
| * |
| * @return contention group tag. |
| */ |
| String value() default ""; |
| } |