87 lines
4.1 KiB
Java
87 lines
4.1 KiB
Java
|
/*
|
||
|
|
* 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;
|
||
|
|
|
||
|
|
// Android-note: Contended-specific implementation notes not relevant for Android.
|
||
|
|
/**
|
||
|
|
* <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
|
||
|
|
*/
|
||
|
|
// Android-changed: RetentionPolicy.SOURCE is sufficient as this is no-op on Android.
|
||
|
|
// @Retention(RetentionPolicy.RUNTIME)
|
||
|
|
@Retention(RetentionPolicy.SOURCE)
|
||
|
|
@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 "";
|
||
|
|
}
|