src/jdk.jfr/share/classes/jdk/jfr/Enabled.java

/*
 * Copyright (c) 2016, 2023, 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.jfr;

import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Event annotation, determines if an event should be enabled by default.
 * <p>
 * If an event doesn't have the annotation, then by default the event is
 * enabled.
 * <p>
 * The following example shows how the {@code Enabled} annotation can be used to
 * create a disabled event. A disabled event will at most have the overhead of
 * an allocation, or none if the runtime JIT compiler is able to eliminate it.
 *
 * {@snippet class = "Snippets" region = "EnabledOverview"}
 *
 * The event can be enabled programmatically, or on command line when needed,
 * for example:
 *
 * {@snippet class = "Snippets" region = "EnabledOverviewCommandLine"}
 *
 * @since 9
 */
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@MetadataDefinition
public @interface Enabled {
    /**
     * Setting name {@code "enabled"}, signifies that the event should be
     * recorded.
     */
    public static final String NAME = "enabled";

    /**
     * Returns {@code true} if by default the event should be enabled, {@code false} otherwise.
     *
     * @return {@code true} if by default the event should be enabled by default, {@code false} otherwise
     */
    boolean value() default true;
}