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

/*
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 * 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,
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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, specifies the default setting value for a periodic event.
 * <p>
 * The following example shows how the {@code Period} annotation can be used
 * to emit events at different intervals.
 *
 * {@snippet class = "Snippets" region = "PeriodOverview"}
 *
 * @since 9
 */
@MetadataDefinition
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Target(ElementType.TYPE)
public @interface Period {
    /**
     * Settings name {@code "period"} for configuring periodic events
     */
    public static final String NAME = "period";

    /**
     * Returns the default setting value for a periodic setting.
     * <p>
     * String representation of a positive {@code Long} value followed by an empty
     * space and one of the following units:<br>
     * <br>
     * {@code "ns"} (nanoseconds)<br>
     * {@code "us"} (microseconds)<br>
     * {@code "ms"} (milliseconds)<br>
     * {@code "s"} (seconds)<br>
     * {@code "m"} (minutes)<br>
     * {@code "h"} (hours)<br>
     * {@code "d"} (days)<br>
     * <p>
     * Example values: {@code "0 ns"}, {@code "10 ms"}, and {@code "1 s"}.
     * <p>
     * A period may also be {@code "everyChunk"} to specify that it occurs at
     * least once for every recording file. The number of events that are emitted
     * depends on how many times the file rotations occur when data is recorded.
     *
     * @return the default setting value, not {@code null}
     */
    String value() default "everyChunk";
}