/*

 * Copyright (c) 2016, 2018, 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, to associate the event type with a category, in the format

 * of a human-readable path.

 * <p>

 * The category determines how an event is presented to the user. Events that

 * are in the same category are typically displayed together in graphs and

 * trees. To avoid the overlap of durational events in graphical

 * representations, overlapping events must be in separate categories.

 * <p>

 * For example, to monitor image uploads to a web server with a separate thread

 * for each upload, an event called File Upload starts when the user uploads a

 * file and ends when the upload is complete. For advanced diagnostics about

 * image uploads, more detailed events are created (for example, Image Read,

 * Image Resize, and Image Write). During these detailed events. other low

 * level-events could occur (for example, Socket Read and File Write).

 * <p>

 * The following example shows a visualization that avoids overlaps:

 *

 * <pre>

 * -------------------------------------------------------------------

 *   |                         File Upload                        |

 * ------------------------------------------------------------------

 *   |       Image Read          | Image Resize |   Image Write   |

 * ------------------------------------------------------------------

 *   | Socket Read | Socket Read |              |    File Write   |

 * -------------------------------------------------------------------

 * </pre>

 *

 * The example can be achieved by using the following categories:

 *

 * <table class="striped">

 * <caption>Recording options and their purpose.</caption> <thead>

 * <tr>

 * <th scope="col">Event Name</th>

 * <th scope="col">Annotation</th>

 * </tr>

 * </thead> <tbody>

 * <tr>

 * <th scope="row">File Upload</th>

 * <td><code>@Category("Upload")</code></td>

 * </tr>

 * <tr>

 * <th scope="row">Image Read</th>

 * <td><code>@Category({"Upload", "Image Upload"})</code></td>

 * </tr>

 * <tr>

 * <th scope="row">Image Resize</th>

 * <td><code>@Category({"Upload", "Image Upload"})</code></td>

 * </tr>

 * <tr>

 * <th scope="row">Image Write</th>

 * <td><code>@Category({"Upload", "Image Upload"})</code></td>

 * </tr>

 * <tr>

 * <th scope="row">Socket Read</th>

 * <td><code>@Category("Java Application")</code></td>

 * </tr>

 * <tr>

 * <th scope="row">File Write</th>

 * <td><code>@Category("Java Application")</code></td>

 * </tr>

 * </tbody>

 * </table>

 * <p>

 * The File Upload, Image Read, and Socket Read events happen concurrently (in

 * the same thread), but the events are in different categories so they do not

 * overlap in the visualization.

 * <p>

 * The following examples shows how the category is used to determine how events

 * are visualized in a tree:

 *

 * <pre>

 *  |- Java Application

 *  |  |- Socket Read

 *  |  |- File Write

 *  |- Upload

 *     |- File Upload

 *     |- Image Upload

 *        |- Image Read

 *        |- Image Resize

 *        |- File Write

 * </pre>

 *

 * @since 9

 */

@MetadataDefinition

@Target({ ElementType.TYPE })

@Inherited

@Retention(RetentionPolicy.RUNTIME)

public @interface Category {

    /**

     * Returns the category names for this annotation, starting with the root.

     *

     * @return the category names

     */

    String[] value();

}