1 /*
   2  * Copyright (c) 2016, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.jfr;
  27 
  28 import java.lang.annotation.ElementType;
  29 import java.lang.annotation.Inherited;
  30 import java.lang.annotation.Retention;
  31 import java.lang.annotation.RetentionPolicy;
  32 import java.lang.annotation.Target;
  33 
  34 /**
  35  * Event annotation, to associate the event type with a category, in the format
  36  * of a human-readable path.
  37  * <p>
  38  * The category determines how an event is presented to the user. Events that
  39  * are in the same category are typically displayed together in graphs and
  40  * trees. To avoid the overlap of durational events in graphical
  41  * representations, overlapping events must be in separate categories.
  42  * <p>
  43  * For example, to monitor image uploads to a web server with a separate thread
  44  * for each upload, an event called File Upload starts when the user uploads a
  45  * file and ends when the upload is complete. For advanced diagnostics about
  46  * image uploads, more detailed events are created (for example, Image Read,
  47  * Image Resize, and Image Write). During these detailed events. other low
  48  * level-events could occur (for example, Socket Read and File Write).
  49  * <p>
  50  * The following example shows a visualization that avoids overlaps:
  51  *
  52  * <pre>
  53  * -------------------------------------------------------------------
  54  *   |                         File Upload                        |
  55  * ------------------------------------------------------------------
  56  *   |       Image Read          | Image Resize |   Image Write   |
  57  * ------------------------------------------------------------------
  58  *   | Socket Read | Socket Read |              |    File Write   |
  59  * -------------------------------------------------------------------
  60  * </pre>
  61  *
  62  * The example can be achieved by using the following categories:
  63  *
  64  * <table class="striped">
  65  * <caption>Recording options and their purpose.</caption> <thead>
  66  * <tr>
  67  * <th scope="col">Event Name</th>
  68  * <th scope="col">Annotation</th>
  69  * </tr>
  70  * </thead> <tbody>
  71  * <tr>
  72  * <th scope="row">File Upload</th>
  73  * <td><code>@Category("Upload")</code></td>
  74  * </tr>
  75  * <tr>
  76  * <th scope="row">Image Read</th>
  77  * <td><code>@Category({"Upload", "Image Upload"})</code></td>
  78  * </tr>
  79  * <tr>
  80  * <th scope="row">Image Resize</th>
  81  * <td><code>@Category({"Upload", "Image Upload"})</code></td>
  82  * </tr>
  83  * <tr>
  84  * <th scope="row">Image Write</th>
  85  * <td><code>@Category({"Upload", "Image Upload"})</code></td>
  86  * </tr>
  87  * <tr>
  88  * <th scope="row">Socket Read</th>
  89  * <td><code>@Category("Java Application")</code></td>
  90  * </tr>
  91  * <tr>
  92  * <th scope="row">File Write</th>
  93  * <td><code>@Category("Java Application")</code></td>
  94  * </tr>
  95  * </tbody>
  96  * </table>
  97  * <p>
  98  * The File Upload, Image Read, and Socket Read events happen concurrently (in
  99  * the same thread), but the events are in different categories so they do not
 100  * overlap in the visualization.
 101  * <p>
 102  * The following examples shows how the category is used to determine how events
 103  * are visualized in a tree:
 104  *
 105  * <pre>
 106  *  |- Java Application
 107  *  |  |- Socket Read
 108  *  |  |- File Write
 109  *  |- Upload
 110  *     |- File Upload
 111  *     |- Image Upload
 112  *        |- Image Read
 113  *        |- Image Resize
 114  *        |- File Write
 115  * </pre>
 116  *
 117  * @since 8
 118  */
 119 @MetadataDefinition
 120 @Target({ ElementType.TYPE })
 121 @Inherited
 122 @Retention(RetentionPolicy.RUNTIME)
 123 public @interface Category {
 124     /**
 125      * Returns the category names for this annotation, starting with the root.
 126      *
 127      * @return the category names
 128      */
 129     String[] value();
 130 }