/* * Copyright (c) 2016, 2020, 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.
*/
/** * This package provides classes to create events and control Flight Recorder. * <p> * <b>Defining events</b> * <p> * Flight Recorder collects data as events. An event has a time stamp, duration * and usually an application-specific payload, useful for diagnosing the * running application up to the failure or crash. * <p> * To define a Flight Recorder event, extend {@link jdk.jfr.Event} and add * fields that matches the data types of the payload. Metadata about fields, * such as labels, descriptions and units, can be added by using the annotations * available in the {@code jdk.jfr} package, or by using a user-defined * annotation that has the {@link jdk.jfr.MetadataDefinition} annotation. * <p> * After an event class is defined, instances can be created (event objects). * Data is stored in the event by assigning data to fields. Event timing can be * explicitly controlled by using the {@code begin} and {@code end} methods * available in the {@code Event} class. * <p> * Gathering data to store in an event can be expensive. The * {@link jdk.jfr.Event#shouldCommit()} method can be used to verify whether * an event instance would actually be written to the system when * the {@link jdk.jfr.Event#commit()} method is invoked. * If {@link jdk.jfr.Event#shouldCommit()} returns {@code false}, * then those operations can be avoided. * <p> * Sometimes the field layout of an event is not known at compile time. In that * case, an event can be dynamically defined. However, dynamic events might not * have the same level of performance as statically defined ones and tools might * not be able to identify and visualize the data without knowing the layout. * <p> * To dynamically define an event, use the {@link jdk.jfr.EventFactory} class * and define fields by using the {@link jdk.jfr.ValueDescriptor} class, and * define annotations by using the {@link jdk.jfr.AnnotationElement} class. Use * the factory to allocate an event and the * {@link jdk.jfr.Event#set(int, Object)} method to populate it. * <p> * <b>Controlling Flight Recorder</b> * <p> * Flight Recorder can be controlled locally by using the {@code jcmd} * command line tool or remotely by using the {@code FlightRecorderMXBean} * interface, registered in the platform MBeanServer. When direct programmatic * access is needed, a Flight Recorder instance can be obtained by invoking * {@link jdk.jfr.FlightRecorder#getFlightRecorder()} and a recording created by * using {@link jdk.jfr.Recording} class, from which the amount of data to * record is configured. * <p> * <b>Settings and configuration</b> * <p> * A setting consists of a name/value pair, where <em>name</em> specifies the * event and setting to configure, and the <em>value</em> specifies what to set * it to. * <p> * The name can be formed in the following ways: * <p> * {@code * <event-name> + "#" + <setting-name> * } * <p> * or * <p> * {@code * <event-id> + "#" + <setting-name> * } * <p> * For example, to set the sample interval of the CPU Load event to once every * second, use the name {@code "jdk.CPULoad#period"} and the value * {@code "1 s"}. If multiple events use the same name, for example if an event * class is loaded in multiple class loaders, and differentiation is needed * between them, then the name is {@code "56#period"}. The ID for an event is * obtained by invoking {@link jdk.jfr.EventType#getId()} method and is valid * for the Java Virtual Machine instance that the event is registered in. * <p> * A list of available event names is retrieved by invoking * {@link jdk.jfr.FlightRecorder#getEventTypes()} and * {@link jdk.jfr.EventType#getName()}. A list of available settings for an * event type is obtained by invoking * {@link jdk.jfr.EventType#getSettingDescriptors()} and * {@link jdk.jfr.ValueDescriptor#getName()}. * <p> * <b>Predefined settings</b> * <table class="striped"> * <caption>Event setting names and their purpose.</caption> <thead> * <tr> * <th scope="col">Name</th> * <th scope="col">Description</th> * <th scope="col">Default value</th> * <th scope="col">Format</th> * <th scope="col">Example values</th> * </tr> * </thead> <tbody> * <tr> * <th scope="row">{@code enabled}</th> * <td>Specifies whether the event is recorded</td> * <td>{@code "true"}</td> * <td>String representation of a {@code Boolean} ({@code "true"} or * {@code "false"})</td> * <td>{@code "true"}<br> * {@code "false"}</td> * </tr> * <tr> * <th scope="row">{@code threshold}</th> * <td>Specifies the duration below which an event is not recorded</td> * <td>{@code "0"} (no limit)</td> * <td>{@code "0"} if no threshold is used, otherwise a string representation of * a positive {@code Long} followed by a space and one of the following units: * <ul style="list-style-type:none"> * <li>{@code "ns"} (nanoseconds) * <li>{@code "us"} (microseconds) * <li>{@code "ms"} (milliseconds) * <li>{@code "s"} (seconds) * <li>{@code "m"} (minutes) * <li>{@code "h"} (hours) * <li>{@code "d"} (days) * </ul> * <td>{@code "0"}<br> * {@code "10 ms"}<br> * "1 s"</td> * </tr> * <tr> * <th scope="row">{@code period}</th> * <td>Specifies the interval at which the event is emitted, if it is * periodic</td> * <td>{@code "everyChunk"}</td> * <td>{@code "everyChunk"}, if a periodic event should be emitted with every * file rotation, otherwise a string representation of a positive {@code Long} * value followed by an empty space and one of the following units: * <ul style="list-style-type:none"> * <li>{@code "ns"} (nanoseconds) * <li>{@code "us"} (microseconds) * <li>{@code "ms"} (milliseconds) * <li>{@code "s"} (seconds) * <li>{@code "m"} (minutes) * <li>{@code "h"} (hours) * <li>{@code "d"} (days) * </ul> * </td> * <td>{@code "20 ms"}<br> * {@code "1 s"}<br> * {@code "everyChunk"}</td> * * </tr> * <tr> * <th scope="row">{@code stackTrace}</th> * <td>Specifies whether the stack trace from the {@link Event#commit()} method * is recorded</td> * <td>{@code "true"}</td> * <td>String representation of a {@code Boolean} ({@code "true"} or * {@code "false"})</td> * <td>{@code "true"},<br> * {@code "false"}</td> * </tr> * </tbody> * </table> * <p> * <b>Null-handling</b> * <p> * All methods define whether they accept or return {@code null} in the Javadoc. * Typically this is expressed as {@code "not null"}. If a {@code null} * parameter is used where it is not allowed, a * {@code java.lang.NullPointerException} is thrown. If a {@code null} * parameters is passed to a method that throws other exceptions, such as * {@code java.io.IOException}, the {@code java.lang.NullPointerException} takes * precedence, unless the Javadoc for the method explicitly states how * {@code null} is handled, i.e. by throwing * {@code java.lang.IllegalArgumentException}. * * @since 9
*/ package jdk.jfr;
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