/* * Copyright (c) 2008, 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 a mechanism for defining and * inserting tracepoints into Java-technology based applications, which * can then be monitored by the tracing tools available on the system. * <p> * To add tracepoints to a program, you must first decide where to place the * tracepoints, what the logical names are for these points, what information * will be available to the tracing mechanisms at each point, and decide upon * any logical grouping. * <p> * You add instrumentation to a program in three steps: * <ul> * <li>First, declare tracepoints by creating interfaces to define * them, and include these interfaces in the program definition. * The declared interfaces are standard Java technology-based * interfaces and are compiled with the program.</li> * <li>Second, add code in the application to create an instance of the * interface at some point during the initialization of the application, * using a factory class provided by the system. The reference to the * instance can be stored as a global static, or passed as context to all * the places where it is needed.</li> * <li>Finally, add the actual tracepoints to the desired locations in the * application by inserting a call to one of the methods defined in the * interface, via the factory-created reference.</li> * </ul> * <p> * The method calls representing the tracepoints have no logical * impact on the program.  The side effect of the call is that any * activated tracing mechanisms will be notified that the tracepoint has * been hit, and will take whatever actions are appropriate (for example, * logging  the tracepoint, or triggering a DTrace probe, etc.).  In most * cases, the impact on performance of adding tracepoints to the application * will be minimal. * <p> * Each logical grouping of tracepoints should be defined in a common * interface, called a <i>provider</i>.  An application can have one or many * providers.  Each provider is independent and can be created whenever * it is appropriate for that provider, for example, when a subsytem is * initialized.  Providers should be disposed of when they are no longer * needed, to free up any associated system resources.  Each tracepoint * in a provider is represented by a method in that interface.  These methods * are referred to as <i>probes</i>.  The method signature determines the probe * parameters.  A call to the method with the specified parameters triggers * the probe and makes its parameter values visible to any associated tracing * mechanism. * <p> * User-defined interfaces which represent providers must extend the * {@code Provider} interface.  To activate the system-defined * tracing mechanisms, you must obtain an instance of the * {@code ProviderFactory} class, and pass the class of the provider to * the {@code createProvider()} method.  The returned instance is then used to * trigger the probes later in the application. * <p> * In addition to triggering the probes, the provider instance can be used * to obtain direct references to the {@code Probe} objects, which can be used * directly for triggering, or can be queried to determine whether the probe is * currently being traced.  The {@code Provider} interface also defines a * {@code Provider.dispose()} method which is used to free up any resources * that might be associated with that provider. * <p> * When a probe is triggered, any activated tracing system will be given * the provider name, the probe name, and the values of the probe arguments. * The tracing system is free to consume this data is whatever way is * appropriate. * By default, the provider name is the same as the class name of the interface * that defines the provider. Similarly, the probe name is * the name of the method that defines the probe. These default values * can be over-ridden by annotations.  The provider definition can be * annotated with the {@code @ProviderName} annotation, whose value will * indicate the provider name that the tracing system will use.  Similarly, * the {@code @ProbeName} annotation annotates a declared method and * indicates the probe name that should be used in the place of the * method name.  These annotations can be used to define providers and * probes with the same name, in cases where the semantics of the Java language * may prevent this. * <p> * Here is a very small and simple usage example: * <p> *<PRE>   import com.sun.tracing.Provider;   import com.sun.tracing.ProviderFactory;    interface MyProvider extends Provider {       void startProbe();       void finishProbe(int value);   }    public class MyApplication {       public static void main(String argv[]) {           ProviderFactory factory = ProviderFactory.getDefaultFactory();           MyProvider trace = factory.createProvider(MyProvider.class);            trace.startProbe();           int result = foo();           trace.finishProbe(result);            trace.dispose();       }   }</PRE> * <p> * The Java Development Kit (JDK) currently only includes one system-defined * tracing framework: DTrace. DTrace is enabled automatically whenever an * application is run on a system and a JDK release that supports it. When * DTrace is enabled, probes are made available for listing and matching by * DTrace scripts as soon as the provider is created. At the tracepoint, an * associated DTrace script is informed of the creation of the provider, and * it takes whatever action it is designed to take. Tracepoints in the * program have the following DTrace probe names:<br> *   {@code <provider><pid>:<module>:<function>:<probe>} * Where: * <ul> * <li>{@code <provider>} the provider name as specified by the application</li> * <li>{@code <pid>} the operating system process ID</li> * <li>{@code <module>} undefined, unless specified by the application</li> * <li>{@code <function>} undefined, unless specified by the application</li> * <li>{@code <probe>} the probe name as specified by the application</li> * </ul> * <p> * The {@code com.sun.tracing.dtrace} package contains additional * annotations that can be used to control the names used for the * <code>module</code> and <code>function</code> fields, as well as annotations * that can be added to the provider to control probe stability and dependency * attributes. * <p> * Integer, float and string probe parameters are made available to DTrace * using * the built-in argument variables, {@code arg0 ... arg_n}.  Integer-types * are passed by value (boxed values are unboxed), floating-point types are * passed as encoded integer * arguments, and {@code java.lang.String} objects are converted * to UTF8 strings, so they can be read into the DTrace script using the * {@code copyinstr()} intrinsic.  Non-string and non-boxed primitive * reference arguments are only * placeholders and have no value. * <p> * Using the example above, with a theoretical process ID of 123, these are * the probes that can be traced from DTrace:<PRE>    MyProvider123:::startProbe    MyProvider123:::finishProbe</PRE> * When {@code finishProbe} executes, {@code arg0} will contain the * value of {@code result}. * <p> * The DTrace tracing mechanism is enabled for all providers, apart from in the * following circumstances: * <ul> * <li>DTrace is not supported on the underlying system.</li> * <li>The property {@code com.sun.tracing.dtrace} is set to "disable".</li> * <li>The RuntimePermission {@code com.sun.tracing.dtrace.createProvider} * is denied to the process.</li> * </ul> * <p> */ package com.sun.tracing;