/*
* 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;