184 lines
8.6 KiB
Java
184 lines
8.6 KiB
Java
/*
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* Copyright (c) 2008, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/**
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* This package provides a mechanism for defining and
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* inserting tracepoints into Java-technology based applications, which
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* can then be monitored by the tracing tools available on the system.
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* <p>
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* To add tracepoints to a program, you must first decide where to place the
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* tracepoints, what the logical names are for these points, what information
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* will be available to the tracing mechanisms at each point, and decide upon
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* any logical grouping.
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* <p>
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* You add instrumentation to a program in three steps:
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* <ul>
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* <li>First, declare tracepoints by creating interfaces to define
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* them, and include these interfaces in the program definition.
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* The declared interfaces are standard Java technology-based
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* interfaces and are compiled with the program.</li>
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* <li>Second, add code in the application to create an instance of the
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* interface at some point during the initialization of the application,
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* using a factory class provided by the system. The reference to the
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* instance can be stored as a global static, or passed as context to all
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* the places where it is needed.</li>
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* <li>Finally, add the actual tracepoints to the desired locations in the
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* application by inserting a call to one of the methods defined in the
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* interface, via the factory-created reference.</li>
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* </ul>
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* <p>
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* The method calls representing the tracepoints have no logical
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* impact on the program. The side effect of the call is that any
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* activated tracing mechanisms will be notified that the tracepoint has
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* been hit, and will take whatever actions are appropriate (for example,
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* logging the tracepoint, or triggering a DTrace probe, etc.). In most
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* cases, the impact on performance of adding tracepoints to the application
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* will be minimal.
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* <p>
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* Each logical grouping of tracepoints should be defined in a common
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* interface, called a <i>provider</i>. An application can have one or many
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* providers. Each provider is independent and can be created whenever
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* it is appropriate for that provider, for example, when a subsytem is
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* initialized. Providers should be disposed of when they are no longer
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* needed, to free up any associated system resources. Each tracepoint
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* in a provider is represented by a method in that interface. These methods
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* are referred to as <i>probes</i>. The method signature determines the probe
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* parameters. A call to the method with the specified parameters triggers
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* the probe and makes its parameter values visible to any associated tracing
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* mechanism.
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* <p>
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* User-defined interfaces which represent providers must extend the
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* {@code Provider} interface. To activate the system-defined
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* tracing mechanisms, you must obtain an instance of the
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* {@code ProviderFactory} class, and pass the class of the provider to
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* the {@code createProvider()} method. The returned instance is then used to
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* trigger the probes later in the application.
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* <p>
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* In addition to triggering the probes, the provider instance can be used
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* to obtain direct references to the {@code Probe} objects, which can be used
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* directly for triggering, or can be queried to determine whether the probe is
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* currently being traced. The {@code Provider} interface also defines a
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* {@code Provider.dispose()} method which is used to free up any resources
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* that might be associated with that provider.
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* <p>
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* When a probe is triggered, any activated tracing system will be given
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* the provider name, the probe name, and the values of the probe arguments.
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* The tracing system is free to consume this data is whatever way is
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* appropriate.
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* By default, the provider name is the same as the class name of the interface
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* that defines the provider. Similarly, the probe name is
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* the name of the method that defines the probe. These default values
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* can be over-ridden by annotations. The provider definition can be
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* annotated with the {@code @ProviderName} annotation, whose value will
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* indicate the provider name that the tracing system will use. Similarly,
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* the {@code @ProbeName} annotation annotates a declared method and
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* indicates the probe name that should be used in the place of the
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* method name. These annotations can be used to define providers and
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* probes with the same name, in cases where the semantics of the Java language
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* may prevent this.
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* <p>
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* Here is a very small and simple usage example:
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* <p>
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*
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<PRE>
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import com.sun.tracing.Provider;
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import com.sun.tracing.ProviderFactory;
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interface MyProvider extends Provider {
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void startProbe();
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void finishProbe(int value);
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}
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public class MyApplication {
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public static void main(String argv[]) {
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ProviderFactory factory = ProviderFactory.getDefaultFactory();
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MyProvider trace = factory.createProvider(MyProvider.class);
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trace.startProbe();
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int result = foo();
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trace.finishProbe(result);
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trace.dispose();
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}
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}
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</PRE>
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* <p>
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* The Java Development Kit (JDK) currently only includes one system-defined
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* tracing framework: DTrace. DTrace is enabled automatically whenever an
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* application is run on a system and a JDK release that supports it. When
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* DTrace is enabled, probes are made available for listing and matching by
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* DTrace scripts as soon as the provider is created. At the tracepoint, an
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* associated DTrace script is informed of the creation of the provider, and
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* it takes whatever action it is designed to take. Tracepoints in the
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* program have the following DTrace probe names:<br>
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* {@code <provider><pid>:<module>:<function>:<probe>}
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* Where:
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* <ul>
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* <li>{@code <provider>} the provider name as specified by the application</li>
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* <li>{@code <pid>} the operating system process ID</li>
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* <li>{@code <module>} undefined, unless specified by the application</li>
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* <li>{@code <function>} undefined, unless specified by the application</li>
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* <li>{@code <probe>} the probe name as specified by the application</li>
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* </ul>
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* <p>
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* The {@code com.sun.tracing.dtrace} package contains additional
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* annotations that can be used to control the names used for the
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* <code>module</code> and <code>function</code> fields, as well as annotations
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* that can be added to the provider to control probe stability and dependency
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* attributes.
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* <p>
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* Integer, float and string probe parameters are made available to DTrace
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* using
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* the built-in argument variables, {@code arg0 ... arg_n}. Integer-types
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* are passed by value (boxed values are unboxed), floating-point types are
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* passed as encoded integer
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* arguments, and {@code java.lang.String} objects are converted
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* to UTF8 strings, so they can be read into the DTrace script using the
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* {@code copyinstr()} intrinsic. Non-string and non-boxed primitive
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* reference arguments are only
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* placeholders and have no value.
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* <p>
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* Using the example above, with a theoretical process ID of 123, these are
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* the probes that can be traced from DTrace:
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<PRE>
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MyProvider123:::startProbe
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MyProvider123:::finishProbe
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</PRE>
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* When {@code finishProbe} executes, {@code arg0} will contain the
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* value of {@code result}.
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* <p>
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* The DTrace tracing mechanism is enabled for all providers, apart from in the
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* following circumstances:
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* <ul>
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* <li>DTrace is not supported on the underlying system.</li>
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* <li>The property {@code com.sun.tracing.dtrace} is set to "disable".</li>
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* <li>The RuntimePermission {@code com.sun.tracing.dtrace.createProvider}
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* is denied to the process.</li>
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* </ul>
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* <p>
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*/
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package com.sun.tracing;
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