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diff --git a/docs/devGuideDB/ltw.xml b/docs/devGuideDB/ltw.xml new file mode 100644 index 000000000..29fc4e1a0 --- /dev/null +++ b/docs/devGuideDB/ltw.xml @@ -0,0 +1,424 @@ +<chapter id="ltw" xreflabel="Load-Time Weaving"> + <title>Load-Time Weaving</title> + + <sect1 id="ltw-introduction"> + <title>Introduction</title> + + <para> The AspectJ 5 weaver takes class files as input and produces class files as output. + The weaving process itself can take place at one of three different times: compile-time, + post-compile time, and load-time. The class files produced by the weaving process (and + hence the run-time behaviour of an application) are the same regardless of the approach + chosen. </para> + + <itemizedlist> + <listitem> <para>Compile-time weaving is the simplest approach. When you have the source code + for an application, ajc will compile from source and produce woven class files as + output. The invocation of the weaver is integral to the ajc compilation process. The + aspects themselves may be in source or binary form. </para></listitem> + <listitem> <para>Post-compile weaving (also sometimes called binary weaving) is used to weave + existing class files and JAR files. As with compile-time weaving, + the aspects used for weaving may be in source or binary form. </para></listitem> + <listitem> <para>Load-time weaving (LTW) is simply binary weaving defered until the point that + a class loader loads a class file and defines the class to the JVM. To support this, + one or more "weaving class loaders", either provided explicitly by the run-time + environment or enabled through a "weaving agent" are required. </para></listitem> + </itemizedlist> + + <para> You may also hear the term "run-time weaving". We define this as the weaving of + classes that have already been defined to the JVM (without reloading those + classes). AspectJ 5 does not provide explicit support for run-time weaving although + simple coding patterns can support dynamically enabling and disabling advice in aspects. </para> + + <sect2 id="weaving-class-files-more-than-once" xreflabel="weaving-class-files-more-than-once"> + <title>Weaving class files more than once</title> + + <para> By default a class file that has been woven by the AspectJ compiler cannot + subsequently be rewoven (passed as input to the weaver). If you are developing + AspectJ applications that are to be used in a load-time weaving environment, you + need to specify the <literal>-Xreweavable</literal> compiler option when building + them. This causes AspectJ to save additional state in the class files that is used + to support subsequent reweaving. </para> + <para><!-- FIXME AV -->As per AspectJ 1.5.0 M3 aspects (code style or annotation style) are + reweavable by default, and weaved classes may be as well in 1.5.0 final.</para> + </sect2> + </sect1> + + <sect1 id="ltw-rules"> + <title>Load-time Weaving Requirements</title> + + <para> All load-time weaving is done in the context of a class loader, and hence the set of + aspects used for weaving and the types that can be woven are affected by the class + loader delegation model. This ensures that LTW complies with the Java 2 security model. + The following rules govern the interaction of load-time weaving with class loading: </para> + + <orderedlist> + <listitem> <para>All aspects to be used for weaving must be defined to the weaver before any + types to be woven are loaded.</para></listitem> + <listitem> <para>All abstract and concrete aspects visible to the weaver + are available for extending (abstract aspects) and using for weaving. + A visible aspect is one defined by the + weaving class loader or one of its parent class loaders.</para></listitem> + <listitem><para>A class loader may only weave classes that it defines. It may not weave + classes loaded by a delegate or parent class loader.</para></listitem> + </orderedlist> + + </sect1> + + <sect1 id="ltw-configuration"> + <title>Configuration</title> + <para>AspectJ 5 supports a number of mechanisms designed to make load-time weaving as + easy to use as possibe. The load-time weaving mechanism is chosen through JVM startup options. + Configuration files determine the set of aspects to be used for weaving and which + types will be woven. Additional diagnostic options allow the user to debug the configuration and + weaving process. </para> + + <sect2 id="enabling-load-time-weaving" xreflabel="enabling-load-time-weaving"> + <title>Enabling Load-time Weaving</title> + <para> AspectJ 5 supports several different ways of enabling load-time weaving for + an application: agents, a command-line launch script, and a set of interfaces for + integration of AspectJ load-time weaving in custom environments. </para> + <variablelist> + <varlistentry> + <term>Agents</term> + <listitem> + <para>AspectJ 5 ships with a number of load-time weaving agents that + enable load-time weaving. These agents and their configuration + are execution environment dependent. Configuration for the supported environments is discussed + later in this chapter.</para> + <para> + Using Java 5 JVMTI you can specify the <literal>-javaagent:pathto/aspectjweaver.jar</literal> option + to the JVM.</para><para> + Using BEA JRockit and Java 1.3/1.4, the very same behavior can be obtained using BEA JRockit JMAPI features with + the <literal>-Xmanagement:class=org.aspectj.weaver.loadtime.JRockitAgent</literal> + </para> + </listitem> + </varlistentry> + <!-- FIXME: must be made consistent (aop.xml , CL hierarchy etc) --> +<!-- <varlistentry>--> +<!-- <term>Command line</term>--> +<!-- <listitem>--> +<!-- <para> AspectJ includes a script "aj" that allows programs executed at--> +<!-- the command line to take advantage of load-time weaving. --> +<!-- The script is customized when AspectJ is installed depending on the chosen --> +<!-- JDK. For example, for JDK 1.4 the script uses the--> +<!-- <literal>-Djava.system.class.loader</literal> system property to replace--> +<!-- the system class loader with a weaving class loader allowing classes --> +<!-- loaded from the CLASSPATH to be woven. --> +<!-- For JDK 1.5 the JVMTI weaving agent is used allowing classes loaded by all--> +<!-- class loaders to be woven. Versions of the JDK prior to 1.3 are not--> +<!-- supported by the "aj" mechanism. </para>--> +<!-- </listitem>--> +<!-- </varlistentry>--> + <varlistentry> + <term>Custom Integration</term> + <listitem> + <para> A public interface is provided to allow a user written class loader + to instantiate a weaver and weave classes after loading and before + defining them in the JVM. This enables load-time weaving to be supported in + environments where no weaving agent is available. It also allows the + user to explicity restrict by class loader which classes can be woven.</para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + + <sect2 id="configuring-load-time-weaving-with-aopxml-files" xreflabel="configuring-load-time-weaving-with-aopxml-files"> + <title>Configuring Load-time Weaving with aop.xml files</title> + + <para>The weaver is configured using one or more <literal>META-INF/aop.xml</literal> + files located on the class loader search path. Each file may define a list of + concrete aspects to be used for weaving, type patterns describing which types + should woven, and a set of options to be passed to the weaver. In addition AspectJ 5 + supports the definition of concrete aspects in XML. Aspects defined in this way + must extend an abstract aspect visible to the weaver. The abstract aspect + may define abstract pointcuts (but not abstract + methods). The following example shows a simple aop.xml file: </para> + <programlisting><![CDATA[ + <aspectj> + + <aspects> + <!-- declare two existing aspects to the weaver --> + <aspect name="com.MyAspect"/> + <aspect name="com.MyAspect.Inner"/> + + <!-- define a concrete aspect inline --> + <concrete-aspect name="com.xyz.tracing.MyTracing" extends="tracing.AbstractTracing"> + <pointcut name="tracingScope" expression="within(org.maw.*)"/> + </concrete-aspect> + + <!-- Of the set of aspects known to the weaver, use aspects matching + the type pattern "com..*" for weaving. --> + <include within="com..*"/> + + <!-- Do not use any aspects with the @CoolAspect annotation for weaving --> + <exclude within="@CoolAspect *"/> + + </aspects> + + <weaver options="-verbose -XlazyTjp"> + <!-- Weave types that are within the javax.* or org.aspectj.* + packages. Also weave all types in the foo package that do + not have the @NoWeave annotation. --> + <include within="javax.*"/> + <include within="org.aspectj.*"/> + <include within="(!@NoWeave foo.*) AND foo.*"/> + <dump within="somepack.*"/><!-- will dump weaved classes to the "./_ajdump" folder on disk (for diagnostic purpose) --> + </weaver> + + </aspectj> + + ]]></programlisting> + + <para> + An aop.xml file contains two key sections: "aspects" defines one + or more aspects to the weaver and controls which aspects are to be + used in the weaving process; "weaver" defines weaver options and which + types should be woven. + </para> + + <para> + The simplest way to define an aspect to the weaver is to + specify the fully-qualified name of the aspect type in an aspect element. + You can also + declare (and define to the weaver) aspects inline in the aop.xml file. + This is done using the "concrete-aspect" element. A concrete-aspect + declaration must provide a pointcut definition for every abstract + pointcut in the abstract aspect it extends. This mechanism is a + useful way of externalizing configuration for infrastructure and + auxiliary aspects where the pointcut definitions themselves can be + considered part of the configuration of the service. + </para> + + <para> + <emphasis> + Note: concrete-aspect is not available in AspectJ 1.5 M3. + </emphasis> + </para> + + <para> + The aspects element may optionally contain one or more include and + exclude elements (by default, all defined aspects are used for weaving). + Specifying include or exclude elements restricts the set of defined + aspects to be used for weaving to those that are matched by an include + pattern, but not by an exclude pattern. The 'within' attribute accepts + a type pattern of the same form as a within pcd, except that && + and || are replaced by 'AND' and 'OR'. + </para> + + <para> + The weaver element is used to pass options to the weaver and to specify + the set of types that should be woven. If no include elements are specified + then all types seen by the weaver will be woven. + </para> + + + <para> When several configuration files are visible from a given weaving class loader + their contents are conceptually merged (this applies to both aop.xml files + and to aop.properties files as described in the next section). + The files are merged in the order they are + found on the search path (regular <literal>getResourceAsStream</literal> lookup) + according to the following rules: </para> + <itemizedlist> + <!-- FIXME AV - looks like we can refine conf in a child CL - not good --> + <listitem> <para>The set of available aspects is the set of all + declared and defined aspects (<literal>aspect</literal> and + <literal>concrete-aspect</literal> elements of the <literal>aspects</literal> + section).</para></listitem> + <listitem> <para>The set of aspects used for weaving is the subset of the available + aspects that are matched by at least one include statement and are not matched + by any exclude statements. If there are no include statements then all non-excluded + aspects are included.</para></listitem> + <listitem> <para> The set of types to be woven are those types matched by at + least one weaver <literal>include</literal> element and not matched by any + weaver <literal>exclude</literal> element. If there are no weaver include + statements then all non-excluded types are included.</para></listitem> + <listitem> <para> The weaver options are derived by taking the union of the + options specified in each of the weaver options attribute specifications. Where an + option takes a value e.g. <literal>-warn:none</literal> the most recently defined value + will be used.</para></listitem> + </itemizedlist> + + <para>It is not an error for the same aspect to be defined to the weaver in + more than one visible <literal>META-INF/aop.xml</literal> file. + However, if a declarative concrete aspect + is declared in more than aop.xml file then an error will be issued. + A concrete aspect + defined in this way will be used to weave types loaded by the + class loader that loaded the aop.xml file in which it was defined. + </para> + + <para> A <literal>META-INF/aop.xml</literal> file will automatically be generated when + using the <literal>-outjar</literal> option of the AspectJ compiler. + It will simply contain a (possibly empty) set of aspect elements, one for + each concrete aspect included in the JAR. </para> + </sect2> + + <!-- TODO someone implement that --> + <!-- + <sect2 id="configuring-load-time-weaving-with-properties-files" xreflabel="configuring-load-time-weaving-with-properties-files"> + <title>Configuring Load-time Weaving with Properties Files</title> + <para> For memory constrained environments or those without support for XML a simple + Java Properties file can be used to configure LTW. Just like XML files, + <literal>META-INF/aop.properties</literal> files are loaded from the class loader + search path. Everything that can be configured through XML can be configured using a + Properties file, with the exception of declarative concrete aspects. For example: </para> + <programlisting><![CDATA[ + aspects.names=com.MyAspect,com.MyAspect.Inner + aspects.include=com..* + aspects.exclude=@CoolAspect + + weaver.options=-verbose -XlazyTjp + weaver.include=javax.* OR org.aspectj.* + ]]></programlisting> + </sect2> + --> + + <sect2 id="weaver-options" xreflabel="weaver-options"> + <title>Weaver Options</title> + <para> The table below lists the AspectJ options supported by LTW. All other options + will be ignored and a warning issued. </para> + <informaltable> + <tgroup cols="2"> + <thead> + <row> + <entry>Option</entry> + <entry>Purpose</entry> + </row> + </thead> + <tbody> + <row> + <entry> + <literal>-verbose</literal> + </entry> + <entry>Issue informational messages about the weaving process. If ever you need to have information + when the load time weaving engine is bootstrapped (hence its logger as per <literal>-XmessageHandlerClass:...</literal> not ready yet), + you can use the option <literal>-Daj.weaving.verbose=true</literal> on the JVM startup command line. Messages will then be printed + on stderr as long as the message handler class is not ready. + </entry> + </row> + <row> + <entry> + <literal>-1.5</literal> + </entry> + <entry>Run the weaver in 1.5 mode (supports autoboxing in + join point matching)</entry> + </row> + <row> + <entry> + <literal>-XlazyTjp</literal> + </entry> + <entry>Performance optimization for aspects making use + of thisJoinPoint (non-static parts)</entry> + </row> + <row> + <entry> + <literal>-Xlintfile:pathToAResource</literal> + </entry> + <entry>Configure lint messages as specified in the given resource (visible from this aop.xml file' classloader)</entry> + </row> + <row> + <entry> + <literal>-Xlint:default, -Xlint:ignore, ...</literal> + </entry> + <entry>Configure lint messages, refer to documentation for meaningfull values</entry> + </row> + <row> + <entry> + <literal>-nowarn, -warn:none</literal> + </entry> + <entry>Suppress warning messages</entry> + </row> + <row> + <entry> + <literal>-proceedOnError</literal> + </entry> + <entry>Continue weaving even if errors occur (for example, + "... already woven" errors)</entry> + </row> + <row> + <entry> + <literal>-Xreweavable</literal> + </entry> + <entry>Produce class files that can subsequently be rewoven</entry> + </row> + <row> + <entry> + <literal>-XnoInline</literal> + </entry> + <entry>Don't inline around advice.</entry> + </row> + <row> + <entry> + <literal>-showWeaveInfo</literal> + </entry> + <entry>Issue informational messages whenever the weaver touches a class file</entry> + </row> + <row> + <entry> + <literal>-XmessageHandlerClass:...</literal> + </entry> + <entry>Provide alternative output destination to stdout/stderr for all weaver messages. + The given value must be the full qualified class name of a class that implements + <literal>org.aspectj.bridge.IMessageHandler</literal> + and that is visible from where the <literal>aop.xml</literal> is packed. + If more than one such options are used, + the first occurence only is taken into account. + You must also be very cautious about using a custom handler since it is likely that it will be invoked + (as well as all its third parties) while the weaving is done, which means that f.e. it cannot be weaved + by the aspects that are configured within the same deployment unit. + </entry> + </row> + </tbody> + </tgroup> + </informaltable> + </sect2> + </sect1> + + <sect1 id="ltw-specialcases"> + <title>Special cases</title> + <para> + Those classes are not exposed to the LTW infrastructure, no matter + the configuration of the <literal>aop.xml</literal> file(s): + <itemizedlist> + <listitem> <para>All <literal>org.aspectj.*</literal> classes (and subpackages) - as those are needed by the infrastructure itself</para></listitem> + <listitem> <para>All <literal>java.*</literal> and <literal>javax.*</literal> classes (and subpackages)</para></listitem> + <listitem> <para>All <literal>sun.reflect.*</literal> classes - as those are JDK specific classes used when reflective calls occurs</para></listitem> + </itemizedlist> + </para> + <para> + Despite these restrictions, it is perfectly possible to match call join points for calls to these types providing the calling + class is exposed to the weaver. Subtypes of these excluded types that are exposed to the weaver may of course be woven. + </para> + <para> + Note that dynamic proxy representations are exposed to the LTW infrastructure and are not considered + a special case. + </para> + </sect1> + + <sect1 id="ltw-packaging"> + <title>Runtime Requirements for Load-time Weaving</title> + <para> To use LTW the <literal>aspectjweaver.jar</literal> library must be added to the + classpath. This contains the AspectJ 5 runtime, weaver, weaving class loader and + weaving agents. It also contains the DTD for parsing XML weaving configuration files. </para> + </sect1> + + <sect1 id="ltw-agents"> + <title>Supported Agents</title> + <sect2 id="jvmti" xreflabel="jvmti"> + <title>JVMTI</title> + <para> When using Java 5 the JVMTI agent can be used by starting the JVM with the + following option (adapt according to the path to aspectjweaver.jar): </para> + <programlisting><![CDATA[ + -javaagent:pathto/aspectjweaver.jar + ]]></programlisting> + </sect2> + <sect2 id="jrockit" xreflabel="jrockit"> + <title>JRockit with Java 1.3/1.4 (use JVMTI on Java 5)</title> + <para> The JRockit agent is configured with the following JVM option: </para> + <programlisting><![CDATA[ + -Xmanagement:class=org.aspectj.weaver.loadtime.JRockitAgent + ]]></programlisting> + </sect2> + </sect1> +</chapter> + |