<chapter id="trace" xreflabel="Tracing">
    <title>Tracing</title>
    
    <sect1 id="trace-introduction">
        <title>Introduction</title>
        
        <para> 
            The AspectJ developers have instrumented the compiler/weaver with
            many "trace" messages for their own debugging use.  These remain in
            the production releases because tracing helps when it is hard to 
            isolate the problem in a test case.  This sections describes how
            to enable tracing so you can provide trace information on bug reports.
        </para> 
        <para> 
            The usual approach to opening a report on Bugzilla is to describe the symptoms of the 
        problem and attach a simple testcase. This allows the AspectJ team to try and reproduce the problem in
        an attempt to fix it as well as improve the test suite. Unfortunately it may not be possible
        to produce such a testcase either because your program is too large or is commercially sensitive. Alternatively 
        the problem may relate to your specific environment where AspectJ is being used and will not be
        reproducible by the AspectJ team. In each of these situations you can produce a
        trace of the compiler when the problem occurs instead. This can then be attached to the bug report. </para>

        <sect2 id="trace-configuration" xreflabel="Configuring Tracing">
            <title>Configuring Tracing</title>
        
            <para> When available (Java 5 or later) AspectJ will use the 
            <ulink url="http://java.sun.com/j2se/1.5.0/docs/guide/logging/index.html">
            java.util.logging</ulink> infrastructure
            configured using a <literal>logging.properties</literal> file. By default only error
            and fatal events will be logged but less severe warnings as well as fine-grained
            method entry and exit events can be obtained using the appropriate configuration. All
            regular compiler messages can also be logged through the infrastructure by setting the
            <literal>org.aspectj.weaving.messages</literal> System property. </para>
            
            <para> If you are running the AspectJ compiler/weaver under JDK 1.4 or earlier, 
                AspectJ will use a simple built-in trace
            infrastructure that logs to stderr. This is enabled by setting the 
            <literal>org.aspectj.weaving.tracing.enabled</literal> System property. You may also override
            the default behaviour or provide your own trace implementation using the
            <literal>org.aspectj.weaving.tracing.factory</literal> System property. </para>
            
            <para> The table below lists the System properties that can be used to configure tracing. </para>
            <informaltable>
                <tgroup cols="2">
                    <thead>
                        <row>
                            <entry>Property</entry>
                            <entry>Description</entry>
                        </row>
                    </thead>
                    <tbody>
                        <row>
                            <entry>
                                <literal>org.aspectj.tracing.debug</literal>
                            </entry>
                            <entry>
                            	Enable simple debugging of the trace infrastructure itself.
                            	<para> Default: <literal>false</literal>. </para>
                            </entry>
                        </row>
                        <row>
                            <entry>
                                <literal>org.aspectj.tracing.enabled</literal>
                            </entry>
                            <entry>
                            	Enable the built-in AspectJ trace infrastructure.
                            	<para> Default: <literal>false</literal>. </para>
                            </entry>
                        </row>
                        <row>
                            <entry>
                                <literal>org.aspectj.tracing.factory</literal>
                            </entry>
                            <entry>
                            	Select trace infrastructure. Specify the fully qualified class name
                            	of the <literal>org.aspectj.weaver.tools.TraceFactory</literal> 
                            	interface to use a custom infrastructure. Specify a value of
                            	<literal>default</literal> to force AspectJ to use it's
                            	built-in infrastructure. 
                            </entry>
                        </row>
                        <row>
                            <entry>
                                <literal>org.aspectj.tracing.messages</literal>
                            </entry>
                            <entry>
                            	Enable tracing of compiler messages. The kind of messages logged
                            	is determined by the selected trace infrastructure not the message
                            	configuration.
                            	<para> Default: <literal>false</literal>. </para>
                            </entry>
                        </row>
                    </tbody>
                </tgroup>
            </informaltable>
        </sect2>

        <sect2 id="trace-examples" xreflabel="trace-examples">
            <title>Examples</title>
        
            <para> Using <literal>-Dorg.aspectj.tracing.factory=default</literal>
            	to force AspectJ to use its internal infrastructure,
            	<literal>-Dorg.aspectj.tracing.enabled=true</literal> to turn it on and  
            	<literal>-Dorg.aspectj.tracing.messages=true</literal> to include messages
            	running a simple HelloWorld with LTW will generate tracing to stderr. Below
            	is an extract from that trace with method arguments removed. 
            	You will notice the millisecond time stamp,
            	thread id and indication of entry/exit/event or message type for each line
            	of trace.
            </para>
	        <programlisting><![CDATA[
15:44:18.630 main > org.aspectj.weaver.loadtime.Aj.<init> 
15:44:18.660 main < org.aspectj.weaver.loadtime.Aj.<init>
15:44:18.660 main > org.aspectj.weaver.loadtime.Aj.preProcess
15:44:18.660 main - org.aspectj.weaver.loadtime.Aj.preProcess
15:44:18.730 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.<init>
15:44:18.730 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.<init>
15:44:18.730 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.initialize 
15:44:18.821 main I [AppClassLoader@92e78c] info AspectJ Weaver Version DEVELOPMENT ...
15:44:18.821 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions
15:44:18.821 main I [AppClassLoader@92e78c] info register classloader ...
15:44:18.821 main - org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions 
15:44:18.841 main - org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions 
15:44:18.841 main I [AppClassLoader@92e78c] info using configuration ...
15:44:18.891 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.parseDefinitions 
15:44:19.021 main > org.aspectj.weaver.World$TypeMap.<init>
15:44:19.021 main < org.aspectj.weaver.World$TypeMap.<init>
15:44:19.021 main > org.aspectj.weaver.CrosscuttingMembersSet.<init>
15:44:19.021 main < org.aspectj.weaver.CrosscuttingMembersSet.<init>
15:44:19.021 main > org.aspectj.weaver.Lint.<init>
15:44:19.021 main < org.aspectj.weaver.Lint.<init>
15:44:19.021 main > org.aspectj.weaver.World.<init> 
15:44:19.111 main < org.aspectj.weaver.World.<init>
15:44:19.201 main > org.aspectj.weaver.bcel.BcelWeaver.<init> 
15:44:19.201 main < org.aspectj.weaver.bcel.BcelWeaver.<init>
15:44:19.201 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerDefinitions 
15:44:19.211 main > org.aspectj.weaver.bcel.BcelWeaver.setReweavableMode 
15:44:19.351 main < org.aspectj.weaver.bcel.BcelWeaver.setReweavableMode
15:44:19.351 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerAspects 
15:44:19.351 main I [AppClassLoader@92e78c] info register aspect Aspect
15:44:19.351 main > org.aspectj.weaver.bcel.BcelWeaver.addLibraryAspect 
15:44:19.501 main - org.aspectj.weaver.bcel.BcelWorld.lookupJavaClass 
15:44:19.632 main > org.aspectj.weaver.CrosscuttingMembersSet.addOrReplaceAspect 
15:44:19.792 main < org.aspectj.weaver.CrosscuttingMembersSet.addOrReplaceAspect 
15:44:19.792 main < org.aspectj.weaver.bcel.BcelWeaver.addLibraryAspect 
15:44:19.792 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerAspects 
15:44:19.792 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.registerDefinitions 
15:44:19.792 main > org.aspectj.weaver.bcel.BcelWeaver.prepareForWeave 
15:44:19.822 main < org.aspectj.weaver.bcel.BcelWeaver.prepareForWeave
15:44:19.822 main > org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.weaveAndDefineConcete...
15:44:19.822 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.weaveAndDefineConcete...
15:44:19.822 main < org.aspectj.weaver.loadtime.ClassLoaderWeavingAdaptor.initialize 
15:44:19.822 main > org.aspectj.weaver.tools.WeavingAdaptor.weaveClass 
...            
			]]></programlisting>
        
            <para> Alternatively when running under Java 5 the <literal>logging.properties</literal>
            	file below could be used to configure Java Logging. The resulting
            	file, just containing trace for the 
            	<literal>org.aspectj.weaver.loadtime</literal> package, will be
            	written to <literal>java0.log</literal> in your <literal>user.home</literal> directory. 
            </para>

	        <programlisting><![CDATA[
handlers= java.util.logging.FileHandler

.level= INFO

java.util.logging.FileHandler.pattern = %h/java%u.log
java.util.logging.FileHandler.count = 1
java.util.logging.FileHandler.formatter = java.util.logging.SimpleFormatter
java.util.logging.FileHandler.level = FINER

org.aspectj.weaver.loadtime.level = FINER
			]]></programlisting>
        
            <para> 
            	By setting the System property <literal>-Dorg.aspectj.tracing.debug=true</literal>
            	you should see a message confirming which trace infrastructure is being used.
            </para>
	        <programlisting><![CDATA[
	TraceFactory.instance=org.aspectj.weaver.tools.Jdk14TraceFactory@12dacd1	        
			]]></programlisting>
        </sect2>
    </sect1>
</chapter>
