[classlib] Using Aspects for Tracing

[Sian January]

Hello,

 

Following a recent discussion on this list I have been looking into how aspects could be used for tracing in the Harmony class library code.  I have been using AspectJ and have written a really simple tracing aspect for the math module, adapted the build.xml script and written some instructions on how to apply it.  At the moment the aspect just does entry and exit tracing and prints to System.out, but this is because it's a first draft - it is possible to do more targeted tracing and to use frameworks such as java.util.logging with aspects.

 

Steps to follow:

1. Download AspectJ from http://www.eclipse.org/aspectj/downloads.php

2. Copy aspectjrt.jar to /depends/jars/aspectj/

3. Copy aspectjtools.jar and aspectjrt.jar to ANT_HOME/lib and if using Eclipse add both of these to your ant runtime configuration (Window > Preferences > Ant > Runtime > Add...)

4. Edit build file to use iajc* instead of javac and include aspect class files (or apply the buildxmlpatch.txt to build.xml in the math module)

5. Write a tracing aspect (or copy the one attached to modules\math\src\main\java\org\apache\harmony\tracing)

6. Re-build the module

7. Make sure to add aspectjrt.jar to the runtime classpath of whatever program you are running.

* - iajc isn't incremental like javac in ant, it will always do a total rebuild.  Also if you switch from using iajc back to javac you will need to do a clean before you do a rebuild. 

Please also note that it's not possible to use this kind of tracing for any classes that are depended on by the AspectJ runtime or there will be errors initializing the classes because of circular dependencies.  However I think most modules apart from luni should be safe.  Also it's important to not trace methods that are called (directly or indirectly) by your tracing methods otherwise you will end up in an endless loop. 

 

If anyone thinks this information might be useful to have available somewhere I would be happy to expand it a bit for a web page or a Wiki page.

Regards,

Sian

--
Sian January

IBM Java Technology Centre, UK

Index: C:/eclipse32harmony/eclipse/workspace/Harmony/modules/math/build.xml
===================================================================
--- C:/eclipse32harmony/eclipse/workspace/Harmony/modules/math/build.xml        
(revision 472874)
+++ C:/eclipse32harmony/eclipse/workspace/Harmony/modules/math/build.xml        
(working copy)
@@ -34,6 +34,11 @@
                         from="^(.*?)(\$$[^/\\\.]*)?\.class$$"
                         to="\1.java"/>
             </present>
+            <present targetdir="${hy.math.src.main.java}">
+                <mapper type="regexp"
+                        from="^(.*?)(\$$[^/\\\.]*)?\.class$$"
+                        to="\1.aj"/>
+            </present>
         </or>
     </fileset>
 
@@ -50,16 +55,20 @@
         </delete>
     </target>
 
+     <taskdef 
resource="org/aspectj/tools/ant/taskdefs/aspectjTaskdefs.properties">
+       <classpath>
+        <pathelement path="${aspectjtools.jar}" /> 
+       </classpath>
+     </taskdef>
+       
     <target name="compile-java">
         <echo message="Compiling MATH classes" />
+               
+               <mkdir dir="${hy.build}" />
 
-        <mkdir dir="${hy.build}" />
-
-        <javac sourcepath=""
+        <iajc 
                srcdir="${hy.math.src.main.java}"
                destdir="${hy.build}"
-               compiler="${hy.javac.compiler}"
-               memoryMaximumSize="${hy.javac.maxmem}"
                source="${hy.javac.source}" 
                target="${hy.javac.target}"
                debug="${hy.javac.debug}">
@@ -69,7 +78,7 @@
                     <include name="**/*.jar" />
                 </fileset>
             </bootclasspath>
-        </javac>
+        </iajc>
     </target>
 
     <target name="copy-resources">