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Apache Tuscany Docs 2.x
Logging, Tracing and Timing
This page describes the logging, tracing, and timing features of Tuscany. These features can be used to debug problems with the Tuscany runtime, understand code flow, and provide timing metrics for competitive analysis or performance claims.
There are two types of logging embeded in the Tuscany runtime: explicit and implicit. The explicit logging is implemented by the Java 2 SE core logging facilities such as java.util.logging.Logger. This is the logging that many Java programmers are familiar with, and the logging requires calls to the Logger programming interface. Throughout the Tuscany code base you see calls to this facility such as this call in Tuscany org.apache.tuscany.sca.node.launcher.NodeLauncher.
Calls to this facility by default go to the standard output of the program. This is the typical result that one sees in the console:
The Java SE core logging works well as a general purpose logger and gives a general idea of the important phases in the Tuscany runtime. However, one drawback is that this logging system only publishes predetermined messages created by the developers. If you wish to change the logging points, you must change the Tuscany source code, build, and run again with your private code base.
Another logging and tracing facility is available in Tuscany that gives the user a bit of flexibility in what gets logged and requires no source code modifications to run. This is an Aspect Oriented Programming (AOP) approach that runs via a Java agent at runtime. Just like a debugger can start and stop and inspect a Tuscany Java program, so too can an AOP agent inspect and report on a Tuscany Java program. Tuscany employs the AspectJ implementation, and its runtime agent is contained in the aspectjweaver.jar file. The AOP agent is specified from a command line option or runtime options:
The AOP logging and tracing agent can be run with any Tuscany program. No additional calls or log statements need be added to the Tuscany code. The results of running a timing for example, look like this:
Full documentation on AspectJ is available at the AspectJ web site. Tuscany provides example usage in the module tracing-aspectj in the build tree and the released code.
In order to understand the aspect oriented approach to logging in Tuscany, one must understand a few basic concepts.
A join point is well defined point in the program flow. An example join point is the entry to a Java method. Another is after an exception is thrown. These join points contain useful information when running a program such as the argument list, the call stack, and the signature of the point that is executing.
A point cut is a subset of all the program join points. For instance, a point cut might be only the join points from exceptions thrown by the Tuscany runtime. Or only the set of calls to a Tuscany API org.apache.tuscany.sca.node.launcher.NodeLauncher.
Advice is the code that is run when a point cut is reached. For instance, your advice might want to print out all the arguments when entering a given method. Or your advice might show the call stack of an exception and print the original cause of the exception.
Finally, an aspect is a module that bundles up a particular set of point cuts and advice. Here is an example aspect that is marked with Java 5 annotations. The name of the aspect is LoggingAspect, there is a point cut defined at Tuscany calls to org.apache.tuscany.sca.* classes (but not inside of Aspect classes), and when the point cut is run, the advice for this point cut prints out the join point signature.
Full explanation of these concepts are in the AspectJ documents. The purpose here is to provide enough information to allow a user to run or modify the Tuscany aspects to one's liking.
Following the approach of AspectJ, Tuscany provides two concrete aspects for logging and tracing. org.apache.tuscany.sca.aspectj.LoggingAspect provides logging for methods, constructors, and static initializers in Tuscany. org.apache.tuscany.sca.aspectj.SimpleTracingAspect provide tracing into user methods, constructors, and static initializers. Both provide detailed information when an Exception or Throwable is thrown by the Tuscany runtime or user SCA program.
Both LoggingAspect and SimpleTracingAspect are run by naming the AspectJ runtime agent aspectjweaver.jar at launch. This is shown in the command line example above, and an example is provided in launcher.bat in the tracing-aspectj module, and a further example is provded by running the command "ant runtraced" on the calculator sample in a binary distribution.
The runtime configuration file aop.xml has references to these aspects. Uncomment one or both of these in aop.xml to run with this logging enabled. Following is an example logging run with the verbose weaver option specified. Note the verbose output of class names, build times, etc. The logging statements too are quite verbose stating the name of the join point, the point cut, and various signatures and arguments.
These aspects provide static point cuts and advice. That is, the various methods, constructors, and exception points are constrained by the source code of the aspects. You can change these items via editing LoggingAspect or SimpleTracingAspect and rerunning the application.
Timing of various calls is also available via the AOP logging and tracing facility in Tuscany. The apsect UserTimingAspect is provided to time certain point cuts. As shown above, this AOP timing feature can be used for timing metrics for competitive analysis of performance gauges. The output of the timing is shown here, as a Logger.info method is called and timed.
Unlike LoggingAspect and SimpleTracingAspect, the pointcut for UserTimingAspect is settable at runtime via the aop.xml runtime configuration file. Look for the UserTimingAspect name, and note the expression in the pointcut element. You may change the name of expression to any valid AspectJ pointcut expression. Here calls to any Logger.info methods, regardless of arguments or return types are logged. For instance you may change this to "call( * calculator.CalculatorServiceImpl.multiply(..))" to time calls in your SCA application.
So far this article discussed logging and tracing for Tuscany applications. Often Tuscany applications are run standalone in a Java 2 SE environment. You can also turn on logging and tracing in various application servers that support Tuscany SCA applications.
Show Apache Tomcat J2EE application server plus Tuscany bundled SCA application.
Show WebSphere 22.214.171.124 plus SOA Feature Pack based on Tuscany output.