Add debugging example to ease life of non-java master

[lttng-ust-java-tests.git] / README.md

LTTng-UST Java Agent Test Package
=================================

This git tree contains integration tests and benchmarks for the
[LTTng-UST](https://lttng.org/) Java Agent. It requires many additional
dependencies compared to the library itself, so it is shipped as a separate
package for now.


Prerequisites
-------------

* Java 1.8
* [Apache Maven](https://maven.apache.org/) 3.0+
* A recent version of [LTTng-Tools](https://lttng.org/download/)
* A recent version of [Babeltrace](http://www.efficios.com/babeltrace)
* A git branch or version of LTTng-UST you want to test

For example, on Ubuntu you can use the
[LTTng PPA](https://launchpad.net/~lttng/+archive/ubuntu/ppa), then Maven and
OpenJDK from the main repository:

    sudo apt-add-repository ppa:lttng/ppa
    sudo apt-get update
    sudo apt-get install lttng-tools babeltrace maven openjdk-8-jre

Also make sure `mvn -version` reports a `Java version: 1.8` or higher. If it
does not, you may need to set your `JAVA_HOME` accordingly.


Usage
-----

First you need to `make install` the LTTng-UST git branch you want to test.
For example:

    git clone git://git.lttng.org/lttng-ust.git
    cd lttng-ust/
    (do some modifications, checkout a different branch, etc.)
    ./bootstrap
    ./configure --enable-java-agent-all
    make
    sudo make install

Then, `cd` back to the directory where you cloned the present git tree, and
issue a

    mvn clean verify

This will run all the tests on the UST agent that was `make install`'ed. Tests
will be skipped if they cannot find their required classes or native libraries,
so make sure the output mentions succesful tests and not skipped ones.

Please make sure you have no `lttng` session active prior to or during the
tests, or it might interfere with the test runs!

Detailed JUnit test reports will be available under
`lttng-ust-java-tests-{jul|log4j}/target/failsafe-reports/`


Setting library paths
---------------------

By default, the tests will look for the Java and JNI libraries in the default
locations of `make install` (`/usr/local/lib`, `/usr/local/share/java`, etc.)

If for example, you installed into the `/usr` prefix instead of `/usr/local`,
you can use the following properties to specify different locations for the
lttng-ust-agent-java jars:

    mvn clean verify
    -Dcommon-jar-location=/usr/share/java/lttng-ust-agent-common.jar
    -Djul-jar-location=/usr/share/java/lttng-ust-agent-jul.jar
    -Dlog4j-jar-location=/usr/share/java/lttng-ust-agent-log4j.jar

To specify a different locations for the JNI .so libraries, you can set the
`-Djava.library.path` property on the JVM:

    mvn (...) -DargLine=-Djava.library.path=/usr/lib

Note: do not use `MAVEN_OPTS` to set the library path, since the `argLine`
property defined in the build will overwrite it.

Running a single test
----------------------

This test suite is comprised of integration tests. We use the failsafe
maven plugin [1]. To run a single test, one can use the test class name and the
following command:

   mvn clean verify -Dit.test=JulAppContextOrderingIT -DfailIfNoTests=false

The `-DfailIfNoTests=false` argument is necessary otherwise maven will fail on
the first test set that is empty. See [2] for more info.


[1] http://maven.apache.org/surefire/maven-failsafe-plugin/index.html
[2] http://maven.apache.org/surefire/maven-failsafe-plugin/examples/single-test.html

Debugging a test
----------------------

Note that for most tests, the test itself is the traced application.
The fastest and "easiest" way of putting a breakpoint is to use eclipse.

Download eclipse (for java dev).
Import a maven project that points to this repo:

   File -> Import -> Project -> Select Maven folder -> Select Existing Maven Projects
   Point the root directory to this repo. Select all projects. Finish

Setup the Debug Configuration:
   Run -> Debug Configurations.
   Select Remote Java Application.
   Press the New Configuration button.
   Give it the name "Remote lttng maven".
   Select the project and select `lttng-tools-java`
   Set the port to 5005
   Go in the Source tab.
   Click Add -> Java project -> Select all
   Click Apply
   Click Close

Now let's run a single test with debug:

   mvn clean verify -Dit.test=JulAppContextOrderingIT -DfailIfNoTests=false -Dmaven.failsafe.debug

Wait for:
   Listening for transport dt_socket at address: 5005

Now go back to eclipse:
   Navigate to where you want to put a break point. For example, JulAppContextOrderingIT.registerAgent.
   Ctrl + shift + b can be used to set a tracepoint at the desired line. 

Then attach to the debugger:
   Run -> Debug Configurations.
   Select on the right "Remote lttng maven"
   Click Debug

You should hit the breakpoint at some point and from there use steps etc.

If you want to debug lttng-ust, you need to insert a breakpoint at a valid point
in time for the test and then use gdb to hook yourself to the java process.
From there debugging is the same as any C application.

Running the benchmarks
----------------------

By default only the unit/integration tests are run. To also run the benchmarks,
run Maven with the `benchmark` profile, as follows:

    mvn clean verify -Pbenchmark

The benchmark results should be part of the standard output.