This is a proof-of-concept Java wrapper for the libstapsdt library, which enables JVM applications to create USDT probes and fire them dynamically, without defining anything ahead of time.
The included Makefile uses two Docker containers to build libstapsdt and the demo application. The first Dockerfile grabs libstapsdt and produces libstapsdt.so; the second Dockerfile builds the JNI wrapper and the demo application, and runs the demo application in a container.
Simply run make to go through the whole process. If you want to use the resulting artifacts in another application, you'll need the wrapper's Java files in java/sdt and the build steps that generate the JNI header and build the JNI library libstapsdt-jni.so.
NOTE: Because I'm very far from being a Java packaging expert, contributions which will clean this up and turn this wrapper into a consumable package would be very much appreciated :-)
To observe the demo, run make and then in another shell, use any tool that supports SystemTap probes. For example, if you have the BCC tools installed, you should be able to see the probes as follows:
# tplist -p $(pidof java) -vv jprovider:*
/tmp/jprovider-FhrqlC.so jprovider:jprobe [sema 0x0]
location #1 0x250
argument #1 4 signed bytes @ di
argument #2 8 signed bytes @ si
argument #3 8 unsigned bytes @ dx
# trace -p $(pidof java) 'u::jprobe "i=%d i*i=%lld msg=%s", arg1, arg2, arg3'
PID TID COMM FUNC -
27845 27846 java jprobe i=269 i*i=72361 msg=iteration #269 done
27845 27846 java jprobe i=270 i*i=72900 msg=iteration #270 done
27845 27846 java jprobe i=271 i*i=73441 msg=iteration #271 done
27845 27846 java jprobe i=272 i*i=73984 msg=iteration #272 done
^C