What's an easy way to start an agent in current JVM after it is running?

Question

I want to be able to start a Java agent in the current JVM. I cannot control how the JVM is started, therefore I cannot specify -javaagent on the java command.
I know the attach API lets me attach to a JVM if I have its PID. But unless I have missed something there is no platform-independent way of getting the current PID to pass to VirtualMachine.attach.
I have run an experiment that seems to work in which my code:
1. Uses File.createTempFile to create a unique temp file.
2. Sets a system property to the temp file's path.
3. Uses VirtualMachine.list to get VirtualMachineDescriptors for all known VMs.
4. For each VMD:
4a. Attaches to the VM using theVirtualMachineDescriptor.id().
4b. Retrieves the system properties from the VM.
4c. Searches the Properties for the system property name and, if found, checks its value.
4d. If they match, the VirtualMachine in the loop is the currently-running VM one and do what I want.
4e. If they do not match, detach from that VM and check the next VM in the list.
This is terribly cumbersome, plus it requires that tools.jar be available.
Is there no simpler way to establish an agent in the current VM? Or to attach to the current VM?
(I also tried passing an empty string and "-1" as the PID to VirtualMachine.attach with no luck. Not that I expected those to work, given that the JavaDoc said nothing about these special values.)
Thanks.
- Tim
Edited slightly for clarity by: tjquinn on Jan 23, 2008 4:26 PM

Answer 1

Thanks a lot for the pointers, Alan.
The real underlying difficulty I didn't mention earlier is that Java Web Start is launching the applications of interest here. The JNLP spec currently provides no way of indicating an agent in the JNLP document, the -javaagent command line option is not one of the ones that Java Web Start chooses to handle (for the obvious security reasons I presume), and JNLP provides no mechanism for defining environment variables. So perhaps this is a lost cause until the JNLP spec and/or the Java Web Start implementation evolve.
(There is a bug from years ago filed against Java Web Start asking for the equivalent of the -javaagent feature.)
My questions in this thread reflect my (unsuccessful) attempts at side-stepping those Java Web Start restrictions.
It does seem to me that the management enhancements over the past several Java SE versions have done a nice job of allowing different JVMs to manage and monitor each other. The special case of a JVM managing or monitoring itself is not so easy. In my particular case I don't really need the ability to attach to a different JVM. If I could just get the VirtualMachine instance for the current JVM (without needing tools.jar) I'd be done and on my way.
Is that worth an RFE against management/monitoring do you think?
- Tim