Java.lang.Process - detecting process termination asynchronously

Question

Hi All,
I was wondering if there is anyway to know when a Process (run with Runtime.exec()) has terminated without dedicating a thread per Process and using waitFor().
The reason I want this is that I have an application running many such processes concurrently, and I wouldn't want to dedicate a thread for each process to detect its termination.
What I would REALLY like is something like the asynchronous IO 'select' method so that a single thread can block until one of a set of processes terminates.
Polling would not be as good, but also a viable alternative. However, the only way I could see is calling exitValue() periodically on all Process objects - this would mean getting IllegalThreadStateExceptions thrown galore, as long as the process doesn't terminate. This is both ugly and inefficient (makes the penalty for polling even worse - we generate an exception for each non-terminated process polled...).
Does anyone have any tips I can use to implement some sort of solution?
Thanks,
Ophir.

Answer 1

>
What's the requirement for detecting the completed
processes? I'm not really sure why the Thread per
process version wasn't acceptable. How many processes
are there?
Well... it's an application server, and I'm providing a generic capability. Theoretically, it could be hundreds of processes.
Also, did you make sure that the Process Object is
indeed not collectable until the process is complete?I have to say I was pretty skeptical about this myself... ;)
I have made the test as well as I know: I ran a long running process, and then terminated it with 'kill'.
I also ran 'sleep 60' to see what happens on normal termination.
I saw nothing added to the queue while the process was up, and immediate enqueuing after process termination.
I guess there's no way of making ABSOLUTELY sure this works but if it didn't become collectable 20 consecutive times when up, and became collectable immediately when terminated, that's pretty strong circumstancial evidence...
Still I just wish there was a neater, tighter solution (though, using your hack, I'm going to get a lot of admiration from some of the people around here - they don't need to know where I got it...).