multithreading - Java threads: Is it possible view/pause/kill a particular thread from a different java program running on the same JVM?

Question

I have a program 'foo' running different threads, fooT1, fooT2, .. fooTn.

Now if I want write another program 'bar', which could kill the thread fooTr, is that possible?

Reason: One of the thread fooTr tracks product license. If this thread is killed; one may run this product indefinitely. And killing 'foo' itself is tolerable as 'foo' as that is exactly what is being done on license expiry.

System: Fedora Distribution of Linux

Note: The commands which start JVM and program foo are placed in /etc/init.d and anyone who has a decent knowledge of rc.1/rc.2/rc.3 structure can change/add the starting parameters to these.

I hope my question is clear. If not, I can always edit it.

Answer 1

Actually the java debugger will allow you to kill a thread by injecting an exception into it. I was just trying to work out how to use this feature to kill a thread without wiping out the whole jvm, when I came across this question. If you run the jvm with command line options like:

java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8888 your.app.Main

and connect the debugger with something like:

jdb -attach 127.0.0.1:8888

you can type:

threads

to get a list of the running threads, and use the kill command to kill a running thread. The bit I'm currently not sure about is the syntax of this kill command, I have tried the obvious:

kill 0xe2e new java.lang.IllegalArgumentException("er");

and I get the messages:

killing thread: Swank REPL Thread
Thread not suspended
Expression must evaluate to an object

("Swank REPL Thread" is the thread I want to kill, and yes, I've tried suspending it first ;)

Still my inability to use the java debugger aside, it looks to me like a thread can be killed at random. Maybe you can just make sure you ignore all exceptions and keep running and that will be enough, but I'm not sure about that.