Java breaking an infinite loop

Question

I have particular situation in our production environment, where a particular piece of code goes into an infinite loop. The cause is mostly data specific and not able to figure out the true cause. In the mean time, what I am hoping to do is spawn a separate child thread to execute that piece of code, and if it executes for say more than 30s, want to stop that child thread from executing

Thread t = new Thread() {
    public void run() {
                    // This is where i will the method that runs in a infinite loop
                    callMethodThatRunsInInfiniteLoop();
    };
};

t.start();
try {
    t.join(2000); // wait 2s
} catch (InterruptedException e) {
    e.printStackTrace();
} 

// if not completed how to break the child thread ???

Answer 1

unfortunately no it is a thirdparty code, and will not be able to change it so easily.

It sounds like you are trying to work around a problem in the third-party library ... or in your code calling the third-party library with bad input or something.

My advice would be to fix THAT problem, rather than trying to kill the errant thread(s). And if you can't do that, then you have two choices:

• modify the 3rd party library to be interrupt aware/responsive, and then use that to stop it, or

• try to find a way to "reach into" the 3rd party library's data structures (e.g. using nasty reflection) and cause it to die.

If you are resorting to the latter, then maybe you should also look at running the 3rd party library in a separate JVM so that you can forcibly kill it using the Process API.

---

Having said that, there are limited circumstances where Thread.stop() is actually (probably) safe to use. Basically, if the errant thread doesn't create child threads, doesn't interact with other threads and doesn't share data structures, and can't be doing class initialization when you kill it, then you are probably going to be safe. The problem is there are so many theoretical scenarios where stopping the thread could cause damage that it is hard to know that you've considered all of them.

Answer 2

Is there a way to cause the infinite loop code to break by throwing an exception? e.g. set some variable to null? A possible advantage is that the affected thread (if well written) will clean up after itself and shut down more nicely than a stop().