I have a multithreaded Java application that makes uses ThreadLocal fields to keep the threads isolated from each other. As part of this application I also have a requirement to implement timeouts on certain functions to prevent DOS attacks.

I’m looking for a way to time out a Java function that is running in the current thread

I’ve seen plenty of solutions such as How to timeout a thread which will create a Future to execute some code, launch it in a new thread and and wait for it to complete. I want to make it work the other way round.

Consider the following multi-threaded code:

class MyClass {
    ThreadLocal<AtomicInteger> counter = ThreadLocal.withInitial(AtomicInteger::new);

    public void entry() throws Exception {
        I_need_a_timeout(100);

        int result = counter.get().get();          // If there is no time out this will be 100
    }

    private void I_need_a_timeout(int loop) throws Exception {
        while (loop-- >= 0) {
            counter.get().incrementAndGet();
            Thread.sleep(100);                  // Do some work
        }
    }
}

I need to be able to terminate I_need_a_timeout if it runs for too long, but if I were to execute it in a future then it would have it’s own thread and therefore it’s own counter so the value read by the calling code would always be 0