Break out of a recursion in java when the time run out

Question

I'm implementing AI for a chess-like game. I intend to use recursion to try all the possible state of the board and choose out the 'best move'.

Because of the time's limit per move, i need to have some mechanism to break out of those recursive procedure whenever the time limit is reached. Of course i can keep checking the time before making a recursion call and break out if the current time is near the limit, but it is a trade-off with the performance of my program.

It would be great if there is a way to break out of those recursive procedure whenever a timer end. However, since i'm new to Java, i don't know if there are any way to do so in java? Can you give an example code? :)

Answer 1

Checking the time, e.g. System.currentTimeMillis() costs about 200 ns per call. However if this is to much for you, you can have another thread set a flag to stop.

There is a mechanism to do this already.

ExecutorService es = Executors.newSingleThreadExecutor();
Future f = es.submit(new Runnable() {
    @Override
    public void run() {
        long start = System.nanoTime();
        while(!Thread.interrupted()) {
            // busy wait.
        }
        long time = System.nanoTime() - start;
        System.out.printf("Finished task after %,d ns%n", time);
    }
});
try {
    f.get(1, TimeUnit.SECONDS); // stops if the task completes.
} catch (TimeoutException e) {
    f.cancel(true);
}
es.shutdown();

prints

Finished task after 1,000,653,574 ns

Note: you don't need to start/stop the ExecutorService every time.