Constantly checking a port without a while loop

Question

In a program (Java) I'm making I need to check for a specific pin in the parallel port. Whenever that pin goes from logical 0 to 1 (a positive edge clock) I have to read the data on the port and save it. This happens about every 10ms but can vary a little.

To do this I made a separate thread with a while loop that is constantly checking the port, but this makes the processor go nuts and I know it's because of the while loop. My question is, how can I constantly scan the port without using a processor intensive while loop? The program doesn't know precisely when a pin change will happen, only that it happens around every 10ms.

Answer 1

Fire a thread which is scheduled to execute the given Runnable at a fixed rate. You can use Timer#scheduleAtFixedRate() or ScheduledExecutorService#scheduleAtFixedRate() for this. The last one is preferred.

ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
scheduler.scheduleAtFixedRate(new PortScanner(), 0, 10, TimeUnit.MILLISECONDS); // Run every 10 ms.

Where PortScanner can look like this:

public class PortScanner implements Runnable {
    @Override
    public void run() {
        // Scan port here.
    }
}

Don't forget to call scheduler.shutdown() at the moment your application exits, else the thread may hang.