6.1.6 �N���XPoll.java

/**
 * RCX access classes.
 */
package josx.platform.rcx;

/**
 * Provides blocking access to events
   from the RCX. Poll is a bit
 * of a misnomer (since you don't
   'poll' at all) but it takes its
 * name from the Unix call of the same name.
 */
public class Poll
{
public static final short SENSOR1_MASK = 0x01;
public static final short SENSOR2_MASK = 0x02;
public static final short SENSOR3_MASK = 0x04;
public static final short ALL_SENSORS  = 0x07;

public static final short RUN_MASK     = 0x08;
public static final short VIEW_MASK    = 0x10;
public static final short PRGM_MASK    = 0x20;
public static final short ALL_BUTTONS  = 0x38;
public static final short BUTTON_MASK_SHIFT  = 3;

public static final short SERIAL_MASK = 0x40;
public static final short SERIAL_SHIFT = 6;

private static Poll monitor = new Poll(true);
    
// This is reflected in the kernel structure  
private short changed;  // The 'changed' mask.

/**
 * Private constructor.
 * Sets up the poller in the kernel.
 */ 
    private Poll(boolean dummy) {
        setPoller();
    }
    
    /**
     * Constructor.
     */ 
    public Poll() {
    }
    
    /**
     * Wait for the sensor/button values
     * to change then return.
     *
     * @param mask bit mask of
          values to monitor.
     * @param millis wait for 
        at most millis milliseconds.
        0 = forever.
     * @return a bit mask of
        the values that have changed
     * @throws InterruptedException
     */
    public final int poll(int mask,
        int millis) throws InterruptedException {
        synchronized (monitor) {
            int ret = mask & monitor.changed;
            
// The inputs we're interested in
// may have already changed
// since we last looked so
// check before we wait.
            while (ret == 0) {
                monitor.wait(millis);
                
// Work out what's changed that
// we're interested in.
                ret = mask & monitor.changed;
            }

// Clear the bits that we're monitoring.
// If anyone else
// is also monitoring these bits its tough.
            monitor.changed &= ~mask;
            return ret;
        }
    }

/**
 * Set a throttle on the
   regularity with which inputs
 * are polled.
 * @param throttle number of
      sensor reads between polls.
 * Default value is 1. 0 means
       poll as often as possible.
 * Sensor reads occur every 3ms.
 */

    public native final void
       setThrottle(int throttle);

  /**
   * Sets up and starts the
     the poller in the kernel.
   */
    private native final void setPoller();
/*
    {
        new Thread() {
            public void run() {
                do {
                    synchronized (monitor) {
                        if (anthing has changed) {
                            monitor.changed =
                              whatever has changed
                            notifyAll();
                        }
                    }
                } while (true);
            }
        }.start();
    }
*/
}