Question

My question isn’t specific to Java but that is the language I’m using to achieve what I want.

I’m experimenting with Bluetooth in Java and have written a simple terminal program i.e. no GUI interface that searches for nearby Bluetooth devices and lists them. My code is as follows:

import javax.bluetooth.*;

public class BluetoothTest implements DiscoveryListener{

    private static boolean isAlive = true;

    public static void main(String[] args) {
        try {
            LocalDevice ld = LocalDevice.getLocalDevice();
            if (LocalDevice.isPowerOn()){
                System.out.println("Power On.");
                System.out.println("Friendly Name: " + ld.getFriendlyName());
                System.out.println("Address: " + ld.getBluetoothAddress());
                DiscoveryAgent da = ld.getDiscoveryAgent();
                da.startInquiry(DiscoveryAgent.GIAC,new BluetoothTest());
                while (isAlive){
                    /* Sleep */
                    try {
                        Thread.sleep(200);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            } else {
                System.out.println("Power Off.");
            }
        } catch (BluetoothStateException e) {
            System.out.println(e.toString());
        }
    }

    public void setAlive(boolean status){
        isAlive = status;
    }

    public void deviceDiscovered(RemoteDevice rd, DeviceClass dc){
        try{
            System.out.println(rd.getFriendlyName(true));
        } catch (java.io.IOException e){
            System.out.println(e.toString());
        }
    }

    public void inquiryCompleted(int discType){
        isAlive = false;
    }

    public void servicesDiscovered(int transID, ServiceRecord[] sr){
    }

    public void serviceSearchCompleted(int transID, int respCode){
    }
}

The startInquiry() of DiscoveryAgent object returns immediately and any devices that are discovered are returned to the DiscoveryListener interface which I have implemented. The problem is unless I include the while() loop the program will terminate before any devices are discovered.

Just how do applications efficiently stay resident? Is it achieved by having a separate ‘working’ thread and a main thread which spawns the working thread but itself sleeps until the worker had finished?

Answer 1

You may use Object wait / notify mechanism to hold main method until BluetoothTest notifies on a common object lock.

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Just a pseudo code,

Define a static final Object _mutex = new Object();

In main method after call of startInquiry call _mutex.wait(); This will hold the main thread.

In inquiryCompleted call _mutex.notify(); This will release the main thread.

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Please note that this code will work only if startInquiry create a new thread and invokes call back methods. I am not much aware of DiscoverAgent class. So if that’s not the case, the above solution might now work.