ShutDownHook in multi-threaded application

Question

I have an application which in its main method spawns a hundred threads (let's say we simulate a hundred accounts). I am experimenting with it and I would like it to just print terminating when intterupted with Control-C.

I read you can do that with ShutDownHooks so I added the following in my main method:

Runtime.getRuntime().addShutdownHook(new Thread() {
            public void run() {
                             System.out.println("Terminating");
                        }
        });

However, when I run it nothing gets printed.

Could you please offer me some guidance as to where I am going wrong (all threads are declared in a for loop and start with invoking their start method)?

Regards, George

EDIT: Please see below for the code:

Bank Class:

public class Bank {
 private final double[] accounts;
   public Bank(int n, double initialBalance) {
    accounts = new double[n];
    for (int i=0; i < accounts.length;i++) {
        accounts[i] = initialBalance;
    }
}
    public double getTotalBalance() {
        double sum = 0.0;
        for (int i=0; i < accounts.length; i++) {
            sum += accounts[i];
        }
        return sum;
    }
    public synchronized void transfer(int fa, int ta, double amt) throws InterruptedException{
        System.out.print(Thread.currentThread());
        if (accounts[fa] < amt){
                        wait();
                    }
        accounts[ta] -= amt;
        System.out.println("Transfer of amount: " + amt + " from: " + fa + " Transfer to: " + ta);
        accounts[fa] += amt;
        System.out.println("Total Balance: " + getTotalBalance());
        notifyAll();

}
public int size() {
    return accounts.length;
}
public double[] getAccounts(){
    return accounts;
}

}

BankTest Class:

public class BankTest {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
            Bank b = new Bank(100,1000);
    int i;
        long timeStart = System.currentTimeMillis();
        long j = System.currentTimeMillis();





            for (i=0; i < b.size(); i++) {
        TransferRunnable tr = new TransferRunnable(b, i, 1000,j);
        Thread t = new Thread(tr);
        t.start();

    }
           Runtime.getRuntime().addShutdownHook(new Thread() {
        public void run() {
                         System.out.println("Terminating");
                    }
    });


        }


    }

TransferRunnable Class:

public class TransferRunnable implements Runnable {
private Bank b;
private int fromAccount;
private double maxAmount;
private final int DELAY = 40;
private long timeStart;
public TransferRunnable(Bank b, int from, double max, long timems) {
    this.b = b;
    fromAccount = from;
    maxAmount = max;
        timeStart = timems;
}
@Override
public void run() {

        try {
        while (true) {
            int ta = (int) (b.size() * Math.random());
            double amount =  maxAmount * Math.random();
                    double[] acc = b.getAccounts();
                    b.transfer(fromAccount,ta,amount);
            Thread.sleep((int) (DELAY*Math.random()));
        }
    }
        catch (InterruptedException e) {

        }

    }

}

Answer 1

It gets printed when I run it. You could add System.out.flush(); to the end of the run() method though, this makes sure that the output is printed immediately.

Answer 2

as others have said, this should just work. What OS are you using? It might be that CTRL+C is killing the process completely rather than asking it to shutdown (eg SIGKILL vs SIGINT). Can you verify which signal you're sending the Java process?

Finally, as a last resort you could try the following bit of Java:

if (FileDescriptor.out.valid()) {
    FileDescriptor.out.sync();
}

I suspect that this won't make any difference though!