exec() only works correctly the first time called

I'm having problems execing programs more than once.

The SIGCHLD handler only gets called with the first exec. Subsequent exec calls seem
to be handled differently. I can verify this because only the first exec prints the messages
pid 14494 status 0
Received sigchild for 14494 exit=0

I'll enclose a sample program and it's output.

ls.java:
public class ls {
    public ls(String file) {
        String args[] = new String[2];
        Process p;
        String buf;
        InputStream s;
        int length;

        args[0] = "/bin/ls";
        args[1] = file;
        try {
            p = Runtime.getRuntime().exec(args);
            s = p.getInputStream();
            DataInputStream din = new DataInputStream(s);

            while ((buf = din.readLine()) != null) {
                System.out.println(buf);
            }
        } catch (IOException e) {
            System.out.println("command failed.");
        }
        System.out.println("got to here");
    }

    public static void main(String args[]) {
        if (args.length == 0) {
            System.out.println("enter file");
        } else {
            System.out.println("first ls for " + args[0]);
            new ls(args[0]);
            System.out.println("second ls for " + args[0]);
            new ls(args[0]);
        }
    }
}

holiday% javac ls.java
holiday% java ls /tmp/foo
first ls for /tmp/foo
pid 14625 status 0
Received sigchild for 14625 exit=0
file1
file2
file3
got to here
second ls for /tmp/foo
file1
file2
file3

The program never exits, and as you see, the sigchild message only got printed on
the first exec