Process.exec() problem

Hi folks,
I'm having a problem which I believe to be with exec'ing a process  
and wonder if someone might be able to help. Sometimes another set of  
eyeballs is all it takes.

The problem is an intermittent failure which appears to be a deadlock  
somewhere. The frequency is about two or three times every hundred  
tries. I've appended the java code below (small extract) and I can't  
see any specific problem with it - after all it works -most- of the  
time. Problem is that the call is made to this method and the process  
then remains asleep. In a few instances, the process list shows a  
zombie process...
31747 pts/49   Z+     0:00 [who] <defunct>

A few items of background - I see this problem on Linux (SuSE 9.1,  
kernel 2.6.4) and Mac OS X (10.4.1, dual processor G5). There had  
been a couple of instances on Linux 2.4.20 SuSE 8.2 but that does not  
seem to be happening now (more testing needed). Testing on Sun Java  
has never produced a failure, even in days of testing. The sable 
+classpath version is 1.1.8 but comparison of that code with current  
doesn't seem to show any substantial difference in this area [I've  
been trying today to get latest code but sablevm.org site is down,  
unfortunately]

I'm suspecting a subtle timing issue within classpath as the root  
cause. All suggestions gratefully accepted.

Thanks.....Peter




    public String[] getConnectedUsers()
    {
       int              count = 0;
       int              status = -1;
       String           s;
       Runtime          rt;
       Process          p;
       ArrayList        return_data = new ArrayList(32);
       String[]         cu = new String[0];

       try {
          rt = java.lang.Runtime.getRuntime();
          p = rt.exec(("who"));
          status = p.waitFor();
          if (status != 0){
             System.err.println("WARNING:  'who' failed,  
getConnectedUsers failed");
             return cu;
          }
          InputStream ain = p.getInputStream();
          if ( ain == null ){
             System.err.println("WARNING:  'who' missing,  
getConnectedUsers failed");
             return cu;
          }
          BufferedReader in = new BufferedReader( new  
InputStreamReader ( ain ) );
          if ( in == null ) {
             System.err.print("getConnectedUsers: in is null -  
command must have failed, status = ");
             System.err.println(status);
          } else {
             while ( (s = in.readLine()) != null) {
                if ( (s.length() < 1) || (s.substring(0,1).equals("#")))
                   continue;    //ignore zero-length line (if any)  
and the user count line
                return_data.add(s.substring(0, 9).trim());
             }
             cu = (String[])return_data.toArray(new String 
[return_data.size()]);
          }
       }
       catch (InterruptedException ie) {
          System.err.println("InterruptedException caught");
       }
       catch (IOException ioe) {
          System.err.println("i/o error");
       }
       return cu;
    }