Thread: Network communication hangs

I am writing a program where I am collecting data via a Runtime function as in:

rt =  Runtime.getRuntime();
String cmd;
cmd = " vmstat 1 2 ";
    do {
      try {
                proc = rt.exec(cmd);
                in = new BufferedReader(new InputStreamReader(proc.getInputStream()));
                while ((fromUser = in.readLine()) != null) {
                try {
                 out.println(hostname +"  vmstat  " + "Y_ "+fromUser + " _Z  " + now());
                 fromRuser = rin.readLine();            // Ack from server
                } catch (SocketException e) {
                 e.printStackTrace();
                System.err.println("Server host socket disconnect --");
                }
                }
                out.println("Y_CC "+hostname+" End VMSTAT _Z  " + now()); //
                int exitVal = proc.waitFor();
                System.out.println("Process -vmstat- exitValue: " + exitVal);
                } catch (Throwable t){
                 t.printStackTrace();
                }
                }while (true); 
                 .....

This isn't the entire program but it seems to run fine, for several iterations then hangs, after which I can do a kill -QUIT nnnn and obtain a dump file that looks like

   java.lang.Thread.State: RUNNABLE
        at java.net.SocketOutputStream.socketWrite0(Native Method)
        at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
        at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
        at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)
        at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)
        at sun.nio.cs.StreamEncoder.implFlush(StreamEncoder.java:276)
        at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:122)
        - locked <0xc95640b8> (a java.io.OutputStreamWriter)
        at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:212)
        at java.io.BufferedWriter.flush(BufferedWriter.java:236)
        - locked <0xc95640b8> (a java.io.OutputStreamWriter)
        at java.io.PrintWriter.newLine(PrintWriter.java:438)
        - locked <0xc9553ae0> (a java.io.BufferedWriter)
        at java.io.PrintWriter.println(PrintWriter.java:585)
        at java.io.PrintWriter.println(PrintWriter.java:696)
        - locked <0xc9553ae0> (a java.io.BufferedWriter)
        at qstatsClient.main(qstatsClient.java:337)
 
"VM Thread" prio=3 tid=0x0004b800 nid=0x3 runnable
 
"VM Periodic Task Thread" prio=3 tid=0x000a3800 nid=0x9 waiting on condition

From the looks of this dump, it seems that I am dealing with a locked resource. Can anyone tell me how to get around this situation?

Thanks in advance for your comments.

Frustrated programmer

what is 'out'? I may be out of my depth - I don't have a java.net.SocketOutputStream in my API! It seems to me like you're attempting (implicitly) a flush on a stream with a limited buffer and the other end isn't emptying the buffer (reading).

What is the client? Are you sure it's reading from the stream that's being written to by 'out'? Socket's typically (I think) have a fairly small buffer - you can't keep writing into it if it's not being emptied.

The socket is an auto-flush socket. I also tried explicitly flushing the 'out' object, ( out.flush(); ) but it didn't change anything.

I can see that, but it's a network socket - what is on the other end, emptying its limited-size buffer? You can't keep writing into that socket without something else emptying it from the other end - as far as I know, I could be wrong. If you've written the client that connects to the socket in your code here, perhaps it isn't reading?